Anion effect in linear silver nanoparticle aggregation as evidenced by efficient fluorescence quenching and SERS enhancement

This work is the first report of the effect of anions of precursor salts on the efficiency of photochemical reduction of Ag (I) to Ag (0). Ultraviolet (UV) irradiation of an aqueous Triton X-100 solution in the presence of Ag (I) produces the green sol at a certain critical concentration of ascorbic acid. The photochemical process of silver sol formation possesses the advantage of producing homogeneous particles of very small size (similar to 6 nm). In the presence of a reduction sensitizer, such as ascorbic acid, these tiny silver dots aggregate beautifully in a symmetric manner to form necklace-like structures. Fluorescence quenching studies carried out with the probe I-aminonaphthalene give an idea about the structure and binding capacities of the sols, the latter effect being more pronounced for the linearly aggregated sol. Fluorescence and AFM studies complimented by surface-enhanced Raman scattering (SERS) studies with pyridine reveal that the green silver sol consists of linear aggregates, whereas the yellow sol does not contain the aggregated arrangement. The most interesting result arising out of this study is that linear aggregation of spherical silver sols leads to enhanced efficiency as fluorescence quenchers as also an improvement in SERS activity. These linear aggregates of silver may hold prospects for the development of interconnecting quantum devices in future. (C) 2000 Elsevier Science S.A. All rights reserved.