A novel near-infrared fluorescence switching sensor based on polyamide derived carbon quantum dots for sequential detections of perfluorobutane sulfonic acid and Fe3⁺ ions

In this work, we report a sustainable near-infrared (NIR) fluorescence switching sensor based on polyamide-derived carbon quantum dots (PACQDs) synthesized from waste, providing a green and scalable route to NIR-active nanomaterials. The ultrasmall PACQDs (1.53 ± 0.33 nm) exhibit a high quantum yield (29%), a large Stokes shift (350/702 nm), zeta potential (–29.82 ± 0.60 mV), and exceptional photostability with no spectral drift over 1056 h. FTIR surface analysis reveal abundant –OH, –NH₂, –COOH, and C = O functionalities that facilitate electrostatic interactions and hydrogen bonding with target analytes. The PACQDs display a distinct sequential fluorescence switching mechanism. First, Perfluorobutane…