Design Of Surface Structure Of Glass Carbon Electrodes For Tuning Electrochemical Sensing Properties

Physiologically active substances can directly or indirectly participate in the physiological and pathological processes of the central nervous system(CNS).Therefore,it is of great significance to establish a method for real-time detection and monitoring of physiological active substances level in vitro and in vivo,from the perspective of gaining a greater understanding of pathogenesis to developing diagnostic and therapeutic tools.However,the complexity of the CNS gives rise to great challenges to make high selective analysis of these neurochemicals.Electrochemical sensing technology has great potential in the field of life science due to its combined advantages of high sensitivity,high spatial resolution and easy to implement real-time sensing.Above all,the surface structure of electrode is the key element to control and determine its electrochemical sensing properties.It is vital to futher to explore the surface structure of carbon materials,and the chemical and physical properties of carbon materials is largrly influenced by the species in carbon which can affect the carbon electrode electrochemical stability,catalytic activity and absorption capacity.This study is expected to establish and develop new principles and methods for detecting physiological molecules on the basis of exploring the relationship between electrode surface structure and its electrocatalytic performance.The main work can be summarized as follows:First,the surface modification was carried out by electrochemically oxidizing at a constant potential of +1.3 V(vs.SCE)for a while in different electrolyte precursors(0.1M ammonium carbamate,ammonium sulfamate,amino acids,phosphate buffer solution with different pH and sodium hydroxide solution solution)to covalently bond different functional groups to the electrode surface such as amino,sulfonic acid,carboxyl and other oxygen-containing functional groups.All these modifications were metal-free,cheap,and facile compared to other carbon-based materials and composites used for electroanalysis.We characterized chemical composition and electrochemical properties of functionalized electrode surface by XPS and several electrochemical techniques,as well as compared and assessed their electrochemical properties comprehensively.Second,ascorbic acid(AA),dopamine(DA)and 3,4-dihydroxyphenylacetic acid(DOPAC)were used as electrochemical probes to evaluate the electrochemical biosensing properties of functionalized electrodes.Through research,we drawed the conclusions:Under physiological conditions,aminated GCE(Am-GCE)was a superior sensor to detect AA in presence of DA.Sulfonated GCE(S-GCE)enabled the simultaneous detection of AA and DA significantly enhancing the sensitivity of DA.DOPAC signal was observed to decrease at S-GCE,which ascribed to the sulfonic acid groups acting as a physical barrier and electrostatically repelling DOPAC,with the result that DOPAC had a lower diffusion rate than DA.Carboxylated GCEs(such as Gly-GCE and other amino acid modified GCE)can be used for the determination of DA in presence of AA within weak acid pH.The surface structure and electrocatalytic performance of functionalized electrodes electrografted with different pH phosphate buffer solution(PBS)and sodium hydroxide solution showed significant differences.Modification of GCE with PBS(pH 7.0)enabled the simultaneous detection of AA and DA significantly enhanced sensitivity of DA at PBS 7.0-GCE.GCE electrografted with sodium hydroxide solution exhibited highly electrocatalytic activity to the oxidation DA and AA.NaOH-GCE provided higher selectivity in voltammetric measurement of DA in presence of excess AA.PBS 4.5-GCE had very effective repelling properties for anionic AA and DOPAC with preferential attraction for cationic DA,which could be used for determination of DA in the presence of excess AA.Moreover,it was found that DA signal decreased as the pH of the electrolyte was increased.Futher exploration is needed to gain a better knowledge of the mechanisms and causes.These electro-grafting pretreatments introduce or alter the nature of functional groups on the electrode surface and that such groups might serve as mediators of electrons between the electrode and the electroactive species.With their low cost and easy to preparation,the functionalized electrodes appear to be of great utility for further sensor development and show great promise for the related physiological and pathological studies.