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Abstract
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Herein, we report a simple, one-step hydrothermal treatment for the synthesis of photoluminescent carbon quantum dots (CDs), using citric acid as the carbon source and L-lysine as the Ndoping precursor and surface passivation agent. The obtained N-CDs were fully characterized by highresolution transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, Raman spectroscopy, UV-vis absorption and photoluminescence (PL) spectroscopy. The on - o fluorescent CDs probe was used for selective selenite (Se (IV)) sensing in an aqueous solution. The sensor was fabricated based on the aggregation and disaggregation of CDs. Firstly, europium ions coordinate with the carboxylate groups on the CDs surface [1, 2], acting as a bridge to link the neighbouring carboxylate groups from the CDs, and inducing the CDs aggregation. Therefore, the PL of CDs is quenched through energy-transfer or electron-transfer processes. Then, the CD aggregates may be disrupted after the introduction of selenite at pH 7.0 because Eu3+ ions display a higher affinity for the oxygen-donor atoms in selenite than for the carboxylate groups on the carbon quantum dots surface. Therefore, turn-on fluorescence can be observed with the addition of selenite due to the strong coordination between selenite and Eu3+ ions. The optimized conditions for detecting selenite, such as pH, incubation time, concentration of CDs were 7.0,.0 min, and 0.17 mg mL , respectively. Under the optimum conditions, the linear range for the detection of selenite was 0.08 to 21.4 μg mL with a detection limit (S/N = 3) of 53.0 ng mL . The relative standard deviation for six replicate measurements of Se(IV) was and 4.1% for 15.6 μgmL of selenite. The fluorescent turn-off/on method recommended good selectivity for detecting selenite in the presence of 20 different types of ions. The applicability of this assay has been validated by determining the concentrations o
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