Development And Applications Of Solid-State Polymeric Membrane Ca²⁺-Selective Electrodes

Polymeric membrane ion-selective electrodes?ISEs?have been routinely used for determination of ionic species in clinical diagnostics,process control,and environmental monitoring owning to their attractive features including low cost,reliable instrument,ease of miniaturization and integration,and resistance to color and turbid interferences.As one of the most commonly used polymeric membrane ISEs,an all-solid-state Ca²⁺-ISE has been widely used to detect Ca²⁺in various fields such as clinical diagnostics and environmental monitoring.Although all-solid-state Ca²⁺-ISEs have become a promising analytical tool,they usually suffer from several limitations.Firstly,the fabrication process of solid contact is tedious and time-consuming and nanomaterial-based solid contact is easy to fall off.Secondly,these electrodes lack of environmental compatibility and are easily affected by the lipophilic species.Lastly,the proposed electrodes can only be used to quantify calcium ions.In this thesis,three strategies are proposed to solve the above three problems.The detail contents are as follows:1.Construction of an all-solid-state polymeric membrane Ca²⁺-ISE based on a magnetic field-directed self-assembly solid contactUsually,in order to construct the all-solid-state Ca²⁺-ISEs,the multilayer drop-casting is used for fabricating solid contacts.However,the multilayer drop-casting process is somewhat complicated and time consuming.In addition,nanomaterials can easily peel off from the electrode surface owing to the poor adhesion between these nanomaterials and the surface of the electrode.By using magnetic graphene as the materials of solid contact,we develop a magnetic field directed self-assembly strategy for the preparation of all-solid-state polymeric membrane Ca²⁺-ISEs.The ISE shows a Nernstian response of 28.2 mV/decade for calcium concentration in the range from 1.0×10^-6–1.0×10^-33 M,and the limit of detection is 4.0×10^-7 M.Additionally,the magnetic graphene-based electrode shows a comparable potential stability performance to other graphene-based all-solid-state ISEs,such as reduced undesirable water layer and insensitive to the interferences of O₂,CO₂ and light.The proposed magnetic graphene-based electrode has been successfully applied for the determination of Ca²⁺in seawater.This work provides a favorable way to prepare robust solid contact for use in the field of all-solid-state ISEs.2.Development of a polydopamine modified all-solid-state polymeric membrane Ca²⁺-ISE with excellent environmental compatibilityIn many cases of practical relevance,a deterioration in the response performance and lifetime of the all-solid-state Ca²⁺-ISEs occurs when these electrodes continuously contact with environmental samples due to the lack of environmental compatibility of these electrodes.Herein,we describe a simple and robust approach for improving the environmental compatibility of all-solid-state polymeric membrane Ca²⁺-ISEs.The approach utilizes a marine mussel-inspired polydopamine polymer as a hydrophilic coating on the surface of conventional ISEs.Experiments show that there is no significant difference on the performance between polydopamine modified electrodes and unmodified electrodes.The polydopamine modified electrode shows a Nernstian response of 28.3 mV/decade for calcium concentration in the range from 1.0×10^-6–1.0×10^-3 M,and the limit of detection is 5.8×10^-7 M.When the proposed electrode contacts with a solution containing bacterial cells of 10⁸ CFU,the slope of the polydopamine-modified electrode remains unchanged within five days,while the slope of the unmodified electrode decreases by 9.8%,suggesting that the proposed hydrophilic Ca²⁺-ISE shows an improved fouling resistance.It can be expected that our approach can provide an appealing way to improving the environmental compatibility in the development of all-solid-state polymeric membrane Ca²⁺-ISEs.3.Construction of an solid-state Ca²⁺-selective electrode based on the modification of phenylboronic acid and its application in the detection of glucose in the environmentAlthough the all-solid-state polymeric membrane Ca²⁺-ISE has been used for several decade years,it is still very difficult for using such electrode to detect other species,such as neutral molecules.In this work,an ion-channel potentiometric Ca²⁺sensor is constructed by modifying the surface of polymeric membrane with benzeneboronic acid group,which is used to detect diol-based neutral species.Specific recognition between the benzeneboronic acid and diol partially blocks the current-induced Ca²⁺transfer across the membrane/aqueous sample interface,thus inducing a potential drop,which can be utilized to measure the concentration of the diol in the sample.By using glucose as a model,the proposed Ca²⁺ion channel sensor shows a stable potential response in the linear range of 3.0-15.0 mM with a detection limit of0.59 mM.This methodology may pave the way to using all-solid-state Ca²⁺-ISEs for measuring non-ionic species.