Etched PtCu nanowires (NWs) were synthesized by a hydrothermal reaction and chemical etching process. The NWs are shown to be viable peroxidase (POx) mimics capable of catalyzing the oxidation of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of HO to form a blue-green coloration. The mechanism of catalysis was investigated and the results demonstrated that HO is decomposed to form hydroxyl radicals which oxidize TMB in the presence of the NWs. Under optimized conditions, a steady-state kinetic analysis revealed that the NWs possess a stronger affinity for HO and TMB compared to the enzyme horseradish POx. Based on the high POx-like activity, a colorimetric assay for HO was established. Absorbance at 652 nm increases linearly in the 0.1-300 μM HO concentration range, and the detection limit is 0.06 μM (at S/N = 3). The assay was successfully applied to the determination of HO in (spiked) milk and contact lens solution. Furthermore, a highly sensitive test strip was designed which represents a low cost and fast alternative for the visual determination of HO. Graphical Abstract Schematic presentation of the colorimetric detection of HO. PtCu nanowires (PtCu NWs) can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by HO to produce blue-green oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB). Based on the color change, test strips were designed for HO detection.