Simple devising of N-doped carbon dots (N-CDs) as a low-cost probe for selective environmental toxin detection and security applications

Nitrogen-doped carbon dots (N-CDs) possess outstanding photostability and interesting physicochemical and photochemical properties. Herein, we present cyan-emitting N-CDs that were fabricated through the treatment of salicylic acid with ethylene diamine using a simple microwave-assisted method. It was observed that the reaction produced N-CDs that strongly emitted cyan light with a quantum yield (QY) of 33%. The N-CDs were examined with the assistance of HR-TEM, XPS, XRD, FTIR, PL, and UV measurements. Due to the fluorescence enrichment effect caused by the N atoms in carbon dots, these N-CDs can be used as a fluorescent material for the detection of nitro-explosives and toxic metal cations. The addition of picric acid resulted in splendid quenching of the N-CDs, with a limit of detection (LOD) value of approximately 82.9 nM that was ascribed to the Förster resonance energy transfer between the N-CDs and the nitro-aromatics. Furthermore, the powerful coordination between oxygen-rich moieties and N-CDs for the detection of Fe3+ and Hg2+ cations induced fluorescence quenching through photo-induced electron transfer and the inner-filter effect pathway, leading to the effective recognition of metal ions. The sensor probe exhibited a wide-ranging linear response with an LOD of approximately 30 nM for Fe3+ and 160 nM for Hg2+ ions. Thus, the as-prepared N-CDs can function as a fluorescence sensor, a secure portable information device, and a paper-based probe for detection in biological systems.