The Study About Electrochemiluminescence Of Mesoporous Silica Supported Quantum Dots And Its Sensing Application

Since Bard’s group published the research on electrochemiluminescence（ECL）of Si quantum dots（QDs）in Science in 2002,the ECL study of QDs has received unprecedented attention,mainly due to the merits of QDs,such as broad absorption,adjustable emissions,large Stokes shift,size tunability and high photochemical stability.In the past decade,many efforts about QDs with good ECL properties and different QDs-based immunosensing platforms have been reported increasingly.However,the ECL studies of QDs still have drawbacks and the neglected aspects,mainly as follows:（1）Compare with the traditional ECL luminophores（bipyridyl ruthenium,luminol,etc.）,the ECL intensities of QDs are weak,which obviously affects the sensitivity of the ECL sensor;（2）Up to now,the ECL mechanism of QDs-co-reactant system has not been studied systematically,which will directly affect applications of QDs.Therefore,it is necessary to systematically study the mechanism of ECL behavior of QDs-co-reactant system and to develop a method for enhancing the ECL intensity has also become very important for highly sensitive detection of immunoassay platforms based on QDs.In this dissertation,we investigated the ECL luminescence mechanism of QDs-co-reactant system and fabricated a sandwich-type immunosensor system based on the mSiO₂/CdTe nanocomposites.The specific research contents are summarized as follows:1.Study on ECL pathway of CdTe QDs-TPrA system based on different methodsIn this chapter,water-soluble CdTe QDs,mSiO₂/CdTe nanocomposites were prepared firstly.The mSiO₂/CdTe was successfully fabricated by loading CdTe QDs into mesoporous silica（mSiO₂）and characterized by ultraviolet-visible spectra,photoluminescence spectra,transmission electron microscopy,fourier transform infrared spectrum and zeta potential.The ECL of QDs-TPrA system was verified by two methods of modifying the different layers of silicon dioxide before modifying CdTe QDs,modifying different layers of mSiO₂/CdTe nanocomposites.The luminescence mechanism,that is,TPrA first oxidizes on the surface of the electrode,and then the intermediate oxidizes CdTe QDs into CdTe QDs^*,which in turn emits light.Firstly,the current density and the ECL intensity of CdTe QDs modified with different layers of silicon dioxide and modified with CdTe QDs were not significantly reduced,indicating that CdTe QDs can still produce ECL without reaching a certain distance away from the electrode surface.However,after the modification of different layers of mSiO₂/CdTe nanocomposites,their current density and ECL intensity were also not significantly reduced.The scanning electron microscopy（SEM）characterization of the cross-section of the modified electrode shows that the modification of different layers of silicon dioxide can reach 1μm on the surface of the electrode,which also effectively proves the ECL emission of the CdTe QDs far away from the electrode surface.This mechanism is the theoretical basis for the application of ECL bioanalysis in the QDs-TPrA system,which is of great guiding significance for the further application of the QDs-TPrA system.2.Novel sandwich-structured electrochemiluminescence immunosensing platform via CdTe quantum dots-embedded mesoporous silica nanospheres as enhanced signal labels and Fe₃O₄@SiO₂@PS nanocomposites as magnetic separable carriersIn this work,a novel sandwich-structured electrochemiluminescence immunosensing platform was proposed by using CdTe quantum dots（QDs）-embedded mesoporous silica nanospheres as enhanced signal probes for labelling the secondary antibodies and magnetite-silica-polystyrene（Fe₃O₄@SiO₂@PS）nanocomposites as magnetic separable carriers for primary antibodies.The electrochemiluminescence intensity of mSiO₂/CdTe is much higher than that of CdTe QDs because a single mSiO₂ can encapsulate hundreds of QDs.Therefore,mSiO₂/CdTe has been chosen as ECL labels for conjugation with secondary antibodies.Meanwhile,Fe₃O₄@SiO₂@PS was used as a carrier of broad primary antibodies owing to convenient magnetic separation capability,large specific surface area,and the special force between the PS and antibodies.Carcinoembryonic antigenas a model tumor mark has been detected to prove the feasibility of our immunosensing platform.The immunosensor for carcinoembryonic antigen was successfully confirmed by cyclic voltammograms and electrochemical impedance spectroscopy.Under the optimal conditions,the immunosensor presented a linear range of 0.001 to 80 ng mL^-1 for carcinoembryonic antigen detection with a low detection limit of 0.3 pg mL^-1（S/N=3）.Furthermore,the immunosensor also displayed outstanding selectivity,good stability,and acceptable reproducibility,indicating its potential applications in clinical diagnostics.