Introducing hierarchical hollow MnO2 microspheres as nanozymes for colorimetric determination of captopril.

A simple sensor was developed for the colorimetric determination of captopril (CPT). Herein, hierarchical hollow MnO2 microspheres (HH-MnO2) were applied as nanozymes with peroxidase-mimetic activity. Free cation radicals with a strong absorption signal (λmax at 653 nm) were generated via a redox reaction between 3, 3', 5, 5'-tetramethylbenzidine (TMB) and HH-MnO2. Captopril could successfully prevent the generation of blue-colored free cation radicals. The influence of CPT concentration on the absorption of the generated radicals was monitored by UV-Vis spectroscopy. The corresponding linear concentration range was from 1.0 to 30.0 μg mL-1 (4.6-138.1 μmol L-1), and the detection limit was found to be 0.26 μg mL-1 (1.2 μmol L-1). As a practical usage, the developed sensor was effectively utilized to measure the content of CPT in pharmaceutical formulations.