Ni3-xMnxO4-driven hydrolase-oxidase bienzyme-mimicking cascade-stimulated aminoantipyrine self-coupling for time-resolved sensing of ascorbic acid derivatives.

Anti-aging of human skin has long been a significant concern for beauty enthusiasts, and the introduction of various ascorbic acid derivatives in cosmetics plays a crucial role in combating free radicals and maintaining healthy and radiant skin, thus their discernment and quantification act as pivotal benchmarks for appraising the quality of cosmetics. Herein, we proposed a bienzyme-mimicking cascade-stimulated aminoantipyrine oxidative self-coupling strategy to enable the time-resolved discrimination and quantification of various ascorbic acid derivatives in complex cosmetic matrices. A series of two-dimensional Ni-Mn bimetallic nanozymes (Ni3-xMnxO4) were successfully synthesized via hydrothermal crystallization combined with doping engineering. Ni3-xMnxO4 demonstrates outstanding hydrolase-like and oxidase-like properties within a single catalytic system. In-situ LC-MS analysis has verified the existence of dimer chromogenic intermediates resulting from the self-coupling of 4-AP via Schiff-base-like chemistry. The hydrolyzed products modulate the time-resolved output of the cascade signal, serving as recognition codes for the analytes. An on-site chemical analytical method has also been established and shows a good linear relationship within various phosphatidic/glucoside derivatives in a wide range of 0.01-105 μM, with a low LOD of 3-5 nM, approximately 0.001-0.5 times that of other reported methods. This study underscores the substantial potential of our novel sensor for on-site analysis of the actual antioxidant capacity of cosmetics, and it provides a controlled approach for the design of hydrolase/oxidase mimics, offering valuable insights for future enzyme engineering.