Papers by Mostafa El-Sayed
ACS Applied Materials & Interfaces, 2014
We have studied ultrafast dynamics in thin films of Eu-doped zinc oxide (ZnO), prepared by radio-... more We have studied ultrafast dynamics in thin films of Eu-doped zinc oxide (ZnO), prepared by radio-frequency sputtering onto sapphire substrates. Following UV excitation of ZnO, a red emission is observed. Postdeposition annealing in an oxygen atmosphere improves the crystallinity and emission intensity of the films, which are highly sensitive to the dopant concentration. Transient-absorption spectroscopy shows that the excited semiconductor host transfers energy to rare-earth ions on a time scale of only a few picoseconds. The dynamics as a function of the probe wavelength change dramatically after annealing, with annealed films showing the fastest dynamics at much lower wavelengths. Our results show that annealing greatly affects the defect energy levels of the films and the dynamics of the trapped carriers. Unannealed films show dynamics consistent with energy transfer from O vacancies to the dopant, while energy transfer in annealed samples involves acceptor-type defects such as Zn vacancies as intermediates.
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Photochemistry and photobiology, Jan 14, 2015
We have synthesized hollow Au nanocages embedded within thick porous shells of cuprous oxide (Cu2... more We have synthesized hollow Au nanocages embedded within thick porous shells of cuprous oxide (Cu2 O). The shell causes a significant redshift of the localized surface plasmon resonance of Au into the near-IR. Electron-phonon coupling in the Au nanocage is 3-6 times faster in the core-shell structure due to the higher thermal conductivity of Cu2 O compared to water. Coherent phonon oscillations within the Au lattice are characterized by a breathing mode of the entire structure for both bare and core-shell nanocages, an assignment made through the use of structural mechanics simulations. The experimental frequencies are obtained through simulations by selectively applying a force to the shell of the core-shell structure. We interpret this as rapid thermal expansion of the gold leading to a mechanical force that acts on the shell.
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PLoS ONE, 2013
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The Journal of Physical Chemistry, 1981
Page 1. 3586 J. PhyS. Chem. 1961, 85, 3566-3568 Temporal and Temperature Dependence of the Energy... more Page 1. 3586 J. PhyS. Chem. 1961, 85, 3566-3568 Temporal and Temperature Dependence of the Energy Transfer Process among EuS+ In an Amorphous Solid Jack R. Morgan and MA El-Sayed" Department of Chemlstv, Unlverslty of California. ...
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The Journal of Physical Chemistry, 1981
Page 1. J. Phys. Chem. 1981, 85, 3569-3571 5589 Spectral 3iffusion in Orientationally Disordered ... more Page 1. J. Phys. Chem. 1981, 85, 3569-3571 5589 Spectral 3iffusion in Orientationally Disordered Organic Solids Paras N. Prasad,+ Jack R. Morgan, and Moslafa A. El-Sayed Chemistry Department, University of California, Los ...
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The journal of physical chemistry letters, Jan 3, 2014
Of all the plasmonic solid nanoparticles, single Ag or Au nanocubes are known to be plasmonic nan... more Of all the plasmonic solid nanoparticles, single Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields, which are concentrated around their corners. However, when nanoparticles aggregate, they do so in a face-to face arrangement. The formation of hot spots between plasmonic nanoparticles in close proximity to each other is known to greatly enhance their plasmonic fields which are important in the field of imaging. Thus, what is the structural development of hot spots between two nanocubes in a dimer? Do they form between the corners or are they between the adjacent facets, and what does this depend on? A detailed discrete dipole approximation (DDA) simulation of Au-Au and Ag-Ag dimers suggests that there is a competition between their formation in these two locations, which depends on the polarization direction of the exciting light (with respect to the interparticle axis in the dimer), its intensity and the wavelength as well as the interparticle s...
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Nanoscale drug delivery is a power full tool for the treatment of solid tumors. Although a range ... more Nanoscale drug delivery is a power full tool for the treatment of solid tumors. Although a range of approaches have been described over the past several years, the vast majority seek to improve cytotoxic chemotherapies that have been in use for decades. Nanoscale delivery strategies integrating rational drug combinations, synthetic lethal RNA interference, stimuli-responsive drugs, or so-called molecularly targeted cancer therapeutics are and remain underexplored. Here, we present work from our laboratory describing the development of a range of such nanoscale platforms for drug delivery to solid tumors. These include: (i) self-assembled peptide co-polymer nanoparticles for synthetic lethal RNA interference of DNA damage response in ovarian and lung cancers, (ii) multivalent anti-androgen and anti-estrogen gold nanoparticles for the treatment of hormone-refractory breast and prostate cancers, (iii) photo-responsive nanoparticles that deliver drugs or achieve photothermal ablation in...
