@article {1660,
	title = {Ambient Ammonia Electrosynthesis from Nitrogen and Water by Incorporating Palladium in Bimetallic Gold{\textendash}Silver Nanocages},
	journal = {Journal of The Electrochemical Society},
	year = {2020},
	author = {Nazemi, M. and Soule, L. and Liu, M. and El-Sayed, M. A.}
}
@article {1661,
	title = {Electrosynthesis of Ammonia Using Porous Bimetallic Pd{\textendash}Ag Nanocatalysts in Liquid- and Gas-Phase Systems},
	journal = {ACS Catalysis},
	year = {2020},
	chapter = {10197},
	keywords = {display},
	author = {Nazemi, M. and Ou, P. and Alabbady, A. and Soule, L. and Liu, A. and Song, J. and Sulchek, T.A. and Liu, M. and El-Sayed, M. A.}
}
@article {1658,
	title = {Observation of Photoinduced Proton Transfer between the Titania Surface and Dye Molecule},
	journal = {The Journal of Physical Chemistry C},
	year = {2020},
	author = {Nishikiori, H. and Kondo, H. and Kageshima, Y. and Hooshmand, N. and Panikkanvalappil, S. R. and Valverde-Ch{\'a}vez, D.A. and Silva, C. and El-Sayed, M.A. and Teshima,K.}
}
@article {1662,
	title = {Systems and Methods for Forming Nitrogen-Based Compounds},
	year = {2020},
	author = {Nazemi, M. and El-Sayed, M.A.}
}
@article {1648,
	title = {Plasmon-enhanced photo (electro) chemical nitrogen fixation under ambient conditions using visible light responsive hybrid hollow Au-Ag2O nanocages},
	journal = {Nano Energy},
	year = {2019},
	author = {Nazemi, M. and El-Sayed, M.A.}
}
@article {1646,
	title = {The Role of Oxidation of Silver in Bimetallic Gold{\textendash}Silver Nanocages on Electrocatalytic Activity of Nitrogen Reduction Reaction},
	journal = {The Journal of Physical Chemistry C},
	year = {2019},
	chapter = {11422},
	author = {Nazemi, M. and El-Sayed, M.A.}
}
@article {1640,
	title = {Electrochemical Synthesis of Ammonia from N2 and H2O under Ambient Conditions Using Pore-Size-Controlled Hollow Gold Nanocatalysts with Tunable Plasmonic Properties},
	journal = {The journal of physical chemistry letters},
	year = {2018},
	author = {M. Nazemi and El-Sayed, M. A.}
}
@article {1637,
	title = {Enhancing the rate of electrochemical nitrogen reduction reaction for ammonia synthesis under ambient conditions using hollow gold nanocages},
	journal = {Nano Energy},
	year = {2018},
	keywords = {display},
	author = {M. Nazemi and Panikkanvalappil, S. R. and El-Sayed, M. A.}
}
@article {1361,
	title = {The Most Effective Gold Nanorod Size for Plasmonic Photothermal Therapy: Theory and In Vitro Experiments},
	journal = {Journal of Physical Chemistry B},
	volume = {118},
	number = {5},
	year = {2014},
	note = {Mackey, Megan A. Ali, Moustafa R. K. Austin, Lauren A. Near, Rachel D. El-Sayed, Mostafa A.},
	month = {Feb},
	pages = {1319-1326},
	isbn = {1520-6106},
	doi = {10.1021/jp409298f},
	author = {Mackey, M. A. and Ali, M. R. K. and Austin, Lauren and Near, R. D. and El-Sayed, M. A.}
}
@article {1356,
	title = {Self-Assembled Nanostructured Photoanodes with Staggered Bandgap for Efficient Solar Energy Conversion},
	journal = {ACS nano},
	year = {2014},
	isbn = {1936-0851},
	author = {Nashed, Ramy and Szymanski, Paul and El-Sayed, Mostafa A. and Allam, Nageh K}
}
@article {1357,
	title = {Stacked Gold Nanorectangles with Higher Order Plasmonic Modes and Top-Down Plasmonic Coupling},
	journal = {The Journal of Physical Chemistry C},
	volume = {118},
	number = {10},
	year = {2014},
	pages = {5453-5462},
	isbn = {1932-7447},
	author = {Malak, Sidney T. and König, Tobias and Near, Rachel and Combs, Zachary A. and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.}
}
@article {1384,
	title = {Bandgap bowing in Ta-W-O system for efficient solar energy conversion: Insights from density functional theory and X-ray diffraction},
	journal = {Applied Physics Letters},
	volume = {103},
	number = {13},
	year = {2013},
	note = {Nashed, Ramy Alamgir, Faisal M. Jang, Seung Soon Ismail, Yehea El-Sayed, Mostafa A. Allam, Nageh K.},
	month = {Sep},
	isbn = {0003-6951},
	doi = {10.1063/1.4823543},
	author = {Nashed, R. and Alamgir, F. M. and Jang, S. S. and Ismail, Y. and El-Sayed, M. A. and Allam, N. K.}
}
@article {1376,
	title = {Electron transfer process in fluorescein-dispersing titania gel films observed by time-resolved fluorescence spectroscopy},
	journal = {The Journal of Physical Chemistry C},
	volume = {117},
	number = {20},
	year = {2013},
	pages = {10308-10314},
	isbn = {1932-7447},
	author = {Setiawan, Rudi Agus and Nishikiori, Hiromasa and Uesugi, Yohei and Miyashita, Kyohei and El-Sayed, Mostafa A. and Fujii, Tsuneo}
}
@article {1350,
	title = {Enhancing Colloidal Metallic Nanocatalysis: Sharp Edges and Corners for Solid Nanoparticles and Cage Effect for Hollow Ones},
	journal = {Acc Chem Res},
	year = {2013},
	note = {MEDLINE AN 2013361444(Journal; Article; (JOURNAL ARTICLE))},
	month = {//},
	abstract = {There are two main classes of metallic nanoparticles: solid and hollow. Each type can be synthesized in different shapes and structures. Practical use of these nanoparticles depends on the properties they acquire on the nanoscale. Plasmonic nanoparticles of silver and gold are the most studied, with applications in the fields of sensing, medicine, photonics, and catalysis. In this Account, we review our group{\textquoteright}s work to understand the catalytic properties of metallic nanoparticles of different shapes. Our group was the first to synthesize colloidal metallic nanoparticles of different shapes and compare their catalytic activity in solution. We found that the most active among these were metallic nanoparticles having sharp edges, sharp corners, or rough surfaces. Thus, tetrahedral platinum nanoparticles are more active than spheres. We proposed this happens because sharper, rougher particles have more valency-unsatisfied surface atoms (i.e., atoms that do not have the complete number of bonds that they can chemically accommodate) to act as active sites than smoother nanoparticles. We have not yet resolved whether these catalytically active atoms act as catalytic centers on the surface of the nanoparticle (i.e., heterogeneous catalysis) or are dissolved by the solvent and perform the catalysis in solution (i.e., homogenous catalysis). The answer is probably that it depends on the system studied. In the past few years, the galvanic replacement technique has allowed synthesis of hollow metallic nanoparticles, often called nanocages, including some with nested shells. Nanocage catalysts show strong catalytic activity. We describe several catalytic experiments that suggest the reactions occurred within the cage of the hollow nanocatalysts: (1) We synthesized two types of hollow nanocages with double shells, one with platinum around palladium and the other with palladium around platinum, and two single-shelled nanocages, one made of pure platinum and the other made of pure palladium. The kinetic parameters of each double-shelled catalyst were comparable to those of the single-shelled nanocage of the same metal as the inside shell, which suggests the reactions are taking place inside the cavity. (2) In the second set of experiments, we used double-shelled, hollow nanoparticles with a plasmonic outer gold surface and a non-plasmonic inner catalytic layer of platinum as catalysts. As the reaction proceeded and the dielectric function of the interior gold cavity changed, the plasmonic band of the interior gold shell shifted. This strongly suggested that the reaction had taken place in the nanocage. (3) Finally, we placed a catalyst on the inside walls of hollow nanocages and monitored the corresponding reaction over time. The reaction rate depended on the size and number of holes in the walls of the nanoparticles, strongly suggesting the confinement effect of a nanoreactor.[on SciFinder (R)]},
	isbn = {1520-4898},
	author = {Mahmoud, Mahmoud A. and Narayanan, Radha and El-Sayed, Mostafa A.}
}
@article {1382,
	title = {Hollow gold nanorectangles: The roles of polarization and substrate},
	journal = {Journal of Chemical Physics},
	volume = {139},
	number = {4},
	year = {2013},
	note = {Near, Rachel D. El-Sayed, Mostafa A.},
	month = {Jul},
	isbn = {0021-9606},
	doi = {10.1063/1.4812931},
	author = {Near, R. D. and El-Sayed, M. A.}
}
@article {1396,
	title = {Plasmonic enhancement of photodynamic cancer therapy},
	journal = {Journal of Photochemistry and Photobiology a-Chemistry},
	volume = {269},
	year = {2013},
	note = {Hayden, Steven C. Austin, Lauren A. Near, Rachel D. Ozturk, Ramazan El-Sayed, Mostafa A.},
	month = {Oct},
	pages = {34-41},
	isbn = {1010-6030},
	doi = {10.1016/j.jphotochem.2013.06.004},
	author = {Hayden, S. C. and Austin, Lauren and Near, R. D. and Ozturk, R. and El-Sayed, M. A.}
}
@article {1380,
	title = {Rapid and Efficient Prediction of Optical Extinction Coefficients for Gold Nanospheres and Gold Nanorods},
	journal = {Journal of Physical Chemistry C},
	volume = {117},
	number = {45},
	year = {2013},
	note = {Near, Rachel D. Hayden, Steven C. Hunter, Ronald E., Jr. Thackston, Daniel El-Sayed, Mostafa A.},
	month = {Nov},
	pages = {23950-23955},
	isbn = {1932-7447},
	doi = {10.1021/jp4082596},
	author = {Near, R. D. and Hayden, S. C. and Hunter, R. E. and Thackston, D. and El-Sayed, M. A.}
}
@article {1348,
	title = {Surface Assembly and Plasmonic Properties in Strongly Coupled Segmented Gold Nanorods},
	journal = {Small},
	year = {2013},
	note = {MEDLINE AN 2013463112(Journal; Article; (JOURNAL ARTICLE))},
	month = {//},
	abstract = {An assembly strategy is reported such that segmented nanorods fabricated through template-assisted methods can be robustly transferred and tethered to a pre-functionalized substrate with excellent uniformity over large surface areas. After embedding the rods, sacrificial nickel segments were selectively etched leaving behind strongly coupled segmented gold nanorods with gaps between rods below 40 nm and as small as 2 nm. Hyper-spectral imaging is utilized to measure Rayleigh scattering spectra from individual and coupled nanorod elements in contrast to common bulk measurements. This approach discerns the effects of not only changing segment and gap size but also the presence of characteristic defects on the plasmonic coupling between closely spaced nanorods. Polarized hyper-spectral measurements are conducted to provide direct observation of the anisotropic plasmonic resonance modes in individual and coupled nanorods, which are close to those predicted by computer simulations for nanorods with ideal shapes. Some common deviations from ideal shape such as non-flat facets and asymmetric tails are demonstrated to result in the appearance of characteristic plasmon resonances, which have not been considered before. The large-scale assembly of coupled noble nanostructures with fine control over geometry and high uniformity provides means to strongly tune the scattering, absorption, and near-field plasmonic properties through the geometric arrangement of precisely controlled nanorod segments.[on SciFinder (R)]},
	isbn = {1613-6829},
	author = {Gupta, Maneesh K. and Konig, Tobias and Near, Rachel and Nepal, Dhriti and Drummy, Lawrence F. and Biswas, Sushmita and Naik, Swati and Vaia, Richard A. and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.}
}
@article {1381,
