The Study On Surface Permeability Of Lysine Membrane Modified Electrode

The changes of cell membrane permeability are closely related to the cellular activities,which play an important role in the study of anticancer drugs and the field of bioelectrochemistry.Amino acids,the basic unit of protein,are a kinds of amphoteric molecules due to the presence of amino and carboxyl groups.In the recent years,amino acid modified electrodes have been widely used to study biosensing applications.In this work,lysine(C₆H₁₄N₂O₂)was assembled on the surface of glassy carbon electrodes by electrochemical oxidation method to prepare the amino acid modified electrodes.The study on the membrane permeability are performed by altering the pH of the electrolyte solution,altering the ionic strength of the electrolyte solution and altering the pinhole size of the modified membrane.Furthermorre,glutamic(C₅H₉NO₄)was assembled on the surface of glassy carbon electrodes by electrochemical oxidation method.The Glu/Pt/GCE electrode was prepared for glucose sensing,which achieved the direct electron transfer in the oxidation process.The main conclusions are as follows:(1)The correlation between the number of assembly cycle and the radius of the membrane surface was studied by electrochemical oxidation method.Experimental results show that the pinhole size of lysine membrane electrode decreases along with the increase of cyclic voltammograms scanning cycles.Electrochemical impedance spectrum results show that with the increase of scanning cycles,the electron transfer resistance of redox species on the electrode have increased,indicating a more assembly dense of the membrane in the electrochemical process.Based on the relationship between pinhole size and the surface coverage formulated by Finklea et al.,the pinhole size for the scanning cycles(4,10,14,22)are determined as 4.0674,3.0121,2.6936,1.8936 microns,respectively.(2)The surface permeability of the modified membrane electrode was studied by using cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The experimental results show that the charged state of lysine modified surface can be regulated by adjusting the pH of electrolyte solution,thus regulating the permeability of lysine modified electrode surface.Due to the different positive or negative charge at the end of the modified membrane electrode,it can affect the permeability of the surface of the modified membrane electrode.(3)As a result of the charge difference between Ca²⁺ions and COO^-ions,the ion-pair will formed between the Ca²⁺ions and COO^-ions,thus decreasing the surface potential.So,the mass transport of redox species on the modified electrode will be accelerated,inducing an enhanced permeability of the modified membrane.(4)On the modified membrane electrode with different pinhole size,we have realized the adjustment of the surface permeability by using the ion-pair method.The electron transfer rate of the redox probe is obtained through the simulation of cyclic voltammetry.It can be seen that,with the decrease of the pinhole size,the electron transfer rate of redox species on the surface is reduced.Combined with the above data,we can conclude that the permeability of the lysine modified surface decrease along with the decrease of its pinhole size.(5)The Glu/Pt/GCE electrode was prepared for glucose sensing,which achieved the direct electron transfer in the oxidation process.Compared with the Pt/GCE electrode,Glu/Pt/GCE electrode showed a higher sensitivity for glucose sensing.The mechanism of the oxidation process was also discussed:the hydrogen bonding was formed between the glucose and Glu,thus more glucose was adsorbed onto the surface.As a result,the extra active site of Pt was covered by the additional glucose,and enhancing the sensitivity of the electrode for glucose sensing.