Aqueous Synthesis of Near-Infrared CdTe Quantum Dots for Biothiols Detection in Biological Fluids

Abstract

As well known that conventional aqueous synthesis of the near-infrared (NIR) CdTe quantum dots (QDs) using thiol ligands as capping reagents is usually very time-consuming. To overcome this defect and prepare NIR CdTe QDs, we present a fast and facile route in aqoueous phase under atmospheric pressure using L-cysteine (L-Cys) as capping reagents. The influences of various experimental conditions on the growth rate and luminescent properties of the obtained CdTe QDs have been systematically investigated, including Te-to-Cd ratio, L-Cys-to-Cd ratio and pH value. The experiment results suggested that lower ratio of Te∶Cd or L-Cys∶Cd and high pH value would markedly shortened the reaction time. Fur- thermore, the obtained QDs were used as a kind of NIR fluorescent probes for thiol detection in biological fluids. The change in the fluorescence intensity of the NIR CdTe QDs in the presence of 5.0 μmolL -1 homocysteine (Hcy), L-Cys or glutathione (GSH) with different interaction time was measured. The effect of pH on the enhanced fluorescence intensity of the NIR CdTe QDs (10 mgL -1 ) at 5.0 μmolL -1 Hcy, L-Cys or GSH and the fluorescence responses of NIR CdTe QDs to 20 essential amino acids (5.0 μmolL -1 for L-Cys, 5.0 mmolL -1 for the other 19 amino acids) in pH 7.0 PBS buffer was investigated. The probe offered good sensitivity and selectivity for detecting L-Cys, Hcy and 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 μmolL -1 thiols in human serum and cell extracts ranged from 90% to 109%. The precision for 11 replicate measurements of the thiols at 5.0 μmolL -1 is in the range of 2.4%~3.3%. The detection limits (3s) for L-Cys, Hcy and GSH are 43, 46 and 63 nmolL -1 , respectively.