	title = {Thin to Thick, Short to Long: Spectral Properties of Gold Nanorods by Theoretical Modeling},
	journal = {Journal of Physical Chemistry C},
	volume = {117},
	number = {36},
	year = {2013},
	note = {Near, Rachel D. Hayden, Steven C. El-Sayed, Mostafa A.},
	month = {Sep},
	pages = {18653-18656},
	isbn = {1932-7447},
	doi = {10.1021/jp4078344},
	author = {Near, R. D. and Hayden, S. C. and El-Sayed, M. A.}
}
@proceedings {1383,
	title = {Towards a perfect system for solar hydrogen production: an example of synergy on the atomic scale},
	year = {2013},
	pages = {88220A-88220A-7},
	publisher = {International Society for Optics and Photonics},
	author = {Nashed, Ramy and Alamgir, Faisal M and Seung-Soon, Jang and Ismail, Yehea and El-Sayed, Mostafa A. and Allam, Nageh}
}
@article {1341,
	title = {Extinction vs Absorption: Which Is the Indicator of Plasmonic Field Strength for Silver Nanocubes?},
	journal = {Journal of Physical Chemistry C},
	volume = {116},
	number = {43},
	year = {2012},
	note = {Times Cited: 0Near, Rachel Hayden, Steven El-Sayed, Mostafa},
	month = {Nov},
	pages = {23019-23026},
	abstract = {This investigation demonstrates the contributions of absorption and scattering to the extinction spectrum of silver nanocubes with multipole resonances and the complexity of the resulting plasmon field strengths for these varying modes. The three-dimensional plasmonic field distribution and orientation around a silver nanosphere (AgNS; 40 nm) and a silver nanocube (AgNC; 40, 60, 86 nm) were calculated in the visible via the discrete dipole approximation. The three-dimensional nature of these particles allows for significant contribution from the quadrupole mode in some cases. The AgNS displays one plasmon band, its dipole mode, and has little contribution from scattering. The maximum plasmon field occurs at the extinction maximum, as expected. The 40 nm AgNC exhibits multiple plasmon bands, and the highest maximum field strength is attained from excitation of the quadrupole mode, not the dipole mode. As the size of the AgNC increases, the contribution from scattering increases. When the contribution from scattering is greater than the contribution from absorption in a AgNC, the field strength within a plasmon mode trends with the absorption and not with the extinction or cattering. This should be considered in applications of AgNCs, as excitation of the largest peak in the experimental extinction spectrum will not always result in the strongest plasmon field strength.},
	isbn = {1932-7447},
	doi = {10.1021/jp309272b},
	author = {Near, R. and Hayden, S. and El-Sayed, M.}
}
@article {1343,
	title = {Photoelectric Conversion Properties of Dye-Sensitized Solar Cells Using Dye-Dispersing Titania},
	journal = {Journal of Physical Chemistry C},
	volume = {116},
	number = {7},
	year = {2012},
	note = {Times Cited: 1Nishikiori, Hiromasa Uesugi, Yohei Setiawan, Rudi Agus Fujii, Tsuneo Qian, Wei El-Sayed, Mostafa A.},
	month = {Feb},
	pages = {4848-4854},
	abstract = {The time-resolved fluorescence and photoelectrochemical properties of dye-sensitized solar cells using crystalline titania electrodes coated with N3 dye-dispersing amorphous titania gel were investigated to clarify the influence of the dye titania interaction and electron transfer on their photoelectric conversion performance. The photocurrent quantum efficiency of the electrodes was remarkably increased by a steam treatment due to the crystallization and densification of the amorphous titania layer compared to that of the untreated electrode. The electron injection from the dye to the crystalline titania foundation via the steam-treated titania dispersing the dye was confirmed to be more efficient than that in the conventional electrodes. The dye-dispersing titania layer prevented interaction between the dye molecules and back electron transfer from the titania to the electrolyte. The charge separation and photoelectric conversion performance of the dye-sensitized solar cells were improved by forming the specific dye-dispersing titania layer.},
	isbn = {1932-7447},
	doi = {10.1021/jp2094388},
	author = {Nishikiori, H. and Uesugi, Y. and Setiawan, R. A. and Fujii, T. and Qian, W. and El-Sayed, M. A.}
}
@article {1342,
	title = {Pronounced Effects of Anisotropy on Plasmonic Properties of Nanorings Fabricated by Electron Beam Lithography},
	journal = {Nano Letters},
	volume = {12},
	number = {4},
	year = {2012},
	note = {Times Cited: 3Near, Rachel Tabor, Christopher Duan, Jinsong Pachter, Ruth El-Sayed, Mostafa},
	month = {Apr},
	pages = {2158-2164},
	abstract = {Gold nanoring dimers were fabricated via EBL with dimensions of 127.6 +/- 2.5 and 57.8 +/- 2.3 nm for the outer and inner diameters, respectively, with interparticle separations ranging from 17.8 +/- 3.4 to 239.2 +/- 3.7 nm. The coupling between the inner and outer surfaces of a single nanoring renders it very sensitive to any anisotropy. We found that anisotropy in the particle geometry and anisotropy introduced by the substrate combine to create very unique spectral features in this system.},
	isbn = {1530-6984},
	doi = {10.1021/nl300622p},
	author = {Near, R. and Tabor, C. and Duan, J. S. and Pachter, R. and El-Sayed, M.}
}
@article {1086,
	title = {Bacteriorhodopsin/TiO(2) nanotube arrays hybrid system for enhanced photoelectrochemical water splitting},
	journal = {Energy \& Environmental Science},
	volume = {4},
	number = {8},
	year = {2011},
	note = {Allam, Nageh K. Yen, Chun-Wan Near, Rachel D. El-Sayed, Mostafa A.},
	month = {Aug},
	pages = {2909-2914},
	abstract = {In recent years, considerable efforts have been made to improve the performance of photoactive nanostructured materials for water splitting applications. Herein, we report on the assembly and use of a bacteriorhodopsin (bR)/TiO(2) nanotube array hybrid electrode system. Photoanode materials composed of similar to 7 mu m long self-ordered and vertically oriented nanotube array of titanium dioxide films were fabricated via the anodization of Ti foil in formamide electrolytes containing NH(4)F at room temperature followed by sensitization of the electrodes with bR. The stability of bR on the TiO(2) surface was found to depend on the pretreatment process of the TiO(2) films. Our results demonstrate the opportunity to fabricate fairly stable bR/TiO(2) hybrid electrodes that can be used as photoanodes for photoelectrochemical water splitting. Under AM 1.5 illumination (100 mW/cm(2)), the hybrid electrodes achieved a photocurrent density of 0.65 mA/cm(2) which is a similar to 50\% increase over that measured for pure TiO(2) nanotubes (0.43 mA/cm(2)) fabricated and tested under the same conditions. In the presence of a redox electrolyte, the photocurrent increased to 0.87 mA/cm(2). To the best of our knowledge, this is the first report on the use of bR/TiO(2) hybrid electrodes in photoelectrochemical water oxidation cells. We believe the proton pumping property of bR can be used in a variety of applications, especially those related to third generation photovoltaic cells.},
	isbn = {1754-5692},
	doi = {10.1039/c1ee01447a},
	author = {Allam, N. K. and Yen, C. W. and Near, R. D. and El-Sayed, Mostafa A}
}
@article {1075,
	title = {Influence of Steam Treatment on Dye-Titania Complex Formation and Photoelectric Conversion Property of Dye-Doped Titania Gel},
	journal = {Journal of Physical Chemistry C},
	volume = {115},
	number = {6},
	year = {2011},
	note = {Nishikiori, Hiromasa Uesugi, Yohei Takami, Shohei Setiawan, RudiAgus Fujii, Tsuneo Qian, Wei El-Sayed, Mostafa A.},
	month = {Feb},
	pages = {2880-2887},
	abstract = {Xanthene dye molecules form a chelate complex with the titanium species on the titania surface in dye-titania systems. The complex formation causes a fast electron injection into the titania conduction band. In this study, simple spectroscopic and photocurrent measurements of the xanthene dye-doped titania gels prepared by the sol-gel method were conducted in order to clarify the influence of a steam treatment on the dye-titania interaction and electron transfer. The photocurrent quantum efficiency of the fluorescein-doped electrode was remarkably increased by the steam treatment compared to that of the untreated electrode consisting of an amorphous titania gel. The photocurrent action spectrum was red-shifted, and the short circuit photocurrent and open circuit voltage values increased with the steam treatment time. The steam treatment promoted the dye-titania complex formation, a negative shift in the conduction band potential of the titania, and the electron injection from the dye to the titania.},
	isbn = {1932-7447},
	doi = {10.1021/jp109958z},
	author = {Nishikiori, H. and Uesugi, Y. and Takami, S. and Setiawan, R. and Fujii, T. and Qian, Wei and El-Sayed, Mostafa A}
}
@article {1084,
	title = {Multimodal plasmon coupling in low symmetry gold nanoparticle pairs detected in surface-enhanced Raman scattering},
	journal = {Applied Physics Letters},
	volume = {98},
	number = {18},
	year = {2011},
	note = {Dreaden, Erik C. Near, Rachel D. Abdallah, Tamer Talaat, M. Hassan El-Sayed, Mostafa A.},
	month = {May},
	abstract = {We report on surface-enhanced Raman scattering of silicon phonon vibrations from arrays of gold nanoprism pairs fabricated by electron beam lithography. We found that resonant excitation of the quadrupolar surface plasmon mode of the nanoprisms increases Raman scattering intensity from the substrate as the distance between the nanoparticle pairs decreases. Finite element modeling and plasmon coupling theory indicate that symmetry is reduced as the nanoparticles approach, resulting in increased dipole-quadrupole coupling. Plasmonic enhancement of the incident and Raman-scattered photons results from the dipolar component of the mixed plasmonic field. This effect is expected to be largest in assemblies/aggregates of nanoparticles. (C) 2011 American Institute of Physics. [doi:10.1063/1.3555429]},
	isbn = {0003-6951},
	doi = {10.1063/1.3555429},
	author = {Dreaden, Erik and Near, R. D. and Abdallah, T. and Talaat, M. H. and El-Sayed, Mostafa A}
}
@article {1083,
	title = {Plasmonic Enhancement of Nonradiative Charge Carrier Relaxation and Proposed Effects from Enhanced Radiative Electronic Processes in Semiconductor-Gold Core-Shell Nanorod Arrays},
	journal = {Journal of Physical Chemistry C},
	volume = {115},
	number = {13},
	year = {2011},
	note = {Dreaden, Erik C. Neretina, Svetlana Qian, Wei El-Sayed, Mostafa A. Hughes, Robert A. Preston, John S. Mascher, Peter},
	month = {Apr},
	pages = {5578-5583},
