A smartphone-assisted colorimetric sensor for sensitive and portable sensing of methimazole based on high-entropy Prussian blue nanozymes.

It is critical to exploit a sensitive, selective, and portable strategy for the credible detection of methimazole (MMI) for human health. Herein, high-entropy Prussian blue analogues (HE-PBAs) nanozyme were successfully fabricated by a facile co-precipitation strategy. The as-synthesized HE-PBAs possess robust peroxidase (POD)-like activity, which can trigger the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB) with the assistance of H2O2, generating a conspicuous chromogenic transition from colorless to blue. However, MMI can reduce oxTMB and consume the ROS, including •OH and O2•-, thereby suppressing the intrinsic POD-mimicking catalytic performance of HE-PBAs. Such an inhibitory effect reduces the absorbance of the sensing system and enables the gradual fading of the blue chromogenic signal. Based on this competitive inhibition mechanism, a novel colorimetric sensing platform was constructed for quantitative MMI determination. The developed sensor achieves high sensitivity toward MMI with a detection limit of 0.032 μM. Considering its simple operation and superior sensing performance, a portable and user-friendly sensor was also designed for visual sensing of MMI by combining a common smartphone. Moreover, this colorimetric sensor has been successfully applied for MMI detection in commercial cosmetic samples, demonstrating its potential practicality. This work not only provides a cheap, user-friendly, and portable sensing platform for visual detection of MMI in resource-limited settings, but also offers a rational design strategy for HEzymes.