A dual-mode sensing system for xanthine oxidase detection based on nitrogen-doped carbon dots and iron-cobalt oxide nanosheets

As one of the existing forms of xanthine oxidoreductase, xanthine oxidase (XOD) exists in many human tissues, and the overactivity of XOD will result in some serious illnesses such as gout and diabetes. Herein, a novel dual-signal sensing system for XOD activity determination was proposed based on fluorescent nitrogen-doped carbon dots (N-CDs) and iron-cobalt oxide nanosheets (FeCo-ONSs). XOD has the ability to oxidise xanthine to uric acid while also producing H2O2. As a sort of peroxidase-like enzyme, FeCo-ONSs can catalyze H2O2 to produce reactive oxygen species (ROS). And N, N-Diethyl-p-phenylenediamine sulfate salt (DPD) was oxidized to DPDox that serves as a chromogenic substrate in the presence of ROS, causing the colorless solution to turn pink. DPDox exhibits two characteristic absorption peaks at 551 nm and 512 nm and it can also efficiently quench the fluorescence emission of N-CDs at 500 nm. Therefore, the fluorometric and colorimetric dual-channel sensing platform was established to assay XOD with the lower LOD of 0.00522 mU/mL and 0.0177 mU/mL, respectively. Additionally, the dual-output strategy was found to be applicable to the quantitative analysis of XOD in serum samples with good reliability and selectivity.