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摘要:
本文详细研究了交联剂1-乙基-3-（3-二甲基氨基丙基）碳二亚胺盐酸盐（EDC）对石墨烯量子点（GQDs）光学性质的影响及原因。采用水热法制备了GQDs，并与EDC反应得到GQDs/EDC复合物，对GQDs和GQDs/EDC的光谱特性进行研究。使用PBS溶液以及人工胃液样品，研究pH对GQDs/EDC荧光影响规律及作用机理。实验结果表明：GQDs表面缺陷被EDC钝化，使得GQDs的荧光在小于1 min内迅速增强，并在5~20 min内保持稳定；相比单独GQDs，GQDs/EDC的荧光强度显著提升约264倍；pH响应实验表明，在pH值为1.75~4.01及4.01~9.28范围内，GQDs/EDC具有荧光和吸收强度线性响应规律。生物兼容性表明，在25~300 µg/mL样品浓度下，人乳腺癌细胞存活率均大于80%；同时，对人工胃液pH具有较高的检测准确性，其相对标准偏差RSD ≤ 1.10%。EDC介导的荧光增强，使GQDs在检测、传感、成像等领域更具优势。同时，GQDs/EDC灵敏的pH响应特性使其在pH值检测应用中具有良好前景。
Abstract:In this paper, the effect of the cross-linking agent 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) on the optical properties of graphene quantum dots (GQDs) and the reasons are investigated in detail. GQDs were prepared by a hydrothermal method and reacted with EDC to obtain GQDs/EDC composites. The spectral properties of GQDs and GQDs/EDC were investigated. The effect of pH on the fluorescence of GQDs/EDC and its mechanism were investigated using PBS solution and artificial gastric juice samples. The experimental results show that EDC passives the surface defects of GQDs, making the fluorescence of GQDs increase rapidly in <1 min time and remain stable up to 20 min. Under different EDC contents the fluorescence intensity of GQDs/EDC is significantly enhanced by about 264 times compared to GQDs alone. The pH response experiments shows that GQDs/EDC had a linear response pattern of fluorescence and absorption intensity in the pH range of 1.75−4.01 and 4.01−9.28. Biocompatibility showed that the cell viability of human breast cancer cells was greater than 80% at sample concentrations of 25−300 µg/mL and remained at 74% even at high concentrations of 500 µg/mL; Finally, the detection of artificial gastric pH has high accuracy with relative standard deviation RSD ≤1.10%. The EDC-mediated fluorescence enhancement makes GQDs more advantageous in the fields of detection, sensing and imaging. Besides, the sensitive pH response characteristics of GQDs/EDC provide a good prospect for pH detection applications.
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Key words:
- graphene quantum dots /
- EDC /
- fluorescence enhancement /
- surface passivation /
- pH response
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图 1 （a）GQDs的TEM图像；（b）尺寸分布柱状图及（c）与JCPDS 75-1621标准对比的GQDs XRD图谱；（d）GQDs/EDC复合材料TEM图像
Figure 1. (a) TEM image of GQDs; (b) histogram of size distribution; (c) XRD pattern of GQDs compared with JCPDS 75-1621 standard; (d) TEM image of GQDs/EDC composites
图 3 （a）EDC，PBS，GQDs和GQDs/EDC的PL光谱及（b）PL光谱的局部放大图
Figure 3. (a) PL spectra of EDC, PBS, GQDs and GQDs/EDC and (b) its local magnification
图 4 不同激发波长下（a）GQDs和（c）GQDs/EDC的荧光光谱，以及不同探测波长下（b）GQDs及（d）GQDs/EDC的激发光谱
Figure 4. Fluorescence spectra of (a) GQDs and (c) GQDs/EDC at different excitation wavelengths, and excitation spectra of (b) GQDs and (d) GQDs/EDC at different detection wavelengths
