Utilizing Ag-Au core-satellite structures for colorimetric and surface-enhanced Raman scattering dual-sensing of Cu (II).

This study develops a dual-channel colorimetric and surface-enhanced Raman scattering (SERS) strategy for detection of Cu2+ utilizing Ag-Au core-satellite nanostructures. 4-mercaptobenzoic acid (MBA) modified Ag nanoparticles (AgNPs@MBA) and 4-mercaptopyridine (Mpy) capped AuNPs (GNPs@Mpy) are first designed via metal-sulfur bonds, respectively. Benefiting from the Cu2+-triggered NPs self-aggregation, the dispersion of AgNPs-GNPs (AgNPs@MBA + GNPs@Mpy) is turned into AgNPs-Cu2+-GNPs core-satellite structures. Because of the presence of pyridyl nitrogen and carboxy group which have specific coordination ability towards Cu2+, induces a certain aggregation of NPs. As well it can be obviously discerned by the visual assay and easily captured by SERS analysis. The UV-Vis method exhibits good linearity in the ranging from 0.1 μM-200 μM for Cu2+, while SERS method displays good linear response from 1 pM to 100 μM. The detection limit of Cu2+ is 0.032 μM by colorimetry and 0.6 pM by SERS method, which is significantly lower than the acceptable limit of Cu2+ in drinking water (20 μM) set by the US EPA. Furthermore, colorimetric and SERS assay based on AgNPs-Cu2+-GNPs core-satellite structures is used to determine Cu2+ in various waters and soils, and the detection results are consistent with the traditional atomic analysis methods. This work offers a new method for detecting Cu2+ in environmental samples, and the plasmonic nanostructure provides new entry point for development of multiplexed sensing platform for in-field application.