TY - JOUR T1 - Enhanced Electrochemical Dark-Field Scattering Modulation on Single Hybrid Core-Shell Nanostructure JF - The Journal of Physical Chemistry C Y1 - 2019 A1 - Zhou, J. A1 - Panikkanvalappil, S.R. A1 - Kang, S. A1 - Yu, S. A1 - Zhang, S. A1 - El-Sayed, M.A. A1 - Tsukruk, V.V. ER - TY - JOUR T1 - Enhancing Plasmonic–Photonic Hybrid Cavity Modes by Coupling of Individual Plasmonic Nanoparticles JF - The Journal of Physical Chemistry C Y1 - 2019 A1 - Zhang, S. A1 - Panikkanvalappil, S.R. A1 - Kang, S. A1 - Smith, M.J. A1 - Yu, S. A1 - El-Sayed, M. A1 - Tsukruk, V.V. ER - TY - JOUR T1 - Operando Investigation into Dynamic Evolution of Cathode–Electrolyte Interfaces in a Li-Ion Battery JF - Nano letters Y1 - 2019 A1 - Chen, D. A1 - Mahmoud, M.A. A1 - Wang, J.H. A1 - Waller, G.H. A1 - Zhao, B. A1 - Qu, C. A1 - El-Sayed, M.A. A1 - Liu, M. ER - TY - JOUR T1 - Dual-excitation nanocellulose-plasmonic membranes for molecular and cellular SERS detection JF - ACS applied materials & interfaces Y1 - 2018 A1 - S. Zhang A1 - R. Xiong A1 - Mahmoud, M A A1 - E. Quigley A1 - H. Chang A1 - El-Sayed, M. A. A1 - Tsukruk, V. V. ER - TY - JOUR T1 - Electrochromic tuning of transparent gold nanorods with poly [(3, 4-propylenedioxy) pyrrole] shells in the near-infrared region JF - Journal of Materials Chemistry C Y1 - 2017 A1 - Zhou, J A1 - et al. ER - TY - JOUR T1 - A force for Egyptian science JF - Proceedings of the National Academy of Sciences Y1 - 2017 A1 - El-Sayed, Mostafa A. A1 - Zewail, Ahmed ER - TY - JOUR T1 - Probing Structural Evolution and Charge Storage Mechanism of Nio2hx Electrode Materials Using in Operando Resonance Raman Spectroscopy JF - Advanced Science Y1 - 2016 A1 - Chen, D. A1 - Xiong, X. A1 - Zhao, B. A1 - Mahmoud, M A A1 - El‐Sayed, M. A. A1 - Liu, M. ER - TY - JOUR T1 - Aggregation and Interaction of Cationic Nanoparticles on Bacterial Surfaces JF - Journal of the American Chemical Society Y1 - 2012 A1 - Hayden, S. C. A1 - Zhao, G. X. A1 - Saha, K. A1 - Phillips, R. L. A1 - Li, X. N. A1 - Miranda, O. R. A1 - Rotello, V. M. A1 - El-Sayed, M. A. A1 - Schmidt-Krey, I. A1 - Bunz, U. H. F. AB - Cationic monolayer-protected gold nanoparticles (AuNPs) with sizes of 6 or 2 nm interact with the cell membranes of Escherichia coli (Gram-) and Bacillus subtilis (Gram+), resulting in the formation of strikingly distinct AuNP surface aggregation patterns or lysis depending upon the size of the AuNPs. The aggregation phenomena were investigated by transmission electron microscopy and UV-vis spectroscopy. Upon proteolytic treatment of the bacteria, the distinct aggregation patterns disappeared. VL - 134 SN - 0002-7863 N1 - Times Cited: 1Hayden, Steven C. Zhao, Gengxiang Saha, Krishnendu Phillips, Ronnie L. Li, Xiaoning Miranda, Oscar R. Rotello, Vincent M. El-Sayed, Mostafa A. Schmidt-Krey, Ingeborg Bunz, Uwe H. F. M3 - 10.1021/ja301167y ER - TY - JOUR T1 - The correlation between emission in freshly prepared porous silicon and the carrier density in silicon water JF - Asian Journal of Spectroscopy Y1 - 2002 A1 - Zou, Bingsuo A1 - Wang, Jianping A1 - El-Sayed, Mostafa A VL - 6 CP - 1 ER - TY - JOUR T1 - Origin of emission from porous silicon: Temperature-dependence correlation with proton conductivity JF - Physical Review B Y1 - 2000 A1 - Zou, Bingsuo A1 - Wang, Jianping A1 - Liu, C. A1 - Zhang, J.Z. A1 - El-Sayed, Mostafa A AB - The excitation, emission, and Fourier transform infrared (FTIR) spectra of freshly prepared and aged porous silicon (PS) are examined. The effects of aging and temperature changing on the emission and excitation spectra of fresh and aged PS samples is also studied. Aging in air is found to result in a redshift in the emission spectrum, but a blueshift in the excitation spectrum. Increasing the temperatures leads to a general