	abstract = {Plasmonic field enhancement of nonradiative exciton relaxation rates in vertically aligned arrays of high aspect ratio CdTe-Au core-shell nanorods was investigated by transient absorption spectroscopy, computational electromagnetics, and kinetic modeling. Increasing shell thickness in the high aspect ratio nanorods was found to result in dramatic differences in polarization-dependent nonradiative exciton relaxation rates, which we attribute to differing mechanisms of plasmonic field enhancement associated with predominant ground- or excited-state absorption processes. These results are compared with previous investigations of low aspect ratio CdTe-Au core-shell nanorods, and overall conclusions regarding plasmonic enhancement of nonradiative relaxation rates in this system are presented. We propose that when the resonantly coupled dipolar plasmon field of the shell is polarized parallel to the ground-state absorption transition moment of the core, Auger recombination dominates carrier relaxation and slower second-order decay kinetics are observed. When contributions of the resonantly coupled plasmon field are nondipolar or orthogonal to the ground-state absorption transition moment of the core, excited-state absorption processes are believed to dominate and increasingly rapid first-order relaxation kinetics are observed. We find that these processes can vary greatly, depending on shell thickness and the orientation of the array, but are insensitive to aspect ratio. These investigations have significant implications in the design of photovoltaic and optoelectronic devices incorporating anisotropic plasmonic elements.},
	isbn = {1932-7447},
	doi = {10.1021/jp112129k},
	author = {Dreaden, Erik and Neretina, Svetlana and Qian, Wei and El-Sayed, Mostafa A and Hughes, Robert A and Preston, John S and Mascher, Peter}
}
@article {808,
	title = {A Reexamination of Active and Passive Tumor Targeting by Using Rod-Shaped Gold Nanocrystals and Covalently Conjugated Peptide Ligands},
	journal = {ACS Nano},
	volume = {4},
	year = {2010},
	note = {doi: 10.1021/nn102055s},
	month = {2010},
	pages = {5887 - 5896},
	publisher = {American Chemical Society},
	abstract = {The targeted delivery of nanoparticles to solid tumors is one of the most important and challenging problems in cancer nanomedicine, but the detailed delivery mechanisms and design principles are still not well understood. Here we report quantitative tumor uptake studies for a class of elongated gold nanocrystals (called nanorods) that are covalently conjugated to tumor-targeting peptides. A major advantage in using gold as a ?tracer? is that the accumulated gold in tumors and other organs can be quantitatively determined by elemental mass spectrometry (gold is not a natural element found in animals). Thus, colloidal gold nanorods are stabilized with a layer of polyethylene glycols (PEGs) and are conjugated to three different ligands: (i) a single-chain variable fragment (ScFv) peptide that recognizes the epidermal growth factor receptor (EGFR); (ii) an amino terminal fragment (ATF) peptide that recognizes the urokinase plasminogen activator receptor (uPAR); and (iii) a cyclic RGD peptide that recognizes the av?3 integrin receptor. Quantitative pharmacokinetic and biodistribution data show that these targeting ligands only marginally improve the total gold accumulation in xenograft tumor models in comparison with nontargeted controls, but their use could greatly alter the intracellular and extracellular nanoparticle distributions. When the gold nanorods are administered via intravenous injection, we also find that active molecular targeting of the tumor microenvironments (e.g., fibroblasts, macrophages, and vasculatures) does not significantly influence the tumor nanoparticle uptake. These results suggest that for photothermal cancer therapy, the preferred route of gold nanorod administration is intratumoral injection instead of intravenous injection.The targeted delivery of nanoparticles to solid tumors is one of the most important and challenging problems in cancer nanomedicine, but the detailed delivery mechanisms and design principles are still not well understood. Here we report quantitative tumor uptake studies for a class of elongated gold nanocrystals (called nanorods) that are covalently conjugated to tumor-targeting peptides. A major advantage in using gold as a ?tracer? is that the accumulated gold in tumors and other organs can be quantitatively determined by elemental mass spectrometry (gold is not a natural element found in animals). Thus, colloidal gold nanorods are stabilized with a layer of polyethylene glycols (PEGs) and are conjugated to three different ligands: (i) a single-chain variable fragment (ScFv) peptide that recognizes the epidermal growth factor receptor (EGFR); (ii) an amino terminal fragment (ATF) peptide that recognizes the urokinase plasminogen activator receptor (uPAR); and (iii) a cyclic RGD peptide that recognizes the av?3 integrin receptor. Quantitative pharmacokinetic and biodistribution data show that these targeting ligands only marginally improve the total gold accumulation in xenograft tumor models in comparison with nontargeted controls, but their use could greatly alter the intracellular and extracellular nanoparticle distributions. When the gold nanorods are administered via intravenous injection, we also find that active molecular targeting of the tumor microenvironments (e.g., fibroblasts, macrophages, and vasculatures) does not significantly influence the tumor nanoparticle uptake. These results suggest that for photothermal cancer therapy, the preferred route of gold nanorod administration is intratumoral injection instead of intravenous injection.},
	isbn = {1936-0851},
	url = {http://dx.doi.org/10.1021/nn102055s},
	author = {Huang, Xiaohua and Peng, Xianghong and Wang, Yiqing and Wang, Yuxiang and Shin, Dong M and El-Sayed, Mostafa A and Nie, Shuming}
}
@article {1114,
	title = {The Dependence of the Plasmon Field Induced Nonradiative Electronic Relaxation Mechanisms on the Gold Shell Thickness in Vertically Aligned CdTe-Au Core-Shell Nanorods},
	journal = {Nano Letters},
	volume = {9},
	number = {11},
	year = {2009},
	note = {Neretina, Svetlana Dreaden, Erik C. Qian, Wei El-Sayed, Mostafa A. Hughes, Robert A. Preston, John S. Mascher, Peter},
	month = {Nov},
	pages = {3772-3779},
	abstract = {The dependence of the plasmon field enhancement of the nonradiative relaxation rate of the band gap electrons in vertically aligned CdTe-Au core-shell nanorods on the plasmonic gold nanoshell thickness is examined. Increasing the thickness of the gold nanoshell from 15 to 26 nm is found to change the decay curve from being nonexponential and anisotropic to one that is fully exponential and isotropic (i.e., independent of the nanorod orientation with respect to the exciting light polarization direction). Analysis of the kinetics of the possible electronic relaxation enhancement mechanisms is carried out, and DDA simulated properties of the induced plasmonic field of the thin and thick gold nanoshells are determined. On the basis of the conclusions of these treatments and the experimental results, it is concluded that by increasing the nanoshell thickness the relaxation processes evolve from multiple enhancement mechanisms, dominated by highly anisotropic Auger processes, to mechanism(s) involving first-order excited electron ejection process(es). The former is shown to give rise to nonexponential anisotropic decays in the dipolar plasmon field of the thin nanoshell, while the latter exhibits an exponential isotropic decay in the unpolarized plasmonic field of the thick nanoshell.},
	isbn = {1530-6984},
	doi = {10.1021/nl901960w},
	author = {Neretina, Svetlana and Dreaden, Erik and Qian, Wei and El-Sayed, Mostafa A and Hughes, Robert A and Preston, John S and Mascher, Peter}
}
@article {1113,
	title = {Exciton Lifetime Tuning by Changing the Plasmon Field Orientation with Respect to the Exciton Transition Moment Direction: CdTe-Au Core-Shell Nanorods},
	journal = {Nano Letters},
	volume = {9},
	number = {3},
	year = {2009},
	note = {Neretina, Svetlana Qian, Wei Dreaden, Erik C. El-Sayed, Mostafa A. Hughes, Robert A. Preston, John S. Mascher, Peter},
	month = {Mar},
	pages = {1242-1248},
	abstract = {We studied the anisotropy of the influence of plasmonic fields, arising from the optical excitation of a gold nanoshell plasmon absorption at 770 nm, on the lifetime of the bandgap state of the CdTe core in vertically aligned CdTe-Au core-shell nanorods. The previously observed decrease in the lifetime was studied as a function of the tilt angle between the long axis of the nanorod and the electric field polarization direction of the plasmon inducing exciting light. It is observed that the strongest enhancement to the exciton relaxation rate occurs when the two axes are parallel to one another. These results are discussed in terms of the coupling between the exciton transition moment of the CdTe rod and the electric field polarization direction of the gold nanoshell plasmon at 770 nm, which was determined from theoretical modeling based on the discrete dipole approximation.},
	isbn = {1530-6984},
	doi = {10.1021/nl900183m},
	author = {Neretina, Svetlana and Qian, Wei and Dreaden, Erik and El-Sayed, Mostafa A and Hughes, Robert A and Preston, John S and Mascher, Peter}
}
@article {1117,
	title = {Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications},
	journal = {Advanced Materials},
	volume = {21},
	number = {48},
	year = {2009},
	note = {Huang, Xiaohuo Neretina, Svetiana El-Sayed, Mostafa A.},
	month = {Dec},
	pages = {4880-4910},
	abstract = {Noble metal nanoparticles; are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle{\textquoteright}s dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle{\textquoteright}s radiative properties, such as absorption and scattering. Moreover, by confining the photon{\textquoteright}s wavelength to the nanoparticle{\textquoteright}s small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.},
	isbn = {0935-9648},
	doi = {10.1002/adma.200802789},
	author = {Huang, Xiaohua and Neretina, Svetlana and El-Sayed, Mostafa A}
}
@article {1110,
	title = {The sensitivity of the energy band gap to changes in the dimensions of the CdSe quantum rods at room temperature: STM and theoretical studies},
	journal = {Chemical Physics Letters},
	volume = {473},
	number = {4-6},
	year = {2009},
	note = {Talaat, H. Abdallah, T. Mohamed, M. B. Negm, S. El-Sayed, Mostafa A.},
	month = {May},
	pages = {288-292},
	abstract = {The energy band gap of a series of different sizes of CdSe quantum rods have been determined by STM technique at room temperature. The results confirm that the band gap of CdSe quantum rods (QRs) depends mainly on the width (the dimension of the electron confinement) and only slightly on the length as shown previously in the literatures. The experimental data is compared to that calculated using two theoretical models, the effective mass approximation (EMA) and the semi-empirical pseudopotential method (SEPM). The theoretical values for the energy band gap at varying radius are in agreement with the experimental results within 0.08 eV. (c) 2008 Published by Elsevier B.V.},
	isbn = {0009-2614},
	doi = {10.1016/j.cplett.2008.11.025},
	author = {Talaat, M. H. and Abdallah, T. and Mohamed, MB and Negm, S. and El-Sayed, Mostafa A}
}
@article {1120,
	title = {Can the observed changes in the size or shape of a colloidal nanocatalyst reveal the nanocatalysis mechanism type: Homogeneous or heterogeneous?},
	journal = {Topics in Catalysis},
	volume = {48},
	number = {1-4},
	year = {2008},
	note = {Narayanan, Radha Tabor, Christopher El-Sayed, Mostafa A.},
	month = {May},
	pages = {60-74},
