Detection Of Di-2-ethylhexyl Phthalate By A Three-dimensional Graphene-loaded In Situ Probe Electrochemical Aptamer Sensor

Phthalates(PAEs)are often used as industrial plasticizers for the softening of PVC materials.They have stable chemical properties and are extremely difficult to degrade in natural environments.Due to the frequent use of PVC materials,a large amount of PAEs are enriched in the natural environment,posing a serious threat to human health and the environment.Therefore,establishing a simple,reliable,and highly sensitive analytical method for the accurate detection of PAEs enriched in the environment is of great significance.Electrochemical methods have attracted much attention due to their high sensitivity,simple operation,and low cost.However,PAEs are electrochemical inert molecules that are difficult to detect by direct electrochemical oxidation.In recent years,electrochemical sensors based on molecular imprinting and antibodies have received widespread attention in the detection of PAEs.However,electrochemical sensors based on molecular imprinting have the disadvantages of incomplete removal of template molecules and slow reaction kinetics;Antibody-based sensors are greatly affected by external environment and have poor stability.Aptamer is a kind of short chain nucleotide sequences that is similar to antibodies,and they have advantages over antibodies,such as small size,easy synthesis,easy modification,and good stability.Therefore,electrochemical aptasensor by combining aptamer with specific recognition ability with highly sensitive electrochemical technique is an effective method for the efficient detection of di-2-ethylhexyl phthalate(DEHP).However,how to convert the binding behavior between the aptamer and the target into detectable signals is the key to improving the analytical performance of the sensor.Currently,the most commonly used method is to label the aptamer with electrically active substances or add electrically active substances to the test system.However,the former may destroy the binding ability of aptamer to its target,while the latter may cause false positive signals,thereby affecting the accuracy of the detection.Therefore,introducing in situ signal probes into the construction of electrochemical sensing platforms can effectively overcome the above shortcomings.In this thesis,using three-dimensional graphene loaded in situ probes as the substrate material,the anti-DEHP aptamer was introduced to the surface of the in situ probe material,and different label-free aptamer-based electrochemical sensing platforms were constructed to achieve the detection of DEHP.Specifically,the following research contents are included:(1)An electrochemical aptasensor was prepared based on in situ probe thionine loaded on three-dimensional graphene hybrids for high selectivity detection of DEHP.Thionine loaded on three-dimensional reduced graphene oxide(Thi-3D r GO)hybrids were synthesized by combining Thionine(Thi)with three-dimensional reduced graphene oxide(3D r GO)via a simple covalent bonding method.Thi has good redox properties and good stability,and can be used as an in situ probe.Due to its special three-dimensional structure,3D r GO has a large surface area and good electrical conductivity.The combination of 3D r GO and Thi not only greatly improves the electrical conductivity of hybrids,but also provides a good adhesion environment for anchoring of aptamer molecules due to the rich functional groups on its surface.A labelfree electrochemical aptasensor for detecting DEHP was constructed by combining amino-modified DEHP aptamers with surface carboxylated Thi-3D r GO hybrids via covalent bonds.The electrochemical sensing platform has high selectivity and sensitivity for the detection of DEHP with a detection linear range of 0.01 ng/L～10 ng/L and a minimum detection limit of 0.001 ng/L.At the same time,the electrochemical sensing platform was used to detect DEHP in actual environmental samples,and satisfactory analytical results were obtained.(2)An electrochemical aptasensor based on in situ probe nickel ferricyanide loaded on 3D r GO hybrid nanomaterials was constructed for high selectivity detection of DEHP.Nickel-iron cyanide nanoparticles-3D r GO hybrids were synthesized for the first time by load of nickel-iron cyanide nanoparticles(Ni HCF NPs)on 3D r GO using in situ co-deposition method.Among them,Ni HCF NPs can be used as in situ signal indicating probes due to good reversibility and stability,and 3D r GO has larger specific surface area and better electrical conductivity due to its special 3D structure,which can not only improve the electrical conductivity of Ni HCF NPs well,but also greatly increase the loading of Ni HCF NPs.The label-free electrochemical sensing platform for the detection of DEHP was constructed by the immobilization of amino acid-ternal aptamer on Ni HCF NPs-3D r GO hybrids.The electrochemical sensing platform has high selectivity and sensitivity for the detection of DEHP with a linear range of 0.01ng/L～1000 ng/L and a minimum detection limit of 3.64 pg/L.