Carbon dot and FITC conjugated dual-emission nanoprobe and its electrospun film for the sensing of ammonia

Nanomaterials are at the forefront of next-generation sensing technologies because of their unique and tunable properties. For monitoring trace ammonia (NH) in human metabolism, we synthesized a dual-emission nanoprobe with an average diameter of 4 nm by conjugating the NH-sensitivity fluorescein derivative, the fluorescein isothiocyanate isomer (FITC, green emitter), onto the surface of carbon dots (CDs, blue emitter). A significant Förster resonance energy transfer (FRET) effect was observed, where the CDs acted as energy donors and FITC moieties acted as energy acceptors. The fluorescent color changed obviously from blue to green once ammonia was introduced into the test chamber. Subsequently, the dual-emission nanoprobe was immobilized in polyvinyl pyrrolidone nanofibers with an average diameter of 400 nm via electrospinning, thus obtaining a ratiometric NH sensor. Results showed that the fabricated sensor with a high surface area exhibited high sensitivity (theoretical detection limit was 0.53 ppm), short response time (∼4.3 s), excellent selectivity, and good reversibility in tracing 0–300 ppm NH. Further prototyped application studies reveal that the sensor is expected to serve as an indicator for monitoring breath/blood ammonia concentration. Thus, the newly developed fluorescent sensor was able to be a feasible solution for the application of nanomaterials in health and medicine.