	abstract = {The surface energy of metallic nanocrystals is relatively high compared to bulk materials due to the metal-metal bond deficiency of the surface atoms. This results in an insufficient chemical valency. In addition, smaller nanoparticles possess a higher degree of curvature, weakening, the bonding of their surface atoms. This is especially true for non-spherical shapes, which are comprised of a large number of sharp corner and edge sites. These atomic sites possess higher surface energies due to the lower number of shared bonds with the nanoparticle, resulting in instability of the surface atoms and rendering them physically unstable and chemically active. In many instances, the constant "bombardment" of these surface atoms by the solvent molecules as well as by the reactant molecules when these nanocrystals are in colloidal solution could lead to surface atom dissolution, both physically and/or chemically. This phenomenon could alter the functionality of the metallic colloidal nanoparticle from supplying catalytically active sites (in heterogeneous catalysis) to serving as a reservoir of catalytically active species to the solution (in homogeneous catalysis). In the latter type, if the atoms of the nanocatalyst appear in the products, the nanoparticle is no longer a catalyst but a reactant. In this review we attempt to answer the question raised in the title by examining our Previous work on the changes in size, shape, and other physical and chemical properties of colloidal transition metal nanoparticles during the nanocatalysis of two fundamentally different and important reactions: (1) the gentle electron-transfer reaction at room temperature involving the reduction of hexacyanoferrate (III) ions with thiosulfate ions and (2) the more harsh Suzuki cross-coupling reaction between phenylboronic acid and iodobenzene that takes place at 100 degrees C for 12 h. Changes in the nanoparticle dimensions were followed with TEM and HRTEM. Raman and FTIR spectroscopies were used to follow the chemical changes. For each change, we will use the above definition to see if the observed change can help us determine whether the catalysis is homogeneous or heterogeneous.},
	isbn = {1022-5528},
	doi = {10.1007/s11244-008-9057-4},
	author = {Narayanan, Radha and Tabor, C. E. and El-Sayed, Mostafa A}
}
@article {811,
	title = {Plasmon Field Effects on the Nonradiative Relaxation of Hot Electrons in an Electronically Quantized System: CdTe-Au Core-Shell Nanowires},
	journal = {Nano Letters},
	volume = {8},
	year = {2008},
	note = {doi: 10.1021/nl801303g},
	month = {2008},
	pages = {2410 - 2418},
	publisher = {American Chemical Society},
	abstract = {The intense electromagnetic fields of plasmonic nanoparticles, resulting from the excitation of their localized surface plasmon oscillations, are known to enhance radiative processes. Their effect on the nonradiative electronic processes, however, is not as well-documented. Here, we report on the enhancement of the nonradiative electronic relaxation rates in CdTe nanowires upon the addition of a thin gold nanoshell, especially at excitation energies overlapping with those of the surface plasmon oscillations. Some possible mechanisms by which localized surface plasmon fields can enhance nonradiative relaxation processes of any quantized electronic excitations are proposed.The intense electromagnetic fields of plasmonic nanoparticles, resulting from the excitation of their localized surface plasmon oscillations, are known to enhance radiative processes. Their effect on the nonradiative electronic processes, however, is not as well-documented. Here, we report on the enhancement of the nonradiative electronic relaxation rates in CdTe nanowires upon the addition of a thin gold nanoshell, especially at excitation energies overlapping with those of the surface plasmon oscillations. Some possible mechanisms by which localized surface plasmon fields can enhance nonradiative relaxation processes of any quantized electronic excitations are proposed.},
	isbn = {1530-6984},
	doi = {10.1021/nl801303g},
	url = {http://dx.doi.org/10.1021/nl801303g},
	author = {Neretina, Svetlana and Qian, Wei and Dreaden, Erik and El-Sayed, Mostafa A and Hughes, Robert A and Preston, John S and Mascher, Peter}
}
@article {1121,
	title = {Some aspects of colloidal nanoparticle stability, catalytic activity, and recycling potential},
	journal = {Topics in Catalysis},
	volume = {47},
	number = {1-2},
	year = {2008},
	note = {Narayanan, Radha El-Sayed, Mostafa A.},
	month = {Mar},
	pages = {15-21},
	abstract = {In this review article, we examine many important aspects of the nanocatalysis field such as size and shape dependent nanocatalysis, the stability of nanoparticles during its catalytic function, and their recycling potential. We provide an overview of some of the work in the literature pertinent to these topics and also discuss some of our own work in these important areas. Some examples of how the catalytic activity is affected by the size of the nanoparticles are discussed as well as how the catalytic process affects the nanoparticle size after its catalytic function. The synthesis of platinum nanoparticles of different shapes is surveyed and the dependence of nanoparticle shape on the catalytic activity is discussed. In addition, changes in the nanoparticle shape and resulting changes in the catalytic activity are also discussed. The recycling potential of the metal nanocatalysts is also highlighted. In addition, a simple examination of the mechanism of nanocatalysis is discussed.},
	isbn = {1022-5528},
	doi = {10.1007/s11244-007-9029-0},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1136,
	title = {Change in titania structure from amorphousness to crystalline increasing photoinduced electron-transfer rate in dye-titania system},
	journal = {Journal of Physical Chemistry C},
	volume = {111},
	number = {26},
	year = {2007},
	note = {Nishikiori, Hiromasa Qian, Wei El-Sayed, Mostafa A. Tanaka, Nobuaki Fujii, Tsuneo},
	month = {Jul},
	pages = {9008-9011},
	abstract = {Thin titania gel films containing well-dispersed fluorescein dye were prepared by the sol-gel method and treated with steam to promote crystal growth of the titania particles. It is known that steam treatment converts the titania structure from amorphousness to crystalline. In the present study, such change is found to increase the rate of the photoinduced electron transfer from and to dispersed fluorescein dye molecules.},
	isbn = {1932-7447},
	doi = {10.1021/jp072625q},
	author = {Nishikiori, H. and Qian, Wei and El-Sayed, Mostafa A and Tanaka, N. and Fujii, T.}
}
@article {1164,
	title = {Carbon-supported spherical palladium nanoparticles as potential recyclable catalysts for the Suzuki reaction},
	journal = {Journal of Catalysis},
	volume = {234},
	number = {2},
	year = {2005},
	note = {Narayanan, R El-Sayed, MA},
	month = {Sep},
	pages = {348-355},
	abstract = {Carbon-supported PVP-Pd nanoparticles prepared by adsorption of colloidal PVP-Pd nanoparticles onto activated carbon are used as catalysts for the Suzuki reaction between phenylboronic acid and iodobenzene to form biphenyl. These carbon-supported nanoparticles result in a lower biphenyl yield during the first cycle than the colloidal Pd nanoparticles that we studied previously. The carbon-supported Pd nanoparticles retain 69\% of its activity upon recycling (second cycle), which is almost double the recycling potential observed in colloidal Pd nanoparticles (37\% retention of activity). In addition, the carbon-supported Pd nanoparticles retain 73 +/- 3\% of their catalytic activity during the second through fifth cycles of the Suzuki reaction, while the catalytic activity of the colloidal Pd nanoparticles greatly decreases during that time frame. The carbon support that the palladium nanoparticles are adsorbed onto helps to preserve its catalytic activity for longer time periods. The effect of catalysis and recycling on the nanoparticle size is also investigated. The average size of the carbon-supported palladium nanoparticles is 1.9 +/- 0.1 nm initially, 2.6 +/- 0.1 nm after the first cycle, and 3.1 +/- 0.1 nm after the second cycle. The continued growth of the supported nanoparticles suggests that the carbon support protects the palladium nanoparticles during the harsh Suzuki reaction and prevents aggregation and precipitation unlike the colloidal palladium nanoparticles. In addition, a narrow size distribution during the growth process (Ostwald ripening) is observed for the carbon-supported nanoparticles. This could be due to the adsorption method for preparing carbon-supported Pd nanoparticles because excess unaggregated palladium atoms will not be adsorbed onto the carbon support. (c) 2005 Elsevier Inc. All rights reserved.},
	isbn = {0021-9517},
	doi = {10.1016/j.jcat.2005.06.024},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1165,
	title = {Catalysis with transition metal nanoparticles in colloidal solution: Nanoparticle shape dependence and stability},
	journal = {Journal of Physical Chemistry B},
	volume = {109},
	number = {26},
	year = {2005},
	note = {Narayanan, R El-Sayed, MA},
	month = {Jul},
	pages = {12663-12676},
	abstract = {While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.},
	isbn = {1520-6106},
	doi = {10.1021/jp051066p},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {836,
	title = {Chemistry and properties of nanocrystals of different shapes},
	journal = {Chemical Reviews},
	volume = {105},
	year = {2005},
	pages = {1025-1102},
	publisher = {ACS Publications},
	isbn = {0009-2665},
	doi = {10.1021/cr030063a},
	url = {http://dx.doi.org/10.1021/cr030063a},
	author = {Burda, Clemens and Chen, X. and Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1167,
	title = {Effect of colloidal nanocatalysis on the metallic nanoparticle shape: The Suzuki reaction},
	journal = {Langmuir},
	volume = {21},
	number = {5},
	year = {2005},
	note = {Narayanan, R El-Sayed, MA},
	month = {Mar},
	pages = {2027-2033},
	abstract = {Dominantly tetrahedral shaped poly(vinylpyrrolidone) -platinum (PVP-Pt) nanoparticles are shown to catalyze the Suzuki reaction between phenylboronic acid and iodobenzene but are not as active as the spherical palladium nanoparticles studied previously. The dominantly tetrahedral PVP-Pt nanoparticles (55 +/- 4\% regular tetrahedral, 22 +/- 2\% distorted tetrahedral, and 23 +/- 2\% spherical nanoparticles) are synthesized by using the hydrogen reduction method. The transmission electron microscopy (TEM) results show that a transformation of shape from tetrahedral to spherical Pt nanoparticles takes place 3 h into the first cycle of the reaction. After the first cycle, the spherical nanoparticles have a similar size distribution to that of the tetrahedral nanoparticles before the reaction and the observed shape distribution is 18 +/- 6\% regular tetrahedral, 28 +/- 5\% distorted tetrahedral, and 54 +/- 5\% spherical nanoparticles. After the second cycle of the Suzuki reaction, the shape distribution is 13 +/- 5\% regular tetrahedral, 24 +/- 5\% distorted tetrahedral, and 63 +/- 7\% spherical nanoparticles. After the second cycle, the transformed spherical nanoparticles continue to grow, and this could be due to the strong capping action of the higher molecular weight PVP (M-w = 360 000), which makes the nanoparticles more resistant to aggregation and precipitation, unlike the Pd nanoparticles capped with the lower molecular weight PVP (M-w = 40 000) used previously. The transformation in shape also occurs when the nanoparticles are refluxed in the presence of the solvent, sodium acetate, and iodobenzene and results in spherical nanoparticles with a similar size distribution to that of the tetrahedral nanoparticles before any perturbations. However, in the presence of phenylboronic acid, the regular tetrahedral nanoparticles remain dominant (51 6\%) and maintain their size. These results support our previous studies in which we proposed that phenylboronic acid binds to the nanoparticle surface and thus acts as a capping agent for the particle and reacts with the iodobenzene. Recycling the nanoparticles results in a drastic reduction of the catalytic activity, and this must be due to the transformation of shape from the dominantly tetrahedral to the larger dominantly spherical nanoparticles. This also supports results in the literature that show that spherical platinum nanoparticles do not catalyze this reaction.},
