Schiff-Base Chemistry-Coupled Catechol Oxidase-Like Nanozyme Reaction as a Universal Sensing Mode for Ultrasensitive Biosensing

Expanding sensing modes and improving catalytic performance of nanozyme-based analytical chemistry are beneficial to realizing the desired biosensing of analytes. Herein, Schiff-base chemistry coupled with a novel catechol oxidase-like nanozyme (CHzyme) is designed and constructed, exhibiting two main advantages, including (1) improving catalytic performance by nearly 2-fold compared with only the oxidase-like role of CHzyme; (2) increasing the designability of the output signal by signal transduction of cascade reaction. Thereafter, the substrate sensing modes based on a cascade reaction between the CHzyme-catalyzed reaction and Schiff-base chemistry are proposed and comprehensively studied, containing catalytic substrate sensing mode, competitive substrate sensing mode, and generated substrate sensing mode, expecting to be employed in environmental monitoring, food analyses, and clinical diagnoses, respectively. More meaningfully, the generated substrate sensing mode is successfully applied to construct a cascade reaction coupling ratiometric fluorescent immunoassay for the detection of clenbuterol, increasing 15-fold in detection sensitivity compared with the traditional enzyme-linked immunosorbent assay. It is expected that the expanded universal substrate sensing modes and the Schiff-base chemistry-enhanced nanozyme can enlighten the exploration of innovative biosensors.