Carbon Black Templated Gold Nanoparticles for Detection of a Broad Spectrum of Analytes by Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is a powerful tool for detection of analytes at low concentrations. Because the electric field generated by surface plasmons decays exponentially with distance, the analyte must be in close proximity to the substrate to generate a measurable Raman signal. This often requires customization of the substrate for a specific subset of molecules. We have produced hybrid carbon–gold nanoparticles for the detection of a broad spectrum of molecules using SERS. Carboxyl-terminated carbon black (CB) nanoparticles were coated with the cationic polyelectrolyte poly­(l-lysine) (PLL) and exposed to a tetrachloroauric acid solution. Gold–carbon black (Au-PLLCB) particles were formed by the reduction of gold chloride ions that concentrated on the surfaces of the PLL-coated CB templates. The Au-PLLCB particles produced strong SERS signals for 4-nitro­benzenethiol (4-NBT) in ethanol and for Congo red, crystal violet, and nitrate and sulfate ions in water. The underlying morphology of the carbon black template and the presence of PLL promoted the formation of highly curved gold structures on the surface, yielding hot spots for Raman enhancement. The underlying carbon acted as an absorbent for organic molecules, allowing analytes with poor affinity for the gold surface to concentrate in regions close enough to the particle surfaces to enable detection by SERS. The morphology and chemical nature of the underlying template make the Au-PLLCB particles applicable for SERS-based detection of a wide range of analytes in solution.