Solid-State Ion-Selective Electrode Arrays

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Prospects of second generation artificial intelligence tools in calibration of chemical sensors

Multivariate data driven calibration models with neural networks (NNs) are developed for binary (Cu++ and Ca++) and quaternary (K+, Ca++, NO3- and Cl-) ion-selective electrode (ISE) data. The response profiles of ISEs with concentrations are non-linear and sub-Nernstian. This task represents function approximation of multi-variate, multi-response, correlated, non-linear data with unknown noise structure i.e. multi-component calibration/prediction in chemometric parlance. Radial distribution function (RBF) and Fuzzy-ARTMAP-NN models implemented in the software packages, TRAJAN and Professional II, are employed for the calibration. The optimum NN models reported are based on residuals in concentration space. Being a data driven information technology, NN does not require a model, prior- or posterior- distribution of data or noise structure. Missing information, spikes or newer trends in different concentration ranges can be modeled through novelty detection. Two simulated data sets generated from mathematical functions are modeled as a function of number of data points and network parameters like number of neurons and nearest neighbors. The success of RBF and Fuzzy-ARTMAP-NNs to develop adequate calibration models for experimental data and function approximation models for more complex simulated data sets ensures AI2 (artificial intelligence, 2nd generation) as a promising technology in quantitation.

Array of potentiometric sensors for the analysis of creatinine in urine samples

The development of potentiometric biosensors for creatinine based on creatinine iminohydrolase (E.C. 3.5.4.21) immobilized on chitosan membranes coupled to a nonactin based ammonium ion selective electrode is described. The response characteristics of three types of biosensors with the enzyme immobilized by three different procedures were evaluated. The biosensors with better response characteristics were obtained by coupling the ammonium ion selective electrodes to chitosan membranes with the enzyme immobilized by adsorption. The linear response range of these biosensors to creatinine was 10(-4) to 10(-2) M, the response time was between 30 and 60 s, they showed an operational lifetime of 44 days and the slope of the response to creatinine in the first day varied between 50 and 52 mV decade-1. An array of six potentiometric sensors, constituted by two creatinine biosensors and four ion selective electrodes for potassium, sodium, ammonium and calcium was calibrated and a multivariate model based on PLS1 for the response to creatinine was obtained and validated. The array was used for the analysis of creatinine in urine samples and the results were compared with the results of a clinical analysis laboratory, based on the Jaffé reaction.

Swelling and delamination of multi-electrode sensor arrays studied by variable-pressure scanning electron microscopy

Multi-electrode sensor arrays are made of soft and wet materials not easily examined by most microscopic techniques. In this paper, we have demonstrated that low-vacuum scanning electron microscopy (LVSEM) and energy-dispersive X-ray analysis (EDX) are adequate for studying the hydration, swelling, and possible delamination of multi-electrode sensor arrays. We found that the LVSEM environment had no detectable effect on the morphology of Na(+), K(+), and Ca(++) sensors, and EDX analysis indicated that all three membranes have similar compositions. However, once hydrated, the sensors exhibited different behaviors. The K(+) and Ca(++) sensors swelled more than the Na(+) sensor did. This swelling is due principally to water sorption in the membrane. We believe that the larger thickness of the K(+) and Ca(++) membrane is partly responsible for the observed swelling effect. A simple Griffith analysis of the interface rupture confirms the experimental evidence that these thicker membranes also are more prone to delamination failure.