Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand.
J Fluoresc. 2011 Sep;21(5):1941-9. doi: 10.1007/s10895-011-0893-4. Epub 2011 May 15.
Luminescent CdS quantum dots capped with thioglycolic acid (CdS-TGA QDs) were demonstrated to serve as a fluorescence probe for a model organic radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(•)), employing the quenching of the CdS-TGA QDs emission signal by the radical. Under the optimum conditions, the quenching efficiency of DPPH(•) on CdS-TGA QDs was proportional to the concentration of DPPH(•), following Stern-Volmer relationship. Different types of surfactants (cationic, anionic and neutral surfactants) were introduced to CdS-TGA QDs in order to increase the detection sensitivity. The fluorescence intensity of CdS-TGA QDs was greatly enhanced by cationic and neutral surfactants. Moreover, the quenching efficiency of DPPH(•) on the QDs in the presence of micelles was remarkably ca. 13 times higher than that in the system without micelles. Effects of pH and concentration of surfactants on the fluorescence quenching of CdS-TGA QDs were investigated. Electron spin resonance (ESR) spectroscopy was also used to monitor the DPPH radical species in CdS-TGA QDs mixtures with and without micelles. Fluorescence quenching mechanisms of CdS-TGA QDs by DPPH(•) in the presence and in the absence of CTAB were proposed.
巯基乙酸（CdS-TGA QDs）包覆的发光 CdS 量子点被证明可以作为一种荧光探针，用于检测有机自由基 2,2-二苯基-1-苦肼基自由基（DPPH(•)），这是通过自由基猝灭 CdS-TGA QDs 的发射信号来实现的。在最佳条件下，DPPH(•)对 CdS-TGA QDs 的猝灭效率与 DPPH(•)的浓度成正比，符合 Stern-Volmer 关系。为了提高检测灵敏度，我们向 CdS-TGA QDs 中引入了不同类型的表面活性剂（阳离子型、阴离子型和中性表面活性剂）。阳离子型和中性表面活性剂大大增强了 CdS-TGA QDs 的荧光强度。此外，在胶束存在的情况下，DPPH(•)对 QDs 的猝灭效率比没有胶束的体系高约 13 倍。我们还考察了 pH 值和表面活性剂浓度对 CdS-TGA QDs 荧光猝灭的影响。电子顺磁共振（ESR）光谱也被用于监测有无胶束存在时 DPPH 自由基在 CdS-TGA QDs 混合物中的存在情况。提出了在有和没有 CTAB 的情况下，DPPH(•)猝灭 CdS-TGA QDs 的荧光猝灭机制。
