以花生碳量子点为探针基于其荧光猝灭-恢复测定多巴胺的研究

碳量子点(CQDs)是一种新型的荧光碳纳米功能材料,其良好的生物相容性和优异的光学性能引起了人们的广泛关注。选用富含蛋白质、脂肪和碳水化合物的花生仁(Peanut,PN)及水为原料,无需添加任何其他试剂,在水热反应釜中于190℃反应20 h,可一步合成绿色发光CQDs。透射电镜(TEM)结果显示,所制备的花生碳量子点(PN-CQDs)的粒径大约在10 nm左右,分布较为均匀;X射线衍射谱(XRD)和傅里叶变换红外光谱(FTIR)显示PN-CQDs晶型为无定型碳,表面富含-OH、-COOH、含氮官能团等亲水性基团,具有良好的水溶性。紫外-可见光谱(UV-Vis)和荧光发射光谱(FL)表明, PN-CQDs在275 nm处有一明显的吸收峰,为CQDs紫外特征吸收峰;该PN-CQDs具有激发波长依赖性,荧光发射峰的位置随激发波长的变化而移动;当激发波长λex为326 nm时,发射波长λem为408 nm处的荧光强度最大, PN-CQDs发出蓝色的荧光。以硫酸奎宁为参照物,利用参比法测得PN-CQDs的荧光量子产率φ为5.0%。基于该PN-CQDs良好的发光特性,以其为探针,构建了"关-开"型荧光体系用于多巴胺(Dopamine,DA)的高灵敏度检测。研究表明,在pH 3.80的HAc-NaAc缓冲介质中, Ce(Ⅳ)存在下, PN-CQDs与Ce(Ⅳ)之间的电子转移反应和Ce(Ⅳ)与该PN-CQDs表面基团结合使PN-CQDs发生的聚集作用共同导致PN-CQDs在λex/λem=326 nm/408 nm处的荧光发生猝灭,荧光信号"关闭";当加入DA后, DA与结合于PN-CQDs表面的强氧化性Ce(Ⅳ)发生反应,从而将Ce(Ⅳ)从PN-CQDs表面移除, PN-CQDs的荧光得以恢复,荧光信号重新"打开"。在优化的实验条件下, DA浓度与PN-CQDs在λex/λem=326/408 nm处的荧光恢复值ΔF呈良好线性关系,线性范围为2.5×10-7~1.0×10-5mol·L^-1,决定系数R2为0.997 6,检出限为9.0×10-8mol·L^-1。探讨了体系的荧光"猝灭-恢复"机理,对PN-CQDs和PN-CQDs-Ce(Ⅳ)体系进行了荧光寿命拟合,其加权平均荧光寿命分别为6.02与5.15 ns, Ce(Ⅳ)对PN-CQDs荧光猝灭类型为动态猝灭;反应中生成的Ce(Ⅲ)于λex/λem=251/350 nm处的荧光对DA的测定无影响。该方法灵敏、简便、快速,应用于实际样品中DA的测定,加标回收率(平均值±SD)在97.5%±1.3%~103%±1.5%之间,结果满意。该研究提供了一种新的DA荧光检测方法,实现了对DA的准确测定。

Determination of Dopamine by Fluorescence Quenching-Recovery Method with Peanut Carbon Quantum Dots as Probe

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.