A miniaturized solid-contact potentiometric multisensor platform for determination of ionic profiles in human saliva

This paper describes a miniaturized multisensor platform (MP-ISES) consisting of electrodes: a reference one (RE) and ion-selective electrodes (ISEs) for monitoring Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and SCN⁻ ions and pH in human saliva. Gold electrode surface was modified by deposition of two layers: electrosynthesized PEDOT:PSS forming an intermediate layer, and ion-selective membrane. The developed ISEs were characterized by a wide linear range and sensitivity consistent with the Nernst model. The entire MP-ISEs are characterized by satisfactory metrological parameters demonstrating their applicability in biomedical research, in particular in measurements concerning determination of ionic profiles of saliva. Saliva samples of 18 volunteers aged from 20 to 26 participating in a month experiment had been daily collected and investigated using the MP-ISEs assigned individually to each person. Personalized profiles of ions (ionograms) in saliva, such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SCN⁻, and H⁺, were obtained.

     

Preparation of thin SnO2 layers by inorganic sol-gel process

SnO₂ sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl₄, (2) washing the precipitates with NH₄NO₃ solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO₃, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO₂ by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared.     

The computational methods in the development of a novel multianalyte calibration technique for potentiometric integrated sensors systems

In recent years, integration and miniaturization of ion-selective electrodes (ISEs) have brought many benefits resulting in the possibility of simultaneous determination of the ions concentration in small volume samples. One of the key problems related to the preparation of potentiometric integrated sensors systems (PISSs) is a calibration procedure due to the necessity to calibrate each particular sensor separately. The main aim of the research was to develop a novel calibration method for PISSs fabricated with the use of an all-solid-state technology, which has been compared with other types of sensor calibration technique. The proposed algorithm concerns the method of calibration solutions composition determination for miniature ion-selective sensors before measuring in biological samples especially human saliva samples. This article also compares the parameters of ion-selective sensors for two types of PISSs, including ISEs based on gold (Au) and glassy carbon (GC) electrodes. In addition, a series of measurements was performed using PISS with Au-ISEs in samples of human saliva, which were preceded by different types of sensor calibration and compared with the results obtained with the clinical analyzer. Moreover, the effect of the viscosity of calibration solutions on the ISE parameters and the lifetime of the sensors were investigated.

     

Highly sensitive glucose sensor based on work function changes measured by an EMOSFET

In this paper, glucose is potentiometrically measured by using a specific field effect transistor, the EMOSFET. In this device, glucose oxidase is immobilized within a bovine serum albumin matrix, using glutaraldehyde. This layer is deposited on the top of an electroactive Os-polyvinylpyridine layer containing horseradish peroxidase, which is used as the gate material of the FET. The basic principle of the sensor is to measure the glucose concentration by means of measuring the change in the work function of the electroactive gate due to its redox reaction with the H2O2, generated by the reaction between glucose and glucose oxidase. The change in the work function can be detected as a change in the threshold voltage of the FET. Moreover, a measuring mode called "constant current potentiometry" has been applied to improve the sensitivity of the sensor. The sensitivity of the sensor working in this mode is found to be much higher than the Nernstian value. The experimental results show that the detection limit of the sensor can be tuned depending on the value of the applied current and the glucose oxidase concentration in the gate.