Construction of dual-mode bimetallic MOF/carbon fiber biosensor and its application in visual detection of L-cysteine

A bimetallic ZnNi-MOF was grown on carbon fiber via a one-pot hydrothermal method. Compared with single-metal MOFs, the resulting material exhibited enhanced luminescence and electrochemical activity, which enabled the construction of a flexible dual-mode sensor for rapid fluorescence-electrochemical detection of L-cysteine. Electrochemical detection exhibited a linear range of 1 nM-10 μM with a limit of detection (LOD) of 0.017 nM, while fluorescence sensing gave a linear range of 1 μM-1 M with a LOD of 0.89 μM. Both modes showed good selectivity and stability. Flexible sensors were also prepared by impregnating filter paper and textiles, wet spinning, and hydrogel microspheres. By combining the sensor with mobile phone software that collects the RGB values of the fluorescence color change, visual detection of L-cysteine can be achieved. The sensor successfully determined L-cysteine in human sweat and milk, with recoveries of 93–114% and RSDs of 2.43–5.32%, demonstrating promising applications in intelligent wearable monitoring, precision medicine, and food safety.