Synthesis Of Cdte-based Type-â…¡Warer-Soluble Near-Infrared Quantum Dots And Their Analytical Applications

Quantum dots (QDs), also called semiconductor nanocrystals, are a kind of inorganic nanomaterials with excellent photoelectric properties. In the past few years, QDs have attracted broad attention in the fields of chemical analysis, fluorescence labeling and photoelectric device. Compared to visible light, near-infrared (NIR) emission (650-900nm) offers several unique advantages, including minimal interferential absorption, low biological autofluorescence, and high tissue penetration. Therefore, the exploration and development of new NIR QDs and ralted biosensing methodologies has caused great interest to researchers. But in fact, QD-based NIR fluorescence and NIR electrogenerated chemiluminescence (NECL) biosensors have not been widely used in the fields of biological analysis and food monitoring, due to the relatively primitive synthetic techniques of NIR QDs especially the poor strategies for direct preparation of highly luminescent and stable aqueous NIR QDs, the less mature NIR analytical technique and the low sensitive of detectors towards NIR emission.Based on this, the main propose of this dissertation is to promote the development of NIR analytical technique. To develop new strategies for the synthesis of aqueous NIR QDs, series of highly luminescent, good stability and low toxic are prepared. The key points are to study the NECL behaviours of NIR QDs and develop highly sensitive and selective NIR biosensors. This dissertation is divided into five parts, a total of six chapters. The specific content is as follow:1. A simple hydrothermal method is developed for the synthesis of high-quality, water-soluble, and NIR type-II core/shell CdTe/CdSe QDs by employing thiol-capped CdTe QDs as core templates and CdCl2and Na2SeO3as shell precursors. Compared with the original CdTe core QDs, the core/shell CdTe/CdSe QDs exhibit an obvious red-shifted emission, whose color can be tuned between visible and NIR regions (620-740nm) by controlling the thickness of the CdSe shell. The photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to44.2%without any post-preparative treatment. Through a thorough study of the core/shell structure by high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) absorption spectra, fluorescence spectra, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the as-prepared CdTe/CdSe QDs demonstrate good monodispersity, hardened lattice structure and excellent photostability, offering a great potential for biological application.2. Highly luminescent, good stability and low toxic N-acetyl-L-cysteine (NAC) capped CdTe/CdS@ZnS-SiO2NIR QDs were successfully via a promising microwave strategy, which employed thiol-capped CdTe/CdS QDs as core templates and ZnCl2, NAC and TEOS as shell precursors. This proposed method can greatly shorted reaction time and increase fluorescence intensity and stability, as well as reduce the cytotoxicity. It was found that Hg2+could effectively selective quench the QD emission based on electron transfer process. On the basis of this fact, a simple, rapid and specific method for Hg2+determination was porposed. Under optimal conditions, the fluorescence intensity decreased linearly with the concentration of Hg2+ranging from5.0x10-9to1.0x10"6mol/L. The limit of detection for Hg2+was1.0x10-9mol/L. The developed method was successfully applied to the detection of trace Hg2+in milk power.3. Cathodic electrochemiluminescence (ECL) from self-designed NIR CdTe/CdS/ZnS QDs on bare Au electrode in aqueous solution was studied. Strong and stable NECL signals at-1.25V with an onset potential of-0.98V produced by the high effectively electron-transfer reaction between electron-injected CdTe/CdS/ZnS QDs and reduced S2O82-are observed. Passivation of the QD surfaces with ZnS shell increased NECL intensity by9times when compared to CdTe/CdS QDs. The good correspondence of the ECL emission peak with the photoluminescence results suggested the surface states of the QDs had been largely passivated by ZnS shell. Furthermore, the effects of pH, buffer solutions, electrode materials and concentrations of K2S2O8on NECL intensity were investigated, and a possible NECL mechanism was also proposed.4. We reported a NECL immunosensor with amplification techniques for ultrasensitive and selective determination of biomarker. In this sensing platform, CdTe/CdS coresmall/shellthick NIR QDs were first selected as NECL emitters. The NECL nanoprobe (SiO2-QD-Ab2) was designed by covalent assembly of goat anti-human IgG antibody (Ab2) on CdTe/CdS QDs tagged silica nanospheres. Gold nanoparticle-graphene nanosheet (Au-GN) hybrids were prepared by a sonication-induced self-assembly and served as an effective matrix for initial antibodies (Abl) attachment. After a sandwich immunoreaction, the functionalized silica nanosphere labels were captured onto the glass carbon electrode surface. Integrating the dual amplification from the promoting electron transfer rate of Au-GN hybrids and the increasing QD loading of SiO2-QD-Ab2labels, the NECL response from CdTe/CdS QDs enhanced16.8-fold compared to the unamplified protocol and successfully fulfilled the ultrasensitive detection of human IgG (HIgG) with a detection limit of87fg/mL. Moreover, as a practical application, the proposed immunosensor was used to monitor HIgG level in human serum with satisfactory results obtained.5. We reported a near-infrared electrochemiluminescence resonance energy transfer (NERET) aptasensor for ultrasensitive and selective determination of thrombin, where CdTe/CdS coresmall/shellthick NIR QDs and Au nanorods (AuNRs) were used as a NECL donor and a NECL acceptor, respectively. Probing DNA modified AuNRs (pDNA-AuNRs) was prepared by a salt aging process, whose longitudinal absorption peaks that are easily tuned to match well with the ECL emission spectrum of the CdTe/CdS QDs film. The effect of degree of overlapping spectra, distance, and hybridization time was studied for the quenching efficiency of NERET between the CdTe/CdS QDs film and AuNRs. The protein detection involves a competition binding event, based on thrombin replacing pDNA-AuNRs which is hybridized with capturing aptamer immobilized on a chitosan/CdTe/CdS QDs film modified glass carbon electrode. At the optimized conditions, the NERET system could be used to ultrasensitivly and specifically detect thrombin of the concentration ranging from1.0x10-16to1.0x10-14mol/L. The detection limit was2x10-17mol/L.