Solid-state pH ultramicrosensor based on a tungstic oxide film fabricated on a tungsten nanoelectrode and its application to the study of endothelial cells

In this paper, preparation of a novel pH ultramicrosensor and its physiological application has been discussed. A tungsten nanoelectrode was produced by an etching method in 0.1 mol/l NaOH solution at the potential of +0.4 V (versus Ag/AgCl reference electrode) for about 100 s and the diameters ranged from 500 to 800 nm. The pH ultramicrosensor was fabricated by producing WO₃ at W nanoelectrode surface by electrooxidation in 2.0 mol/l H₂SO₄ solution between 1.0 and 2.0 V. At last, Nafion was coated on the surface of WO₃ to protect the pH ultramicrosensor. The W/WO₃ pH ultramicrosensor exhibited a good pH linear region from 2.0 to 12.0 with a super-Nernstian slope of −53.5 ± 0.5 mV/pH unit. Response times ranged from 3 s at about pH 6.0-7.0 up to 15 s at high pH. An interference of various ions to the pH measurement was also studied in this paper. We also studied the lifetime, stability and reproducibility of the W/WO₃ pH ultramicrosensor. In order to testing the performance of W/WO₃ ultramicrosensor, we applied it to measure the extracellular pH values and a pH variation was also given about the normal, damaged and recovery endothelial cells.