On the optical and thermal properties of in situ/ex situ reduced Ag NP's/PVA composites and its role as a simple SPR-based protein sensor

Silver/polyvinyl alcohol (Ag-PVA) nanocomposite films have been prepared via in situ generation of silver nanoparticles (Ag NPs) by the respective metallic salts and dispersion of preformed Ag NPs (ex situ synthesis) inside polyvinyl alcohol (PVA) and its effect of sensing towards a model protein (bovine serum albumin-BSA) was investigated. The influence of Ag NPs, irrespective of their reduction methodology on the optical and the thermal properties of the PVA, had been investigated using UV-Vis spectrophotometer and differential scanning calorimetry. The absorption peak around 400 nm indicates the surface plasmon resonance response of Ag NPs. The interaction of the dispersed and preformed Ag NPs with the PVA chains is confirmed by the corresponding vibrational signatures of the PVA through Fourier transform infrared spectroscopy (FTIR). The changes in the glass transition and melting temperatures (T-g and T-m) of the pure PVA upon the presence of Ag NPs are reported using differential scanning calorimeter (DSC). The sizes of the synthesized Ag NPs are found to be in the range of 200 +/- 10 nm for in situ reduction of silver nitrate (AgNO3) and 100 +/- 10 nm for the external addition of preformed Ag NPs by sodium borohydride (NaBH4) reduction using scanning electron microscopy (SEM).