The Electrochemical DNA Biosensor Based On MOFs And Au/Ag Nanomaterials

For the fabrication of electrochemical DNA sensors,the recognition element and the electrochemical signal are mainly considered.In recent years,the emergence of DNAzyme,aptamer and base mismatch provided the recognition elements with the strong recognition ability,simple structure and high stablity for the identification of heavy metal ions and tumor markers.Metal-organic frameworks?MOFs?are often applied in the energy storage and sensors because of their large specific surface area and rich and ordered catalytic active sites.Au and Ag or bimetallic nanoparticles?Au/Ag NPs?have excellent electrical conductivity and biocompatibility,but small-size Au/Ag NPs are difficult to be applied lonely and often need a carrier to support.In this paper,DNAzyme,aptamer and DNA rich in thymine?T?as the recognition elements,and MOFs and Au/Ag NPs as the electrocatalysts,four electrochemical DNA sensors were constructed for the detection of heavy metal ions and carcinoembryonic antigen?CEA?with the satisfactory results.The main work is as follows:?1?For the fabrication of the electrochemical DNA sensor to detect Pb²⁺,the carboxyl functionalized graphene?CFGR-COOH?with the good conductivity was chosen as the electrode modifier to immobilize 8-17 DNAzyme containing terminal amino groups for the specific recognition with Pb²⁺.Then Fe-MIL-101 with the catalytic center of Fe³⁺was combined on the surface of the modified electrode through the biological recognition between streptavidin?SA?and biotin,where Fe-MIL-101 was applied as the electrocatalyst to catalyze the electrochemical reaction of H₂O₂ and the electrochemical signal of H₂O₂ was the detection signal of the electrochemical DNA sensor.The fabrication process was characterized by the cyclic voltammetry?CV?,differential pulse voltammetry?DPV?and electrochemical impedance spectroscopy?EIS?.The detection of Pb²⁺was determined by CV.The experimental results showed that the electrochemical DNA sensor exhibited a wide linear range(1.0×10^-131.0×10^-7 mol·L^-1)and low detection limit(1.4×10^-14 mol·L^-1),which could be applied for the actual detection of Pb²⁺in the tap water and lake water.?2?Based on Au/Ag NPs@Fe-MIL-101 and aptamers,two electrochemical DNA sensors were constructed for detecting Pb²⁺and CEA,respectively.For the electrochemical DNA sensor to detect Pb²⁺,CFGR-COOH was used to fix the Pb²⁺aptamer with carboxyl groups at the end.And Au/Ag NPs@Fe-MIL-101 was immobilized on the electrode surface through the auxiliary DNA chain with thiol at the end and applied as the electrocatalyst to catalyze the electrochemical reaction of H2O2.The oxide current of H2O2 was employed as the detection signal.In order to further develop the application of Au/Ag NPs@Fe-MIL-101 composites,Au/Ag NPs@Fe-MIL-101 was chosen to modify electrode for immobilizing the stem-loop CEA aptamer with mercapto at the end.This electrochemical DNA sensor was used to detect CEA.The electrochemical technologies such as CV,DPV and EIS were used to study the fabrication process and the detection of Pb²⁺and CEA.These two sensors had wide linear ranges for Pb²⁺and CEA(1.0×10^-141.0×10^-99 mol·L^-1 for Pb²⁺and0.0001⁵0 ng·mL^-1 for CEA)and lower detection limits(1.28×10^-1515 mol·L^-1 for Pb²⁺and 0.012 fg·mL^-1 for CEA).?3?To further explore the applications of metal nanoparticles,two-dimensional MoSe2 was employed to modify the electrode and then Au nanoparticles?Au NPs?was deposited on the MoSe2 modified electrode,and the obtained electrode was named as Au NPs@MoSe2/GCE.Then DNA chain with rich T and thiol in the end was immobilized on the Au NPs@MoSe2/GCE surface through Au-S bond and the electrochemical DNA sensor based on the T-Hg²⁺-T mismatch structure was fabricated.The electrochenmical reaction of methylene blue?MB?at the end of DNA chain was employed as the electrochemical signal to indirectly detect Hg²⁺.The experimental results showed that the detection range of the sensor to Hg²⁺was1.0×10^-71.0×10^-16 mol·L^-1 and the detection limit was as low as 1.12×10^-17 mol·L^-1.The sensor also could be used for the detection of real samples.