Research On Miniaturized Detection Systems Based On All-solid-state Phenethylamine And Acetylcholine Ion-selective Electrodes

Neurotransmitters are important chemical signaling molecules in the nervous system.They have regulating effects on cognition,physiological activities and mental conditions.Realizing real-time and online monitoring of neurotransmitter concentrations is crucial for emotion im-provement,research on brain mechanism,treatment of mental diseases and so on.Because the secretion of neurotransmitters has the characteristics such as trace amounts,rapid and large changes in concentration when stimulated.High requirements are put forward for online detec-tion of neurotransmitters.At present,the common online detection methods include microdial-ysis and non-destructive imaging technology.These methods always perform high sensitivity and accuracy,but they are restricted with low time resolution,expensive equipment,compli-cated and professional operation.The ion-selective electrode is a typical electrochemical sensor that converts the activity or concentration of the analyte into a measurable membrane potential.It has the advantages of high sensitivity,good selectivity,rapid response and convenient oper-ation.Therefore,ion-selective electrodes have been applied in many fields,such as biological and medical determination.The traditional ion-selective electrode is a liquid-contact electrode.The existence of the internal reference electrode and the internal electrolyte solution makes it difficult to store.Besides,it is bulky and easy to be polluted.Based on the advantages and response mechanism of ion-selective electrodes,we prepared all-solid-state miniaturized detec-tion systems for phenethylamine and acetylcholine in this thesis.The systems provide a feasible method for the implantable and real-time monitoring of neurotransmitters.Based on the mechanism of traditional liquid-junction ion-selective electrodes,solid-state electrolytes were used to replace the traditional internal electrolyte solutions and internal ref-erence electrodes in this thesis.As a result,the shape and size of the electrodes are more di-verse,and they are easy to store and use.By optimizing the composition and ratio of the selec-tive membrane,the all-solid-state phenethylamine ion-selective electrodes were fabricated and tested.Then by optimizing the electropolymerization time and coating process,the needle-like all-solid-state phenethylamine selective electrode was made.The electrode based on 500μm gold wire as the conductive substrate,PEDOT:PSS conductive polymer as the ion-to-electron transduction layer and a selective membrane containing a neutral ionophore was developed.The electrode structure was changed from two-dimensional to a three-dimensional structure.The characteristics of the electrode and the application in plasma and drugs were tested,which provided the foundation for the miniaturization of the electrode.Based on the research of disc-shaped and needle-shaped electrodes,the thesis used carbon fiber as the conductive substrate.It significantly reduced the size of electrode by optimizing the preparation process.By character-izing the electrode and analyzing the characteristics,the miniaturized phenethylamine electrode showed a wide linear range,good sensitivity and anti-interference characteristics,etc..The re-covery rate of phenylethylamine is close to 100%under the condition of artificial cerebrospinal fluid as the background,indicating that the miniaturized sensor offered a fast,sensitive and convenient detection method for phenethylamine.Rely on the research on the miniaturized all-solid-state phenethylamine electrode,the miniaturized all-solid-state acetylcholine ion-selective electrode was directly prepared by op-timizing the ratio and composition of the acetycholine selective membrane.The sensitivity,detection limit,linear range,selectivity,stability,repeatability and consistency,life span and other characteristics were tested.Besides,the response characteristics of the electrode in ar-tificial cerebrospinal fluid were analyzed.The good recovery rate at a lower concentration illustrated that the electrode could be applied to acetylcholine detection in actual samples.In potentiometric detection,the reference electrode has the function of providing a sta-ble reference potential.It always requires good stability.The traditional standard reference electrode is usually a silver/silver chloride electrode or a calomel electrode,etc.,in which the presence of an internal electrolyte solution and a salt bridge makes the electrode difficult to miniaturize and store.In this thesis,based on the research of miniaturized all-solid-state neu-rotransmitters ion-selective electrodes,the miniaturized all-solid-state reference electrode was designed.The reference electrode has good anti-interference properties for different electrolyte solutions,different p H ranges,different O₂and CO₂conditions,etc..The miniaturized all-solid-state detection systems for phenethylamine and acetylcholine were constructed respectively,and the response characteristics of the miniaturized systems in homogenate were tested.They were expected to be applied to online and real-time detection of phenethylamine and acetylcholine in clinical and biological research.