One stone two birds: smartphone-assisted colorimetric sensing system based on copper peroxide for iron(II) and tannic acid detection.

Copper peroxide (CuO2), known for its self-decomposition to generate H2O2, has been widely used in medical and antibacterial applications. In sensing systems, it is often combined with other materials to enhance performance. Herein, we report a dual-analyte colorimetric sensing platform based solely on CuO2. This system utilizes the self-decomposition of CuO2 to produce H2O2, which reacts with Fe2+ to amplify the Fenton reaction (Fe2+-H2O2), generating free radicals for Fe2+ detection. Meanwhile, tannic acid (TA) inhibits the Fenton reaction-generated free radicals, leading to suppressed TMB oxidation and enabling TA detection. This platform provides a simple, rapid, and cost-effective method for highly sensitive detection of Fe2+ and TA, with wide linear ranges of 0.1-100 μM and 10-100 μM, respectively. It was successfully applied to the analysis of various food samples. Furthermore, a portable smartphone-based approach using CuO2 was developed for on-site detection of Fe2+ (20-1000 μM) and TA (1-500 μM), integrating visual and digital analysis.