Cyanamide-functionalized carbon nitride based photocatalysis for non-enzymatic colorimetric sensing of serum glucose

The cascaded catalytic reactions of glucose oxidase (GO_x) and horseradish peroxidase (HRP)-like nanozymes have been extensively used for the colorimetric detection of serum glucose. Nevertheless, the usage of biological enzyme and the adjustment of buffer pH due to the inconsistent pH of this two-step catalytic reactions are involved during the detection of serum samples. Herein, the photocatalysis of cyanamide-functionalized carbon nitride (CACN) with high efficient electron-hole separation and photoelectron storage ability was utilized for non-enzymatic colorimetric sensing of serum glucose without the need to adjust the buffer pH and the usage of biological enzyme. Under the irradiation of visible light, glucose was utilized as electron donor to quench the photogenerated holes of CACN and to facilitate the reduction of 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) by the photoelectrons into orange-yellow product (formazan). The absorbance of formazan at 470 nm showed a linear response toward glucose over 1.8-22.0 mmol L^-1 with the limit of detection of 0.27 mmol L^-1 (S/N = 3). Furthermore, the digital image colorimetric (DIC) method was also developed by a portable mobile. Finally, the colorimetric and DIC methods were utilized for the detection of serum glucose with high accuracy, reproducibility and recovery. This work not only proposed a new strategy for the colorimetric sensing of serum glucose but also extended the photocatalysis of carbon nitride application in the field of biosensing.