Tissue pH electrodes for clinical applications

Abstract

The reduction of peripheral blood flow, which occurs during shock or in patients with occlusive arterial disease of the lower limb is accompanied by an increase in hydrogen ion activity in tissue cells. If this change could be measured, it could possibly be used as an indicator of tissue perfusion in such patients. Investigations have been carried out into various pH microelectrode designs in order to construct one which could be used clinically to measure extracellular pH changes in skin. Experiments with antimony and externally insulated glass micro-electrodes demonstrated that these were unsatisfactory for the purpose. The successful design was insulated internally by means of a glass to glass fuse. It was robust, stable, sensitive and had a fast response time. Use of the electrode in normal volunteers produced reproducible skin pH values and demonstrated the feasibility of the system. Preliminary results using the micro-electrodes in patients indicate their possible application to the assessment of peripheral vascular disease, and to the monitoring of patients under intensive care.

A sprayed graphene transistor platform for rapid and low-cost chemical sensing

“…A linear fit of the Dirac point values (red dashed line) reveals a sensitivity of 25.8 ± 0.5 mV per pH, over a linear range of pH 11 to pH 3. This sensitivity is below the theoretical maximum predicted by the Nernst eqn (59.16 mV per pH) 87 and is higher than that observed for graphene pH sensors prepared by alternative graphene fabrication techniques such as CVD-grown graphene on SiO 2 (21–22 mV per pH), 88 suspended graphene (17 mV per pH), 89 epitaxial graphene on silicon carbide (19 mV per pH) 90 and mechanically exfoliated graphene on SiO 2 (20 mV per pH), 91 and within the same order of magnitude for reduced graphene oxide (rGO) based devices (29–40 mV per pH). 92,93…”

Physiological monitoring of tissue pH: In vitro characterisation and in vivo validation of a quinone-modified carbon paste electrode

“…The ionic strength of the solutions was calculated using Equation (6), where z is the charge and c represents the concentration of the ions. Using this Equation, the ionic strength of the PBS was altered to give ionic strengths of 0.46 M, 0.92 M and 0.23 M and the sensitivities compared.…”

“…The presence of lactate contributes to an increase in H þ ion activity, which is proportional to a decrease in pH. Thus, pH can be used as an indication of a reduction of tissue perfusion [6,7,9].…”