Biosensors Based On Nucleic Acid Aptamers

DNA is a kind of very important biomolecule,as the carrier of genetic information,playing an important role in biologic activity.DNA is widely applied in bio-chemical analysis as the molecular probe.Aptamers is one of the most popular DNA probes,and aptamers offer several advantages over antibodies,owing to their relative ease of isolation and modification,high selectivity,tailored binding affinity, and resistance against denaturizing.Aptamers have been used in biochemistry, diagnosis,drug screening and environmental monitoring,etc.Aptamers are now widely used in many areas.In this work,we designed an aptamer-based biosensor by using quantum dots and up-converting nanophosphors as labels to selectively detect thrombin and target DNA at low levels.The detailed points of the thesis are described as follows:1.Introduction of aptamer and its application in bioanalysisA review on aptamers and its application in bioanalysis is presented.This part includes:(1) introduction of SELEX technologies(2) brief introduction of the recent research progress in aptamers,including the combination with other techniques,(3) trend of aptamers in bioanalysis application,(4) purpose and significance of this thesis.2.Aptamer-based biosensor for sensitive thrombin detectionA sensitive aptamer-based sandwich-type sensor is presented to detect human thrombin using quantum dots as electrochemical label.CdSe quantum dots were labeled to the secondary aptamer,which were determined by the square wave tripping voltammetric analysis after dissolution with nitric acid.The aptasensor has a lower detection limit at 1 pM,while the sample consumption is reduced to 5 ll.The proposed approach shows high selectivity and minimizes the nonspecific adsorption, so that it was used for the detection of target protein in the human serum sample.Such an aptamer-based biosensor provides a promising strategy for screening biomarkers at ultratrace levels in the complex matrices. 3.Up-converting nanophosphors based biosensor for DNA detectionUp-converting rare-earth nanophosphors(UCNPs) have superior potential to revolutionize biological luminescent labels,which are resistant to photobleaching and photodamage,nontoxic,biocaompatible,chemical stable,high quantum yielding.The most important one is that the long-wavelength(low-energy) light penetrates deeper (hundreds of micrometers) into samples.In this work,we demonstrate a novel biosensor for the detection of target DNA which is based on FRET between bioconjugated UC nanoparticles and gold nanoparticles.The strong green UC luminescence from suspensions of the nanoparticles in water upon excitation with a 980-nm laser was absorbed by the 5 nm gold nanoparticles,which had a strong absorption at 520 nm wavelength.The results indicated that such a FRET system was simple for the DNA detection.The UCNPs would be applied in biological analyses such as cell imaging and tissue imaging in future.