	isbn = {0743-7463},
	doi = {10.1021/la047600m},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1166,
	title = {FTIR study of the mode of binding of the reactants on the Pd nanoparticle surface during the catalysis of the Suzuki reaction},
	journal = {Journal of Physical Chemistry B},
	volume = {109},
	number = {10},
	year = {2005},
	note = {Narayanan, R El-Sayed, MA},
	month = {Mar},
	pages = {4357-4360},
	abstract = {In the Suzuki reaction between phenylboronic acid and iodobenzene catalyzed by palladium nanoparticles, our previous studies suggested that the phenylboronic acid adsorbs on the nanoparticle surface and then interacts with the iodobenzene that is present in solution. In the present study, FTIR is used to examine the change in the vibrational frequencies of phenylboronic acid in films with and without the addition of palladium nanoparticles. The large change in the B-O stretching frequency of phenylboronic acid from 1348 to 1376 cm(-1) in the presence of sodium acetate and palladium nanoparticles strongly suggests that the mode of binding of phenylboronic acid to the Pd nanoparticle surface involves a B-O-Pd type of bonding. Shifts in the B-C stretching mode and the out-of-plane phenyl C-C ring deformation bands associated with phenylboronic acid provide additional confirmations of the binding process. It is also shown that the phenylboronic acid needs to be in the deprotonated form in the presence of sodium acetate (phenylboronate anion) to bind to the palladium nanoparticle surface. No changes in the characteristic bands of iodobenzene were observed in films made in the presence of the palladium nanoparticles. The FTIR studies provide proof of the mode of binding that occurs in the nanoparticle Surface for the first time and also confirms the mechanism of the Suzuki reaction that we proposed previously.},
	isbn = {1520-6106},
	doi = {10.1021/jp044659t},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {820,
	title = {Raman Studies on the Interaction of the Reactants with the Platinum Nanoparticle Surface during the Nanocatalyzed Electron Transfer Reaction},
	journal = {The Journal of Physical Chemistry B},
	volume = {109},
	year = {2005},
	note = {doi: 10.1021/jp053526k},
	month = {2005},
	pages = {18460 - 18464},
	publisher = {American Chemical Society},
	abstract = {Raman studies are conducted to understand the specific interactions between the individual reactants and the platinum nanoparticle surface during the nanocatalyzed electron transfer reaction between hexacyanoferrate (III) ions and thiosulfate ions. When Pt nanoparticles are added to the thiosulfate ion solution, a shift in the symmetric SS stretching mode is observed compared to the frequency observed for the free thiosulfate ions in solution, suggesting that binding to the Pt nanoparticle surface occurs via the S- ion. It is also observed that there are no shifts in the symmetric and asymmetric OSO bending or SO stretching frequencies. This suggests that the thiosulfate ions do not bind to the nanoparticle surface via the O- ion. When platinum nanoparticles are added to the hexacyanoferrate(III) ion solution, evidence is found for both adsorbed hexacyanoferrate(III) ions and a platinum cyanide complex. For adsorbed hexacyanoferrate(III) ions, the CN stretching frequency is observed at 2101 cm-1 and the Fe?C stretching frequency is found at 368 cm-1. The observed CN stretching frequencies located at 2147 and 2167 cm-1 provide strong evidence that there is a Pt(CN)42- platinum cyanide complex formed. In addition, the Pt?C?N band is also observed at 2054 cm-1. These observed bands provide spectroscopic evidence that the hexacyanoferrate(III) ions dissolve by forming a complex with the surface platinum atoms of the nanoparticles. Raman spectra of the product mixtures are obtained after the completion of the reaction when carried out with higher reactant concentrations to observe the Raman spectra, but with a similar 10:1 ratio of thiosulfate to hexacyanoferrate(III) ions as used previously, with and without PVP?Pt nanoparticles at a correspondingly higher concentration. It is observed that there are no shifts in the characteristic Raman bands associated with hexacyanoferrate(II) ions and no evidence for the formation of adsorbed hexacyanoferrate(II) species or platinum cyanide complexes in the presence of the platinum nanoparticles. In addition, there is evidence for the shifted symmetric SS stretching mode, suggesting that some of the unreacted thiosulfate (present in large excess) is bound to the Pt nanoparticle surface. Thus, under the actual reaction conditions, the hexacyanoferrate(III) ions preferentially react with adsorbed thiosulfate ions to form the reaction products, and this supports the surface catalytic mechanism we proposed previously.Raman studies are conducted to understand the specific interactions between the individual reactants and the platinum nanoparticle surface during the nanocatalyzed electron transfer reaction between hexacyanoferrate (III) ions and thiosulfate ions. When Pt nanoparticles are added to the thiosulfate ion solution, a shift in the symmetric SS stretching mode is observed compared to the frequency observed for the free thiosulfate ions in solution, suggesting that binding to the Pt nanoparticle surface occurs via the S- ion. It is also observed that there are no shifts in the symmetric and asymmetric OSO bending or SO stretching frequencies. This suggests that the thiosulfate ions do not bind to the nanoparticle surface via the O- ion. When platinum nanoparticles are added to the hexacyanoferrate(III) ion solution, evidence is found for both adsorbed hexacyanoferrate(III) ions and a platinum cyanide complex. For adsorbed hexacyanoferrate(III) ions, the CN stretching frequency is observed at 2101 cm-1 and the Fe?C stretching frequency is found at 368 cm-1. The observed CN stretching frequencies located at 2147 and 2167 cm-1 provide strong evidence that there is a Pt(CN)42- platinum cyanide complex formed. In addition, the Pt?C?N band is also observed at 2054 cm-1. These observed bands provide spectroscopic evidence that the hexacyanoferrate(III) ions dissolve by forming a complex with the surface platinum atoms of the nanoparticles. Raman spectra of the product mixtures are obtained after the completion of the reaction when carried out with higher reactant concentrations to observe the Raman spectra, but with a similar 10:1 ratio of thiosulfate to hexacyanoferrate(III) ions as used previously, with and without PVP?Pt nanoparticles at a correspondingly higher concentration. It is observed that there are no shifts in the characteristic Raman bands associated with hexacyanoferrate(II) ions and no evidence for the formation of adsorbed hexacyanoferrate(II) species or platinum cyanide complexes in the presence of the platinum nanoparticles. In addition, there is evidence for the shifted symmetric SS stretching mode, suggesting that some of the unreacted thiosulfate (present in large excess) is bound to the Pt nanoparticle surface. Thus, under the actual reaction conditions, the hexacyanoferrate(III) ions preferentially react with adsorbed thiosulfate ions to form the reaction products, and this supports the surface catalytic mechanism we proposed previously.},
	isbn = {1520-6106},
	doi = {10.1021/jp053526k},
	url = {http://dx.doi.org/10.1021/jp053526k},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1176,
	title = {Changing catalytic activity during colloidal platinum nanocatalysis due to shape changes: Electron-transfer reaction},
	journal = {Journal of the American Chemical Society},
	volume = {126},
	number = {23},
	year = {2004},
	note = {Narayanan, R El-Sayed, MA},
	month = {Jun},
	pages = {7194-7195},
	isbn = {0002-7863},
	doi = {10.1021/ja0486061},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {819,
	title = {Effect of Colloidal Catalysis on the Nanoparticle Size Distribution:  Dendrimer-Pd vs PVP-Pd Nanoparticles Catalyzing the Suzuki Coupling Reaction},
	journal = {The Journal of Physical Chemistry B},
	volume = {108},
	year = {2004},
	note = {doi: 10.1021/jp037169u},
	month = {2004},
	pages = {8572 - 8580},
	publisher = {American Chemical Society},
	abstract = {A comparison of the stability and catalytic activity of PAMAM?OH generation 4 dendrimer?Pd nanoparticles (1.3 {\textpm} 0.1 nm) with the previously studied PVP?Pd nanoparticles (2.1 {\textpm} 0.1 nm) in the Suzuki coupling reaction between phenylboronic acid and iodobenzene is conducted. After the first cycle, the average size of the PVP?Pd nanoparticles increases by 38\% and the dendrimer?Pd nanoparticles increases by 54\%. After the second cycle, the PVP?Pd nanoparticles decrease in size by 24\% whereas the dendrimer?Pd nanoparticles continue to increase in size by 35\%. The strong encapsulating action of the PAMAM?OH generation 4 dendrimer?Pd nanoparticles could make the rate of conversion to the full nanoparticle size slow, resulting in a large excess Pd metal atom concentration in solution, resulting in the continuous growth of the nanoparticles during the catalytic reaction. The effect of the individual reactants on the stability of the dendrimer?Pd nanoparticles has also been investigated and found to be similar to that observed for the PVP?Pd nanoparticles previously. It was found that the nanoparticle size growth occurs while refluxing in the presence of only the solvent, sodium acetate, or iodobenzene. However, the presence of phenylboronic acid is found to inhibit the particle growth, suggesting that it acts as a capping agent. Thus, the reaction mechanism must involve the adsorption of phenylboronic acid to the nanoparticle surface, which subsequently reacts with the iodobenzene in solution. This is similar to the mechanism found previously on PVP?Pd nanoparticles, suggesting that the mechanism is insensitive to the capping material used. The ratio of the yield of biphenyl formed in the second cycle to that in the first cycle is higher for the dendrimer?Pd nanoparticles catalyzed reaction than for the PVP?Pd nanoparticles. This could be due to the greater stability of the dendrimer?Pd nanoparticles and the increase in its size during the reaction. The larger PVP?Pd nanoparticles studied previously is believed to