Constructions Of Potentiometric Detection Systems Based On Calcium,Copper And Lead Ion-selective Microelectrodes And Their Applications In Environmental Analysis

Microelectrodes show the advantages of small size,fast mass transfer,low i R drop,and short response time,and have been widely used in life sciences,environmental mornitoring,and clinical diagnosis.As a classical type of electrochemical sensor,ion-selective electrodes have been developed as an ideal tool for ion analysis and potentiometric sensing.Ion-selective microelectrodes are especially promising for measuring ionic species in single-cell and sediment pore water analyses.Single cells living in the natural water bodies are ideal models for toxicological research,which could provide a theoretical basis for the physiological and toxicological effects.Changes of cellular ion concentrations are the early stage of cell toxicological effects under environmental stimuli.Compared with the patch clamp and fluorescent indication technologies for detection of cellular ions at single-cell levels,potentiometric microelectrodes have the advantages of low cost,simple operation,fast response,wide linear range,and high temporal and spatial resolutions.Therefore,the development of potentiometric microelectrodes for single-cell analysis is of great importance in terms of scientific values and application prospects for the studies of cell stress responses under environmental stimuli.The bioavailabilities and biogeochemical processes of heavy metals in coastal seawater are affected by their concentrations in sediment pore water.Therefore,it is important to measure heavy metals in pore water.The general procedures for these measurements are based on the on-the-spot extraction of the pore water combined with the subsequent laboratory chemical analysis.In recent years,the DET?diffusive equilibration in thin-film?and DGT?diffusive gradient in thin-films?techniques have been proposed for determination of heavy metals in sediment pore water.However,these techniques suffer from problems of complex and time-consuming procedures.The development of new potentiometric microelectrodes can provide a new approach for rapid,sensitive and selective detection of heavy metals in sediment pore water.Compared with conventional liquid-contact ion-selective electrodes,all-solid-state ion-selective electrodes have the advantadges of ease of miniaturize,high sensitivity and fast response.However,all-solid-state microelectrodes used for single-cell and pore water analyses are rather rare.In this work,all-solid-state ion-selective microelectrodes?IS?Es?with high sensitivities,good selectivities and stable potential responses are proposed.Their applications in single cell analysis and coastal sediments pore water detection have been explored.Under optimized conditions,the proposed potentiometric microelectrodes have been used for detection of the calcium uptake of single-celled Paramecium.The measurements of copper and lead ions in sediment pore water have also been investigated.The proposed potentiometric microelectrodes could provide a powerfull tool for single cell analysis and in-situ detection of heavy metals in sediments.The contents are as follows:1. Fabrication and characterization of a calcium ion-selective microelectrodeCalcium ion is a common element in cells,and is also an important second messenger,which is crucial to the physiological activities of cells.Compared with the fluorescent indicators,the calcium ion-selective microelectrode has the advantages of wide linear range and good selectivity.Therefore,it is an ideal tool for the detection of celluar Ca²⁺.So far,the all-solide-state calcium IS?Es are rather rare.In this study,a carbon fiber microelectrode?1-2?m in diameter?has been prepared by the flame fusion method.The microelectrode has been modified with a PEDOT?PSS?conducting film via electrodeposition,and then covered with a calcium ion-selective membrane.Thus,a calcium ion-selective carbon fiber microelectrode(Ca²⁺-IS?E)can be obtained.The potential response linear range,selectivity and reproductivity of the Ca²⁺-IS?E have been characterized.The results show that the PEDOT?PSS?film can improve the potential stability of the Ca²⁺-IS?E.The Ca²⁺-IS?E electrode exhibites a2. Fabrication and characterization of a reference microelectrodeThe fabrication and characteristics of a reference microelectrode are critical for the establishment of a micro detection system.Agarose has thermo reversible ability,which makes it sucked easily into the tip of the glass capillary tube after being melted.The agarose gel consists of bundles of agarose chains linked by hydrogen bonds.In this work,a reference microelectrode?8-10?m in diameter?has been fabricatied by using agarose gel as salt bridge.The electrochemical properties of the proposed reference microelectrode have been characterized.The result shows that the micro-reference electrode has good stability in the electrolytes with divalent and monovalent ions at different concentrations in the range of 10^-5 M-10^-1 M,in the p H range of 3-10 and at different ratios of the redox pair Fe?CN?