Colorimetric and Raman spectroscopic array for detection of hydrogen peroxide and glucose based on etching the silver shell of Au@Ag core-shell nanoparticles.

Gold-silver core-shell nanoparticles (Au@Ag NPs) were prepared by two successive reductions in a seed-growth method. The Au@Ag NPs are used as both a colorimetric and Raman spectroscopic probe for ultrasensitive determination of H2O2 and glucose. It is found that H2O2 (as produced from glucose by the action of glucose oxidase) can directly oxidize and gradually corrode the silver shell of the Au@Ag NPs. This results in a drop in the surface plasmon resonance absorbance at 400 nm, and the color of the solution changes from brownish yellow to purple. Without adding any additional chromogenic agents, the color change can be visually observed and detected photometrically. Silver NPs also are an excellent surface-enhanced Raman scattering (SERS) substrate. Due to corrosion of the silver shell, the SERS intensity (measured at 1083 cm-1) gradually decreases with increasing glucose concentration. The detection limits are 300 nM of glucose for the colorimetric assays, and 20 nM for the SERS assay. Graphical abstractSchematic representation of the method for glucose determination. H2O2 can oxidize and gradually corrode the silver shell of the gold-silver core-shell nanoparticles. This results in a distinct color change of the solution from brownish yellow to purple, and a drop in SERS intensity. The effect is applied in colorimetric and Raman spectroscopic assays for glucose.