Turn‐Off and Fluorescence Color Change Carbon Quantum Dots for Detection of Fluoroquinolones and Tetracyclines

In this study, we report gram flour‐derived carbon quantum dots (GFCQDs) synthesized via a green microwave‐assisted approach that acts as dual sensor for the sensing of both fluoroquinolones and tetracyclines, showing fluorescence enhancement with a slight bathochromic shift in emission wavelength and fluorescence quenching, respectively. Mechanistic studies revealed that the detection of tetracycline relies on the inner filter effect, while ciprofloxacin detection involves hydrogen bond‐based interactions. GFCQDs can selectively detect tetracycline by a fluorescence color change from blue to green in the presence of calcium and can also detect antibiotics within a mixed antibiotic pool. The practical applicability was evaluated in real samples (milk, tap water, and food) and pharmaceutical formulations with recovery rates ranging from 97% to 99%. GFCQDs can be transformed into portable cellulose paper strips as a handy tool for on‐site and off‐site detection of antibiotics. Furthermore, GFCQDs successfully sensed tetracycline through a blue fluorescence “turn‐off” response in the bacterial strain Bacillus subtilis .