@article {1112,
	title = {On the Use of Plasmonic Nanoparticle Pairs As a Plasmon Ruler: The Dependence of the Near-Field Dipole Plasmon Coupling on Nanoparticle Size and Shape},
	journal = {Journal of Physical Chemistry A},
	volume = {113},
	number = {10},
	year = {2009},
	note = {Tabor, Christopher Murali, Raghunath Mahmoud, Mahmoud El-Sayed, Mostafa A.},
	month = {Mar},
	pages = {1946-1953},
	abstract = {The localized surface plasmon resonance (LSPR) spectral band of a gold or silver nanoparticle is observed to shift as a result of the near-field plasmonic field of another nanoparticle. The dependence of the observed shift on the interparticle distance is used as a ruler in biological systems and gave rise to a plasmonic ruler equation in which the fractional shift in the dipole resonance is found to decrease near exponentially with the interparticle separation in units of the particle size. The exponential decay length constant was observed to be consistent among a small range of nanoparticle sizes, shapes, and types of metal. The equation was derived from the observed results on disks and spherical nanoparticles and confirmed using results on a DNA conjugated nanosphere system. The aim of the present paper is to use electron beam lithography and DDA calculations to examine the constancy of the exponential decay length value in the plasmonic ruler equation on particle size and shape of a number of particles including nanoparticles of different symmetry and orientations. The results suggest that the exponent is almost independent of the size of the nanoparticle but very sensitive to the shape. A discussion of the nanoparticles most suitable for different applications in biological systems and a comparison of the plasmonic ruler with Forster resonance energy transfer (FRET) is mentioned.},
	isbn = {1089-5639},
	doi = {10.1021/jp807904s},
	author = {Tabor, C. E. and Murali, R. and Mahmoud, M A and El-Sayed, Mostafa A}
}
@article {1137,
	title = {On the universal scaling behavior of the distance decay of plasmon coupling in metal nanoparticle pairs: A plasmon ruler equation},
	journal = {Nano Letters},
	volume = {7},
	number = {7},
	year = {2007},
	note = {Jain, Prashant K. Huang, Wenyu El-Sayed, Mostafa A.},
	month = {Jul},
	pages = {2080-2088},
	abstract = {Localized surface plasmon resonances (LSPR) in lithographically fabricated gold (Au) nanodisc pairs are investigated using microabsorption spectroscopy and electrodynamic simulations. In agreement with previous work, we find that the fractional plasmon wavelength shift for polarization along the interparticle axis decays nearly exponentially with the interparticle gap. In addition, we find that the decay length is roughly about 0.2 in units of the particle size for different nanoparticle size, shape, metal type, or medium dielectric constant. The near-exponential distance decay and the interesting "universal" scaling behavior of interparticle plasmon coupling can be qualitatively explained on the basis of a dipolar-coupling model as being due to the interplay of two factors: the direct dependence of the single-particle polarizability on the cubic power of the particle dimension and the decay of the plasmonic near-field as the cubic power of the inverse distance. Using this universal scaling behavior, we are able to derive a "plasmon ruler equation" that estimates the interparticle separation between Au nanospheres in a biological system from the observed fractional shift of the plasmon band. We find good agreement of the interparticle separations estimated using this equation with the experimental observations of Reinhard et al.},
	isbn = {1530-6984},
	doi = {10.1021/nl071008a},
	author = {Jain, Prashant K and Huang, Wenyu and El-Sayed, Mostafa A}
}
@article {1138,
	title = {Universal scaling of plasmon coupling in metal nanostructures: Extension from particle pairs to nanoshells},
	journal = {Nano Letters},
	volume = {7},
	number = {9},
	year = {2007},
	note = {Jain, Prashant K. El-Sayed, Mostafa A.},
	month = {Sep},
	pages = {2854-2858},
