N-doped carbon dots as the multifunctional fluorescent probe for mercury ion, glutathione and pH detection

Recently, carbon dots (CDs) have exhibited promising applications in the fluorescence detection of various ions and biomolecules. In this work, one kind of nitrogen-doped CDs (N-CDs) with high fluorescence intensity was synthesized, characterized by transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier-transform infrared, UV–vis absorption spectra, and fluorescence spectra. The results show that the spherical and uniform N-CDs (quantum yield: 60.2%) have remarkable fluorescence properties and photostability, which makes N-CDs can be utilized as an 'on-off-on' sensor for Hg2+ and glutathione (GSH). In addition, the pH-sensitive behavior of N-CDs makes it also applicable to H+ detection under acid conditions (pKa = 3.53). The linear range of the 'turn-off' sensor detecting Hg2+ was 0.014–50 μM, with a 0.014 μM limit of detection (LOD). GSH was detected by the fluorescence 'turn-on' method with a linear range of 0.125–60 μM and a LOD of 0.125 μM. The outstanding performance of N-CDs makes it potential applications in ecological pollution and biomolecule visualization monitoring.