@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 {1074, title = {Tailoring Plasmonic and Electrostatic Field Effects To Maximize Solar Energy Conversion by Bacteriorhodopsin, the Other Natural Photosynthetic System}, journal = {Nano Letters}, volume = {11}, number = {9}, year = {2011}, note = {Yen, Chun-Wan Hayden, Steven C. Dreaden, Erik C. Szymanski, Paul El-Sayed, Mostafa A.}, month = {Sep}, pages = {3821-3826}, abstract = {We have explored the plasmonic field enhancement of current production from bacteriorhodopsin (bR) by maximizing the blue light effect, where the influx of blue photons absorbed by the long-lived M intermediate drastically shortens the time scale of the bR photocycle, leading to current enhancement. To this end, we used three approaches in our solution-based cell: proton selective Nafion membrane. (2) We maximized the plasmonic surface (1) We improved the charge carrier separation in solution through the use of a field effects by selecting the capping polymer with minimum surface field screening and best nanopartide stability. (3) We selected the plasmonic nanoparticle with the strongest plasmonic field whose surface plasmon resonance has the largest spectral overlap with the blue light absorbing M-intermediate. Theoretical models are used to explain experimental results, which show a 40 nm cuboidal nanoparticle capped with 55k PVP polymer to give the best photocurrent enhancement. Enhanced by this particle, bR in our Nafion membrane solution cell gave a photocurrent of 0.21 mu A/cm(3), which is 5000 times larger than the published results for thin film bR electrochemical cells even with an applied bias. Additional possible enhancements are proposed.}, isbn = {1530-6984}, doi = {10.1021/nl2018959}, author = {Yen, C. W. and Hayden, S. C. and Dreaden, Erik and Szymanski, P. and El-Sayed, Mostafa A} } @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 {1118, title = {Tamoxifen-Poly(ethylene glycol)-Thiol Gold Nanoparticle Conjugates: Enhanced Potency and Selective Delivery for Breast Cancer Treatment}, journal = {Bioconjugate Chemistry}, volume = {20}, number = {12}, year = {2009}, note = {Dreaden, Erik C. Mwakwari, Sandra C. Sodji, Quaovi H. Oyelere, Adegboyega K. El-Sayed, Mostafa A.}, month = {Dec}, pages = {2247-2253}, abstract = {The breast cancer treatment drug tamoxifen has been widely administered for more than three decades. This small molecule competes with 17 beta-estradiol for binding to estrogen receptor, a hormone receptor upregulated in a majority of breast cancers, Subsequently initiating programmed cell death. We have synthesized a thiol-PEoylated tamoxifen derivative that can be used to selectively target and deliver plasmonic gold nanoparticles to estrogen receptor positive breast cancer cells with tip to 2.7-fold enhanced drug potency in vitro. Optical microscopy/spectroscopy, tirne-dependent dose-response data, and estrogen competition studies indicate that augmented activity is due to increased rates of intracellular tamoxifen transport by nanoparticle endocytosis, rather than by passive diffusion of the free drug. Both ligand- and receptor-dependent intracellular delivery of gold nanoparticles suggest that plasma membrane localized estrogen receptor alpha may facilitate selective uptake and retention of this and other therapeutic nanoparticle conjugates. Combined targeting selectivity and enhanced potency provides opportunities for both multimodal endocrine treatment strategies and adjunctive laser photothermal therapy.}, isbn = {1043-1802}, doi = {10.1021/bc9002212}, author = {Dreaden, Erik and Mwakwari, S. C. and Sodji, Q. H. and Oyelere, A. K. and El-Sayed, Mostafa A} } @article {1131, title = {Gold nanorod assisted near-infrared plasmonic photothermal therapy (PPTT) of squamous cell carcinoma in mice}, journal = {Cancer Letters}, volume = {269}, number = {1}, year = {2008}, note = {Dickerson, Erin B. Dreaden, Erik C. Huang, Xiaohua El-Sayed, Ivan H. Chu, Hunghao Pushpanketh, Sujatha McDonald, John F. El-Sayed, Mostafa A.}, month = {Sep}, pages = {57-66}, abstract = {Plasmonic photothermal therapy (PPTT) is a minimally-invasive oncological treatment strategy in which photon energy is selectively administered and converted into heat sufficient to induce cellular hyperthermia. The present work demonstrates the feasibility of in vivo PPTT treatment of deep-tissue malignancies using easily-prepared plasmonic gold nanorods and a small, portable, inexpensive near-infrared (NIR) laser. Dramatic size decreases in squamous cell carcinoma xenografts were observed for direct (P < 0.0001) and intravenous (P < 0.0008) administration of pegylated gold nanorods in nu/nu mice. Inhibition of average tumor growth for both delivery methods was observed over a 13-day period, with resorption of >57\% of the directly-injected tumors and 25\% of the intravenously-treated tumors. Published by Elsevier Ltd.}, isbn = {0304-3835}, doi = {10.1016/j.canlet.2008.04.026}, author = {Dickerson, E. B. and Dreaden, Erik and Huang, Xiaohua and El Sayed, I.H. and Chu, H. H. and Pushpanketh, S. and McDonald, J. F. 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} }