Photochemical preparation, characterization and formation kinetics of riboflavin conjugated silver nanoparticles

Riboflavin conjugated silver nanoparticles (RF-AgNPs) have been synthesized by photoreduction of Ag+ ions and characterized by UV-visible, X-ray diffraction (XRD), FTIR spectroscopy, spectrofluorimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). The RF-AgNPs exhibit a typical surface plasmon resonance (SPR) peak at 422 nm due to the interaction of RF and AgNPs. FTIR studies indicate the appearance of an intense absorption peak at 2920 cm(-1) due to the interaction of RF and Ag. AFM studies indicate that the RF-AgNPs are spherical and polydisperse in nature (57-73 nm), which nicely complement the hydrodynamic radii (57.9-72.2 nm) measured by DLS. None of the tested concentrations (1-250 mu g mL(-1)) of RF-conjugated AgNPs show any adverse effect on normal mouse fibroblast and cancerous non-small lung carcinoma cell lines. At acidic pH (2.0-6.2) aggregation of RF-AgNPs occurs due to an increase in the ionic strength of the medium. The rates of formation of RF-AgNPs on UV and visible light irradiation have been determined in the pH range of 8.0-10.5 and at different concentrations of Ag+ ions. The photochemical formation of RF-AgNPs follows a biphasic first-order reaction probably due to the formation of AgNPs in the first phase (fast) and the adsorption of RF on AgNPs to yield RF-AgNPs in the second phase (slow).