Preparation Of CdS Quantum Dots By Double Stabilizer And Its ECL Detection Of Small Molecules

Electrochemiluminescence(ECL) detection technique exhibits many advantages such as high-sensitivity, high-selectivity, excellent temporal and spatial controllability,and has been widely used in the field of analytical chemistry. Quantum Dots(QDs), as a kind of potential luminescent reagents, possess good luminescent stability and high photoluminescence efficiency, and has been widely used in the field of biological sensor and fluorescence imaging. Recently, based on the excellent optial and electrical performance, many ECL sensors with Quantum Dots as ECL emitters have been developed. In this paper, a dual-stabilizer-capped CdS QDs was syntheszed with mercaptopropionic acid and sodium citrate as stabilizer, and the ECL performence was examined. An ECL sensor with dual-stabilizer-capped CdS QDs as emitter was developed and applied for determination of small biological molecules with satisfactory results.The dissertation includes the following four parts:1. Introduction The concept, properties and preparation methods of quantum dots was introduced; the merits and fundamental mechanism the of elctrochemiluminescence( ECL) was explained; ECL sensing technology and its applications of quantum dots were also summarized and introduced; and finally the purpose and significance of this dissertation have been explained.2. The preparation and characterication of dual-stabilizer-capped CdS QDsA kind of dual-stabilizer-capped CdS QD was synthized by a one-pot method with cadmium chloride as the source of cadmium, mercaptopropionic acid and sodium citrate as dual stabilizers. The optical properties of CdS QDs have been characterized by UV-Visible absorption spectrum, fluorescence spectroscopy and ECL, and the size propertie has been characterized with transmission electron microscopy(TEM). The results showed the obtained dual-stabilizer-capped CdS QDs presents a relatively narrow size distribution with the average diameter of 3-5 nm, a strong and stable ECL emission was observed. The synthesis conditions of pH and reflux time were examined and the measured conditions of ECL of CdS QDs were optimized. Under optimized conditions the obtained dual-stabilizer-capped CdS QDs produced strong cathode ECL signal, which can be quenced by dopamine. Based on this foundition a simple ECL method for sensitive detection of dopamine was established.3. The construcation of dual-stabilizer-capped CdS QDs sensor and its application for dopamine determinationIn order to save the luminescent material and achieve rapid online analysis,we designed and construcated a dual-stabilizers-capped CdS QDs ECL sensor by immobilizing of dual-stabilizers-capped CdS QDs on a glassy carbon electrode(GCE).First the amino-group was introduced in the GCE surfaces by electropolymerization of p-Aminobenzoic acid(ABA) on GCE to form ABA-GCE. Then the dual-stabilizer-capped CdS QDs was immobilized on the ABA-electrode by covalent bondtion of amino group and carboxyl group with 1,3-propanediamine(PDA) as link molecule. In order to accelerate the electron transfer of electrode surface, a conductive amterial of multiwalled carbon nanotube(MWCNTs) were also introduced in the ABA-GCE before CdS QDs. The obtained sensor was recorded as CdS QDs/PDA/MWCNTs /ABA-GCE. The building processes of the sensor were characterized step by step. The obtained sensor shows strong ECL emission with potassivation persulfate as coreactant and can be used for determination of dopamine in real sameples with satisfactory result. The detection limit is 1.6 nM(S/N=3). This strategy is promising for highly sensitive bimolecular detection.4. Ultrasensitive determination of L-Cysteine based on its sensibilization to the ECL emission of rich Cd2+- CdS QDs.It is known the ECL efficiency of QDs was deeply influenced by its surface state.In experiment we found the ECL signal of CdS QDs was influenced by adding of L-Cysteine, the reason for the result was speculated to be the interation of the Cd2+ of CdS QDs surface and the thiol of L-Cysteine which lead to the change of surface state of CdS QDs. In this part, we synthized a series of rich Cd2+- CdS QDs. Under proper concentration ratio of Cd2+and S2-, the ECL emission of CdS QDs was greatly enhanced by L-Cysteine. Based on this foundation, we established a ECL method for the detection of L-Cysteine. The enhancement ECL intensities were linear with the concentration of L-Cysteine in the range from 5.0×10-9 M to 1.0×10-5 M, the detection limit is 1.2 nM(S/N=3). Compared to other methods, this method has advantages of anti-interference, good reproducibility and high sensitivity and has the promising in actual samples.