Solid-state potentiometric biosensors for pH quantification in biological samples

This paper reports on manufacturing and characterization of an all-solid-state potentiometric sensor aimed at monitoring pH in dialysate or blood plasma for patients who undergo dialysis. The sensing polymer-based membrane, coated on top of the Au working electrodes, contains a polymer matrix - poly(vinyl chloride), octadecyl isonicotinate as sensor molecule, plasticizer bis(2-ethyl hexyl) sebacate, and potassium-tetrakis(4-chlorophenyl) borate. The sensor was first calibrated over a wider pH interval, i.e. 5.0 - 9.0, and then for a pH interval which overlaps with the physiological pH, i.e. 7.0 - 8.0, followed by tests in human blood plasma. The response of the sensor is linear over the studied pH range, with a lifetime of two weeks and an accuracy of ~ 0.08 pH. The response of the sensor is influenced by the storage conditions, and tests with sensors stored dry prior to potential measurements in buffers show that the sensor needs a few hours to reach an equilibrium, as opposed to seconds for the sensors stored in pH buffers prior to data collection. Monitoring the potential for 18 h continuously shows that the sensor does not drift. Toxicity and leaching of components from the sensor membrane into the liquid environment around it were studied, and determined which components were selected to further develop the pH sensor.