Trace colorimetric detection of Pb2+ using plasmonic gold nanoparticles and silica-gold nanocomposites

A novel, simple and highly sensitive plasmonic colorimetric method is developed for the detection of Pb2+ in aqueous samples. The method is based on the aggregation of gold nanoparticles (AuNPs) or SiO2core-Au-shell nanocomposites (SiO2@Au NCs) in the presence of Pb2+ ions. It was found that the colour of AuNPs or SiO2@Au NCs changes in the presence of Pb2+ ions and the intensity of surface plasmon resonance (SPR) peak of AuNPs or SiO2@Au NCs decreased. Thus, the synthesis of sensitive surface enhanced Raman scattering (SERS) materials; similar to 20 nm spherical AuNPs and similar to 360 nm SiO2@Au NCs leads to the development of nanosensor for the detection of Pb2+ ions. Both AuNPs and SiO2@Au NCs by virtue of their versatility show localized surface plasmon resonance (LSPR) peaks at 522 nm and 541 nm respectively. The synthesized AuNPs, SiO2@Au NCs and analyte samples prepared were characterised using a scanning electron microscope, a transmission electron microscope and a UV-vis spectrophotometer. The SERS study was also used to compare sensitivities of both AuNPs and SiO2@Au NCs towards Pb2+ ions using crystal violet (CV) as a target molecule. The analyte Pb2+ was detected as low as 500 nM using 20 nm AuNPs and 50 nM using 360 nm SiO2@Au NCs. It was confirmed that SiO2@Au NCs were found ten times more sensitive as compared to AuNPs for the detection of Pb2+ ions.