红色荧光碳量子点用于肿瘤微酸环境诊断

Red Fluorescent Carbon Quantum Dots for Diagnosis of Acidic Microenvironment in Tumors

实现肿瘤的早期诊断对于提高癌症患者的存活率或延长生存时间非常重要。由于肿瘤细胞的糖酵解失调,导致肿瘤组织呈现微酸环境(pH<6.8),因此可以通过设计在pH 6.8响应的荧光材料实现对于肿瘤的早期诊断。在本工作中,我们以4-二甲氨基苯酚为前驱体,高碘酸钾为氧化剂,采用溶剂热法制备了发射波长为640 nm的水溶性红色荧光碳量子点(R-CQDs)。将单甲醚聚乙二醇衍生物(MeO-PEG-PDPA)修饰到R-CQDs表面,获得在pH 6.8响应的R-CQDs(pRF-RCQDs),pH<6.8时呈现红色荧光,pH>6.8时荧光淬灭。通过透射电子显微镜(TEM)、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱、拉曼(Raman)光谱、X射线粉末衍射(XRD)图谱、荧光(PL)光谱、紫外可见(UV-Vis)吸收光谱对R–CQDs进行结构与性质测定。研究了pRF-R-CQDs在组织成像及活体成像中的应用。结果表明:肿瘤微酸环境(pH<6.8)中,pRF-R-CQDs的氨基质子化而呈现红色荧光。正常组织(pH>6.8)中,pRF-R-CQDs的氨基去质子化导致荧光淬灭。pRF-R-CQDs的浓度在高达100μg·mL−1时仍未表现出明显的细胞毒性。pRF-R-CQDs能够用于区分出肿瘤和正常组织,可用于肿瘤的早期诊断。

Cancer remains a major global cause of morbidity and mortality.Diagnosis at an early stage can significantly improve the survival of cancer patients.Cancers of different origins often have vastly different genotypes and phenotypes.Therefore,it is challenging to establish a universal strategy for cancer detection.Universal cancer detection can be potentially achieved by using pH-responsive probes.An acidic microenvironment is mainly caused by lactic acid accumulation in rapidly growing tumor cells.Based on the difference in pH between tumor and normal tissues,fluorescent materials that respond to a pH of around 6.8 are ideal for tumor detection.Carbon quantum dots(CQDs)have attracted much attention in bioimaging owing to their outstanding characteristics such as stable photoluminescence,low cytotoxicity,excellent biocompatibility,and resistance to photobleaching.In this study,red fluorescent CQDs(R-CQDs)were synthesized by the solvothermal treatment of 4-(dimethylamino)phenol in the presence of potassium periodate.The UVVis spectrum of the R-CQDs showed a characteristic absorption peak at 545 nm.The photoluminescence spectrum revealed an emission peak at 640 nm.The brightness of this photoluminescence peak was quantified to be 12.8%in terms of the absolute quantum yield(QY).Transmission electron microscopy(TEM)images showed that the R-CQDs have uniform sizes with an average diameter of 4 nm and a lattice spacing of 0.21 nm.Fourier transform infrared(FT-IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)confirmed that the R-CQDs have a large number of carboxyl groups.The Raman spectrum of the R-CQDs showed the characteristic D band at 1340 cm^(−1) and G band at 1585 cm^(−1).The X-ray powder diffraction(XRD)pattern showed a broad(002)peak centered at around 23°.The R-CQDs were responsive to highly acidic or alkaline conditions.The incorporation of a block copolymer(MeO-PEG-PDPA),prepared by atom transfer radical polymerization(ATRP),on the R-CQDs produced pH-responsive fluorescent CQDs(pRF-R-CQDs).Photoluminescence(PL)spectra showed that the pRF-R-CQDs were responsive at pH 6.8.At pH>6.8,the fluorescence of the pRF-R-CQDs would be quenched because of deprotonation of the amine groups.In contrast,protonation of the amine groups would lead to a dramatic increase in fluorescence emission.TEM images showed that the pRF-R-CQDs self-assemble and disassemble at pH 6.8 because of their pH-responsive properties.Compared with most existing fluorescent materials,the pRF-R-CQDs can effectively resist photobleaching and autofluorescence.Moreover,these pRFR-CQDs have minimal toxicity and can distinguish tumors from normal tissues.Therefore,pRF-R-CQDs have great potential for use as a universal material in tumor microenvironment diagnosis.