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Study On Quantun Dot-based High Sensitive Electrochemical Biosensor

Posted on:2013-11-16Degree:MasterType:Thesis
Country:ChinaCandidate:H X ZhangFull Text:PDF
GTID:2248330371972130Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
The analysis of proteins, nucleic acids, cells in the human body, and whether the content of heavy metal elements is excessive in the environment, and so on, has gradually become one of the most important tasks of modern analytical chemistry research. Therefore, many high sensitivity, high specificity, rapid analysis and detection methods have emerged. Electrochemical biosensor for its unique advantages is well received by the researchers, such as high sensitivity, simple equipment, low cost, easy to carry, a wide range of detection of target, fast response, easy to realize miniaturization. Now, it has a broad space for development and a good prospect in many areas, such as the food and drug analysis, synthetic drug screening, medical testing, environmental monitoring and so on. Quantum dots, as a new type of inorganic nanomaterials, has shown great potential for development in the field of biological research, especially, the disciplines of biochemistry, immunobiology, cell biology etc for significant advantages. Quantum dots can be used as markers for the study of biological systems, which has become one of the most promising application areas. This paper used quantum dots as labels for detection of biological molecules and heavy metal ions. The specific research contents are as follows:Part 1 Aptamer/quantum dot-based simultaneous electrochemical detection of multiple small moleculesA novel strategy for "signal on" and sensitive one-spot simultaneous detection of multiple small molecular analytes based on electrochemically encoded barcode quantum dot (QD) tags is described. The target analytes, adenosine triphosphate (ATP) and cocaine, respectively, are sandwiched between the corresponding set of surface-immobilized primary binding aptamers and the secondary binding aptamer/QD bioconjugates. The captured QDs yield distinct electrochemical signatures after acid dissolution, whose position and size reflect the identity and level, respectively, of the corresponding target analytes. Due to the inherent amplification feature of the QD labels and the "signal on" detection scheme, as well as the sensitive monitoring of the metal ions released upon acid dissolution of the QD labels, low detection limits of 30 nmol/L and 50 nmol/L were obtained for ATP and cocaine, respectively, in our assays. Our multi-analyte sensing system also shows high specificity to target analytes and promising applicability to complex sample matrix, which makes the proposed assay protocol an attractive route for screening of small molecules in clinical diagnosis.Part 2 Quantum dot layer-by-layer assemblies as signal amplification labels for ultrasensitive electronic detection of uropathogensThe preparation and use of a new class of signal amplification label, quantum dot (QD) layer-by-layer (LBL) assembled polystyrene microsphere composite, for amplified ultrasensitive electronic detection of uropathogen-specific DNA sequences is described. The target DNA is sandwiched between the capture probes immobilized on the magnetic beads and the signaling probes conjugated to the QD LBL assembled polystyrene beads. Because of the dramatic signal amplification by the numerous QDs involved in each single DNA binding event, subfemtomolar level detection of uropathogen-specific DNA sequences is achieved (0.22 fmol/L), which makes our strategy among the most sensitive electronic approach for nucleic acid-based monitoring of pathogens. Our signal amplified detection scheme could be readily expanded to monitor other important biomolecules (e.g., proteins, peptides, amino acids, cells, etc.) in ultralow levels and thus holds great potential for early diagnosis of disease biomarkers.Part 3 DNAzyme-based highly sensitive electronic detection of lead via quantum dot-assembled amplification labelsAn electronic DNAzyme sensor for highly sensitive detection of Pb2+ is demonstrated by coupling the significant signal enhancement of the layer-by-layer (LBL) assembled quantum dots (QDs) with Pb2+specific DNAzymes. The presence of Pb2+ cleaves the DNAzymes and releases the biotin-modified fragments, which further hybridize with the complementary strands immobilized on the gold substrate. The streptavidin-coated, QD LBL assembled nanocomposites were captured on the gold substrate through biotin-streptavidin interactions. Subsequent electrochemical signals of the captured QDs upon acid dissolution provide quantitative information on the concentrations of Pb2+ with a dynamic range from 1 to 1000 nmol/L. Due to the dramatic signal amplification by the numerous QDs, subnanomolar level (0.6 nmol/L) of Pb2+ can be detected. The proposed sensor also shows good selectivity against other divalent metal ions and thus holds great potential for the construction of general DNAzyme-based sensing platform for the monitoring of other heavy metal ions.
Keywords/Search Tags:electrochemical biosensors, quantum dots, aptamer, DNAzyme
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