Dual-mode probe for identifying multiple polyphenols by colorimetry and surface-enhanced Raman scattering

Astringency is closely associated with polyphenols found in food and beverages. Given their importance to both the food industry and human health, accurate detection of polyphenols has become a focal point of research. In this study, a dual-mode probe was constructed for polyphenol detection by colorimetry alongside surface-enhanced Raman scattering (SERS). The probe is core-molecule-shell gold/4-MBA/silver nanorods (Au@M@Ag NRs). The silver shell on the surface of Au@M@Ag NRs can be etched by hydrogen peroxide (H₂O₂), resulting in a significant red-shift in UV absorption spectra and a marked decrease in SERS signal output from 4-MBA. Upon introducing polyphenols with strong antioxidant properties, the etching process of the silver shell is inhibited, thereby protecting the shell-core ratio of Au@M@Ag NRs. This process can be readily monitored through both colorimetry and SERS analysis. In our work, harnessing the anti-etching effect exhibited by kaempferol, a type of polyphenol, our dual-mode sensor demonstrates superior detection limits (43.2 nM for colorimetry and 0.786 nM for SERS) compared to previously reported methods. We successfully distinguished five different polyphenols with varying antioxidant capacities: chlorogenic acid, epicatechin, epigallocatechin gallate, kaempferol, and tannic acid through linear discriminant analysis (LDA). This dual-mode sensor can decrease false-positive results while offering promising applications for determining and identifying polyphenols within complex food samples.