Application Of Aptamer In Fluorescent Biosensors

In recent years, under the impetus of biology, materials science and information development results, biosensor technology to the rapid development, and developed into a door by a multi-disciplinary emerging disciplines. Wherein, as the fluorescence signal detecting means is a fluorescent biosensor, has moved emission wavelength, fluorescence quenching or enhancement. Meanwhile, the fluorescence biosensor has many unique advantages, such as: easy operation, good selectivity, high sensitivity, rapid analysis, etc., are very effective in promoting the field of analytical chemistry of biological, chemical, food, environmental, medical, pharmaceutical and other in application. Now, the fluorescence biosensor technology has become an indispensable advanced biotechnology, also attracted a lot of interest researchers.Aptamers are a class of artificially synthesized and screened in vitro single-stranded oligonucleotides, mainly through the in vitro screening techniques-systematic evolution of ligands by exponential enrichment method(systematic evolution of ligands by exponential enrichment, SELEX) obtained by screening RNA or DNA fragments. Physical screening out aptamers can specifically and efficiently bind target molecule, such as metal ions, proteins, small molecules and the like. Meanwhile, the aptamers with good stability, good biocompatibility, ease of synthesis, easy of modification, and many other advantages, making it in the construction of biosensors as an important material has been widely used. In recent years, concern in many areas, such as diagnostics, environmental monitoring, clinical diagnosis of disease and the like.Evaluation good or bad performance of a sensor, which is of the main parameters of selectivity and sensitivity. This research paper which were introduced advantages aptamers and fluorescent biosensor namely the use of fluorescence-based biosensor to detect fluorescence signals a of solution and by means of nucleic acid specific binding aptamers were constructed based on a series of new fluorescent biological aptamers sensing technology enables highly sensitive and selective to detect heavy metal ions, proteins, MiRNA. Specific contents are as follows: Part 1 Graphene nanosensor for highly sensitive fluorescence turn-on detection of Hg2+ based on target recycling amplificationThe development of sensitive and selective methods for the monitoring of toxic heavy metal ions is highly demanded because of their threats to the environment and human health. Based on a new exonuclease III(Exo III)-assisted target recycling amplification strategy, a highly sensitive fluorescence turn-on nanosensor for Hg2+ detection using graphene oxide(GO)-quenched FAM-ssDNA nanoprobes is developed. The target Hg2+ ions bind and fold the GO-adsorbed FAM-ssDNA into duplex structures through the formation of T-Hg2+-T base pairing, resulting in the release of the FAM-ssDNA from the surface of GO and recovery of the fluorescent signal. Besides, the released and folded duplex can be digested by Exo III to liberate the bound Hg2+ ions, which can again associate with the fluorescence quenched FAM-ssDNA nanoprobes and trigger the target recycling process to cause cyclic cleavage of the GO-adsorbed FAM-ssDNA. This target recycling process therefore leads to the release of numerous FAM labels back into the solution and significantly amplified fluorescent signal is obtained for highly sensitive detection of Hg2+ down to the sub-nanomolar level. The developed nanosensor also exhibits high selectivity against non-specific ions and can be potentially employed to monitor other toxic heavy metal ions at ultralow levels. Part 2 Label-free and homogeneous aptamer proximity binding assay for fluorescent detection of protein biomarkers in human serumBy using the aptamer proximity binding assay strategy, the development of a label-free and homogeneous approach for fluorescent detection of human platelet-derived growth factor BB(PDGF-BB) is described. Two G-quadruplex forming sequence-linked aptamers bind to the PDGF-BB proteins, which leads to the increase in local concentration of the aptamers and promotes the formation of the G-quadruplex structures. Subsequently, the fluorescent dye, N-methylmesoporphyrin IX, binds to these G-quadruplex structures and generates enhanced fluorescence emission signal for sensitive detection of PDGF-BB. The association of the aptamers to the PDGF-BB proteins is characterized by using native polyacrylamide gel electrophoresis. The experimental conditions are optimized to reach an estimated detection limit of 3.2 nmol/L for PDGF-BB. The developed method is also selective and can be applied for monitoring PDGF-BB in human serum samples. With the advantages of label-free and homogeneous detection, the demonstrated approach can be potentially employed to detect other biomarkers in a relatively simple way.Part 3 Coupling hybridization chain reaction with catalytic hairpin assembly enables non-enzymatic and sensitive fluorescent detection of microRNA cancer biomarkersThe identification and quantification of sequence-specific microRNAs(miRNAs) plays an important role in early diagnosis of different diseases. In this work, by integrating two independent signal amplification approaches, hybridization chain reaction and catalytic hairpin assembly, we report an enzyme-free and dual amplified approach for highly sensitive detection of a human prostate cancer biomarker, miR-141. The presence of miR-141 triggers the self-assembly of two hairpin DNAs into dsDNA polymers, which colocalize two split segments of ssDNA into proximity. Subsequently, these co-localized ssDNA sequences further act as triggers to initiate catalytic assembly of twofluorescently quenched hairpin DNAs to form numerous dsDNA strands, resulting in the recovery of thefluorescent emissions and remarkably amplified signals for highly sensitive detection of miR-141 down to 0.3 fmol/L. In addition, this method is also selective for the target miRNA against other control sequences. With the advantages of high sensitivity and nanomaterial/enzyme-free detection format, the developed method can be a general sensing platform for the detection of trace amounts of sequence-specific nucleic acid targets.