Bifunctional Nitrogen-Doped Yellow-Green Carbon Dots: Integrated Fluorescent Probe for Sensitive Antibiotic Detection and Oxygen “Breathing Color” Tracking

Nitrofurantoin (Nit), a widely used antimicrobial agent classified as a Group 3 carcinogen, demands rapid, sensitive detection and practical monitoring for environmental and food safety. This study's unique contribution lies in developing bifunctional nitrogen-doped yellow-green carbon dots (YG-CDs) integrating sensitive Nit detection and oxygen “breathing color” tracking. YG-CDs were synthesized via a one-step solvothermal method using bromothymol blue and 2-mercaptobenzimidazole, with structural/optical characterization via Fourier transform infrared, X-ray photoelectron spectroscopy, UV–vis, and fluorescence spectroscopy; YG-CDs-gelatin composites were fabricated for visualization. Key findings: YG-CDs emit at 555 nm (long-wavelength) with a quantum yield of 26.1%, excellent stability (salt, temperature, UV), and high selectivity/anti-interference for Nit, achieving a detection limit of 2.1 μM and 96.5–100.5% recovery in lake water. The YG-CDs-gelatin composite exhibits oxygen-responsive color shifts (yellow-green to green), enabling instrument-free food freshness monitoring. This work provides a novel, integrated strategy for on-site antibiotic residue detection and intelligent packaging, advancing practical applications in environmental monitoring and food safety.