Synthesis of Cu–Ag core–shell nanoparticles as highly active surface-enhanced Raman scattering substrates for sensitive detection of caffeic acid

Core–shell nano-metal structures as SERS probes have drawn attention and have been applied to detecting analytes at low concentrations. Here, we have developed a novel SERS probe composed of Cu–Ag for the quantitative, rapid and ultrasensitive detection of caffeic acid. The surface of Cu–Ag was modified with 4-mercaptophenylboronic acid (4-MPBA) to allow the probe to detect caffeic acid, wherein 4-MPBA specifically binds to caffeic acid by an esterification reaction. The results obtained in this work show that the SERS performance of the 4-MPBA substrate is better than that of the Cu–Ag substrate. To determine the binding of caffeic acid to 4-MPBA, the B-OH stretching vibration at 1170 cm–1 was selected as the representative signal. It was found that there is a linear relationship between the intensity of the peak at 1170 cm–1 and the concentration of caffeic acid.