Modern directions for potentiometric sensors

This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the basic membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications

Solid-contact potentiometric polymer membrane microelectrodes for the detection of silver ions at the femtomole level

In recent years, ion-selective electrodes based on polymer membranes have been shown to exhibit detection limits that are often in the nanomolar concentration range, and thus drastically lower than traditionally accepted. Since potentiometry is less dependent on scaling laws that other established analytical techniques, their performance in confined sample volumes is explored here. Solid-contact silver-selective microelectrodes, with a sodium-selective microelectrode as a reference, were inserted into a micropipette tip used as a 50-μl sample. The observed potential stabilities, reproducibilities and detection limits were attractive and largely matched that for large 100-ml samples. This should pave the way for further experiments to detecting ultra-small total ion concentrations by potentiometry, especially when used as a transducer after an amplification step in bioanalysis

Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes

This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscalematerials

Visible Light-Induced Ion-Selective Optodes Based On A Metastable Photoacid For Cation Detection

A new platform of ion-selective optodes is presented here to detect cations under thermodynamic equilibrium via ratiometric analysis. This novel platform utilizes a \u27one of a kind\u27 visible light-induced metastable photoacid as a reference ion indicator to achieve activatable and controllable sensors. These ion-selective optodes were studied in terms of their stability, sensitivity, selectivity, and theoretical aspects

Solid Contact Potentiometric Sensors for Trace Level Measurements

A simple procedure for the development of a range of polymeric ion-selective electrodes (ISEs) with low detection limits is presented here. The electrodes were prepared by using a plasticizer-free methylmethacrylate–decylmethacrylate copolymer as membrane matrix and poly(3-octylthiophene) as intermediate layer deposited by solvent casting on gold sputtered copper electrodes as a solid inner contact. Five different electrodes were development for Ag(+), Pb(2+), Ca(2+), K(+) and I(−), with detection limits mostly in the nanomolar range. In this work the lowest detection limits reported thus far with solid contact ISEs for the detection of silver (2.0 10(−9) M), potassium (10(−7) M) and iodide (10(−8) M) are presented. The developed electrodes exhibited a good response time and excellent reproducibility

Development And Characterization Of Needle-Type Ion-Selective Microsensors For In Situ Determination Of Foliar Uptake Of Zn\u3csup\u3e2+\u3c/sup\u3e In Citrus Plants

For over a decade, the incidence of Huanglongbing (HLB) has grown at an alarming rate, affecting citrus crops worldwide. Current methods of nutrient therapy have little to no effect in alleviating symptoms of HLB, and scarce research has been put forth towards non-destructive tools for monitoring zinc transport in citrus plants. Here, we have developed and characterized a solid contact micro-ion-selective electrode (SC-μ-ISE) for the determination of zinc transport in sour orange seedlings using a non-invasive microelectrode ion flux estimation (MIFE) technique. The SC-μ-ISE displayed a 26.05±0.13 mV decade−1 Nernstian response and a LOD of (3.96±2.09)×10−7 M. Results showed a significant Zn2+ uptake in the leaves and roots of sour orange seedlings when bulk concentrations were higher than 5.99 mM. Above this concentration, a linear relationship between flux and bulk Zn2+ concentration was observed. This relationship suggests passive diffusion may be a key mechanism for Zn transport into plants. Overall, this study is the first to use a Zn2+ SC-μ-ISE for the determination of ion transport processes in plants. This novel tool can be used to further knowledge the effect of nutrient therapy and disease progression on HLB infected citrus plants