decrease in the emission intensities of both samples: however, the green emission of fresh sample shows an unusually large and sudden increase in its intensity at the same temperature at which the proton conductivity in the silicon wafer increases. The temperature dependence of the O-H vibration intensity of silicon wafers shows a sudden decrease at that temperature. These results are consistent with a model in which the excitation leads to the formation of exciton in the confined nanostructure, and the formation of electron and hole that are trapped by surface traps, whose nature is dependent on the chemical composition of the surface (and thus its age). These conclusions are confirmed by the results of the FTIR spectra of the two samples, the temperature dependence of the emission, and its correlation with the proton conductivity in the fresh PS. PB - APS VL - 62 UR - http://link.aps.org/doi/10.1103/PhysRevB.62.16595 CP - 24 M3 - 10.1103/PhysRevB.62.16595 ER - TY - JOUR T1 - Comparison between the polarized Fourier-transform infrared spectra of aged porous silicon and amorphous silicon dioxide films on Si (100) surface JF - Journal of Molecular Structure Y1 - 1999 A1 - Wang, Jianping A1 - Zou, Bingsuo A1 - El-Sayed, Mostafa A AB - The s- and p-polarized Fourier transform infrared spectra were measured for an aged porous silicon (PS) film on Si (100) surface. The asymmetric stretching and symmetric stretching modes as well as the bending or rocking mode of the Si-O-Si group are studied. The deconvoluted spectra in Si-O-Si asymmetric stretching frequency region at different polarization directions show two pairs of vibrational modes, and can be assigned to the longitudinal-optic (LO) and transverse-optic (TO) pair of the corresponding vibrational modes. The smaller LO-TO pair splitting, the broader bandwidth, and the lower polarization ratio of the PS vibration bands as compared with those observed in an a-SiO2 film on Si wafer, suggest a less ordered SiO2 structure and a shorter range of coulombic interaction in PS. (C) 1999 Elsevier Science B.V. All rights reserved. VL - 508 SN - 0022-2860 N1 - Wang, JP Zou, BS El-Sayed, MA M3 - 10.1016/s0022-2860(99)00003-4 ER - TY - JOUR T1 - Effect of different capping environments on the optical properties of CdS nanoparticles in reverse micelles JF - International Journal of Quantum Chemistry Y1 - 1999 A1 - Zou, Bingsuo A1 - Little, Reginald A1 - Wang, Jianping A1 - El-Sayed, Mostafa A AB - CdS(E = 2.5 eV) nanoparticles were synthesized in reversed micelles and capped with materials of different band gaps and charge compensation ability: Cd(OH)(2) (4.0 eV), ZnS (3.2 eV), and CdO (2.3 eV). The preparations allowed the examination and comparison of the efficiencies of confinement of the electron and hole by the various capping materials. The absorption and emission spectra of the capped CdS nanoparticles suggest the following: (1) Efficient capping and strong quantum confinement are observed for CdS particles of small size (< 3.8 nm), showing well-resolved photoexcitation spectra; (2) the confinement efficiency improves with capping thickness; (3) although ZnS has smaller band gap than Cd(OH)(2), it was more efficient in surface-charge compensation and it is the best capping agent of the three materials; and (4) the similar band gaps of CdO and CdS resulted spectroscopically in strong mixing between the excited states of these materials. (C) 1999 John Wiley & Sons, Inc. VL - 72 SN - 0020-7608 N1 - Zou, BS Little, RB Wang, JP El-Sayed, MA M3 - 10.1002/(sici)1097-461x(1999)72:4<439::aid-qua27>3.0.co;2-q ER - TY - JOUR T1 - Time-resolved Fourier-transform infrared and visible luminescence spectroscopy of photoexcited porous silicon JF - Physical Review B Y1 - 1999 A1 - Wang, Jianping A1 - Song, Li A1 - Zou, Bingsuo A1 - El-Sayed, Mostafa A AB - In order to identify the luminescent centers in aged porous silicon, both the time-resolved vibration spectra in the 750-2000-cm(-1) region and the visible luminescence spectra are studied for the same sample in the 0-440-mu s time domain. Laser excitation gives rise to emission characteristics of the porous silicon as well as strong bleach in the infrared spectrum in the region of the ground-stale silicon-oxygen stretching vibration frequencies at 1100 and 1235 cm(-1). In addition, new transient absorption bands appear in this region as a result of the laser excitation. Three characteristic Lifetimes in the decay of the bleach band at 1235 cm(-1) are observed on the 1-, 10-, and 100-mu s time scale. These are similar to the observed decay times of the photoluminescence from porous silicon. These results suggest that the emitting centers in aged porous silicon are trapped excitation sites in an inhomogeneously defected oxidized silicon surface. [S0163-1829(99)09207-3]. VL - 59 SN - 0163-1829 N1 - Wang, JP Song, L Zou, BS El-Sayed, MA M3 - 10.1103/PhysRevB.59.5026 ER - TY - JOUR T1 - Application of liquid waveguide to Raman spectroscopy in aqueous solution JF - Applied Spectroscopy Y1 - 1998 A1 - Song, Li A1 - Liu, S. Y. A1 - Zhelyaskov, V. A1 - El-Sayed, Mostafa A VL - 52 SN - 0003-7028 N1 - Song, L Liu, SY Zhelyaskov, V El-Sayed, MA ER - TY - JOUR T1 - Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- ions. JF - Biophysical journal Y1 - 1997 A1 - Zhang, K A1 - Song, Li A1 - Dong, J A1 - El-Sayed, Mostafa A KW - Bacteriorhodopsins KW - Binding Sites KW - Biophysical Phenomena KW - Biophysics KW - Cations KW - Chlorides KW - Kinetics KW - Ligands KW - Spectrum Analysis KW - Water KW - X-Rays KW - Zinc KW - Zinc Compounds AB - The binding of Zn2+ in Zn2+-regenerated bacteriorhodopsin (bR) was studied under various conditions by x-ray absorption fine structures (XAFS). The 0.9:1 and 2:1 Zn2+:bR samples gave similar XAFS spectra, suggesting that Zn2+ might have only one strong binding site in bR. It was found that in aqueous bR solution, Zn2+ has an average of six oxygen or nitrogen ligands. Upon drying, two ligands are lost, suggesting the existence of two weakly bound water ligands near the cation-binding site in bacteriorhodopsin. When excess Cl- ions were present before drying in the Zn2+-regenerated bR samples, it was found that two of the ligands were replaced by Cl- ions in the dried film, whereas two remain unchanged. The above observations suggest that Zn2+ has three types of ligands in regenerated bR (referred to as types I, II, and III). Type I ligands are strongly bound. These ligands cannot be removed by drying or by exchanging with Cl- ions. Type II ligands cannot be removed by drying, but can be replaced by Cl- ligands. Type III ligands are weakly bound to the metal cation and are most likely water molecules that can be removed by evaporation under vacuum or by drying with anhydrous CaSO4. The results are discussed in terms of the possible structure of the strongly binding site of Zn2+ in bR. VL - 73 CP - 4 U1 - http://www.ncbi.nlm.nih.gov/pubmed/9336205?dopt=Abstract M3 - 10.1016/S0006-3495(97)78240-7 ER - TY - JOUR T1 - The effect of different metal cation binding on the proton pumping in bacteriorhodopsin JF - Israel journal of chemistry Y1 - 1995 A1 - El-Sayed, Mostafa A A1 - Yang, Difei A1 - Yoo, Seoung-Kyo A1 - Zhang, N. AB - The first section of this paper is a detailed summary of studies made by us and others on metal cations binding to deionized bacteriorhodopsin (dIbR) and its variants. Our studies include the luminescence experiments of Eu3+ binding to dIbR and potentiometric studies of Ca2+ binding to dIbR, to deionized bR mutants, to bacterioopsin, and to dIbR with its C-terminus