Surface Effects in Measurements of Blood Electrolytes By Ion-Sensors
Authors: Lewenstam Andrzej 
Published: February 2020

The main blood electrolytes (Na+, K+, Cl-, and HCO3
-), pH and PCO2 belong to the most frequently requested tests in routine clinical laboratory [1]. These parameters are measured potentiometrically by ion-sensors located in high throughput random access analyzers. To comply with the demands of a hospital laboratory (e.g. automation, reliability, traceability), medical doctors (e.g. sample volume) and/or business units (e.g. cost per test) ion-sensors have to be continually developed. For the researchers this means a call for improved and manageable response time, selectivity, enhanced life time as well as a request for designing maintenance free integrated sensors that allow for direct measurement in a short time and in a small sample volume.

The lecture will refer to above challenges and emphasize how addressing the surface effects and interfacial processes may contribute in facilitating application of ion-sensors. Two sensor surfaces will be considered: the surface in contact with blood/urine sample and the surface acting as the internal contact, and accordingly two strategies will be presented. The theoretical, based on coupled Nernst-Planck-Poisson model [2], which inspects the interfacial processes and allows benefiting of short-time non-equilibrium response. The empirical, called “solid-contact” strategy [3], in which owing to application conducting polymers or nanostructures, maintenance-free sensors are designed and applied in biomedical analysis.
The main blood electrolytes (Na+, K+, Cl-, and HCO3
-), pH and PCO2belong to the most frequently requested tests in routine clinical laboratory work [1]. These parameters are measured potentiometrically by ion-sensors located in high throughput random access analyzers. To comply with the demands of hospital laboratories (e.g. automation, reliability, traceability), medical doctors (e.g. sample volume) and/or business units (e.g. cost per test), ion-sensors have to be continually developed. For researchers, such demands call for improved and manageable response time, selectivity, and enhanced life time, as well as the need to design maintenance-free integrated sensors that allow for direct measurement in a short time and in a small sample volume.
The lecture addresses these challenges and emphasizes how the surface effects and interfacial processes may contribute to facilitating the application of ion-sensors. Two sensor surfaces will be considered: the surface in contact with the blood/urine sample and the surface acting as the internal contact, and accordingly two strategies will be presented. The first is a theoretical strategy based on the coupled Nernst-Planck-Poisson model [2], which inspects the interfacial processes and provides the benefit of a short-time non-equilibrium response. The second is an empirical one, called “solid-contact” strategy [3], in which owing to the application's conducting polymers or nanostructures, maintenance-free sensors are designed and applied in biomedical analysis.

References

[1] A. Lewenstam, Clinical analysis of blood gases and electrolytes by ion-sensitive sensors, in: S. Alegret, A. Merkoci (eds.), Electrochemical Sensor Analysis (Comprehensive Analytical Chemistry vol. 49), Chapter 1, Elsevier, Amsterdam 2007.
[2] A. Lewenstam, J. Solid State Electrochem., 15 (2011) 15.
[3] A. Lewenstam, in: G. Inzelt, A. Lewenstam, F. Scholz (Eds.), Handbook of Reference Electrodes, Springer, Heidelberg New York Dordrecht London, 2013, pp. 279-288.