Aqueous phase one-pot green synthesis of SnSe nanosheets in a protein matrix: negligible cytotoxicity and room temperature emission in the visible region

In recent times, SnSe has attracted considerable attention as an environmentally friendly alternative to cadmium- and lead-based photovoltaic materials. Herein, we report a rapid, facile, reproducible, and purely green method for the synthesis of SnSe nanosheets (NS) in an aqueous solution of bovine serum albumin (BSA). Interestingly, BSA itself acted as a reducing agent, stabilizing agent and shape directing template. Time dependent TEM imaging showed the self-assembly of the nanoparticles (NPs) into single crystalline NS. A probable mechanism has been proposed on the basis of the alteration of the intrinsic a-helix structure of BSA into beta-pleated sheets at the pH (similar to 3.0) of the reaction mixture. This directs the self-assembly of small SnSe NPs into the NS like structure. It was further evident that the -NH and the -S-S- linkages in the protein are involved in the functionalization of the NPs. As grown SnSe nanomaterial was found to display room temperature photoluminescence (PL), which has been rarely reported. The PL spectra appeared to be the convolution of two bands at 425 and 470 nm, which were attributed to the band-gap and trap/surface state emission, respectively. Moreover, the reduction potential values obtained from the cyclic voltammetry indicate better thermodynamic feasibility for the reduction of SnSe, while the cytotoxicity studies revealed no toxic effects up to a concentration of 100 mu M. This signifies the potential application of these nanomaterials in photovoltaics and biomedical contexts.