Construction Of Electrochemical Aptasensor And Its Application In Melamine And Steroid Hormones Detection

Due to the progress in various areas of life,people have higher demands for their own health.In recent years,food safety,environmental pollution and disease prevention have become common concerns of researchers.Therefore,the development of fast and reliable sensing equipment has attracted more and more people’s interest.Aptamers have attracted attention in the field of electrochemical sensing due to their excellent target molecule specificity and high binding affinity.By combining the specific recognition of the aptamer and the excellent sensitivity of the electrochemical sensor,the electrochemical aptasensors have the advantages of strong specificity,good biocompatibility,small size and low cost.However,there are still some challenges,such as bad selectivity,low stability and poor conductivity,which limit their further development and application.In this paper,molecular imprinting technology was introduced into the electrochemical aptasensors to improve the specificity of the target analyte.Furthermore,we used nanomaterials to modify the electrode,which stabilize the aptamer,increasing the specific surface area and amplifying the electrical signal.The specific content is as follows:1.Gold nanoparticles were prepared by a simple sodium citrate reduction method for electrode modification to increase the surface area of the sensing platform and improve the conductivity.A molecularly imprinted polymer membrane was prepared by electropolymerization of dopamine using poly（thymidine）aptamer as functional monomer and melamine as template molecule.Finally,the template was removed with the eluent to construct a molecularly imprinted electrochemical aptasensor.After optimized a series of conditions,the detection range of this sensor for melamine was10^-12 M～10^-4 M,and the detection limit was 6.7×10^-13 M.This sensor shows good anti-interference ability,excellent selectivity and outstanding stability to melamine.It has been successfully applied to the detection of melamine in liquid milk samples with satisfactory recovery rates of 97.5%～103.4%.2.A three-dimensional imprinted network was formed on the surface of electrode by using the composite of functionalized graphene and carbon quantum dots.The functional monomer aptamer and the template molecule cortisol were adsorbed on the electrode by electrostatic adsorption.Then,the cortisol template was removed by eluent,and the molecularly imprinted electrochemical aptasensor was prepared for trace analysis of cortisol.Under the optimal conditions of the concentration of template molecule,the ratio of template to functional monomer,elution time and adsorption time,the detection range of this sensor was 10^-12 M to 10^-8 M and the detection limit was3.3×10^-13 M.Compared with other reported methods,the results are satisfactory.Besides,it has been successfully applied to the determination of cortisol in actual saliva samples,the recovery rates range from 98.6%to 105.4%.3.Molybdenum disulfide was combined with carboxylated multi-walled carbon nanotubes to increase the number of immobilized aptamers on the electrode surface.The template molecule progesterone and the dual functional monomer pyrrole and aptamer were imprinted on the electrode surface by a simple electropolymerization method.The modification of the composite material increased the electrical signal of the sensor and the use of dual functional monomer benefited to improve the sensitivity and stability of the molecularly imprinted electrochemical aptasensor.Under the optimized conditions,the linear range of this sensor was 10^-11 M～10^-7 M,and the detection limit was 1.8×10^-12 M.It has been successfully used to detect progesterone in tap water with satisfactory results.