Biosensors Based On Nucleic Acid Aptamer And Its Application In Detecting Bacteria

All along,bacterial pathogens have had a certain impact on people's lives and health,restricting the development of social economy.Rapidly,specifically and high-sensitively monitoring of pathogen bacteria in life is of great importance to ensure public health.Although traditional detection methods are available,they are time consuming,labor intensive,unsuitable for on-site detection,and need highly trained personnel.To overcome these limitations,nucleic acid aptamer-based biosensors,as emerging analytical methods,have opened new horizons for simple,specific and sensitive detection of microorganisms including pathogen bacteria.Gold nanoparticles(AuNPs)have the advantages of good localized plasma resonance(LSPR)characteristic,stability,biocompatibility,and easy to surface modification.Building a new type of biological and chemical sensor provides support,they are widely used in the preparation and nucleic acid adaptation of biosensor.In this paper,AuNPs with a good dispersity of about 25 nm were synthesized by seed growth method and characterized by UV-vis absorption spectroscopy(UV-vis),laser particle size analyzer and transmission electron microscopy(TEM).The poly adenine(Poly A)can be adsorbed on the surface of gold or AuNPs as an anchoring group.The grafting density of the nucleic acid aptamer on the surface of AuNPs can be controlled by controlling the length of Poly A.The prepared surface-immobilized nucleic acid aptamer has an L configuration,which facilitates hybridization and reduces non-specific adsorption.In this research,the affinity of Poly A and Au was used to immobilize the nucleic acid aptamer specifically binding to E.coli on the surface of AuNPs by changing the ionic strength in the buffer solution and the length of Poly A(10A and 30A)to change the grafting density of the nucleic acid aptamer.The fixed grafting density was characterized by UV-Vis and laser particle size analyzer,and the optimal ionic strength was selected.When the length of Poly A was 10A,the optimum concentration of sodium chloride is 20 mM;when the length of Poly A is 30 A,the optimum concentration of sodium chloride is 30 mM.Bacterial were detected by the extended probe sequences specifically binding to E.coli and characterized by UV-Vis.It is concluded that when the length of Poly A is 10A,the sample is agglomerated,the detection of E.coli is not good,and the detection limit cannot be determined.When the length of Poly A is 30A,the detection limit for E.coli is 4 CFU/mL.