Smartphone-assisted fluorescence detection of malachite green using a hydrogel-confined Tb-MOFs sensor

Tb-MOFs embedded in agarose hydrogel form a flexible, anti-aggregation film for easy retrieval. • Malachite green quenches fluorescence via energy transfer, enabling visible color change within 5 min. • Integrated with a smartphone RGB colorimeter, the platform achieves 1.73 μM detection limit with reliable recovery. A flexible Tb-MOFs@agarose hydrogel film was developed as a smartphone-assisted fluorescence sensing platform for the detection of malachite green (MG). The Tb-MOFs are spatially confined within a hydrophilic agarose network, and upon MG exposure, the system exhibits a distinct ‘bright-green to dark-green’ fluorescence transition within 5 min at 60 °C (or within approximately 40 min at room temperature) via fluorescence resonance energy transfer (FRET) from Tb 3+ to MG. A Convolutional Neural Network (CNN) model was further developed to enable automated image recognition from smartphone-captured fluorescence images. Under optimized conditions (pH 6.0, 60 °C, 0.03 mg/mL Tb-MOFs), the platform shows a linear detection range of 5–140 μM with a limit of detection of 0.63 mg/L. Recoveries of 75.5–127.6% (RSD < 5.4%) were obtained in crucian carp, shrimp, and lake-water samples, with negligible interference from seven co-existing antibiotics. This simple, low-cost approach offers a practical solution for field screening of prohibited MG residues in aquatic products. Smartphone-enabled on-site detection of malachite green using a hydrogel-confined Tb-MOFs sensor. Download: Download high-res image (144KB) Download: Download full-size image