一步法合成特异性pH响应碳量子点及其发光机理研究

doi:10.15541/jim20190089

摘要/Abstract

摘要：

本研究利用溶剂热反应, 以柠檬酸为碳源, 甲酰胺和水为混合溶剂, 一步合成氮掺杂碳量子点。研究表明, 所制备的氮掺杂碳量子点具有良好的水溶性和明亮的蓝光发射, 以及典型的依赖于激发光的荧光发射特性。特别的是, 该碳量子点显示出不同于普通碳量子点的、独特的pH响应行为, 除了具有传统的荧光强度随着pH变化的响应行为外, 还表现出在碱性条件下, 产生新的不依赖于激发光的红光发射的性能。通过系统研究碳量子点在不同碱性环境和不同羟基含量溶液中的荧光特性, 结合拉曼光谱、红外、XPS等表征, 分析其化学组成与表面态分子, 探讨了其发光机制, 证实这种特异性pH响应行为是由于在强碱性环境中含有的大量氢氧根结合在碳量子点表面, 从而改变碳量子点的表面状态, 形成新的稳定的发光中心。最后, 通过细胞毒性实验及细胞成像分析表明, 所获得的碳量子点具有低细胞毒性, 并可作为荧光探针应用于细胞成像, 显示其在生物成像领域的潜在应用价值。

关键词: 碳量子点, 特异性pH响应, 红光发射, 发光机理, 细胞标记

Abstract:

Nitrogen-doped carbon quantum dots (CDs) were synthesized via a facile one-step solvothermal reaction using citric acid, formamide and water. Subsequent characterizations indicate that the nitrogen-doped CDs are featured by good water solubility, bright blue emission and typical excitation-dependent emission. However, unlike from conventional pH response of most CDs, the as-prepared CDs possess unique pH response. Apart from that fluorescence intensity varies with the pH value, the prepared CDs can generate excitation-independent red emission in alkaline conditions. Through scientific research towards fluorescent property of prepared CDs in different alkaline environments as well as solution with different hydroxyl content, combined with chemical composition and surface states based on Raman spectrum, FT-IR and XPS, the fluorescent mechanism of the unique pH response are attributed to a large number of hydroxyl groups in strong alkaline environment bonded to the surface of CDs, thus changing the surface states of CDs, further forming a new stable luminescence center. Finally, cytotoxicity tests and cell imaging experiments showed that the prepared CDs have low cytotoxicity, and can be used as fluorescent probe for cell imaging, indicating their potential application in the field of biological imaging.

Key words: carbon quantum dots, specific pH-response, red emission, luminescence mechanism, cell labeling

中图分类号:

TQ174

高东, 张煜亮, 孙静, 范宏筠. 一步法合成特异性pH响应碳量子点及其发光机理研究[J]. 无机材料学报, 2019, 34(12): 1309-1315.

GAO Dong, ZHANG Yu-Liang, SUN Jing, FAN Hong-Jun. One-step Synthesis of Specific pH-responsive Carbon Quantum Dots and Their Luminescence Mechanism[J]. Journal of Inorganic Materials, 2019, 34(12): 1309-1315.

图/表 7

图1 碳量子点的TEM照片(插图为粒径分布图)(a)、HRTEM照片(b)、XRD图谱(c)和拉曼光图谱(d)

Fig. 1 TEM image (a), HRTEM image (b), XRD pattern (c), and Raman spectrum (d) of the prepared CDs with inset in (a) showing diameter distribution

图2 (a)碳量子点的FT-IR谱图及高分辨XPS能谱图; (b) C1s; (c) N1s; (d) O1s

Fig. 2 (a) FT-IR spectrum of prepared CDs, high-resolution XPS spectra of C1s (b), N1s (c) and O1s (d) of prepared CDs

图3 紫外吸收光谱(插图为碳量子点在紫外光下的光学照片) (a)和不同波长激发下的荧光光谱(b)

Fig. 3 UV-Vis absorption spectrum of prepared CDs with insets showing optical images of prepared CDs under UV lamp (365 nm) (a) and ?uorescent spectra under various excitation wavelengths (b)

图4 不同pH条件下碳量子点的荧光光谱(a~g)、pH值与碳量子点荧光强度的关系(EX=360 nm)(h)和不同pH值的碳量子点溶液在紫外灯下的荧光照片(i)

Fig. 4 Fluorescent spectra of as-prepared CDs with different pH values under various excitation wavelengths (a-g), fluorescent intensity at different pH under excitation of 360 nm (h) and optical images of prepared CDs with different pH under UV lamp (365 nm) (i)

图5 所制备的碳量子点在甲醇中的荧光光谱(a)和所制备的碳量子点在乙醇中的荧光光谱(b)

Fig. 5 Fluorescent spectra of prepared CDs in methanol (a) and ethanol (b) under various excitation wavelengths

图6 碳量子点在不同比例甲醇和水混合溶液中的荧光图谱

Fig. 6 Fluorescent spectra of prepared CDs in the mixed solution of methanol and water at methanol concentration of 75% (a), 50% (b) and 25% (c) under various excitation wavelengths, and their optical images under UV lamp excitation (365 nm) (d)

图7 碳量子点对MG-63细胞活性没有显著影响(a), 所标记的MG-63细胞在紫外(b)、蓝光(c)和绿光(d)照射下的荧光照片

Fig. 7 Cell viability (a) and fluorescence images of MG-63 cells excited by UV (b), blue (c), and green light (d)

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