aggregate and precipitate out of solution during the second cycle. The presence of excess dendrimer is found to severely diminish the catalytic activity of the dendrimer?Pd nanoparticles and also diminishes the change in the Pd nanoparticle size during the catalysis.A comparison of the stability and catalytic activity of PAMAM?OH generation 4 dendrimer?Pd nanoparticles (1.3 {\textpm} 0.1 nm) with the previously studied PVP?Pd nanoparticles (2.1 {\textpm} 0.1 nm) in the Suzuki coupling reaction between phenylboronic acid and iodobenzene is conducted. After the first cycle, the average size of the PVP?Pd nanoparticles increases by 38\% and the dendrimer?Pd nanoparticles increases by 54\%. After the second cycle, the PVP?Pd nanoparticles decrease in size by 24\% whereas the dendrimer?Pd nanoparticles continue to increase in size by 35\%. The strong encapsulating action of the PAMAM?OH generation 4 dendrimer?Pd nanoparticles could make the rate of conversion to the full nanoparticle size slow, resulting in a large excess Pd metal atom concentration in solution, resulting in the continuous growth of the nanoparticles during the catalytic reaction. The effect of the individual reactants on the stability of the dendrimer?Pd nanoparticles has also been investigated and found to be similar to that observed for the PVP?Pd nanoparticles previously. It was found that the nanoparticle size growth occurs while refluxing in the presence of only the solvent, sodium acetate, or iodobenzene. However, the presence of phenylboronic acid is found to inhibit the particle growth, suggesting that it acts as a capping agent. Thus, the reaction mechanism must involve the adsorption of phenylboronic acid to the nanoparticle surface, which subsequently reacts with the iodobenzene in solution. This is similar to the mechanism found previously on PVP?Pd nanoparticles, suggesting that the mechanism is insensitive to the capping material used. The ratio of the yield of biphenyl formed in the second cycle to that in the first cycle is higher for the dendrimer?Pd nanoparticles catalyzed reaction than for the PVP?Pd nanoparticles. This could be due to the greater stability of the dendrimer?Pd nanoparticles and the increase in its size during the reaction. The larger PVP?Pd nanoparticles studied previously is believed to aggregate and precipitate out of solution during the second cycle. The presence of excess dendrimer is found to severely diminish the catalytic activity of the dendrimer?Pd nanoparticles and also diminishes the change in the Pd nanoparticle size during the catalysis.},
	isbn = {1520-6106},
	doi = {10.1021/jp037169u},
	url = {http://dx.doi.org/10.1021/jp037169u},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1177,
	title = {Effect of nanocatalysis in colloidal solution on the tetrahedral and cubic nanoparticle SHAPE: Electron-transfer reaction catalyzed by platinum nanoparticles},
	journal = {Journal of Physical Chemistry B},
	volume = {108},
	number = {18},
	year = {2004},
	note = {Narayanan, R El-Sayed, MA},
	month = {May},
	pages = {5726-5733},
	abstract = {The stability of tetrahedral and cubic platinum nanoparticles during the catalysis of the electron-transfer reaction between hexacyanoferrate (III) and thiosulfate ions in colloidal solution at room temperature was studied by using TEM and HRTEM. Before the reaction, the dominantly tetrahedral nanoparticles have a shape distribution of 55 +/- 4\% regular tetrahedral, 22 +/- 2\% distorted tetrahedral, and 23 +/- 2\% spherical nanoparticles, and the dominantly cubic nanoparticles have an initial shape distribution of 56 4\% regular cubes, 13 +/- 1\% distorted cubes, and 31 +/- 3\% truncated octahedral nanoparticles. The amount of tetrahedral nanoparticles decreases by 60 +/- 5\% after the first cycle and by 62 +/- 4\% after the second cycle of the reaction. In the case of cubic nanoparticles, the amount of cubic nanoparticles decreases by 39 +/- 5\% after the first cycle and by 66 +/- 5\% after the second cycle compared to before the reaction. After the first and second cycles of the reaction, there are a greater percentage of distorted tetrahedral and distorted cubic nanoparticles present. The rate of the dissolution of the surface Pt atoms is faster for the tetrahedral nanoparticles than for the cubic nanoparticles. This suggests that tetrahedral nanoparticles, with their sharp corners and edges, are more sensitive and more liable to shape changes during nanocatalysis. The presence of just hexacyanoferrate ions in the solution with the nanoparticles is found to increase the amount of distorted tetrahedral and distorted cubes present much more than during the reaction. The presence of only the thiosulfate ions does not seem to affect the size or shape distribution which might result from the capping ability of this anion and thus protects the nanoparticles.},
	isbn = {1520-6106},
	doi = {10.1021/jp0493780},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1175,
	title = {Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution},
	journal = {Nano Letters},
	volume = {4},
	number = {7},
	year = {2004},
	note = {Narayanan, R El-Sayed, MA},
	month = {Jul},
	pages = {1343-1348},
	abstract = {The activation energies and the average rate constants are determined in the 298 K-318 K temperature range for the early stages of the nanocatalytic reaction between hexacyanoferrate (111) and thiosulfate ions using 4.8 +/- 0.1 nm tetrahedral, 7.1 +/- 0.2 nm cubic, and 4.9 +/- 0.1 nm "near spherical" nanocrystals. These kinetic parameters are found to correlate with the calculated fraction of surface atoms located on the corners and edges in each size and shape.},
	isbn = {1530-6984},
	doi = {10.1021/nl0495256},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1186,
	title = {Effect of catalysis on the stability of metallic nanoparticles: Suzuki reaction catalyzed by PVP-palladium nanoparticles},
	journal = {Journal of the American Chemical Society},
	volume = {125},
	number = {27},
	year = {2003},
	note = {Narayanan, R El-Sayed, MA},
	month = {Jul},
	pages = {8340-8347},
	abstract = {The small size of nanoparticles makes them attractive in catalysis due to their large surface-to-volume ratio. However, being small raises questions about their stability in the harsh chemical environment in which these nanoparticles find themselves during their catalytic function. In the present work, we studied the Suzuki reaction between phenylboronic acid and iodobenzene catalyzed by PVP-Pd nanoparticles to investigate the effect of catalysis, recycling, and the different individual chemicals on the stability and catalytic activity of the nanoparticles during this harsh reaction. The stability of the nanoparticles to the different perturbations is assessed using TEM, and the changes in the catalytic activity are assessed using HPLC analysis of the product yield. It was found that the process of refluxing the nanoparticles for 12 h during the Suzuki catalytic reaction increases the average size and the width of the distribution of the nanoparticles. This was attributed to Ostwald ripening in which the small nanoparticles dissolve to form larger nanoparticles. The kinetics of the change in the nanoparticle size during the 12 h period show that the nanoparticles increase in size during the beginning of the reaction and level off toward the end of the first cycle. When the nanoparticles are recycled for the second cycle, the average size decreases. This could be due to the larger nanoparticles aggregating and precipitating out of solution. This process could also explain the observed loss of the catalytic efficiency of the nanoparticles during the second cycle. It is also found that the addition of biphenyl to the reaction mixture results in it poisoning the active sites and giving rise to a low product yield. The addition of excess PVP stabilizer to the reaction mixture seems to lead to the stability of the nanoparticle surface and size, perhaps due to the inhibition of the Ostwald ripening process. This also decreases the catalytic efficiency of the nanoparticles due to capping of the nanoparticle surface. The addition of phenylboronic acid is found to lead to the stability of the size distribution as it binds to the particle surface through the O- of the OH group and acts as a stabilizer. Iodobenzene is found to have no effect and thus probably does not bind strongly to the surface during the catalytic process. These two results might have an implication on the catalytic mechanism of this reaction.},
	isbn = {0002-7863},
	doi = {10.1021/ja035044x},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1185,
	title = {Effect of catalytic activity on the metallic nanoparticle size distribution: Electron-transfer reaction between Fe(CN)(6) and thiosulfate ions catalyzed by PVP-platinum nanoparticles},
	journal = {Journal of Physical Chemistry B},
	volume = {107},
	number = {45},
	year = {2003},
	note = {Narayanan, R El-Sayed, MA},
	month = {Nov},
	pages = {12416-12424},
	abstract = {The electron-transfer reaction between hexacyanoferrate(III) ions and thiosulfate ions is known to be catalyzed by platinum nanoparticles. In the present study, the stability and catalytic activity of the PVP-Pt nanoparticle during its catalytic function for this electron-transfer reaction is studied. The stability of the nanoparticles after various perturbations was assessed using TEM, and the kinetics of the reaction was followed using absorption spectroscopy. The studies were conducted on four different concentrations of PVP-Pt nanoparticles. It was found that the average size and width of the PVP-Pt nanoparticles decrease slightly after the first and second cycles of the electron-transfer reaction. The size and size distribution width do not change in the presence of only the thiosulfate reactant, whereas the presence of only the hexacyanoferrate reactant results in a reduction of the nanoparticle size. The reduction in the nanoparticle size in the presence of hexacyanoferrate(HI) ions is proposed to result from the dissolution of surface Pt atoms through complexation with the strong cyanide ligand. Thiosulfate ions bind to the nanoparticle surface and act as a capping material, resulting in the stability of the nanoparticles. Judging from these observations, it is possible that the mechanism of this catalytic reaction involves the thiosulfate ions binding to the free sites on the surface of the nanoparticles, followed by reaction with hexacyanoferrate ions approaching the nanoparticle surface from the solution. Conducting the reaction with the nanoparticles preexposed to thiosulfate results in very little change in the centers and widths of the size distributions of the nanoparticles, thus suggesting that thiosulfate ions bind to the nanoparticle surface and inhibit desorption of Pt atoms by hexacyanoferrate(III) ions. The kinetics of the electron-transfer reaction during the first and second cycles is similar. The activation energy of the nanoparticle catalytic reaction is found to decrease linearly with increasing nanoparticle concentration during both the first and second cycles. If increasing the nanoparticle concentration leads to more aggregation, then these results suggest that the aggregated Pt has greater catalytic activity than the individual nanoparticles.},
