Nitrogen and copper (Ⅱ) co-doped carbon dots as multi-functional fluorescent probes for Fe3+ ions and tetracycline

This paper synthesized carbon dots (Cu-NCDs) doped with nitrogen and copper, which could be used as a sensor for measurement of Fe3+ and tetracycline (TC). The average particle sizes of CDs and Cu-NCDs were determined as 3.9 nm and 4.8 nm, respectively. The presence of carbon, oxygen, nitrogen and Cu atoms was confirmed in the structure of Cu-NCDs. Both CDs and Cu-NCDs exhibited a strong fluorescence (FL) emission peak at 450 nm, but the doping of Cu and N makes the surface of Cu-NCDs positively charged, which enhances the fluorescence intensity. The carbon dots doped with copper had more significant optical effects than those doped with other metals, and the relative quantum yield (QY) of the Cu-NCDs was as high as 53.6%. Cu-NCDs can be used as multi-functional fluorescent probes to selectively detect Fe3+ and TC based on fluorescence quenching. The limit of detection of Fe3+ and TC separately was found as 1.189 µM and 0.416 µM. This probe is also suitable for the indirect determination of Fe2+ because the Fe2+ is oxidated to Fe3+ by H2O2. The mechanisms of the quenching process for Fe3+ and TC were explored that is the complex process of dynamic quenching and static quenching based on internal filtration effect (IFE), respectively. The fabricated sensors were successfully applied to determine Fe3+ and TC in tap and lake water samples, suggesting a promising application in environment analysis.