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This paper reports on a colorimetric assay for H2O2 and glucose. It is based on the use of human serum albumin-templated MnO2 nanosheets that possess oxidase-like activity. They are capable of oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with oxygen to give a blue product (oxTMB) with an absorbance maximum at 652 nm. When H2O2 is introduced, the MnO2 nanosheets are reduced to Mn(II) ions, and this inhibits the formation of oxTMB. Based on these findings, a colorimetric assay was established for H2O2 that has a 0.56 μM detection limit. If glucose is oxidized by glucose oxidase under formation of H2O2, the nanosheets can be used to quantify H2O2 and thereby to sense glucose. Response is linear in the 0.5 μM to 50 μM glucose concentration range, and the detection limit is 0.32 μM. The method was applied to the determination of glucose in spiked serum samples and gave satisficatory results.Human serum albumin (HSA) is used as a template for the synthesis of MnO2 nanosheet. These possess oxidase mimicking activity. H2O2 can reduce the nanosheets. The effect is exploited in colorimetric assays for H2O2 and glucose using tetramethylbenzidine (TMB) as a chromogenic substrate. [ABSTRACT FROM AUTHOR]