A. Nanoscience: Synthesis and Study of the Properties of Nanomaterials of Different Shape: The type of electronic motion in matter determines its properties and its applications. This motion is determined by the forces acting on the electrons, which in turn, determine the space in which they are allowed to move. One expects that if we reduce the size of material to below its naturally allowed characteristic length scale, new properties should be observed which change with the size or shape of the material. These new properties are different from those of the macroscopic material, as well as of its building blocks (atoms or molecules). This phenomenon occurs on the nanometer length scale. Our group makes and studies the properties of these nanometer materials. The properties examined are:
Ultrafast electron-hole dynamics in semiconductor nanoparticles and composites
Shape-controlled synthesis and stability of metallic nanoparticles
Enhanced light absorption and scattering processes, electronic relaxation, and photothermal properties of gold and silver nanocrystals of different shapes
B. Nanotechnology: Potential Use of Nanoparticles in: a) Nanomedicine - Diagnostics and Selective Photothermal Therapy of Cancer: When gold or silver nanoparticles are conjugated to cancer antibodies or other cancer targeting molecules, the cancer cells selectively labeled with those nanoparticles and can be easily detected under a simple microscope due to their strongly enhanced light scattering properties. The fact that these nanoparticles can also absorb light strongly and rapidly convert this energy into heat allows for the selective destruction of cancer cells at laser energies not sufficient to harm surrounding healthy cells. The concept of plasmonic photothermal therapy has been demonstrated in both cell culture and in live animal models in our laboratory. In addition, we are also researching the use of plasmonic particles as selective drug delivery and imaging contrast agents. b) Nanocatalysis - Shape Dependent Catalysis: Due to their large surface to volume ratio, nanoparticles are expected to be good catalysts. Since different shapes of nanoparticles made of the same material have their surface atoms arranged differently, one expects them to have different catalytic properties. In our group, we are examining the effects of both the nanoparticle shape and the cavity size of hollow nanoparticles on the catalytic properties of transition metal nanocrystals. We are also studying the shape-stability of these nanoparticles in the harsh chemical environment of the catalytic reactions in colloidal solution. c) Plasmonics: The intense electromagnetic fields generated at the surfaces of noble metal nanoparticles – localized surface plasmons – are known to enhance radiative and non-radiative processes, as well as energy transfer processes in nearby molecules and compounds. By combining plasmonic particles with biomolecular photosystems, the rates of important chemical processes, such as retinal isomerization in photosynthetic baceriorhodopsin (bR) and its associated proton pump rate, can be tuned. This property was recently used to enhance the photocurrent from bR by a factor of 5000. Rates of radiative (emission) and non-radiative relaxation in excitonic systems, such as semiconductor quantum dots and rods, can also be dramatically enhanced by plasmon coupling interactions. LDL also studies the fundamental interactions of plasmons as they couple to one another in individual (i.e. nanoshell and nanocage) particles, as well as in groups of nanoparticles as their size, shape, distance, and orientation are varied.