pH and Temperature Sensor Platform for Detecting Inflammation at Specific Sites in the Oral Cavity

Abstract

Our goal is to make electrochemical sensors for measuring oral fluids and tissues to aid in more accurate diagnosis and monitoring of oral diseases. In this work, we developed a sensor platform capable of measuring simultaneously pH and temperature for detecting inflammation at specific sites in the mouth. Miniaturized, planar pH sensing and reference electrodes were combined on a flexible polymer platform along with a platinum resistance temperature detector (RTD) using a combination of microfabrication and electrodeposition techniques. The resistance of the platinum RTD was linear between 20 and 60 °C, with a precision of ±0.1 °C. The pH response and reproducibility of sputtered iridium oxide (IrOx) was compared with those of electrochemically deposited IrOx. The voltage of the pH sensor was measured in solutions of varying pH, chloride concentration, and temperature mimicking the oral environment. At room temperature, sputtered IrOx sensors exhibited a linear response (-47 to -55 mV/pH) for pH 2-10 whereas electrodeposited IrOx was linear (-72 to -82 mV/pH) over pH 4-8, which is within the range expected in the oral cavity. The sensitivity of the sputtered IrOx was more reproducible between individual sensors than electrochemically deposited IrOx; however, sputtered IrOx electrodes were more difficult to fabricate and had a lower sensitivity to pH. Voltage stabilized (within 1-2 mV) in 10-120 s and reached 90 % of this stable value within 5 s at each pH value. The electrodeposited Ag/AgCl reference responded linearly to [Cl-] as well asvaried by <2 mV over pH 4-8. Repetitions of reproducible sensors at one pH were ≈0.1 pH unit. Preliminary measurements indicated that pH sensitivity of the IrOx sensors was ≈0.1 mV/pH/°C, producing an apparent change of ≈0.2 pH between room temperature (21 °C) and the mouth (35 °C); therefore, the voltage will need to be calibrated based on temperature.