Uniform covalent organic framework nanoparticles (COF NPs) with a well-defined pore structure may provide a robust platform for scaffolding enzymes. Herein, bipyridine-based spherical COF NPs have been successfully prepared in this work through the Schiff base condensation reaction. Moreover, they are functionalized by metal modification and are further used for biosensor fabrication. Experimental results reveal that the metal-modified COF NPs also display impressive peroxidase-like catalytic activities, while they can load enzymes, such as glucose oxidase (GOx) and sarcosine oxidase (SOx), to develop a cascade catalysis system for design of various kinds of biosensors with very well performance. For example, the optimized GOx@Fe-COFs can achieve a sensitive detection of glucose with a low limit of detection (LOD) of 12.8 μM. Meanwhile, the enzymes also exhibit a commendable preservation of 80% enzymatic activity over a span of 14 days under ambient conditions. This work may pave the way for advancing cascade catalysis and the analysis of different kinds of biological molecules based on COF NPs.