Nanozyme-mediated smartphone platform for colorimetric detection of total leucomalachite green and malachite green

As a parasiticide, malachite green (MG) and its primary metabolite, leucomalachite green (LMG), are widely used in aquaculture to boost fishery yields. However, these compounds pose significant risks to both the food chain and human health. This study presents an innovative colorimetric sensing platform utilizing MnO₂ nanozymes for rapid and precise quantification of total LMG and MG in aquatic products. The innovation of platform lies in three key aspects: (1) development of an environmentally benign synthesis protocol for high-performance MnO₂ nanozymes using gelatin as a biological template and KMnO₄ as precursor; (2) exploitation of the distinctive oxidative catalytic properties of MnO₂ nanozymes, enabling in situ conversion of LMG to MG within 1 min under substrate-free conditions, coupled with the characteristic absorption peak of MG at 618 nm for highly sensitive and selective detection (LOD: 33.00 μg/kg); and (3) seamless integration with smartphone technology to create a cost-effective, portable, and user-friendly intelligent detection system (LOD: 120.08 μg/kg). The actual sample analysis results show that the integrated detection platform exhibits excellent analytical performance in complex matrices such as fish muscle, shrimp tissue, and fish pond water. The spike recovery rate of UV-vis spectroscopy and smartphone colorimetric analysis reaches 97.92 %-106.50 % and 97.21 %-104.17 %, respectively. It has high detection efficiency and real-time monitoring capabilities, providing a powerful solution for aquatic product safety assessment, public health protection and environmental monitoring.