Construction of colorimetric sensing systems for on-site diagnosis attracts growing interests as a rapid and cost-effective mean of public health care. A good example is monitoring the physiological abnormalities (i.e., diabetes and hypoglycemia) from the blood glucose level. For this purpose, smart bioanalysis and clinical diagnostic analysis of glucose are conducted through the coupled oxidase (GOx)-peroxidase (HRP) biomimetics. Although there are some reported examples of nanomaterials-based biomimetic catalysts, metal-free nanozymes with multiple functions from low-cost preparation are highly desired.
In this work, we prepared a modified carbon nitride (C3N4) with alkali-incorporation through one-pot thermal polycondensation as a new bifunctional nanozyme. The introduced chemical functionalities (i.e., KCl-bridged adjacent layers and hydroxyl group grafting) promote the two-electron reduction of dioxygen via the rapid formation of 1,4-endoperoxide species in the polymeric structure, which was in line with the theoretical simulation. The resultant metal-free photocatalyst (nanozyme) generated hydrogen peroxide (H2O2) with an apparent quantum yield of 100% (at 420 nm) and a good catalytic stability. The nanozyme of modified C3N4 exhibited the bifunctional biomimetic roles (see in the figure below): (1) it plays the role of photoenzyme to mimic GOx that oxidizes glucose with the concurrent production of H2O2 under visible light; (2) it mimics HRP that oxidizes the chromogenic substrate (TMB) to induce blue coloration in the dark. The bio-mimicking catalytic process could be facilitated within a few seconds in a continuous flow microfluidic reactor that serves as a smart and miniature device for the real-time colorimetric detection of glucose.
Our study investigated the bifunctional nanozyme in cascade systems for the sensitive detection of glucose through the in-situ generated H2O2. This strategy can be applied to other eco-friendly processes for new catalysts in photocatalytic oxidation, selective organic synthesis, disinfection, and enzyme-mimicking systems involving in-situ generated H2O2. If you are interested in our research, please read our article in Nature communication:
“Modified carbon nitride nanozyme as bifunctional glucose oxidase-peroxidase for metal-free bioinspired cascade photocatalysis”, Peng Zhang, Dengrong Sun, Ara Cho, Seunghyun Weon, Seonggyu Lee, Jinwoo Lee, , Dong-Pyo Kim and Wonyong Choi*, Nature Communications, https://doi.org/10.1038/s41467-019-08731-y.
I am very grateful to all the coauthors for their contributions, particularly, Dr. Peng Zhang who led the project with profound insights, hard work and devotion. We would like to express our sincerest gratitude to anonymous referees for their critical comments which greatly helped improve the quality of the manuscript.