Green fluorescent carbon dots from chitosan as selective and sensitive “off-on” probes for nitrite and “on-off-on” probes for enrofloxacin detection

In this work, green emission fluorescence carbon dots (G-CDs) were prepared using chitosan and p-phenylenediamine as precursors. Furthermore, the fluorescence of the prepared G-CDs was quenched by Nitrite (NO2-) with excellent selectivity and sensitivity due to internal filtration effect (IFE) Therefore, G-CDs was applied to monitor NO2- as an “on-off” fluorescence probe and obtained a wide linear range (1–300 μM) with limit of detection (LOD) 1.00 μM. Another hand, the fluorescence of G-CDs was also quenched by Au3+ due to fluorescence resonance energy transfer (FRET) effect caused by the in-situ formed Au nanoparticles (AuNPs). Interestingly, the addition of enrofloxacin (Enr) to G-CDs/AuNPs system led to the aggregation of AuNPs with partly lager size G-CDs, and the quenched fluorescence of the G-CDs/AuNPs system was restored, accompanying with visible fluorescence color change from green to blue. The “on-off-on” detection method through the constructed G-CDs/AuNPs system to Enr obtained good effects, such as high selectivity, sensitivity, visibility, relatively wide linear range (1–50 mg/L) and low LOD (0.04 mg/L). Additionally, the prepared G-CDs could be used for the detection of NO2- and Enr in actual water samples, proving it is an excellent candidate for environmental detection of NO2- and Enr.