Gelatin-nanogold bioconjugates as effective plasmonic platforms for SERS detection and tagging.

It is well known that standard citrate-reduced gold nanoparticles (AuNPs) are unstable at high ionic strength solution, which limits their applications in the biomedical field. In this work we present an environmentally friendly approach for the stabilization of citrate-reduced AuNPs in aqueous solution. Specifically, the stability of the AuNPs against salt-induced aggregation was greatly improved in the presence of gelatin biopolymer and stabilization of individual or small assemblies of nanoparticles can be controlled by the amount of gelatin. Furthermore, the gelatin-nanogold bioconjugates were demonstrated to be operational as highly sensitive surface-enhanced Raman scattering (SERS) active substrate for the detection of Rose Bengal fluorophore in solution at very low concentration. The results suggest that such bioconjugates can be successfully employed not only for detection of analytes, but more interestingly for building SERS-active tags in view of imaging purpose. The stabilization of bioconjugates was analyzed by localized surface plasmon resonance spectroscopy (LSPR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta-potential, and the chemical interaction of gelatin with AuNPs was inferred from Fourier transform infrared spectroscopy (FT-IR).