Enzyme-nanozyme cascade colorimetric sensor platform: a sensitive method for detecting human serum creatinine.

Creatinine, as a significant biomarker for kidney, thyroid, and muscle dysfunction-related diseases, detection is of great important meaning. In this paper, an enzyme-nanozyme cascade sensing platform was developed for visual creatinine detection. Perovskite oxide BiFeO3 synthesized by a sol-gel method was applied as a nanozyme, showing excellent peroxidase-like activity. During detection, creatinine was oxidized in turn by three natural enzymes (creatinase, creatininase, and sarcosine oxidase) to produce H2O2, and H2O2 was then catalyzed by the BiFeO3 nanozyme, resulting in the change of achromatous 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). Based on this principle, visual quantification of creatinine was realized. Due to the high stability and catalytic efficiency of nanozyme, the cascade sensing platform can be used to detect creatinine in a broad range of 0.5-150 μM with a detection limit of 0.09 μM. Meanwhile, thanks to the specificity of the natural enzymes, the platform exhibited admirable selectivity for creatinine determination despite the existence of a variety of interfering substances, which were successfully adopted to measure the level of creatinine in human serums. The cascade sensing platform is expected to serve the determination of a large number of biomarkers by simply alternating the natural enzymes.