Surface molecular imprinting on g-C3N4 photooxidative nanozyme for improved colorimetric biosensing

Graphitic carbon nitride (g-C₃N₄), as a visible-light-active organic semiconductor, has attracted growing attentions in photocatalysis and photoluminescence-based biosensing. Here, we demonstrated the intrinsic photooxidase activity of g-C₃N₄ and then surface molecular imprinting on g-C₃N₄ nanozymes was achieved for improved biosensing. Upon blue LED irradiation, the g-C₃N₄ exhibited superior enzymatic activity for oxidation of chromogenic substrate like 3,3',5,5'-tetramethylbenzidine (TMB) without destructive H₂O₂. The oxidation was mainly ascribed to ^·O₂ that was generated during light irradiation. The surface molecular imprinting on g-C₃N₄ can lead to an over 1000-fold alleviation in matrix-interference from serum samples, 4-fold improved enzymatic activity as well as enhanced substrate specificity comparing with bare g-C₃N₄ during colorimetric sensing. Also, the MIP-g-C₃N₄ possesses a high affinity to TMB with a K_m value of only 22 μmol/L, much lower than other comment nanozymes like AuNPs, Fe₃O₄ NPs, etc. It was successfully applied for detection of cysteine in serum sample with satisfactory recoveries.