Electrochemically synthesized Nitrogen-doped Carbon Dots as Fluorescence Nano-sensors for the Selective Screening of Tetracyclines

The growing release of antibiotics, especially chlorinated variants, into aquatic systems presents serious risks to ecosystems and human health, highlighting the need for rapid, low-cost detection tools. Here we report the first use of nitrogen-doped carbon dots (N-CDs) produced through a simple single-step electrochemical synthesis in water, for simultaneous speciation and quantification of tetracycline antibiotics. The synthesised N-CDs exhibited excitation-dependent fluorescence with dual emission at 425 and 515 nm, enabling two distinct sensing responses within the same probe. All tetracycline, tetracycline (TET), oxytetracycline (OTC) and chlortetracycline (CTC), induced pronounced fluorescence quenching at 515 nm (λex = 410 nm), attributed to a combination of inner-filter effect, and static and dynamic quenching mechanisms. However, CTC also uniquely enhanced N-CDs emission at 425 nm (λex = 350 nm), allowing tetracyclines speciation. Under optimized conditions, the sensor achieved micromolar sensitivity and high selectivity, maintaining performance in complex matrices including tap and river water, with recoveries of 92–117% and RSD < 9%. This sustainable nanomaterial platform offers a simple, robust approach for monitoring antibiotic contamination and supporting safer water management.