Dual-responsive carbon dots-based luminophore for ratiometric fluorescence and room-temperature phosphorescence detection of oxytetracycline

Dual-responsive probes emitting both fluorescence and phosphorescence signals are greatly advantageous to sensing. Here, we present a carbon dots-based luminophore (CDs@LP) with blue fluorescence and ultra-long yellow room-temperature phosphorescence (RTP) with lifetime of 1.33 s (that was visible to the naked eye for ∼ 13 s) for ratiometric detection of oxytetracycline (OTC). The CDs@LP was prepared by molten salt method through one-step treatment of 2, 6-diaminopyridine, KNO3, MgCl2, and KH2PO4. Upon the addition of OTC into CDs@LP aqueous solution, the fluorescence at 386 nm and RTP at 538 nm of CDs@LP were quenched as a result of the inner filter effect (IEF), while the fluorescence at 522 nm of OTC steadily enhanced due to the molecular restriction through the formation of OTC-Mg2+ complexes. Both fluorescence and RTP signals have excellent linear relationships with OTC concentration. The CDs@LP had a low detection limit of 3.2 nM (fluorescence) and 0.27 μM (phosphorescence), which also exhibited satisfactory selectivity and anti-interference performance towards other antibiotics. Moreover, the CDs@LP was successfully loaded on a filter paper and used for OTC sensing. Thus, it is a promising tool for OTC detection and can act as a foundation for producing dual-signal sensing tools.