Silver nanoparticles (AgNPs) have found a variety of uses including biomedical materials; however, studies of the cytotoxicity of AgNPs by size effects are only in the beginning stage. In this study, we examined the size-dependent cellular toxicity of AgNPs using three different characteristic sizes (∼ 10, 50, and 100 nm) against several cell lines including MC3T3-E1 and PC12. The cytotoxic effect determined based on the cell viability, intracellular reactive oxygen species generation, lactate dehydrogenase release, ultrastructural changes in cell morphology, and upregulation of stress-related genes (ho-1 and MMP-3) was fairly size- and dose-dependent. In particular, AgNPs stimulated apoptosis in the MC3T3-E1 cells, but induced necrotic cell death in the PC12 cells. Furthermore, the smallest sized AgNPs (10 nm size) had a greater ability to induce apoptosis in the MC3T3-E1 cells than the other sized AgNPs (50 and 100 nm). These data suggest that the AgNPs-induced cytotoxic effects against tissue cells are particle size-dependent, and thus, the particle size needs careful consideration in the design of the nanoparticles for biomedical uses.

The adsorption behavior of 4-biphenylisocyanide (BPNC) has been studied by means of surface-enhanced Raman scattering (SERS). BPNC has been found to adsorb on silver and gold via the carbon lone pair electrons assuming a standing geometry with respect to the surfaces. The presence of the ν(CH) band in the SERS spectra indicated a vertical orientation of the biphenyl ring of BPNC on Ag and Au. Neither a substantial red shift nor a significant band broadening of the ring breathing modes implied that a direct ring π orbital interaction with metal substrates should be quite low. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Ag and Au surface by determining the relative enhancement factor of each vibrational band. The band analysis indicated that BPNC should have a slightly more vertical orientation on silver than on gold. The frequency of the ν(NC) band on gold increased by ∼10 cm -1 than that on silver surface. Such a higher blue shift of the ν(NC) stretching vibration in the gold sol SER spectrum may be due to a higher electronegativity of gold.

The adsorption behavior of 4-cyanobiphenyl (CNBP) has been investigated by means of surface-enhanced Raman scattering (SERS). CNBP appeared to assume a tilted orientation on silver and gold. The presence of the ring C-H band denoted a rather vertical orientation of the biphenyl ring on Ag and Au. On the other hand, considerable red shifts of the ring-breathing modes with the increase in their bandwidths indicated a substantial π-type interaction between the benzene rings and metal substrates. On gold, the concentrationdependent SERS experiment showed CNBP to have a slightly perpendicular stance at its high surface coverage. The presence of the BH4ion in sols was found to affect the adsorption reaction and surface orientation of CNBP. The spectral band analysis based on electromagnetic selection rule indicated that CNBP should have a slightly more vertical orientation on gold than on silver at the concentration of ∼10 -4 M.