@article {1423, title = {Synthesis and Optical Properties of Small Au Nanorods Using a Seedless Growth Technique}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Jun}, pages = {9807-9815}, abstract = {Gold nanoparticles have shown potential in photothermal cancer therapy and optoelectronic technology. In both applications, a call for small size nanorods is warranted. In the present work, a one-pot seedless synthetic technique has been developed to prepare relatively small monodisperse gold nanorods with average dimensions (length x width) of 18 x 4.5 nm, 25 x 5 nm, 15 x 4.5 nm, and 10 x 2.5 nm. In this method, the pH was found to play a crucial role in the monodispersity of the nanorods when the NaBH4 concentration of the growth solution was adjusted to control the reduction rate of the gold ions. At the optimized pH and NaBH4 concentrations, smaller gold nanorods were produced by adjusting the CTAB concentration in the growth solution. In addition, the concentration of silver ions in the growth solution was found to be pivotal in controlling the aspect ratio of the nanorods. The extinction coefficient values for the small gold nanorods synthesized with three different aspect ratios were estimated using the absorption spectra, size distributions, and the atomic spectroscopic analysis data. The previously accepted relationships between the extinction coefficient or the longitudinal band wavelength values and the nanorods{\textquoteright} aspect ratios found for the large nanorods do not extend to the small size domain reported in the present work. The failure of extending these relationships over larger sizes is a result of the interaction of light with the large rods giving an extinction band which results mostly from scattering processes while the extinction of the small nanorods results from absorption processes.}, isbn = {0743-7463}, doi = {10.1021/la301387p}, author = {Ali, M. R. K. and Snyder, B. and El-Sayed, M. A.} } @article {1324, title = {Synthesis and Optical Properties of Small Au Nanorods Using a Seedless Growth Technique}, journal = {Langmuir}, volume = {28}, number = {25}, year = {2012}, note = {Times Cited: 2Ali, Moustafa R. K. Snyder, Brian El-Sayed, Mostafa A.}, month = {Jun}, pages = {9807-9815}, abstract = {Gold nanoparticles have shown potential in photothermal cancer therapy and optoelectronic technology. In both applications, a call for small size nanorods is warranted. In the present work, a one-pot seedless synthetic technique has been developed to prepare relatively small monodisperse gold nanorods with average dimensions (length x width) of 18 x 4.5 nm, 25 x 5 nm, 15 x 4.5 nm, and 10 x 2.5 nm. In this method, the pH was found to play a crucial role in the monodispersity of the nanorods when the NaBH4 concentration of the growth solution was adjusted to control the reduction rate of the gold ions. At the optimized pH and NaBH4 concentrations, smaller gold nanorods were produced by adjusting the CTAB concentration in the growth solution. In addition, the concentration of silver ions in the growth solution was found to be pivotal in controlling the aspect ratio of the nanorods. The extinction coefficient values for the small gold nanorods synthesized with three different aspect ratios were estimated using the absorption spectra, size distributions, and the atomic spectroscopic analysis data. The previously accepted relationships between the extinction coefficient or the longitudinal band wavelength values and the nanorods{\textquoteright} aspect ratios found for the large nanorods do not extend to the small size domain reported in the present work. The failure of extending these relationships over larger sizes is a result of the interaction of light with the large rods giving an extinction band which results mostly from scattering processes while the extinction of the small nanorods results from absorption processes.}, isbn = {0743-7463}, doi = {10.1021/la301387p}, author = {Ali, M. R. K. and Snyder, B. and El-Sayed, M. A.} } @article {1091, title = {Polystyrene Microspheres: Inactive Supporting Material for Recycling and Recovering Colloidal Nanocatalysts in Solution}, journal = {Journal of Physical Chemistry Letters}, volume = {1}, number = {1}, year = {2010}, note = {Mahmoud, M. A. Snyder, B. El-Sayed, M. A.}, month = {Jan}, pages = {28-31}, abstract = {Alumina and silica have been the most commonly, used solid supports in the recovery of colloidal nanocatalysts in solution. In order to avoid possible involvement of the support in the catalytic mechanism, polystyrene microspheres are here demonstrated to be effective and nonreactive supports on which the nanocatalyst can be easily attached by using the swelling and shrinking properties of the polystyrene microspheres. The activation energy of the reduction of 4-nitrophenol with sodium borohydride on platinum nanocubes free in solution is comparable to those on polystyrene microspheres.}, isbn = {1948-7185}, doi = {10.1021/jz9000449}, author = {Mahmoud, M A and Snyder, B. and El-Sayed, Mostafa A} } @article {1090, title = {Surface Plasmon Fields and Coupling in the Hollow Gold Nanoparticles and Surface-Enhanced Raman Spectroscopy. Theory and Experiment}, journal = {Journal of Physical Chemistry C}, volume = {114}, number = {16}, year = {2010}, note = {Mahmoud, M. A. Snyder, B. El-Sayed, M. A.}, month = {Apr}, pages = {7436-7443}, abstract = {Most gold nanoparticles have surface plasmon fields only surrounding their surfaces. Recently, hollow nanoparticles have been studied, such as gold nanocages (AuNC) and gold nanoframes (ALINE). Those particles have two types of surfaces, one facing the outside and the other within the cavity. Their coupling provides a surface field inside the hollow particle and on the outside surface. Using DDA computational method, we have shown that the coupling between these fields gives field intensities and distribution inside and outside the nanoparticles that are sensitive to the thickness (the distance between the two surfaces) as well as the nanoparticle size. For small sizes, the coupling between the fields on the opposite sides of the cage is detected. These effects are detected by following the changes in the experimentally observed surface plasmon resonance spectra of these nanoparticles and the surface-enhanced Raman spectra of adsorbed molecules. The effect of the interaction between the external and internal field as well as the available surface area inside and outside the nanoparticle effects on the Raman-enhancement is detected by comparing the Raman intensities dependence on the interparticle distance with those observed on solid nanocubes surfaces.}, isbn = {1932-7447}, doi = {10.1021/jp9109018}, author = {Mahmoud, M A and Snyder, B. and El-Sayed, Mostafa A} }