Photoactivated CdTe/CdSe Quantum Dots as a Near Infrared Fluorescent Probe for Detecting Biothiols in Biological Fluids

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Abstract
The important roles of biothiols in biological systems have attracted great interest in the determination of biothiols. Although great progress has been made in fluorescent biothiol probes, near-infrared (NIR) fluorescent probes for biothiols are rather few even such NIR probes can avoid interference from biological media such as tissue autofluorescence and scattering light, and thereby facilitate relatively interference-free sensing. Herein, we report photoactivated CdTe/CdSe quantum dots (QDs) as a novel NIR fluorescent probe for biothiols. The photoactivated CdTe/CdSe QDs based NIR fluorescent probe offers good sensitivity and selectivity for detecting cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) in the presence of 20 other amino acids, main relevant metal ions, and some other molecules in biological fluids. The recovery of spiked 5.0 μM thiols in human urine, plasma, and cell extracts ranges from 90% to 109%. The precision for nine replicate measurements of the thiols at 5.0 μM is in the range from 1.6% to 1.8%. The detection limits for Cys, Hcy, and GSH are 131, 26, and 20 nM, respectively. This assay is based on both the superior photoactivity of CdTe/CdSe QDs and the strong affinity of thiols to photoactivated CdTe/CdSe QDs. The addition of thiols into the photoactivated CdTe/CdSe QDs improves the passivation of the illumination-induced traps, meanwhile reduces most of Se(IV) and Te(IV) on the surface of photoactivated CdTe/CdSe QDs so as to improve the fluorescence property.