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Tetramethylbenzidine (TMB) and are produced by an enzyme-catalyzed reaction between H 2 O 2 and TMB. [13] Most of these sensors' linear ranges (LRs) lie in micromolar magnitude (ranging from several micromoles to hundreds of micromoles), and a higher concentration of H 2 O 2 would not gain more linear signals, [14,15] which was determined by the feature of enzyme reactions following Michaelis-Menten equation.However, some real samples usually contain high concentration of H 2 O 2 (>3% or 1 m), such as bacterial cleaner and industrial effluents. [16,17] During H 2 O 2 assay, the conventional dilution (even 100fold) cannot match with the sensors' LR, which means more dilution is needed. It would complicate the assay procedure. [18,19] What's more, the dilution level is not easy to forecast, and the insufficient dilution would lead to inaccurate detection. Nowadays, most of the POD-based sensors were focusing on how to decrease H 2 O 2 's detection of limit (LOD), [20,21] but few studies paid more attention to extending LR. Therefore, it is more practical and necessary to develop POD-based H 2 O 2 sensors with wider LRs and higher LR maximum. Sample dilution which decreases the H 2 O 2 amount involved in POD catalysis is just a method to adapt to this narrow LR. Instead of dilution, simultaneous H 2 O 2 decomposition from catalase (CAT) might hopefully achieve a similar goal and expand the LR during PODdependent sensing. It could be inferred that the combination of POD and CAT would be a kind of H 2 O 2 sensor with wider LR.The complex, integrating more than one kind of enzyme together, was named as Cascade Enzyme System (CES), which was an enzyme reactor and could usually achieve the goal of cooperative catalysis. [22] Nowadays, different kinds of CESs have been developed and applied to analytical sensors and disease treatment. For example, a glucose sensor could be made by coupling POD with glucose oxidase (GOx). [23,24] Also, researchers constructed a CES combining superoxide dismutase (SOD) and catalase (CAT) to treat radical-related inflammation. [25][26][27] As far as we know, there is no research on constructing POD/ CAT-integrated CES (PCCES), exploring the new effect of POD catalysis and developing its sensing applications. Thus, it is necessary to figure out PCCES's catalysis feature and application prospects. Peroxidase (POD) Nanozyme-based hydrogen peroxide (H 2 O 2 ) detection is popular, but hardly adapt to high concentration of H 2 O 2 owing to narrow linear range (LR) and low LR maximum. Here, a solution of combining POD and catalase (CAT) is raised to expand the LR of H 2 O 2 assay via decomposing part of H 2 O 2 . As a proof of concept, a cascade enzyme system (rGRC) is constructed by integrating ruthenium nanoparticles (RuNPs), CAT and graphene together. The rGRC-based sensor does perform an expanded LR and higher LR maximum for H 2 O 2 detection. Meanwhile, it is confirmed that LR expansion is closely associated with apparent K m of rGRC, which is determined by the relative enzyme activity betw...