<p>Nanozymes are a class of nanomaterials with intrinsic enzyme-like properties, which overcome the limitations of natural enzymes, such as poor stability, high cost, and difficulty in storage, thus achieving rapid development. Herein, the enzyme-like activity of ferrocene-functionalized indium-oxo cluster (TPP⁺)[In₇FcDCA₆(µ₄-O²⁻)₃(µ₃-OCH₃)(Cl⁻)₃], named [In₇Fc₆], was analyzed. The obtained [In₇Fc₆] cluster has good peroxidase-like activity, which can catalyze the reaction of 3,3′,5,5′-tetramethylbenzidine (TMB), <i>o</i>-phenylenediamine (OPD), and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with H₂O₂. Therefore, based on the peroxidase-like activity of [In₇Fc₆], a colorimetric sensor for the detection of H₂O₂ was developed, which could detect H₂O₂ in the concentration range of 1–170&#xa0;μM, and the detection limit was 0.24&#xa0;μM. In addition, we also established a colorimetric sensor for detecting ascorbic acid (AA) in the range of 3–130&#xa0;μM with a detection limit of 0.81&#xa0;μM. The practicability of the established colorimetric sensor was also verified in cells and serum. This research opens up new horizons for exploring new application possibilities for clusters in biomolecular detection.</p> Graphical Abstract <p></p>