Development of A Flat Dry-pH-Sensor for Skin Surface pH Measurement

Recent reports suggest that skin barrier function and atopic dermatitis (AD) are related to the skin surface pH. The final aim of this study is to develop a multi-function skin measurement system for portable use, to evaluate data as pH, water content and etc. The system adopts a non-invasive measurement method of skin’s surface pH without the use of any addition of water. In previous study, we reported about a Dry-pH-sensor that consists of a platinum wire electrode and Ag/AgCl wire electrode, based on the Nerstian response. Using the Dry-pH-sensor measurement system on the skin, we found that the voltage was constantly elevated. It is unclear whether elevated response may cause skin’s water evaporation. We developed the Flat Dry-pH-sensor on the same basis of the previous one and realizing the sensor by adopting the ion-plating process. This paper describes the effects on the skin water content when measuring the skin surface pH with the Flat Dry-pH-sensor. The sensor was tested by using a standard pH solution. The correlation between pH-potential and voltage was found. All experiments were carried out on the left forearm of a male healthy subject, at room constant temperature and humidity (23°C, 30%RH). First, skin surface pH was measured for 2 min, then skin water content was measured for also 2 min; both measurements were executed in the same region of the forearm. Using the Flat Dry-pH-sensor resulted in the observation that with an elevated voltage value also the water content result was elevated, according to the time. Both the responses were analyzed by using the straight-line approximation. A negatively correlation between the sensor voltage and water content was found on the slope, also finding correlation on the intercept with the y axis. The response of the pH sensor voltage was influenced by the skin water content and the evaporation phenomenon was revealed.