₆^3-/Fe?CN?₆^4-.The reference microelectrode can be used for the construction of a micro-detection system.The proposed micro-reference electrode has the advantages of high stability,simple operation and easy miniaturization.3. A Ca²⁺-selective microelectrode system for detection of calcium uptake by a single Paramecium cell exposed to chlorpyrifosChlorpyrifos?CPF?is one of the organophosphate insecticide compounds and environmental stimuli for the biological systems in natural water bodies.Paramecium can be used as a single-cell model for the study of the environmental toxicological process of chlorpyrifos.So far,the toxicological effect of chlorpyrifos on Paramecium has rarely been studied.In this work,a single-cell analysis system based on a potentiometric microelectrode system combined with an inverted microscope and a micromanipulator has been established.This platform can be used to detect the results show that the presene of CPF could cause a potential decrease via uptake of calcium ions through the ion channels into the Paramecium cell,and the potential decrease increases with increase in the concentration of CPF.The CPF concentration sensitivity for Paramecium ranges from 1-5?M.4. Construction of an all-solid-state copper ion-selective microelectrode and its applications in detection of copper ions in coastal sediment pore waterThe measurements of heavy metals in sediment pore water require a high mechanical strength for the microelectrode.Therefore,an all-solid-state microelectrode?14?m in diameter?has been fabricated through the flame fused method by using a gold wire,which is denoted as Au?E.The Au?E can be electrodeposited with poly?3,4-ethylenedioxythiophene?-poly?sodium4-styrenesulfonate?and dip-coated with a copper ionophore-based ion-selective membrane to obtain an all-solid-state Cu²⁺-IS?E.The composition of the membrane has been optimized,and the potential response linear range,selectivity and conditions,the proposed all-solid-state Cu²⁺-IS?E shows a Nernstian response toward distribution profile of Cu²⁺in coastal sediment pore water with a small volume?e.g.,300?L?.The results agree with those obtained by the anodic stripping voltammetry,which indicates that the proposed potentiometric technique based on the all-solid-state IS?E is promising for detection of Cu²⁺in the coastal sediment pore water samples.Moreover,the method for the preparation of the IS?E can be extended to detect other heavy metal ions in sediments by using different ion-selective membranes.5. Construction of an all-solid-state lead ion-selective microelectrode and its applications in in-situ detection of lead ions in coastal sediment pore waterAn all-solid-state lead ion-selective microelectrode(Pb²⁺-IS?E)based on a poly?3,4-ethylenedioxythiophene?-poly?sodium 4-styrenesulfonate??PEDOT/PSS?modified gold wire with a diameter of 14?m has been fabricated.The proposed millimeter depth intervals.The Pb²⁺-IS?E shows a Nernstian response for Pb²⁺within into a coastal sediment core with a micro-manipulator,the proposed Pb²⁺-IS?E allows the direct measurement of the vertical profile of Pb²⁺in the pore water.The in-situ handling.Moreover,the detection system can be extended to assess the vertical distribution profiles of other heavy metal ions in sediment pore water by using different ion-selective microelectrodes.6. Chronopotentiometry based on an all-solid-state copper ion-selective microelectrodeFree heavy metal ions in seawater are only a very small proportion of the total dissolved heavy metals.It is highly desired to develop a microelectrode with a lower detection limit.Experiments show that the detection of trace heavy metal ions in sediments by the potentiometric microelectrode could be difficult for many samples.Chronopotentiometry based on ion-selective polymeric membranes can be used to achieve higher sensitivities,and good reversibilities.Herein,we demonstrate that chronopotentiometry based on an IS?E for heavy metal detection.Taking copper as a chronopotentiometry.The thikness of the membrane and the magnitude of the applied current have been optimized.The Cu²⁺-IS?E shows a linear response in the activity promising for sensitive analysis of heavy metal ions in coastal sediment pore water.