Electrochemiluminescence Of Quantum Dot Aggregate And Its Biosensing Application

Electrochemiluminescence（ECL）technology is a significant detection method in analytical chemistry and the process of ECL can be simply defined as the emission of light generated by the excited state molecules in the electrochemically induced reaction.In recent years,the research of ECL illuminants has focused on metal complexes,luminol and nanomaterials.Among them,since the ECL phenomenon of Si quantum dots（QDs）has been reported,the ECL research of QDs in basics and application has been rapidly developed because of significant optical properties about QDs,such as narrow emission spectrum,wide absorption range,large Stokes shift,and high quantum yield.The QD-based ECL sensor,involved in nanotechnology,optics,materials science and electrochemistry,is a new type of analysis platform,with the great application potential for ultra-sensitive and real-time analysis,especially in analytical and bioanalytical applications.However,QD-based ECL sensors still have some problems to be solved,such as improvement of ECL efficiency of QDs on the electrode surface,and cytotoxicity of the QDs composed of heavy metals.Therefore,novel QDs of self-enhanced ECL were prepared in this paper,and the intramolecular electron transfer shortens the path to enhance ECL efficiency.In addition,a novel biosensor was constructed for the detection of microRNAs（miRNAs）based on QDs-based labeling.Further,a seeded-watermelon-like mesoporous nanospheres（mSiO₂@CdTe@SiO₂,mSQS NSs）was prepared to improve the utilization efficiency of QDs in the sensor and reduce its cytotoxicity.Moreover,a dual-signal-amplified ECL biosensor,with excellent sensitivity,stability and specificity,was proposed for the first time to detect miRNAs based on cyclic enzyme and mSQS NSs.The specific research content is summarized as follows:1.The preparation of self-enhanced ECL novel quantum dot based on ligand exchange methodFirst,3-mercaptopropionic acid（MPA）-protected CdTe was prepared,and then a layer of CdSe QDs was coated on the surface to obtain CdTe@CdSe QDs.Subsequently,the protective agent of MPA on the surface of the core-shell structure was exchanged with 2-diethylaminoethanethiol（DEAET）to obtain a novel DEAET-CdTe@CdSe QDs.The optical properties and ECL behavior of QDs before and after ligand exchange were explored.After surface ligand exchange of QDs,particle size reduced,and a blue-shifted was observed about the fluorescence emission peak,and a strong ECL signal can be emitted when there was no co-reactant in the electrolyte.2.Preparation of an ECL biosensor based on CdTe quantum dot as a marker and circulating enzyme for signal amplificationIn this study,an ECL biosensor was designed to detect miRNA-182.The specific steps were listed as follow:first,MPA-CdTe QDs labeled signal probe DNA-F and hairpin DNA probe（DNA-P）conjugated to Fe₃O₄@Au NPs.Simultaneous introduction of miRNAs and duplex-specific nuclease（DSN）into the sensor,DNA/RNA heteroduplexes were structured and were recognized by DSN enzyme;then,DNA was hydrolyzed and RNA was released;at this point,the DNA-F with the signal marker produced a complementary pairing with the remaining of DNA-P;the RNA released into the solution continued to form a heteroduplex with the hairpin structure DNA;repeatedly,more CdTe/DNA-F bound the periphery of Fe₃O₄@Au/DNA-P to complete the construction of the biosensor.3.Dual-signal-amplified electrochemiluminescence biosensor for microRNA detection by coupling cyclic enzyme with CdTe QDs aggregate as luminophorIn this paper,an ECL biosensor based on seeded-watermelon-like mesoporous nanospheres（mSQS NSs）and DSN enzyme was constructed.First,the process of preparing mSQS NSs was as follows:mesoporous silica（mSiO₂ NSs）was obtained by etching SiO₂ NSs;large numbers of QDs were embedded in mesopores of mSiO₂ NSs to obtain mSiO₂@CdTe NSs（mSQ NSs）;afterwards,the surface of mSQ NSs was coated with a non-toxic silica shell to obtain mSQS NSs.Sensor was fabricated as similar procedure:the aminated mSQS NSs and DNA-F were crosslinked by glutaraldehyde as the signal unit of the sensor;Fe₃O₄@Au NPs as a nanocarrier immobilized hairpin probe DNA-P;the DSN enzyme was still used for the identification of heteroduplexes.The biosensor was collected on the surface of the electrode by the action of a magnet.The prepared ECL biosensor could detect miRNAs sensitively with optimal conditions.