Electrochemical tape-and-paper-based sensors suitable for oral pH measurements

Abstract

Low oral pH (<5.5) has been shown to play an important role in dental erosion. The measurement of oral pH can be useful in preventative care, in aiding the dental caregiver in determining the likeliness of future dental cavities. The measurement of oral pH has become a popular area of research in an effort to develop a more quantitative method for the diagnosis of dental caries. We are developing an electrochemical tape-and-paper-based pH sensor for future applications in oral pH measurements. These tape-and-paper-based devices are low-cost, easy to fabricate, sterilizable, disposable and portable. The presence of intrinsic material defects of the painted graphite electrode generates oxo-groups which are electroactive. Some of these electroactive species, such as quinone, are pH-dependent and allow for the measurement of pH using cyclic voltammetry. There is shift in the potential of the redox peaks corresponding to the sensing species that can be correlated with the pH of a sample. We optimized the assay with a conditioning oxidative potential pre-treatment step and an ionic adjuster to carry out the pH measurements. We characterized the devices in different buffer solutions, as well as commercial pH standards and establish calibration curves. The reproducibility of the electrochemical response of the devices was also successfully across multiple devices and users. Their shelf-life was demonstrated to be at least three months. The devices successfully measured the pH of beverage and mouthwash, and different formulations of artificial saliva. Their performance in the presence bacteria and in growth media was assessed. Some complex matrices such as growth media required some additional optimization. Towards this objective we fabricated and tested devices with various formulations of carbon paste for the painted working electrode. These flexible tape-and-paper-based devices are promising sensors for pH measurements in oral samples and potentially even for in vivo and in situ pH measurements.