	isbn = {1520-6106},
	doi = {10.1021/jp035647v},
	author = {Narayanan, Radha and El-Sayed, Mostafa A}
}
@article {1187,
	title = {Medium effect on the electron cooling dynamics in gold nanorods and truncated tetrahedra},
	journal = {Advanced Materials},
	volume = {15},
	number = {5},
	year = {2003},
	note = {Link, S Hathcock, DJ Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {393-+},
	abstract = {A study on the electron relaxation dynamics and thermal cooling of colloidal gold nanoparticles (see Figure) in air and water finds that the local energy exchange with the surrounding medium occurs on the picosecond time scale, comparable with the electron-phonon relaxation, while a slow heat dissipation by water ensures that the particles remain heated for hundreds of picoseconds.},
	isbn = {0935-9648},
	doi = {10.1002/adma.200390088},
	author = {Link, Stephan and Hathcock, D. J. and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {847,
	title = {Preparation and Growth Mechanism of Gold Nanorods (NRs) Using Seed-Mediated Growth Method},
	journal = {Chemistry of Materials},
	volume = {15},
	year = {2003},
	note = {doi: 10.1021/cm020732l},
	month = {2003},
	pages = {1957 - 1962},
	publisher = {American Chemical Society},
	isbn = {0897-4756},
	url = {http://dx.doi.org/10.1021/cm020732l},
	author = {Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {844,
	title = {Surface-Enhanced Raman Scattering Studies on Aggregated Gold Nanorods},
	journal = {The Journal of Physical Chemistry AThe Journal of Physical Chemistry A},
	volume = {107},
	year = {2003},
	note = {doi: 10.1021/jp026770+},
	month = {2003},
	pages = {3372 - 3378},
	publisher = {American Chemical Society},
	abstract = {Surface-enhanced Raman scattering (SERS) of adsorbed molecules on gold nanorods (NRs) with dimensions of 10 nm ? 27 nm was studied on silica surface with low to high surface coverage of NRs. The study was carried out to investigate both the dependence of the SERS intensity on the number of NRs and the NRs spacing on the silica surface. SERS of adsorbed molecules such as 2-aminothiophenol (2-ATP) and the capping molecules (hexadecyltrimethylammonium bromide) was studied on these surfaces using a near-IR laser excitation source (1064 nm). To produce silica surfaces covered with NRs, two approaches were used. In the first approach, monodispersed NRs gradually deposited from solution to silica surface and their number was increased by increasing the deposition time. In the second one, the NRs were first aggregated in solution and then deposited on the surface. Although using the first approach it was possible to prepare surfaces with high NR surface coverage, SERS intensity was found to be stronger for adsorbed molecules on surfaces covered with aggregated NRs. The observed increase in the SERS intensity in the case of aggregation was attributed to the enhancement of the electric field between the particles in the aggregates. It is shown that aggregated NRs in comparison with aggregated nanospheres (NSs) have stronger SERS enhancement under similar experimental conditions. In this comparison, some of the enhanced vibrational bands of 2-ATP on aggregated NRs are weakly enhanced or absent on aggregated NSs. Monitoring the SERS intensity of adsorbed 2-ATP versus its exposure time to the aggregated NRs shows that the SERS intensity of the adsorbed molecules reaches saturation, whereas the peak intensities of the capping molecules remain unchanged. The intensity saturation was discussed in terms of factors such as the saturation of the SERS active sites for 2-ATP on the gold surface and the partial damping of the plasmon band due to the stronger interaction of the adsorbate molecules with the metal surface.Surface-enhanced Raman scattering (SERS) of adsorbed molecules on gold nanorods (NRs) with dimensions of 10 nm ? 27 nm was studied on silica surface with low to high surface coverage of NRs. The study was carried out to investigate both the dependence of the SERS intensity on the number of NRs and the NRs spacing on the silica surface. SERS of adsorbed molecules such as 2-aminothiophenol (2-ATP) and the capping molecules (hexadecyltrimethylammonium bromide) was studied on these surfaces using a near-IR laser excitation source (1064 nm). To produce silica surfaces covered with NRs, two approaches were used. In the first approach, monodispersed NRs gradually deposited from solution to silica surface and their number was increased by increasing the deposition time. In the second one, the NRs were first aggregated in solution and then deposited on the surface. Although using the first approach it was possible to prepare surfaces with high NR surface coverage, SERS intensity was found to be stronger for adsorbed molecules on surfaces covered with aggregated NRs. The observed increase in the SERS intensity in the case of aggregation was attributed to the enhancement of the electric field between the particles in the aggregates. It is shown that aggregated NRs in comparison with aggregated nanospheres (NSs) have stronger SERS enhancement under similar experimental conditions. In this comparison, some of the enhanced vibrational bands of 2-ATP on aggregated NRs are weakly enhanced or absent on aggregated NSs. Monitoring the SERS intensity of adsorbed 2-ATP versus its exposure time to the aggregated NRs shows that the SERS intensity of the adsorbed molecules reaches saturation, whereas the peak intensities of the capping molecules remain unchanged. The intensity saturation was discussed in terms of factors such as the saturation of the SERS active sites for 2-ATP on the gold surface and the partial damping of the plasmon band due to the stronger interaction of the adsorbate molecules with the metal surface.},
	isbn = {1089-5639},
	doi = {10.1021/jp026770+},
	url = {http://dx.doi.org/10.1021/jp026770+},
	author = {Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1195,
	title = {The quenching of CdSe quantum dots photoluminescence by gold nanoparticles in solution},
	journal = {Photochemistry and Photobiology},
	volume = {75},
	number = {6},
	year = {2002},
	note = {Nikoobakht, B Burda, C Braun, M Hun, M El-Sayed, MA},
	month = {Jun},
	pages = {591-597},
	abstract = {The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the {110} facets only in the NR, which have higher surface energy.},
	isbn = {0031-8655},
	doi = {10.1562/0031-8655(2002)075<0591:tqocqd>2.0.co;2},
	author = {Nikoobakht, Babak and Burda, Clemens and Braun, Markus and Hun, M. and El-Sayed, Mostafa A}
}
@article {1194,
	title = {Surface-enhanced Raman scattering of molecules adsorbed on gold nanorods: off-surface plasmon resonance condition},
	journal = {Chemical Physics Letters},
	volume = {366},
	number = {1-2},
	year = {2002},
	note = {Nikoobakht, B Wang, JP El-Sayed, MA},
	month = {Nov},
	pages = {17-23},
	abstract = {The Raman spectra of several molecules adsorbed on gold nanospheres (NSs) (12 nm in diameter) and nanorods (NRs) (25 nm x 10 nm) are studied using an off-plasmon resonance excitation condition. The studies are carried out in colloidal solution and on solid substrates. Enhancement factors on the order of 10(4)-10(5) are observed for the adsorbed molecules on the NRs, however, no such enhancement was observed on NSs under similar condition. These factors are two orders of magnitude larger than the calculated value using the Wang and Kerker electromagnetic model. This suggests a contribution from the chemical mechanism in the observed enhancement. (C) 2002 Published by Elsevier Science B.V.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(02)01492-6},
	author = {Nikoobakht, Babak and Wang, Jianping and El-Sayed, Mostafa A}
}
@article {1209,
	title = {Evidence for bilayer assembly of cationic surfactants on the surface of gold nanorods},
	journal = {Langmuir},
	volume = {17},
	number = {20},
	year = {2001},
	note = {Nikoobakht, B El-Sayed, MA},
	month = {Oct},
	pages = {6368-6374},
	abstract = {The surface structure of gold nanorods (NRs) capped with cationic surfactants in water was studied by FTIR, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). For gold nanorods, the FTIR results show the formation of new bands, which indicate binding of the surfactant headgroup to the surface of the NR. These bands are stable at temperatures as high as 350 degreesC. For a surfactant mixture (used as capping material), TGA shows a weak weight loss peak at 235 degreesC and a strong peak at 298 degreesC assigned to the surfactant molecules in monomer and aggregated forms, respectively. For gold nanorods, three weight loss peaks at about 230, 273, and 344 degreesC are observed. For gold nanospheres (NSs), TGA shows a strong mass loss at 225 degreesC and two weak mass loss peaks at 255 and 288 degreesC. The released material after combustion in the TGA process was analyzed by FTIR spectroscopy and found to be CO2. Our results suggest the following for both NRs and NSs: (1) There are two different binding modes for the surfactant molecules capping these nanoparticles. (2) Surfactant molecules form a bilayer structure around the gold nanoparticles in which the inner layer is bound to the gold surface via the surfactant headgroups. (3) With increase of the temperature, the outer layer desorbs at lower temperature and consequently the inner layer leaves the surface at higher temperature. (4) The higher desorption temperature of the bilayer in the NRs compared to NSs is explained in terms of the difference in packing of the surfactant molecules and their adsorption energy to the different facets present in these nanoparticles. (5) TEM results suggest that the shape transformation of NRs to NSs occurs as the inner layer is released from the surface. (6) The CH2 rocking mode at 720 cm(-1) suggests that the methylene chains have free rotation and surfactants are packed in a hexagonal structure.},
	isbn = {0743-7463},
	doi = {10.1021/la010530o},
	author = {Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1229,
	title = {Femtosecond transient-absorption dynamics of colloidal gold nanorods: Shape independence of the electron-phonon relaxation time},
	journal = {Physical Review B},
	volume = {61},
	number = {9},
	year = {2000},
	note = {Link, S Burda, C Mohamed, MB Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {6086-6090},
	abstract = {We studied the femtosecond dynamics of colloidal gold nanorods encapsulated in micelles after excitation with 400 nm pulses of 100 fs duration. It is found that the laser heating of the electron gas of gold nanorods with an average aspect ratio of 3.8 leads to the bleaching of both the transverse and longitudinal mode of the surface plasmon oscillation at 520 and 750 nm. The bleach recovers with the same time constant for both the transverse and longitudinal oscillation, for gold nanodots prepared by photothermal reshaping of the rods as well as for nanodots synthesized chemically by citrate reduction (and known to have twin boundaries and surface defects). Since the bleach recovery on the 3 ps time scale is assigned to electron-phonon relaxation processes, these results suggest that phonon dependent relaxation processes in gold nanoparticles are independent of the shape, size, type of the surfaces, or the mode of the surface plasmon, oscillation excited. The fact that the mean free path of the electron in metallic gold is in the nanometer length scale (similar to 50 nm) raised the question of the importance of surface scattering to the electron-phonon relaxation process in gold nanoparticles. Our previous studies showed little dependence of the relaxation rate of the size of gold nanodots (from 9 to 48 nm). In the present study, the electron-phonon relaxation is measured in gold nanorods, which have different facets from those of gold nanodots.},
