Cu(I)-cysteamine-X (X = Cl⁻, Br⁻, and I⁻) compounds with peroxidase-like activity for colorimetric and smartphone detection of formaldehyde by overcoming pH and temperature limitations

Facile and efficient detection of formaldehyde is crucial yet challenging, particularly when using natural peroxidases and peroxidase mimics, which typically exhibit optimal catalytic activity under acidic conditions and at temperatures around 40 °C. In this study, we report for the first time that Cu-Cy-X (Cy = cysteamine; X = Cl⁻, Br⁻, and I⁻) compounds exhibit peroxidase-like activity, with the catalytic efficiency following the order of Cu-Cy-Cl > Cu-Cy-Br > Cu-Cy-I. Furthermore, the integration of graphene oxide (GO) markedly boosts the peroxidase-like activity of Cu-Cy-Cl. The resulting Cu-Cy-Cl/GO demonstrates a broad operational pH range from 3 to 9 and a temperature range from 10 to 70 °C, with optimal catalytic performance at neutral pH and room temperature. Additionally, Cu-Cy-Cl/GO demonstrates remarkable cost-effectiveness and exceptional stability against heating, storage, and reuse for at least seven cycles. Moreover, the inhibition of peroxidase-like activity of Cu-Cy-Cl/GO by formaldehyde at neutral pH is utilized to develop a colorimetric and smartphone-based sensing platform. This platform exhibits a wide detection range (4–10⁶ μg/L) and an exceptionally low detection limit (0.424 μg/L) for detecting formaldehyde. Furthermore, this method has been successfully applied to detect formaldehyde in beer, fish, frozen shrimp, and frozen chicken, providing new insights into the fabrication of peroxidase mimics and enabling on-site formaldehyde detection.