A Comparison of Three Electrodes for the Measurement of pH in Small Volumes

Abstract

An ion-sensitive field effect transistor (ISFET, Sentron®, Sentron, Inc.) electrode was compared with a glass combination micro-electrode (MI-410, Micro-electrodes, Inc.) and a solid-state metal wire oxide pH sensor (Beetrode®, World Precision Instruments, Inc.) with a liquid junction reference electrode (MERE1, World Precision Instruments, Inc.). The electrodes were assessed for linearity, reproducibility, accuracy, drift from the initial calibration between pH 4 and pH 7 and the time taken to record a stable reading. The ISFET was used to determine the pH in dental plaque samples (1 mg suspended in 20 µl). The pH values correlated with the hydrogen ion concentration for all the electrodes (r = 0.98). The M1-410 fractured before this evaluation was completed. Coefficients of variation were 0.65% (pH 4) and 0.08% (pH 7) for the ISFET and 4.69% (pH 4) and 3.46% (pH 7) for the Beetrode. Both electrodes gave readings that differed significantly from the initial calibration, but the drift was greater for the Beetrode (F = 7.93; p = 0.0005) than the ISFET (F = 1.89; p = 0.1519). However, this drift was smaller than the change in pH as measured in dental plaque samples. The Beetrode gave a stable reading after 3.39 ± 0.83 s and the ISFET after 2.2 ± 0.76 s, while the MI-410 required at least 20 s. The ISFET type electrode is suitable for use in small volumes such as plaque suspensions, is easier to operate and yields results closer to the initial calibration than the Beetrode and is more robust than the MI-410 and the Beetrode.

Depth Penetration and Detection of pH Gradients in Biofilms by Two-Photon Excitation Microscopy

“…In-dwelling electrodes have been used to measure the pH at the base of biofilms developing on teeth. Such electrodes are often larger than microelectrodes (34), and the assumption that biofilm develops on the electrode in a manner similar to that on the surrounding tooth surface is made. In the case of in-dwelling (telemetric) electrodes, although studies indicate a correlation between pH values determined following plaque sampling and from in-dwelling electrodes (19), this approach has been questioned more recently (1).…”

Investigating Acid Production by Streptococcus mutans with a Surface-Displayed pH-Sensitive Green Fluorescent Protein

“…In-dwelling electrodes were used to measure the pH at the base of biofilms developed on teeth [5], but their size limited the ability to accurately detect spatial pH changes in the microenvironment of oral biofilms. Micro-touch electrodes that have been employed for several biological systems [6], [7] exhibited similar limitations due to their tip size [8].…”

The clinical application of surface pH measurements to longitudinally assess white spot enamel lesions

“…This study sought to use an Ion Sensitive Field Effect Transistor (ISFET) pH probe [11][12][13][14] to measure the surface pH of WSEL and the sound enamel surrounding it with the prior removal of the overlying plaque. This pH probe has been used previously to examine the pH of arrested and active dentine caries in vitro and validated against a pH imaging microscope.…”