	isbn = {1098-0121},
	doi = {10.1103/PhysRevB.61.6086},
	author = {Link, Stephan and Burda, Clemens and Mohamed, MB and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1228,
	title = {Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {26},
	year = {2000},
	note = {Link, S Burda, C Nikoobakht, B El-Sayed, MA},
	month = {Jul},
	pages = {6152-6163},
	abstract = {Gold nanorods have been found to change their shape after excitation with intense pulsed laser irradiation. The final irradiation products strongly depend on the energy of the laser pulse as well as on its width. We performed a series of measurements in which the excitation power was varied over the range of the output power of an amplified femtosecond laser system producing pulses of 100 fs duration and a nanosecond optical parametric oscillator (OPO) laser system having a pulse width of 7 ns. The shape transformations of the gold nanorods are followed by two techniques: (1) visible absorption spectroscopy by monitoring the changes in the plasmon absorption bands characteristic for gold nanoparticles; (2) transmission electron microscopy (TEM) in order to analyze the final shape and size distribution. While at high laser fluences (similar to 1 J cm(-2)) the gold nanoparticles fragment, a melting of the nanorods into spherical nanoparticles (nanodots) is observed when the laser energy is lowered. Upon decreasing the energy of the excitation pulse, only partial melting of the nanorods takes place. Shorter but wider nanorods are observed in the final distribution as well as a higher abundance of particles having odd shapes (bent, twisted, phi-shaped, etc.). The threshold for complete melting of the nanorods with femtosecond laser pulses is about 0.01 J cm(-2). Comparing the results obtained using the two different types of excitation sources (femtosecond vs nanosecond laser), it is found that the energy threshold for a complete melting of the nanorods into nanodots is about 2 orders of magnitude higher when using nanosecond laser pulses than with femtosecond laser pulses. This is explained in terms of the successful competitive cooling process of the nanorods when the nanosecond laser pulses are used. For nanosecond pulse excitation, the absorption of the nanorods decreases during the laser pulse because of the bleaching of the longitudinal plasmon band. In addition, the cooling of the lattice occurring on the 100 ps time scale can effectively compete with the rate of absorption in the case of the nanosecond pulse excitation but not for the femtosecond pulse excitation. When the excitation source is a femtosecond laser pulse, the involved precesses (absorption of the photons by the electrons (100 fs), heat transfer between the hot electrons and the lattice (<10 ps), melting (30 ps), and heat loss to the surrounding solvent (>100 ps) are clearly separated in time.},
	isbn = {1089-5647},
	doi = {10.1021/jp000679t},
	author = {Link, Stephan and Burda, Clemens and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1223,
	title = {Self-assembly of gold nanorods},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {36},
	year = {2000},
	note = {Nikoobakht, B Wang, ZL El-Sayed, MA},
	month = {Sep},
	pages = {8635-8640},
	abstract = {Self-assembly of gold nanorods (NRs) with aspect ratio of similar to 4.6 (12 nm in diameter and 50-60 nm in length) has been studied using transmission electron microscopy (TEM). Under appropriate conditions such as nanoparticle concentration, solvent evaporation, narrow size distribution, ionic strength, and surfactant concentration of the parent solution, gold nanorods assemble into one-, two-, and three-dimensional structures. Some of the three-dimensional assemblies extend to superlattices of NRs. The translation and orientation symmetries of the self-assembled structures are determined. The factors affecting the formation of the ordered self-assembly are discussed.},
	isbn = {1089-5647},
	doi = {10.1021/jp001287p},
	author = {Nikoobakht, Babak and Wang, Z.L. and El-Sayed, Mostafa A}
}
@article {1220,
	title = {Surface reconstruction of the unstable {110} surface in gold nanorods},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {23},
	year = {2000},
	note = {Wang, ZL Gao, RP Nikoobakht, B El-Sayed, MA},
	month = {Jun},
	pages = {5417-5420},
	abstract = {Gold nanorods prepared electrochemically and capped in micelles are examined using high-resolution transmission electron microscopy (TEM), It is found that they have an axial growth direction of [001] and have surfaces made of {100} and the unstable {110} facets. A detailed examination of the defect sites of both of these facets shows that while the defective regions of the stable {100} facets show atom-height steps with no reconstruction, the less stable higher energy {110} surfaces show missing-row reconstruction. The role of micelles in stabilizing the {110} facet in the gold nanorod is briefly discussed.},
	isbn = {1089-5647},
	doi = {10.1021/jp000800w},
	author = {Wang, Z.L. and Gao, R. P. and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1247,
	title = {The effect of low and high temperature anneals on the hydrogen content and passivation of Si surface coated with SiO2 and SiN films},
	journal = {Journal of the Electrochemical Society},
	volume = {146},
	number = {5},
	year = {1999},
	note = {Ebong, A Doshi, P Narasimha, S Rohatgi, A Wang, J El-Sayed, MA},
	month = {May},
	pages = {1921-1924},
	abstract = {A detailed comparison of the passivation quality and its dependence on the low and high temperature anneals is presented for various promising Si surface passivation schemes. The passivation schemes investigated in this study include: conventional furnace oxide (CFO), rapid thermal oxide (RTO), belt line oxide (BLO), plasma deposited oxide (PDO), SiN deposited by plasma enhanced chemical vapor deposition (PECVD), CFO/SiN, RTO/SiN, BLO/SiN, PDO/SiN, and RTO/PDO. Passivated low resistivity (1 Ohm cm) p-type silicon samples were subjected to three annealing treatments: (a) 400 degrees C in forming gas (FGA), (b) 730 degrees C in air, and (c) 850 degrees C in air, to simulate heat-treatments, which are typically used for contact anneal, front ohmic contacts, and back surface field formation, respectively, for screen printed silicon solar cells. It is found that the passivation quality of PDO, SiN, RTO, and CFO single layers improves significantly after the 400 degrees C FGA and 730 degrees C thermal cycles with RTO resulting in the lowest surface recombination velocities (S-eff) of 154 and 405 cm/s, respectively. Silicon wafers coated with belt oxide (BLO and BLO/SiN) did not show any improvement in S-eff, which remained at 5000 cm/s due to the inferior quality of BLO formed in compressed air. The oxide/ nitride stack passivation is found to be far superior to single-layer passivation resulting in S-eff Of 70 cm/s for the RTO/SiN scheme after the two high temperature anneals (850 and 730 degrees C). The hydrogen concentration measurements by Fourier transform infrared spectroscopy show a greater decrease in the hydrogen content in the annealed RTO/SiN stack compared to the as-deposited SiN single layer after the 730 and 850 degrees C anneals. A combination of reduced hydrogen content and very low S-eff in the RTO/SiN stack suggests that the release of hydrogen from SiN during the anneal further passivates the RTO/Si interface underneath. (C) 1999 The Electrochemical Society. S0013-4651(98)08-117-8. All rights reserved.},
	isbn = {0013-4651},
	doi = {10.1149/1.1391866},
	author = {Ebong, A. and Doshi, P. and Narasimha, S. and Rohatgi, A. and Wang, Jianping and El-Sayed, Mostafa A}
}
@article {1245,
	title = {How long does it take to melt a gold nanorod? A femtosecond pump-probe absorption spectroscopic study},
	journal = {Chemical Physics Letters},
	volume = {315},
	number = {1-2},
	year = {1999},
	note = {Link, S Burda, C Nikoobakht, B El-Sayed, MA},
	month = {Dec},
	pages = {12-18},
	abstract = {Using pump-probe femtosecond transient absorption spectroscopy, we determined the rate of the bleach of absorption around 700-800 nm due to the longitudinal surface plasmon band of gold nanorods. Using TEM of the spotted, completely irradiated solutions suggest that the dominant products of the photothermal conformation of the rods are spheres of comparable volume. This lead to the conclusion that the melting of the rods is at least 30-35 ps, independent of the power used (5-20 mu J) or the nanorod aspect ratio (1.9-3.7). (C) 1999 Elsevier Science B.V. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(99)01214-2},
	author = {Link, Stephan and Burda, Clemens and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1246,
	title = {Laser photothermal melting and fragmentation of gold nanorods: Energy and laser pulse-width dependence},
	journal = {Journal of Physical Chemistry A},
	volume = {103},
	number = {9},
	year = {1999},
	note = {Link, S Burda, C Mohamed, MB Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {1165-1170},
	abstract = {We studied the shape transformation (by use of TEM and optical absorption spectroscopy) of gold nanorods in micellar solution by exposure to laser pulses of different pulse width (100 fs and 7 ns) and different energies (mu J to mJ) at 800 nm, where the longitudinal surface plasmon oscillation of the nanorods absorb. At moderate energies, the femtosecond irradiation melts the nanorods to near spherical particles of comparable volumes while the nanosecond pulses fragment them to smaller near-spherical particles. At high energies, fragmentation is also observed for the femtosecond irradiation. A mechanism involving the rate of energy deposition as compared to the rate of electron-phonon and phonon-phonon relaxation processes is proposed to determine the final fate of the laser-exposed nanorods, i.e., melting or fragmentation.},
	isbn = {1089-5639},
	doi = {10.1021/jp983141k},
	author = {Link, Stephan and Burda, Clemens and Mohamed, MB and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1287,
	title = {Fourier Transform Infrared Spectroscopic Studies of the Effect of Ca2+ Binding on the States of Aspartic Acid Side Chains in Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {99},
	year = {1995},
	note = {doi: 10.1021/j100019a066},
	month = {1995},
	pages = {7776 - 7781},
	publisher = {American Chemical Society},
	abstract = {View http://dx.doi.org/10.1021/j100019a066 for article{\textquoteright}s front page in lieu of an abstract},
	isbn = {0022-3654},
	doi = {doi: 10.1021/j100019a066},
	url = {http://dx.doi.org/10.1021/j100019a066},
	author = {Masuda, Satoshi and Nara, Masayuki and Tasumi, Mitsuo and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