removed. The results suggest the presence of two classes of binding sites, one class has two high-affinity constants, and one has one low-affinity constant. For Ca2+ binding, there is one metal cation in each of the two high-affinity sites which are coupled to the charged aspartates 85 and 212 (known to be in the retinal cavity) but not coupled to each other. The low-affinity class can accommodate 0-6 Ca2+ ions and most of them are bound to the surface. Mg2+ has a slightly smaller value for its binding constant to the highest-affinity site. Thus, one expects more Ca2+ than Mg2+ bound to the two high-affinity sites. In the second section, we summarize our recent study on the effect of metal cation charge density (Ca2+, Mg2+, Eu3+, Tb3+, Ho3+, Dy3+) on the kinetics of both Schiff base deprotonation and proton transport to the extracellular surface. For all metal cations, the apparent rate constant of the slow components of the deprotonation process is the same as that for the transport process at 22 degrees C. The temperature studies, however, show this apparent equality to be fortuitous and to result from cancellation of the contribution of the energy and entropy of activation. Thus, while the entropy of activation is positive for the deprotonation process, it is negative for the proton transport process. These kinetic parameters depend weakly on the charge density, but in an opposite sense for the two processes. These results suggest that the deprotonation is not the rate-limiting step for the proton transport process. A possible mechanism is proposed in which a hydrated metal cation is used to induce the deprotonation of the protonated Schiff base and to dissociate one of its H2O molecules to donate the proton in the L-->M process. PB - Weizmann VL - 35 SN - 0021-2148 CP - 3-4 ER - TY - JOUR T1 - Fourier-transform infrared spectroscopic comparison of cultured human fibroblast and fibrosarcoma cells JF - Proceedings of SPIE Y1 - 1995 A1 - Yang, Difei ED - Castro, D. ED - El Sayed, I.H. ED - El-Sayed, Mostafa A ED - Saxton, R. ED - Zhang, N. AB - Infrared vibration spectroscopy appears to be a more powerful technique for diagnosis than visible or UV spectroscopy. Advantages of IR spectra include: 1) vibrational motion has a smaller tissue absorption coefficient than electronic motion, 2) scattering of infrared radiation has a lower cross section than visible or UV light, (these two facts allow deeper penetration of IR radiation) and 3) vibration spectra provide a better fingerprint of chemical groups present in cells than the unresolved broad electronic spectrum of biological molecules. In the present work, Fourier-transform IR spectroscopy was used to compare cultured human fibroblast and malignant fibrosarcoma cells. Significant differences were observed by comparing the spectra of the normal cells with that of the cancer cells. the PO2 symmetric stretching mode at 1082cm-1 in the cancer cell is reduced in intensity. These observations are similar to those reported previously by Wong et al in comparing the IR spectra of pairs of normal and cancerous cells from the colon and cervix. However, the observed increase in the relative intensity of the symmetric to antisymmetric CH3 bending mode are only found in fibrosarcoma and basal cell carcinoma. The decrease in intensity of the CH2 bending mode relative to that of CH3 mode was observed only for fibrosarcoma cells. This finding with paired human fibroblast and fibrosarcoma cells suggests that fatty acid chains or side chains of protein in the cancer cells are partially degraded leading to more terminal carbon. It is also possible that changes in the environment upon carcinogenesis induces a change in the relative absorption cross sections for the CH3 and CH2 bending vibrations. PB - SPIE VL - 2389 