Plasmonic detection of Cd2+ ions using surface-enhanced Raman scattering active core–shell nanocomposite

Abstract

The present study was structured to address development of an efficient devise for sensing of toxic Cd2+ ions at trace level in aqueous media. In order to achieve this objective, the speckled core–shell nanocomposites (NCs) of silica-gold (SiO2@Au) using ~30nm diameter of spherical gold nanoparticles (Au NPs) with 420nm diameter of silica cores was synthesized. Au NPs showed the surface plasmon resonance (SPR) peak at 522nm and spherical core–shell particles at 541nm. Both Au NPs and SiO2@Au solutions were found to be sensitive to Cd2+ ions in aqueous sample. The colour change occurred in presence of SiO2@Au at 0.1ppm (100ppb) of Cd2+ ions whereas 2ppm (2000ppb) concentration of Cd2+ ions was necessary for the colour change in Au NPs solution confirmed that SERS active SiO2@Au core–shell NCs 20 times more sensitive compared to Au NPs. The technique using SiO2@Au NCs is quantitative between 100 and 2000ppb (0.1 to 2ppm) while effective but non-quantitative above upto 10ppm, the maximum concentration studied in present investigation. The detection limit using SiO2@Au NCs is 100ppb (0.1ppm) while Au NPs is able to detect Cd2+ as low as 2000ppb (2ppm). The scanning electron microscopy (SEM) of Au NPs and SiO2@Au particles showed aggregation of Au NPs and SiO2@Au NCs in the presence of Cd2+ ions. The surface enhanced Raman spectroscopy (SERS) was used to compare sensitivities of Au NPs and SiO2@Au towards Cd2+ ions and confirmed that SiO2@Au core–shell NCs is 20 times more sensitive than Au NPs.