Implantable Electrochemical Sensor Based On Liquid/Liquid Interface For In Vivo Analysis

Chemical information obtained from the living brain is crucial for understanding the molecular mechanisms of the brain function and early diagnosis and treatment of brain diseases.Electrochemical method has great advantages in vivo analysis due to high spatial and temporal resolution,real-time in vivo,and easy miniaturization of electrodes.The most popular sensing strategies are established at solid/electrolyte interface generated by oxidation-reduction reaction.But this analytical strategy poses great challenges when faced with the detection of non-electroactive substances.Electrochemistry at the liquid/liquid interface is an effective bridge between the chemical and electrochemical sensing.The migration of charged ions at the liquid/liquid interface can generate voltammetric signals,while obtaining qualitative and quantitative information.However,the traditional liquid/liquid interface has low mechanical strength and poor interface stability,leading to the penetration of organic solvent into the rat brain easily,and making it difficult to achieve the analysis in vivo.In addition,there are many interfering substances in the brain that cause great interference.In response to these challenges,this thesis has developed two analysis strategies of K⁺in vivo based on the concept of liquid/liquid interface by reasonably selecting ionic liquids to construct solidified organic colloidal electrode interfaces with specific ionic carriers.The specific contents of research are as follows:（1）Firstly,we reasonably selected hydrophobic ionic liquids,using1-decyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide(C₁₀M)as both an organic solvent and a supporting electrolyte,and added poly（ionic liquids）to solidify the organic phase to prepare ionic liquid-colloidal microelectrode.Subsequently,a kind of potassium ion carrier was dissolved in the ionic liquid colloid.The functional ionic liquid-colloid/water interface was constructed by contacting the ionic liquid-colloidal microelectrode with aqueous solution,accelerating the migration of K⁺at the liquid/liquid interface,and establishing an analytical method for K⁺in the rat brain.The results indicated that the ionic liquid-colloidal microelectrode had a good linear response to K⁺ranging from 0.8-60 m M,with a detection limit of 0.13 m M.This electrode exhibited high selectivity in the systems rich in other interfering substances such as metal ions,anions,amino acids,and neurotransmitters.It also displayed excellent anti-biofouling ability after the continuous immersion in BSA solution for60 days,with the deviation of electrochemical signal less than 8.5%.In addition,the liquid level in the microtubule did not move and no ionic liquid colloid infiltrated into the brain after the electrode was implanted into the rat brain for continuous testing for 30 minutes,demonstrating good interfacial stability.Based on ionic liquid-colloidal microelectrodes,the detection of changes in K⁺concentration in the cerebral cortex of acute and chronic hyperkalemia rats was realized.Studies have found that acute changes in plasma K⁺concentration of acute hyperkalemia rat caused a slow increase in brain extracellular K⁺concentration of about 23.6%,while chronic hyperkalemia rat were not susceptible to the chronic change in plasma K⁺concentration.（2）Based on the above work,we further optimized the support framework of the liquid/liquid interface,and designed an electrochemical detection platform of functional ionic liquid/water interface based on hydrophobic hydrogel.The porous hydrogel was prepared by repeated freezing and thawing,and the hydrophobic coating with long alkyl chain was grafted on the hydrogel surface by amidation reaction,which successfully inhibited the material exchange between the hydrogel and the water environment.Through the hydrophobic interaction,the ionic liquid containing potassium ion carrier was filled into the internal pores of hydrogel,and then contacted with the aqueous solution to form a stable double hydrophobic interface,which further accelerated the migration of K⁺at the liquid/liquid interface.The results shown that the hydrogel could form a porous structure after repeated freezing and thawing for 6-8 times.The hydrophobic alkyl chain of stearic acid was stably grafted onto the surface of hydrogel through the amidation reaction,and ionic liquid(C₁₀M)was filled after hydrophobic treatment.Then,a stable functional ionic liquid/water interface was formed in the aqueous system.The linear range of response to K⁺was 0.2-35 m M,the detection limit was reduced by 38.5%,the sensitivity was increased by 1.96 times,and the response time was shortened by 2 minutes.In addition,the hydrogel electrode had good flexibility and biocompatibility with low Young’s modulus of 125 k Pa.It was implanted into the rat brain for 7 days without obvious tissue damage.Finally,the hydrogel electrode was successfully implanted into the brain of cerebral ischemia model rats for the real-time detection of changes of K⁺content in the hippocampus and reticular nuclei.The study found that the concentration of K⁺in the hippocampus increased from 3.3 m M to 32.1 m M,and that in the reticular nuclei increased from 2.8 m M to 25.3 m M after cerebral ischemia for 20minutes.Besides,the change in the K⁺concentration in the hippocampus was significantly faster than that in the reticular nuclei.