Abstract：As a new type of fluorescent carbon nano-functional materials, carbon quantum dots (CQDs) have extensively captivated attention due to their excellent biocompatibility and outstanding optical properties. In this work, a one-step method was developed for the preparation of green non-polluting CQDs with strong fluorescence by using water and peanut rich in protein, fat and carbohydrate as precursors in a hydrothermal reactor at 190 ℃ for 20 h. Transmission electron microscopy (TEM) showed that the particle size distribution of the peanut CQDs （PN-CQDs） was relatively uniform. X-ray powder diffraction (XRD) showed that the crystalline form of PN-CQDs was amorphous carbon, which was attributed to highly disordered carbon particles. The infrared transform spectrum (FTIR) indicated that the surface of the PN-CQDs was rich in hydrophilic groups such as hydroxyl, carboxyl and nitrogen-containing functional groups, so it had good water solubility. Then the ultraviolet-visible spectra (UV-Vis) of the PN-CQDs was measured. There was an obvious absorption peak at 275 nm, which was the characteristic ultraviolet-visible absorption peak of CQDs. The fluorescence spectra results showed that CQDs prepared by peanut had a characteristic of excitation wavelength dependence, and their emission peaks significantly changed with the excitation wavelengths. When excited at the optimal excitation wavelength of 326 nm, the maximum emission wavelength was 408 nm, and PN-CQDs could emit blue fluorescence with highest fluorescence intensity. The fluorescence quantum yield of PN-CQDs measured by the reference method was 5.0%. Based on its luminescent properties, a “off-on” fluorescent method was constructed for high sensitivity detection of dopamine by using the PN-CQDs as a probe. The experiments indicated that in pH 3.80 HAc-NaAc buffer solution, when Ce(Ⅳ)was added in PN-CQDs solution, the fluorescence of PN-CQDs was quenched, and the fluorescence signal of the system was in the “off” state. It was found that both electron transfer from PN-CQDs to Ce(Ⅳ) and aggregation of PN-CQDs were responsible for the PN-CQDs fluorescence quenching at λex/λem=326 nm/408 nm. In the presence of dopamine, the fluorescence of PN-CQDs was recovered because Ce(Ⅳ) preferred to react with dopamine, which resulted in the departure of Ce(Ⅳ) from the surface of the PN-CQDs, and the fluorescence signal of the system was “open”. Under the optimal conditions, the recovered fluorescence value ΔF of PN-CQDs at λex/λem=326 nm/408 nm were linearly related with the dopamine concentration in the range 2.5×10-7 to 1.0×10-5 mol·L-1, the detection limit was 9.0×10-8 mol·L-1 and the coefficient of determination R2 was 0.997 6. The fluorescence quenching-recovery mechanism of the system was discussed. The fluorescence lifetimes of PN-CQDs and PN-CQDs-Ce(Ⅳ) systems were 6.02 and 5.15 ns, respectively. The fluorescence quenching type of Ce(IV)on PN-CQDs was dynamic quenching. The fluorescence of Ce(Ⅲ) generated in the reaction at λex/λem=251 nm/350 nm had no effect on the determination of dopamine. The method was sensitive, selective, simple and rapid. It has been applied to the determination of dopamine in practical samples with satisfactory results. The recovery (mean±SD) was between 97.5%±1.3%～103%±1.5%. The study can expand the application of CQDs in the field of analytical chemistry and provide new ideas for pharmaceuticals fluorescence analysis.
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