Identification of catechin species using a colorimetric and fluorescence dual-mode sensor array based on peroxidase-like PtNi bunched nanoparticles

Catechins in tea, as promoters of human health, have attracted widespread attention. Herein, a dual-signal mode (colorimetric and fluorescence) sensor array for catechin species fingerprinting was built based on PtNi bunched nanoparticle (PtNi-BNP)-<i>o</i>-phenylenediamine (OPD)-H₂O₂ system. PtNi-BNPs catalyze the reaction between OPD and H₂O₂ to produce oxidized OPD (oxOPD) with both colorimetric (yellow) and fluorescent properties. As an antioxidant, catechins can inhibit the above reaction, resulting in a lighter color and reduced fluorescence intensity in the reaction solution. Owing to the varying inhibitory effects of different catechins on the reaction, they produce unique colorimetric-fluorescence response patterns. These diverse responses were recorded and processed using linear discriminant analysis (LDA), and six catechin species were identified using the sensor array. Furthermore, our work provides a convenient method for simultaneous differentiation of catechins in mixtures and real samples. Such a sensor array with minimal sensor element and abundant signal outputs considerably saves cost and time, thus providing a powerful tool for the discrimination and assessment of catechins.