Graphene Oxide-Mediated Low Background Biosensor For Environmental Contaminants Detection

In the water,air and soil on which we depend,there may be a variety of environmental pollutants that directly or indirectly damage the ecosystem and imperil the lives of animals,plants and mankind.Hence,the development of accurate,fast and efficient environmental pollutants detection methods is extremely important for understanding the form and content of their presence in the environment for further processing.Biosensor is a type of analytical device that integrates the biological recognition with physical-chemical detectors for analytes detection,among that,fluorescent biosensors utilize fluorescent signals to reflect the interaction between recognition molecules and analytes,which are favored by researchers due to their fast response speed,stable signal,and high sensitivity.In addition,with the development of nanoscience,graphene and its derivatives are frequently introduced into the construction of biosensors on account of their peculiar physical and chemical character and biocompatibility.The combination of nanomaterials and fluorescence analysis methods provides a promising strategy for the construction of more stable and sensitive biosensors for the determination of environmental contaminants.In this thesis,several fluorescent biosensor platforms were designed and constructed based on the interaction between Graphene oxide（GO）and nucleic acid molecules as well as their unique fluorescence quenching ability,and were respectively used for the detection of typical heavy metal pollutant Hg²⁺,environmental endocrine disrupting chemicals bisphenol A,and target DNA.The details are as follows:（1）A fluorescent biosensor for Hg²⁺detection in water based on double-stranded DNA and graphene oxide.A simple ds DNA/GO-based fluorescent biosensing platform was constructed for the rapid detection of Hg²⁺,which was based on the special binding phenomenon between the thymine base pair with Hg²⁺,as well as the fluorescence resonance energy transfer when the FAM fluorophore is close to GO.This method exhibited a good ability to detect Hg²⁺in both buffer solution and actual samples with an extremely high specificity（the detection limit was 0.110μM under the optimum conditions）,which provided an accurate and reliable strategy for the quantitative analysis of Hg²⁺in water.（2）Target induced nucleic acid structure change of biosensor for bisphenol A detection.Based on the study of content（1）,the construction of DNA/GO probes in the first place increased the difficulty of binding the target and its specific DNA due to the strong interaction between GO and DNA.In order to overcome this deficiency,this study proposed a graphene biosensing platform that used the specific binding of bisphenol A with its nucleic acid aptamer and induced the release of trigger chains,and finally added GO to regulate the background signals.This method could achieve high sensitivity and specificity detection of BPA（the detection limit is about 0.5035μg/m L）,and also displayed excellent detection ability in actual samples.（3）Ultrasensitive biosensor for DNA based on graphene oxide regulated low-background and exonuclease III assisted signal amplification.In order to improve the sensitivity of the system for the quantitative detection of some low-concentration target substances,we introduced the enzyme-assisted signal amplification technology on the basis of the content（2）.That is,exonuclease III can cut the blunt ends of ds DNA and release the target for another recycle in detection system,so the output signal can be amplified several times.This fluorescent biosensing method using Exo III-assisted signal amplification and graphene oxide for background regulation can be effectively used for highly sensitive detection of target DNA with detection limit as low as 11.2p M.This method could well distinguish the mismatched base sequence similar to the target DNA and be applied to actual samples,which has a potential application prospect in the accurate detection of pathogenic microorganism DNA/RNA.