Bacterium-Derived Carbon Dots as a Novel “Turn-On-On-Off-On” Sensor for Cr(VI) and 4-Nitrophenol Detection Based on Inner Filter Effect Mechanism

Phenolic compounds, especially 4-nitrophenol (4-NP), and chromium (VI) are highly toxic environmental pollutants. Thus, it is significantly important to establish a rapid and sensitive sensor for 4-NP and Cr(VI) monitoring in environment. In this paper, a novel approach has been adopted where E. coli -derived CDs (CDs- WT ) prepared by one step hydrothermal method previously and sensitized by ampicillin (turn-on) were used as fluorescence nanoprobe (CDs- WT -Amp) for 4-NP and Cr(VI) determination based on the inner filter effect quenching mechanism (turn-off). Then, the quenching fluorescence was reversed by addition of ampicillin (turn-on). The linear ranges of 4-NP and Cr(VI) detection were 0–50 μ M and 0–25 μ M, with the limits of detection 88.89 nM and 64.75 nM, respectively. The “turn-on-on-off-on” fluorescent nanosensor system was successfully used to determine Cr(VI) and 4-NP in water with satisfactory results. It shows that the “turn-on-off-on” nanoprobe has great promising potential for application to environmental pollutant detection.