	abstract = {It has been recently shown that the strength of plasmon coupling between a pair of plasmonic metal nanoparticles falls as a function of the interparticle gap scaled by the particle size with a near-exponential decay trend that is universally independent of nanoparticle size, shape, metal type, or medium dielectric constant. In this letter, we extend this universal scaling behavior to the dielectric core-metal shell nanostructure. By using extended Mie theory simulations of silica core-metal nanoshells, we show that when the shift of the nanoshell plasmon resonance wavelength scaled by the solid nanosphere resonance wavelength is plotted against the shell thickness scaled by the core radius, nanoshells with different dimensions (radii) exhibit the same near-exponential decay. Thus, the nanoshell system becomes physically analogous to the particle-pair system, i.e., the nanoshell plasmon resonance results from the coupling of the inner shell surface (cavity) and the outer shell surface (sphere) plasmons over a separation distance essentially given by the metal shell thickness, which is consistent with the plasmon hybridization model of Prodan, Halas, and Nordlander. By using the universal scaling behavior in the nanoshell system, we propose a simple expression for predicting the dipolar plasmon resonance of a silica-gold nanoshell of given dimensions.},
	isbn = {1530-6984},
	doi = {10.1021/nl071496m},
	author = {Jain, Prashant K and El-Sayed, Mostafa A}
}
@article {1148,
	title = {Ultrafast cooling of photoexcited electrons in gold nanoparticle-thiolated DNA conjugates involves the dissociation of the gold-thiol bond},
	journal = {Journal of the American Chemical Society},
	volume = {128},
	number = {7},
	year = {2006},
	note = {Jain, PK Qian, W El-Sayed, MA},
	month = {Feb},
	pages = {2426-2433},
	abstract = {Using UV-visible extinction spectroscopy and femtosecond pump-probe transient absorption spectroscopy, we have studied the effect of femtosecond laser heating on gold nanoparticles attached to DNA ligands via thiol groups. It is found that femtosecond pulse excitation of the DNA-modified nanoparticles at a wavelength of 400 nm leads to desorption of the thiolated DNA strands from the nanoparticle surface by the dissociation of the gold-sulfur bond. The laser-initiated gold-sulfur bond-breaking process is a new pathway for nonradiative relaxation of the optically excited electrons within the DNA-modified gold nanoparticles, as manifested by a faster decay rate of the excited electronic distribution at progressively higher laser pulse energies. The experimental results favor a bond dissociation mechanism involving the coupling between the photoexcited electrons of the nanoparticles and the gold-sulfur bond vibrations over one involving the conventional phonon-phonon thermal heating processes. The latter processes have been observed previously by our group to be effective in the selective photothermal destruction of cancer cells bound to anti-epidermal growth factor receptor-conjugated gold nanoparticles.},
	isbn = {0002-7863},
	doi = {10.1021/ja056769z},
	author = {Jain, Prashant K and Qian, Wei and El-Sayed, Mostafa A}
}
@article {1149,
	title = {Ultrafast electron relaxation dynamics in coupled metal nanoparticles in aggregates},
	journal = {Journal of Physical Chemistry B},
	volume = {110},
	number = {1},
	year = {2006},
	note = {Jain, PK Qian, W El-Sayed, MA},
	month = {Jan},
	pages = {136-142},
	abstract = {We report the effect of aggregation in gold nanoparticles on their ultrafast electron-phonon relaxation dynamics measured by femtosecond transient absorption pump-probe spectroscopy. UV-visible extinction and transient absorption of the solution-stable aggregates of gold nanoparticles show a broad absorption in the 550-700-nm region in addition to the isolated gold nanoparticle plasmon resonance. This broad red-shifted absorption can be attributed to contributions from gold nanoparticle aggregates with different sizes and/or different fractal structures. The electron-phonon relaxation, reflected as a fast decay component of the transient bleach, is found to depend on the probe wavelength, suggesting that each wavelength interrogates one particular subset of the aggregates. As the probe wavelength is changed from 520 to 635 nm across the broad aggregate absorption, the rate of electron-phonon relaxation increases. The observed trend in the hot electron lifetimes can be explained on the basis of an increased overlap of the electron oscillation frequency with the phonon spectrum and enhanced interfacial electron scattering, with increasing extent of aggregation. The experimental results strongly suggest the presence of intercolloid electronic coupling within the nanoparticle aggregates, besides the well-known dipolar plasmon coupling.},
	isbn = {1520-6106},
	doi = {10.1021/jp055562p},
	author = {Jain, Prashant K and Qian, Wei and El-Sayed, Mostafa A}
}
@article {1146,
