Smartphone-integrated colorimetric sensor for rapid and highly selective detection of spermine in food based on the laccase-mimicking activity of flower-shaped Mn3O4 nanoparticles

Colorimetric methods have the benefits of rapid detection and easy operation in the detection of spermine (SPM). However, the existing colorimetric sensor for detecting SPM still face challenges in terms of performance stability, result reliability and safety of sensing materials. Herein, it was first found that flower-like Mn3O4 nanoparticles (Mnf) exhibit excellent laccase-mimicking activity. Since SPM can effectively inhibit this activity, a colorimetric sensor was developed to detect SPM in food. The addition of positive charged SPM will induce the aggregation of multiple Mnf with negative charge through electrostatic interactions. In this case, the specific surface area of Mnf is reduced, and some surface-active sites are occupied by SPM, leading to a decrease in the laccase-mimicking activity of Mnf. Consequently, the colorimetric sensor appears light pink. Furthermore, a smartphone was utilized to convert the color of the reaction solution into the corresponding G/B value, facilitating on-site and fast analysis of SPM quantity. The proposed colorimetric sensor exhibits outstanding sensitivity and selectivity, with a limit of detection (LOD) as low as 0.094 μg·mL−1. The colorimetric sensor also features stable performance, reliable results and environmentally friendly safety, all of which will provide strong support for the monitoring of SPM in the food industry.