| Wearable sensors can perform real-time,continuous and non-invasive detection of health-related chemical biomarkers in human biological fluids,typically like sweat.It can help individuals pay attention to their health information in a more convenient and efficient way,and better meet the needs of modern society for personalized medicine.Solid-contact ion-selective electrodes(SC-ISEs)have become a significant monitoring unit in the field of wearable biosensors based on its miniaturization and integration feature.ISEs can monitor various electrolyte ions in body fluids to monitor human health state.Solid-contact ion-selective working electrodes and solid-contact reference electrodes(SC-REs)are important components of sensors.At present,most SC-ISEs are faced with the challenges of potential drift caused by interface water layer and toxic components leakage in ion-selective membrane(ISM).The existence of ISM,restricting their further development in the field of biosensors.In this paper,we propose the idea of constructing ISM-free SC-ISEs based on silver/silver insoluble salts electrodes for applying to sweat analysis sensor.In addition,a novel SC-RE based on silver/organic insoluble silver salt electrode was developed to replace the widely used Ag/Ag Cl solid reference electrode.The detailed research works are as follows:1.Solid-contact anion sensing based on classic silver/silver insoluble salts electrodes without ion-selective membraneAiming at the scarcity of anionic carrier,the defect of water layer and toxic component leakage caused by the introduction of ISM,classic metal/metal insoluble salts electrodes without an ISM offer an alternative,such as Ag(s)/Ag Cl(s)electrode.In this work,the constant current electrodeposition method was used to obtain a Ag(s)/Ag Cl(s)electrode.It was directly used for potential detection of Cl~-without modification of ISM.We first compared the two types of all-solid-state sensor electrodes of Cl~-with/without the ISM.It is found that the ISM-free Ag(s)/Ag Cl(s)electrode discloses a comparable selectivity regarding organic chloride ionophores.Additionally,the electrode exhibits better comprehensive performances(stability,reproducibility,and anti-interference ability)than the ISM-based Cl~-sensor electrode.In addition to Cl~-,other Ag(s)/Ag X(s)electrodes also work toward single and multi-valent anions sensing.Finally,a flexible sweat sensor based on ISM-free Ag(s)/Ag Cl(s)electrode was fabricated to real-time monitoring of human sweat Cl~-with satisfactory accuracy.These results indicate that silver/silver insoluble salts ISM-free sensor electrodes can be used in wearable anion sensors.2.Solid-contact reference electrode based on silver/silver organic insoluble saltThe SC-REs remains relatively less focused regarding to various improved solid-contact ion-selective work electrodes in wearable sensing.Currently,most of the SC-REs used for wearable sensors are coated with a solid electrolyte polymer membrane on the surface of Ag(s)/Ag Cl(s)electrodes.It has the risks of high concentration inorganic electrolyte leakage and so on,affecting electrode potential stability and low detection limit.Herein,we report a type of SC-RE based on the silver/silver tetraphenylborate[Ag(s)/Ag TPB(s)]organic insoluble salt electrode.The SC-RE consists of an Ag(s)substrate,a solid contact layer Ag TPB(s)and a plasticized polyvinyl chloride membrane containing the hydrophobic organic salt of tetrabutylammonium tetraphenylborate(TBATPB).The results demonstrate that the Ag(s)/Ag TPB(s)SC-RE shows a stable potential response in various electrolyte solutions(even in deionized water).On this basis,the SC-RE can also maintain potential stability in bending state under flexible substrate.Finally,the Ag(s)/Ag TPB(s)SC-RE was integrated with the above-mentioned ISM-free Ag(s)/Ag Cl(s)electrode to construct an all-solid-state flexible Cl~-sensor,realizing in-situ and real-time monitoring of Cl~–in human sweat with satisfactory accuracy. |
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