Amplification of resonance Rayleigh scattering of gold nanoparticles by tweaking into nanowires: Bio-sensing of α-tocopherol by enhanced resonance Rayleigh scattering of curcumin capped gold nanowires through non-covalent interaction

Tuning optical properties by controlling size and shape of the metallic nanoparticles has been of great interest to design novel bio-sensing techniques. Here, as a first example we illustrate that resonance Rayleigh scattering (RRS) signal of Au nanoparticles (NPs) can be amplified > 10-fold by growing into Au nanowires (NWs). These thin and long NWs of similar to 20-25 nm diameter and > 1 mu m length can be achieved by suitably manipulating the temperature during green synthesis using curcumin. Interestingly, mixture of Au NWs and NPs or shorter NWs gives a moderate increase in RRS signal suggesting formation of longer NWs is crucial for optimal enhancement of RRS signal. Curcumin along with CTAB act as capping and stabilizing agent for Au NWs/NPs in different temperatures, which is confirmed by XRD, TGA, DSC, EDX and FT-IR data. This amplified RRS signal of Au NWs has been employed to design a new optical biosensor for alpha-tocopherol (alpha-TOH), which is among the most biologically active form of vitamin E. Association of alpha-TOH with Au NWs further enhances the RRS signal of Au NWs, similar to 10 fold through non-covalent interaction. No interference from other antioxidant substances like ascorbic acid and 6-O-Palmitoyl-L-ascorbic acid is observed. The sensing method is simple, fast and offers remarkable linear dynamic ranges, 12.8-1004 mu mol L-1, which is larger than reported values. The detection limit for alpha-TOH estimation has been found to be 50 nmol L-1. The biosensor is found to be stable both in the absence and presence of alpha-TOH and provides an excellent recovery for synthetic samples.