Single-particle cadmium(Ⅱ) and chromium(Ⅲ) ions assay using GNP@Ag core−shell nanoparticles with dark-field optical microscopy

Heavy metal pollution is a serious environmental problem in some regions. Regular monitoring heavy metal contaminations in the environment is quite significant for human life and health. In this work, we utilize [email protected] nanoparticles (NPs) as the probe for sensitively detecting Cd2+ and Cr3+ in aqueous solution by dark-field optical microscopy (DFM) based single-particle detection (SPD) method. Herein, Cd2+ will cause the probe aggregation and exhibit an obvious red-shift of the localized surface-plasmon resonance (LSPR) peak. In the presence of Cr3+, noticeable increase in scattering intensity from the probe together with a weak red-shift of its LSPR peak is shown. Moreover, Cd2+ and Cr3+ can be quantified statistically through calculating the ratio of color change by DFM. Under optimal conditions, the linear dynamic ranges are obtained from 1 to 5 and 2 to 10 μM with detection limit of 11.5 and 26.8 nM for Cd2+ and Cr3+, respectively. Due to the ultra-high sensitivity and excellent specificity, this method is expected to have broad applications such as environmental monitoring and groundwater analysis in the future.