Portable fluorescence sensing coupled with smartphone-based image analysis for visual quantitative detection of streptomycin sulfate

Nitrogen‑doped carbon dots with 24.9% quantum yield were prepared by one‑step hydrothermal synthesis. • Streptomycin was detected by fluorescence over 0–500 μM with a 0.47 μM LOD. • Smartphone G/B analysis enabled visual detection over 0–600 μM with a 0.21 μM LOD. • Water-sample recoveries of 91.8%–116.5% support on-site residue screening. Streptomycin sulfate (SM), a representative aminoglycoside antibiotic, is widely used for the treatment of tuberculosis and Gram-negative bacterial infections, but residues in water and food-related matrices may pose risks to human health. Here, we developed a portable sensing platform for on-site antibiotic residue monitoring. The platform uses carbon dots prepared from 4-aminobutyric acid and 5-amino-o-cresol by a hydrothermal route as a composite fluorescent nanoprobe. The probe showed a quantum yield of 3.8% in water and enabled both visual recognition and quantitative detection of SM. As the SM concentration increased, the probe color shifted from blue-green to yellow, allowing direct visual readout. The fluorescence assay showed a linear response over 0–500 μM with a limit of detection (LOD) of 0.47 μM, whereas the smartphone-assisted colorimetric readout was linear over 0–600 μM with an LOD of 0.21 μM. Selectivity, interference-resistance and spiked-recovery tests in real samples indicate that the method provides a sensitive, stable and matrix-tolerant route for low-cost screening of SM in food and environmental samples. Download: Download high-res image (179KB) Download: Download full-size image