| Polychlorinated biphenyls（PCBs）are persistent and ubiquitous organic pollutants（POPs）,which present a hazard to ecosystems and threaten food safety due to their high toxicity,poor degradation,long-term stability and bioaccumulation potential.Although the commercial production and usage of PCBs has been banned in many countries worldwide for more than two decades,trace levels of PCBs still exist in the environment,continuing to pose a serious threat to public and environmental health.Therefore,it is imperative that simple and efficient methods are developed for the detection of PCBs in food and environment samples.Electrochemical bioanalytical technologies are powerful analytical techniques and widely applied in clinical testing and diagnosis,environmental monitoring and food safety,owing to the portable,sensitive and low-cost advantages.Among these,electrochemical aptasensors constructed with nucleic acid aptamer（Apt）recognition elements have been widely applied over the past decade,providing high efficiency,selectivity,sensitivity,easy synthesis and specific Apt affinities compared to traditional antibodies.Consequently,an electrochemical aptasensor has been developed for the detection of PCBs in this study.In this thesis,a single PCB aptamer is used as the identification element,the aptamer was modified on different nanomaterials,and different electrochemical aptamer sensors was constructed to detect PCBs.The research content is as follow:（1）An electrochemical aptasensor based on CoxP decorated porous carbonmicrospheres and Au NRs labelled methylene blue as signal labels for sensitive detection of PCB77In this work,an ultra-sensitive,specific and simple electrochemical aptasensor was successfully manufactured based on a novel signal reduction strategy for the detection of3,3′,4,4′-tetrachlorobiphenyl（PCB77）.This aptasensor was proposed by electrodeposition of gold nanoparticles（Au NPs）on Au electrode（Au E）modified with cobalt phosphide（CoxP,a mixture of Co P and Co2P）decorated porous carbon microspheres.In this protocol,the thiolated single-complementary DNA（c DNA）was immobilized to the surface of the modified electrode via an Au-S bond.Subsequently,the gold nanorods@methylene blue connection aptamer（Au NRs@MB-Apt）signal labels were immobilized onto the modified electrode through the principle of complementary base pairing.Then,the Apt preferentially binds to PCB77,decreasing the amount of Au NRs@MB-Apt.The DPV current response was related to the PCB77 concentration.Under the optimized experimental conditions,the low detection limit of 5.9×10-2 ng/L and a wide linear range of 1.0×10-11–1.0×10-4 mg/m L（S/N=3）for PCB77 were respectively achieved.Moreover,the proposed aptasensor offered a high selectivity,stability and reproducibility,indicating the broad potential application in environmental monitoring.（2）An electrochemical aptasensor was constructed based on Ag-Cu2O/GO and Ce O2/Au Pt for detection of PCB77We constructed a signal amplification detection method based on Au Pt bimetallic nanoparticles modified cerium dioxide（Ce O2）nanocomposite.A two-step reduction method was used to prepare silver nanoparticles loaded with cuprous oxide coated graphene（Ag-Cu2O/GO）as a supporting platform.Due to the synergistic effect,Ce O2/Au Pt modified electrode exhibited enhanced electrocatalytic activity to H2O2 reduction.Then,Ce O2/Au Pt was combined with streptavidin（SA）to prepare electrochemical tracer.SA-Ce O2/Au Pt was introduced into the electrode surface capturing PCB77 aptamer through the recognition of biotin and streptavidin,which lead to a strong electrochemical signal from H2O2 reduction.When PCB77 existed in solution,the aptamer was bonded with PCB77 preferentially,and electrochemical signal reduced.The proposed approach showed a wide linear range from 10-1-104 ng/L and a low detection limit of 0.069 ng/L（S/N=3）.Meanwhile,the aptasensor showed good reproducibility,stability and selectivity,which was successfully applied for PCB77 detection in tap water and domestic sewage.（3）Ultrasensitive detection of PCB77 based on Exonuclease III-powered DNA walking machineIn view of the urgent need to determine PCBs in the environment,we report a simple and sensitive electrochemical aptasensor to detect PCB77 based on Exonuclease III-powered DNA walking machine using poly（diallyldimethylammonium chloride）（PDDA）,which was functionalized hollow porous graphitic carbon nitride/Ni-Co hollow nanoboxes/Au-Pd-Pt nanoflowers composite material.Upon the addition of PCB77,the specific binding between PCB77 and the aptamer（Apt）could trigger the Exo III-assisted cyclic amplification process and release unlocking probes to deblock the Swing arm/Blocker duplex.Finally,the hybridized hairpin 3（HP3）,a short oligonucleotide,was left on the electrode via Exo III digestion of hybridized HP2,and thus a strong methylene blue（MB）signal was obtained.As expected,the proposed aptasensor exhibits exceptional PCB77 detection performances with a very low detection limit of 5.13 pg/L and a wide linear range of 0.01-100 ng/L based on the calibration curve.Moreover,the aptasensor presents a high level of selectivity and stability,with an acceptable degree of reproducibility.The results of this study have indicated that the proposed aptasensor has great potential application prospects,as demonstrated by its successful use in real environmental water samples. |
