A MELET- and IFE-based UV–visible luminescent ratiometric probe for quantization of mercury(II) and nitrofurantoin in environmental sewage

[Display omitted] •The green Cnanodots shows a dual-emission with excitation-independent properties.•The probe shows ratiometric response for HgII and Nit with low LODs based on MELET and IFE mechanisms.•This sensor has good selectivity for HgII and Nit in complex environmental systems.•This work expands the property and application of carbon-based nanomaterials. A novel fluorimetric ratiometric probe of green and eco-friendily nitrogen-enriched, oxygen-doped carbon nanodots (Cnanodots) was prepared for the quantitative analysis of mercury(II) (HgII) and nitrofurantoin (Nit) in the environmental sewage. The Cnanodots exhibits dual-emission peaks respectively at 345 and 445 nm under 285 nm excitation, with excitation-independent properties. Unexpectedly, this Cnanodots displays two obvious ratiometric responses to HgII and Nit through decreasing the signal at 345 nm and remaining invariable at 445 nm. Experimental results confirm that the highly sensitive analysis of HgII and Nit are achieved respectively based on matching energy-level electron transfer and inner filter effect mechanisms. The fluorescence (FL) ratiometric intensity of [FL345nm/FL445nm] expresses a good linear relationship with the concentration of HgII in the scope of 0.01–20 μM, while the logarithm of [Log(FL0345nm-FL345nm)] on the quenching degree of the probe by Nit also shows a good linear correlation within the range of 0.01–100 μM. The detection limits were calculated to be 4.14 nM for HgII, and 7.84 nM for Nit. Moreover, recovery experiments of Cnanodots for HgII and Nit sensing in real sewage samples obtained satisfactory results, comfirming the feasibility of practical application.