Characterization of nC60 in the presence and absence of carboxylic acids
Work in this area during the past year has focused on the development of an in situ UV-Vis method to monitor changes in the interfacial properties of nC60. Systematic analysis of the UV-Vis spectrum of nC60 has established that the broad absorption band in the 400-600 nm region is due to nanoparticle aggregation and not the result of electron donor-acceptor interactions as had been previously reported. In addition, we have established that UV-Vis spectra can be evaluated to examine the interfacial chemistry of nC60 in the presence of citrate and other low molecular weight carboxylic acids. Such insights have established that carboxylate groups interact with the C60 surface via non-covalent interactions. These interactions alter the colloidal and chemical stability of nC60.
Chemical Stability of Silver and Gold Nanoparticles
Our efforts in this area over the past year have focused on the development of an atomic force microscope (AFM) assay to characterize the dissolution of surface adhered silver and gold nanoparticles. In these experiments, surface arrays of silver or gold nanoparticles are produced via a technique known as nanosphere lithography (NSL). Silver nanoparticles produced by NSL undergo dissolution in NaCl solutions and the kinetics of dissolution directly correlate with the NaCl concentration. Experiments with gold nanoparticles under the same conditions indicate no dissolution. Current plans are to extend these studies by coating the nanoparticles with polymers (PVP, PEG) and by varying the solution chemistry (HS-, cysteine, etc…).
Gold Nanoparticle Transport, Fate, and Organismal Uptake
We routinely produce spherical gold nanoparticles in a range of sizes between 5-50 nm and rod-shaped gold nanoparticles with average length and diameter of 65.5 and 19.7 nm, respectively. As produced, these nanoparticles are surface functionalized with citrate (spherical particles) or with hexadecyl-cetyltrimethylammonium bromide (CTAB; rods). We have recently produced nanoparticles with alternative surface coatings (e.g., BSA, polyethylene glycol (PEG), DNA, peptides) and are in the process of initiating studies to examine the effects of these surface coatings on nanoparticle uptake by C. fluminea. In collaboration with MacCuspie (NIST) we have systematically probed the stability of citrate-stabilized gold nanoparticles in solutions of variable ionic strength. A major focus of this effort was on the development of a metric to characterize the colloidal stability of gold and silver nanoparticle suspensions that is based upon monitoring of the localized surface plasmon resonance (LSPR) band for these materials.