Design The Modification Process Exploration Of Glassy Carbon Electrode Based On Aptamer For The Detection Of VD₃

Vitamin D₃ is a sunshine vitamin required by the body for various physiological activities.Deficiency of vitamin D₃ can cause dental diseases,sarcopenia,osteoporosis,depression,type 2 diabetes and cancer.Additionally,elevated levels of vitamin D₃ can result in numerous infirmities such as anorexia,irregular heartbeat,hypercalcemia and fatigue.Hence,a periodic detection can help maintain an appropriate level of vitamin D₃ in vivo.Conventional techniques used for the detection of vitamin D₃ are expensive,time consuming,require skilled work force and a specialised laboratory.Herein,we reported a portable electrochemical aptasensor for the detection of vitamin D₃.Due to the good conductivity,high selectivity,accurate sensitivity,economical and practical,portable and easy to detect in real time,electrochemical bioelectrodes have quite common applications in many fields.Nucleic acid aptamers are single-stranded DNA or RNA with high affinity,selectivity and specificity that can bind to target molecules,selected by the Systematic Evolution of Exponentially Enriched Ligands（SELEX）technique,which has many advantages over antibodies.Over time,the unique binding ability between nucleic acid aptamers and their targets has become a hot topic of research for many scientists.Vitamin D₃ is mainly stored in human body in the form of 25-hydroxyvitamin D₃.In this dissertation,novel label-free electrochemical aptamer biosensors with hexacyanoferrate as redox electrochemical probes were developed based on 25-Hydroxyvita Min D₃.The properties and application of these biosensors were discussed.The details are as follows:（1）A novel electrochemical aptamer sensor for the determination of VD₃ based on graphene modified glassy carbon electrode.Graphene oxide was reduced to graphene on line by electrochemical method,which overcame the disadvantages that the preparation of procedure drop coating was unstable and easy to fall off.The VD₃ aptamer DNA was immobilized on the graphene modified electrode through the interaction with graphene to prepare the VD₃ electrochemical aptamer sensor.With ferricyanide-ferrocyanide（1:1）as the electrochemical probe,quantitative determination of different concentration of VD₃ was used by differential pulse voltammetry（DPV）through the bonding of aptamer with VD₃induced the different blocking of the electron transfer of[Fe（CN）6]3-/4-.The results showed that the peak currents linearly correlated with the VD₃concentration over a linear range of 0.5 n M to 500 n M.The standard curve of progesterone in the fetal bovine serum matrix was:?I=31.091*lg C_VD+25.123（R²=0.9776）.（2）The sensor based on a nanocomposite was consisted of reduced graphene oxide（r GO）and the conducting poly（3,4-ethylenedioxythiophene）（PEDOT）.The PEDOT/r GO interface was prepared by electrochemical polymerization of EDOT using graphene oxide as the dopant which is later electrochemically reduced to form r GO.Then the specific aptamer was covalently modified on the composite PEDOT/r GO with large surface area.A highly sensitive and selective detection of VD₃ was achieved by DPV.The detection range was from 0.5n M to 750 n M,the standard curve of progesterone in the fetal bovine serum matrix was:?I=23.002*lg C_VD+28.839（R²=0.9807）.（3）To enhance the stability of the electrochemical biosensor,gold nanoparticles were electrodeposited on the surface of glassy carbon electrode before nickel hexacyanoferrate electrodeposition in order to enhance the electron-transfer,with gold nanoparticles as the immobilization matrix for the aptamer,the VD₃ aptamer was immobilized on the electrode surface.The electrochemical behavior of the aptamer biosensor was investigated by DPV.The biosensor showed a good linear range of 1.0 n M～1000 n M for VD₃,with a detection limit of 1.0 n M.The standard curve of progesterone in the fetal bovine serum matrix was:?I=36.418*lg C_VD+17.477（R²=0.9696）.Overall,the fabracation and optimization of glassy carbon electrode based on aptamer for the detection of VD₃ were carried out in this study.The biosensors developed showed a desired linearity and sensitivity for the quantification of 25-Hydroxyvita Min D₃ in fetal bovine serum matrix,which have the great potential to be a portable VD₃ diagnostic device for rapid detection.