Covalent Coupling-Regulated rGO/VN Nanocomposite Enabling Nitrogen Defects to Remarkably Boost the Peroxidase-Like Catalytic Efficiency for the Ultrasensitive Colorimetric Assay of Uric Acid
Xin Zhang, Ziyan Yuan, Ziting Lin, Zihan Bian, Mingyang Wang, Shuqing Yang, Yujiao Zhang, Mingjun Liu, Luteng Luo, Lingxing Zeng, Xuhui Yang, Aihua Liu
Abstract
It remains challenging to rationally design superior nanozymes and understand the underlying mechanism. Herein, a facile covalent coupling-modulated nitrogen defect is reported for significantly boosting peroxidase (POD)-like activity. Vanadium nitride (VN) nanoparticles are grown on graphene oxide (GO) via C–N bonding to form VN/rGO nanocomposites by varying with the VO x /GO ratio. The initial increasing GO amount enables formation of the C–N bond, dramatically boosting POD-like activity. Nevertheless, with a higher GO amount, the nitrogen defects decrease due to forming mainly V 2 O 3 . The defect-rich VN/rGO nanocomposite with 20 wt % GO (VG-2) exhibits the best catalytic efficiency ( V max / K m = 0.0187 s –1 ), which is 778-fold higher than that of natural horseradish peroxidase. Theoretical calculations and structure characterization reveal that the rich-N defects originate from VN covalent binding onto rGO with an rich-electron structure, impeding VN agglomeration, which greatly reduces the energy barrier of the rate-determining step of the catalytic reaction. Finally, coupling urate oxidase with VG-2 as an enzyme cascade, an ultrasensitive and selective colorimetric detection was developed for uric acid (UA), one of the indicators of kidney function or gout attacks, with a linear detection ranging 1–100 μM and 0.1–2.5 mM with a limit of detection of 0.24 μM UA (S/N = 3). The proposed method was applicable to detecting UA in human serum samples satisfactorily. This work could inspire more effective insights into designing other robust nanozymes through covalent coupling for a variety of biochemical analysis and biocatalysis applications.