Structurally tailored Rh–Au heterodimers: plasmon-boosted oxidase mimetics for facile tea authentication via colorimetric sensing

Abstract

While nanozymes show remarkable potential in colorimetric sensing, conventional systems often suffer from compromised sensitivity and operational complexity in complex analytical scenarios. Herein, a novel heterostructured nanozyme by integrating Au nanoparticles with Rh nanocubes is engineered to address this challenge. By precisely constructing cubic-spherical Rh–Au heterodimers (dimers) with controlled interfacial geometry, a 2.5-fold enhancement in oxidase-mimetic activity compared to the monometallic counterpart is achieved along with a (54 ± 5)% decrease in the activation energy (E_a) for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), using the absorbance of oxidized TMB (oxTMB) as the signal. This result arises from the localized surface plasmon resonance (LSPR) effect, which catalyzes the increased production of reactive oxygen species (ROS). Taking the absorbance of oxTMB as the signal, a multi-channel colorimetric sensing system for tea polyphenol discrimination and tea authentication is developed based on Rh–Au dimers, eliminating the conventional requirement for hydrogen peroxide in the detection process. The experimental data were systematically analyzed through principal component analysis (PCA) and hierarchical cluster analysis (HCA), enabling effective classification of seven polyphenols down to 1 μM. Besides, polyphenol mixtures of 7 components as the real sample mimics, together with diverse tea samples of different storage times, brands and types, are successfully differentiated. The developed colorimetric sensing platform establishes a robust analytical framework for polyphenol evaluation in complex tea samples, showing great potential in the field of food quality monitoring.