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MRS Proceedings, 2015
ABSTRACT Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields ... more ABSTRACT Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields concentrated around their corners1. When these nanoparticles aggregate the individual plasmonic oscillations of each particle begin to couple. The coupling between the two plasmonic nanoparticles is assumed to be dipolar in nature which results in an exponential red shift dependence of their localized surface plasmon resonance (LSPR) on the dimer separation2. Unfortunately, this exponential behavior is shown to fail as the separation distance between the two 42 nm nanocube dimer becomes 6nm or smaller3. Hooshmand et al4 have noted that these separation distances are marked by the formation of hot spots between the facets of the dimer.This dipolar exponential behavior results from a treatment of the coupling between the two excited nanocubes as a coupling between two oscillating dipole moments2. As a result, the vectorial addition of all the oscillating electronic dipoles is assumed to interact with the nearest nanoparticle as a single oscillating electronic dipole. Herein we suggest that as the separation distance becomes increasingly small, the coupling between the individual oscillating dipoles on the different nanocubes becomes significant. Thus, the dipolar exponential behavior fails to accurately predict the near field coupling between two nanoparticles with small separation distances.This leads to the realization that the interaction between the individual oscillating dipoles on the two nanocubes changes in a complicated manner as a function of separation distance. At 2nm, a good fraction of the oscillating dipoles are between the adjacent facets of the nanocubes as well as between the the corners. While at 3 nm less are in between the two facets of the nanocubes and a larger portion are localized at the corners. Thus, the coupling is not only dependent on the separation distance but also on what the separation does to the net interaction between the oscillating dipoles on each facet of the two coupled nanocubes. This results in the failure of the exponential behavior as the dipole moment on each nanocube is changing with distance in a complicated manner.
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The Journal of Physical Chemistry, 1981
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The relaxation dynamics of Au arrays prepared via nanosphere lithography were investigated1 using... more The relaxation dynamics of Au arrays prepared via nanosphere lithography were investigated1 using femtosecond pump-probe spectroscopy. The hot electron relaxation dynamics of arrays of truncated tetrahedra shaped 90 nm gold nanoparticles on glass, 50nm gold thin film, and gold nanodots in solution are compared. The initial relaxation (due to the electron-phonon relaxation) of the Au array is longer (2.9 ps)
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Physical Review B, 2001
The femtosecond time-resolved exciton dynamics of the CdS/(HgS) 2 /CdS quantum-dotquantum-well s... more The femtosecond time-resolved exciton dynamics of the CdS/(HgS) 2 /CdS quantum-dotquantum-well system (QDQW), which contains a double-layer HgS QW, was investigated and compared to the dynamics of the QDQW system with a single-layer HgS QW. The ...
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The Journal of Physical Chemistry, 1991
... James D. Boggus Frances L. DeTar Research Associates of Michael Kasha Robin M. HochstrasserGe... more ... James D. Boggus Frances L. DeTar Research Associates of Michael Kasha Robin M. HochstrasserGeorge M. Holzwarth Paul M. Horowitz Kazuhiro Ishida Kenji Kawaoka Ahsan U. Khan Vaughn J. Koester Aleksander Kubicki Jean Marc Lhoste Ph.D. Students ...
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Physical Review B, 2000
... from these results that the bleach recovery dynamics and thus the electron-phonon and 6090 LI... more ... from these results that the bleach recovery dynamics and thus the electron-phonon and 6090 LINK, BURDA, MOHAMED, NIKOOBAKHT, AND EL ... and planar defects40 while the nanodots prepared by chemical reduction with sodium citrate are found to have twin boundaries and ...
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Fundamentals, Applications and Recent Developments(In 4 Volumes)Volume 1: Materials for NanomedicineVolume 2: Applications in TherapyVolume 3: Applications in DiagnosticsVolume 4: Biology, Safety and Novel Concepts in Nanomedicine, 2014
ABSTRACT Gold nanoparticles are rapidly emerging platforms for multifunctional diagnostic and the... more ABSTRACT Gold nanoparticles are rapidly emerging platforms for multifunctional diagnostic and therapeutic nanotechnologies. Tumor-specific cellular delivery of a gold nanoparticle however, is a complex, multistep process involving systemic circulation, transvascular flux, intratumoral penetration, and intracellular delivery. Each of these steps present unique constrains which determine the optimal architecture for gold nanoparticle construct including at its most fundamental level, size, shape, and surface chemistry. Gold nanoparticles, given their highly well-defined chemical synthesis and surface chemistry, represent one of the most versatile and reliable platforms for designing and understanding tumor-targeting nanotechnologies. Here, we review a recent body of work examining the effects of gold nanoparticle size, shape, and surface chemistry on circulation kinetics, tumor extravasation, interstitial tumor transport, and cellular uptake with the aim of delineating optimal design parameters for each of these processes. Discussions here focus primarily on poly(ethylene glycol)-functionalized gold nanoparticles with an emphasis on practical design considerations for new researchers in the field.
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Papers by Mostafa El-Sayed