图 5 （a）EDC，GQDs，GQDs/EDC的吸收光谱，以及460 nm探测波长下GQDs/EDC的激发光谱。（b）GQDs的吸收光谱及其460 nm探测波长下的激发光谱。（c）GQDs和（d）GQDs/EDC在不同探测波长下的瞬态PL衰减曲线。各样品最终体积定容至2 mL，EDC含量为50 µL，15.28 mg/mL
Figure 5. (a) Absorption spectra of EDC, GQDs, GQDs/EDC, and excitation spectrum of GQDs/EDC at 460 nm detection wavelength. (b) Absorption spectrum of GQDs and excitation spectrum at 460 nm detection wavelength. Transient PL decay curves of (c) GQDs and (d) GQDs/EDC at different detection wavelengths. The final volume of each sample was 2 mL and EDC content is 50 µL, 15.28 mg/mL
图 6 （a）GQDs分别与浓度为0~1700 µL的EDC混合反应后的荧光光谱以及（b） 荧光积分强度随EDC含量的变化趋势图。（c）pH值分别为7.2和2.3条件下，荧光积分强度随GQDs与EDC反应时间的变化关系
Figure 6. (a) Fluorescence spectra of GQDs/EDC with different EDC contents (0−1700 µL), and (b) the trend of fluorescence integrated intensity with EDC content. (c) The integrated PL intensity varies with the reaction time of GQDs/ EDC with the pH value of 7.2 and 2.3, respectively
图 7 不同pH环境下的GQDs/EDC混合反应10 min后测得的（a）荧光光谱(λex=360 nm)和（c）吸收光谱。以及去基线后（b）荧光积分强度和（d）吸收积分强度随pH值的变化曲线。以及不同pH环境下GQDs/EDC的（e）明场和365 nm光源激发下的（f）暗场实物图
Figure 7. (a) Fluorescence spectra (λex=360 nm) and (c) absorption spectra of EDC and GQDs at different pH values after 10 min mixed reaction. (b) Integrated fluorescence and (d) absorption intensity as a function of pH value, after removing the baseline. (e) Bright-field and (f) dark-field images of GQDs/EDC under different pH environments with excitation by a 365 nm light source
图 8 （a）不同EDC含量及（b）不同pH值条件时GQDs/EDC的瞬态荧光衰减曲线
Figure 8. (a) Transient fluorescence attenuation curves of GQDs/ EDCs under different EDC contents and (b) different pH conditions
图 9 （a）选择性测试，GQDs/EDC对H+和其他常用离子 (5 mM)的荧光强度响应，其中Blank组为仅有PBS(pH 7.2)溶液（b）细胞与不同浓度GQDs/EDC共培养24 h后，MTT法测得的MCF-7细胞存活率
Figure 9. (a) Selective tests, the fluorescence intensity response of GQDs/EDC to H+ and other commonly used ions (5 mM), the Blank group was only PBS (pH 7.2) solution. (b) The survival rate of MCF-7 cells was determined by MTT method after 24 h co-culture with different concentrations of GQDs/ EDC
表 1 不同方法的量子点荧光法测定pH值比较结果
Table 1. Comparison of pH values of quantum dots by different fluorometric determination methods
Sensors Medium Linear range Ref N,S co-doped carbon QDs Intracellular 5.5~7.0 [28] Carbon dots Intracellular 6.1~7.8 [29] Carbon dots Intracellulat 6.03~8.91 [30] N-doped GQDs Aqueous solution 1.25~13.56 [31] CMC/GODs Hydrogels film Not given [32] GQDs Intracellular Not given [33] CuInS2/ZnS ODs Aqueous solution 5.7~8 [34] GODs Aqueous solution 1.76~4.01
4.01~9.28This work 
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表 2 胃液pH值的测定
Table 2. Determination of pH value of gastric juices
Gastric juice sample pH value RSD (%)b Glass electrodea Proposed methoda 1 1.81±0.01 1.83±0.02 0.92 2 2.13±0.02 2.18±0.01 0.60 3 2.46±0.01 2.39±0.03 1.10 a平均值±标准差(n=3)；b相对标准偏差
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