Bifunctional TiO2@AgNP Superstructures as a SERS-Sensing Platform for Identifying Flavonoids in Chinese Herbal Medicine

<i>Acanthopanax senticosus</i> is an essential medicinal herb in traditional Chinese medicine, with its pharmacological properties largely attributed to bioactive flavonoids. The types and amounts of these flavonoids act as vital quality markers for both the raw materials and the resultant products. In this work, we introduce a TiO₂@AgNP nanocomposite designed as a surface-enhanced Raman scattering (SERS) sensor aimed at the preliminary quantification and identification of flavonoids. This is achieved by leveraging the effective molecular adsorption properties of TiO₂ alongside the 'hot spots' generated by AgNPs. By optimizing SERS performance through adjustment of the molar ratio between TiO₂ and Ag, we can quantitatively evaluate four flavonoids-luteolin, kaempferol, quercetin, and rutin-with low detection concentrations of 10^-6 M, 10^-5 M, 5 × 10^-6 M, and 10^-6 M, respectively. Additionally, we observe a nearly linear relationship between the SERS signals and the flavonoid concentrations, allowing for dual or multiplex analysis of these compounds. Furthermore, we successfully differentiated <i>Acanthopanax senticosus</i> samples from six different geographical regions in China based on the detection of significant flavonoid constituents. This serves as a proof of concept for practical applications that can enhance the identification and distinction of traditional Chinese medicine, as well as assess quality and medicinal efficacy.