	title = {Ultrafast electronic relaxation and charge-carrier localization in CdS/CdSe/CdS quantum-dot quantum-well heterostructures},
	journal = {Nano Letters},
	volume = {6},
	number = {9},
	year = {2006},
	note = {Schill, Alexander W. Gaddis, Christopher S. Qian, Wei El-Sayed, Mostafa A. Cai, Ye Milam, Valeria T. Sandhage, Kenneth},
	month = {Sep},
	pages = {1940-1949},
	abstract = {The relaxation and localization times of excited electrons in CdS/CdSe/CdS colloidal quantum wells were measured using subpicosecond spectroscopy. HRTEM analysis and steady-state PL demonstrate a narrow size distribution of 5-6 nm epitaxial crystallites. By monitoring the rise time of the stimulated emission as a function of pump intensity, the relaxation times of the electron from the CdS core into the CdSe well are determined and assigned. Two-component rise times in the stimulated emission are attributed to intraband relaxation of carriers generated directly within the CdSe well ( fast component) and charge transfer of core-localized carriers across the CdS/CdSe interface ( slow component). This is the first reported observation of simultaneous photon absorption in the core and well of a quantum-dot heterostructure. With increasing pump intensity, the charge-transfer channel between the CdS core CdSe well contributes less to the stimulated emission signal because of filling and saturation of the CdSe well state, making the interfacial charge-transfer component less efficient. The interfacial charge-transfer time of the excited electron was determined from the slow component of the stimulated emission build-up time and is found to have a value of 1.2 ps.},
	isbn = {1530-6984},
	doi = {10.1021/nl061054v},
	author = {Schill, A. W. and Gaddis, C. S. and Qian, Wei and El-Sayed, Mostafa A and Cai, Y. and Milam, V. T. and Sandhage, K.}
}
@article {1155,
	title = {Using silica films and powders modified with benzophenone to photoreduce silver nanoparticles},
	journal = {Journal of Photochemistry and Photobiology a-Chemistry},
	volume = {181},
	number = {2-3},
	year = {2006},
	note = {Eustis, Susie Krylova, Galina Smirnova, Natalie Eremenko, Anna Tabor, Christopher Huang, Wenyu El-Sayed, Mostafa A.},
	month = {Jul},
	pages = {385-393},
	abstract = {Porous silica (SiO2 films and powders), modified with benzophenone (BP), facilitates the formation of stable sliver nanoparticles by taking advantage of the solid supported photosensitizer. The silica serves as a carrier for the BP into an aqueous solution and its subsequent removal. Benzophenone, bound to a silica film, was able to reduce silver ions to generate nanoparticles in solution, while silica powder with bound BP generates silver nanoparticles that are attracted to the silica. Silver nanoparticles are also fabricated in porous silica films by incorporating silver ions into the films before casting and then irradiating the film in a solution containing BP. From pH studies, it is concluded that the ketyl-radicals and anion-radicals of BP and IPA both take part in the reduction of silver ions. These synthetic studies provide a new photochemical reduction method by immobilizing the reactant on a silica surface allowing generation of silver nanoparticles in solution attached to powders or inside a film for catalytic applications or increased conductivity of silica films. (c) 2006 Elsevier B.V. All rights reserved.},
	isbn = {1010-6030},
	doi = {10.1016/j.jphotochem.2005.12.024},
	author = {Eustis, Susie and Krylova, G. and Smirnova, N. and Eremenko, A. and Tabor, C. E. and Huang, Wenyu and El-Sayed, Mostafa A}
}
@book {1285,
	title = {Ultrafast Processes in Chemistry and Photobiology},
	year = {1995},
	publisher = {Blackwell Science},
	organization = {Blackwell Science},
	abstract = {This new volume continues the tradition of the {\textquoteright}Chemistry for the 21st Century{\textquoteright} Series in exploring areas of active research in chemistry today which are likely to have a profound effect on the science of chemistry in the future. Lasers have had, and will have, a positive impact on chemistry with the short pulse width of the laser enabling chemists to measure the primary processes of important chemical changes. This use of lasers to measure ultrafast processes in chemistry and photobiology is one of the most active as well as one of the most fundamental field of research. This volume presents expert contributions summarizing the state-of-the-art in this most important area.},
	isbn = {086542893X},
	author = {El-Sayed, Mostafa A and Tanaka, I. and Molin, I.U.N.}
}
