Cdse/Zns Capped Thiolate for Application in Glucose Sensing

Abstract

A semiconducting water soluble core-shell quantum dot (QD) capped with thiolated ligand is used in this study for application in glucose sensing. These QDs were prepared in house based on hot injection technique. The ZnS shell at the outer surface of CdSe core QDs is made via specific process namely, SILAR (successive ionic layer adsorption and reaction). The distribution, morphology and optical characteristics of prepared core shell QDs have been assessed by transmission electron microscopy (TEM) and spectrofluorescence, respectively. The results show that the mean particle size of prepared QDs is in the range of 10-12 nm and the optimum emission condition was displayed at 620nm. The prepared CdSe/ZnS core shell QDs were modified by utilizing six organic ligands L-cysteine, L-histidine, thio-glycolic acid (TGA), mercapto-propionic acid (MPA), mercapto-succinic acid (MSA) and mercapto-undecanoic acid (MUA) at room temperature through a ligand-exchange procedure. This ligand exchange process was chosen in order to produce a very dense water solubilizing agent the QDs surrounding surface. The result shows that CdSe/ZnS capped with thioglycolic acid (CdSe/ZnS-TGA) exhibit the strongest fluorescence emission; therefore it was used in advanced sensing application for the detection of glucose. The highly active CdSe/ZnS-TGA was then interacted with Glucose Oxidase enzyme (GOx) and horseradish peroxidase enzyme (HRP). In this study, determination of glucose level is depending on the QDs fluorescence intensity quenching effect, which is correlated to reaction of the conjugated enzyme-QDs. In the presence of 0.1 mM glucose, fluorescence intensity of the bioconjugate QDs was quenched about 12, 000 a.u. This bioconjugated GOX/HRP/QDs-capped TGA was further analyzed with known concentrations of glucose. Quenched fluorescence intensity was proportionate with glucose concentration. The resultant GOX/HRP/QDs-capped TGA system can be a suitable platform for glucose determination in real samples.