UR - http://dx.doi.org/10.1117/12.210030 CP - 1 M3 - 10.1117/12.210030 ER - TY - JOUR T1 - A Fourier-transform infrared spectroscopic comparison of cultured human fibroblast and fibrosarcoma cells: a new method for detection of malignancies JF - Journal of clinical laser medicine & surgery Y1 - 1995 A1 - Yang, Difei A1 - Castro, D. A1 - El Sayed, I.H. A1 - El-Sayed, Mostafa A A1 - SAXTON, R.E. A1 - ZHANG, N.Y.I. AB - Infrared vibration spectroscopy appears to be a more powerful technique for tumor diagnosis than visible or UV spectroscopy. In the present work, Fourier-transform infrared (FTIR) spectroscopy was used to compare cultured normal fibroblast and fibrosarcoma cells. Significant differences were observed by comparing the spectra of the normal human cells with that of the cancer cells. The PO2 symmetric stretching mode at 1082 cm-1 is shifted to a higher frequency in the cancer cell and a broad band, whose center is located at 1064 cm-1 in the cancer cell is reduced in intensity. In addition, the decrease in intensity of the CH2 bending mode relative to that of CH3 mode is detectable only in the fibrosarcoma cell. This FTIR difference between fibroblast and fibrosarcoma cells suggests that either fatty acid chains or protein side chains of the cancer cells are partially degraded resulting in more terminal carbon (e.g., CH3). It is also possible that changes in the environment upon carcinogenesis induces a change in the relative absorption cross section for CH3 and CH2 bending vibrations. These results suggest that FTIR spectroscopy may become a promising and sensitive technique for tumor identification. VL - 13 SN - 1044-5471 CP - 2 ER - TY - JOUR T1 - On the molecular mechanisms of the rapid and slow solar-to-electric energy storage processes by the other natural photosynthetic system, bacteriorhodopsin JF - Pure and applied chemistry Y1 - 1995 A1 - El-Sayed, Mostafa A A1 - Griffiths, Jennifer A. A1 - Song, Li A1 - Zhang, N. AB - Upon the absorption of solar energy by retinal in bacterioi..>dopsin highly specific photoisomerization of the retinal around the C13 -C14 bond takes place. This is followed by the formation of a number of intermediates resulting from conformational changes of the protein around the retinal which leads to the deprotonation of the protonated Schiff base of the retinylidene system. Thisis the switch of the proton pump which leads to the last step in the storage of solar energy in the form of electric energy by this photosynthetic system. The removal of metal cations from bR is found to inhibit the deprotonation process. In the present paper we summarize the results of our studies and the others regarding two important questions in the conversion process: 1) what is(are) the molecular mechanism(s) of the protein catalysis of the photoisomerizationprocess and 2) what is the role of metal cations in the deprotonation process of the protonated Schiff base (the switch of the proton pump)? In order to answer the first question, the results of the subpicosecondphotoisomerization rate of retinal in bR and in a number of its relevant mutants are discussed in terms of the steric and electronic factors. In an effort to answer the second question,we discussed the results of the binding studies of Ca*+to bR, to its mutants and to bR after its C- terminus is cleaved. From these results and the results of Roux et al. on the 31P NMR of Nd3+ regenerated bR, we concluded that one or two metal cations strongly bound to the protein but not on the surface, are functionally important. The model in which these metal cation@)control the pK values of Aspartic acids in the 85 and 212 positions and that of the protonated Schiff base (PSB) during the photocycle is discussed. PB - BLACKWELL SCIENTIFIC PUBLICATIONS VL - 67 SN - 0033-4545 ER -