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 Cu 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 Cu-triggered NPs self-aggregation, the dispersion of AgNPs-GNPs (AgNPs@MBA + GNPs@Mpy) is turned into AgNPs-Cu-GNPs core-satellite structures. Because of the presence of pyridyl nitrogen and carboxy group which have specific coordination ability towards Cu, 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 Cu, while SERS method displays good linear response from 1 pM to 100 μM. The detection limit of Cu is 0.032 μM by colorimetry and 0.6 pM by SERS method, which is significantly lower than the acceptable limit of Cu in drinking water (20 μM) set by the US EPA. Furthermore, colorimetric and SERS assay based on AgNPs-Cu-GNPs core-satellite structures is used to determine Cu 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 Cu in environmental samples, and the plasmonic nanostructure provides new entry point for development of multiplexed sensing platform for in-field application.