Enhanced peroxidase-like activity of AuNPs loaded graphitic carbon nitride nanosheets for colorimetric biosensing.

Nanozymes have emerged as promising alternatives to overcome the high cost and low stability issues of natural enzymes. Particularly, those with peroxidase-like activities have been extensively studied to construct versatile biosensors. In this article, we demonstrate that the modification of the graphitic carbon nitride nanosheets (g-C3N4 nanosheets) by plasmonic gold nanoparticles (AuNPs) greatly enhances its catalytic performance as peroxidase mimetic. In the presence of H2O2, the AuNPs@g-C3N4 nanosheets can catalyze the redox reaction of 3,3',5,5'- tetramethylbenzidine (TMB) to produce a blue color. Based on the observation, a colorimetric sensing method for glucose is further developed with the assistance of glucose oxidase (GOx). The linear range for glucose is from 5 to 100 μmol L-1 (R2 = 0.9967) and the limit of detection (LOD) is 1.2 μmol L-1. The LOD can be further lowered down to 0.75 μmol L-1 by using H2SO4 as termination agent and measuring the absorbance of the yellow product at λ = 451 nm. Moreover, the practical usefulness of AuNPs@g-C3N4 nanosheets as a peroxidase nanozyme for glucose determination in human serum and urine is also demonstrated.