Optimization of Polyaniline based Flexible pH Sensor for Diabetic Wound Sensing

pH is a very important parameter for many different applications where the acidic or basic nature of the media can affect the outcomes. One such application is continuous real-time monitoring of the pH of a diabetic wound is of great importance along with other parameters like glucose, lactate etc. pH of the diabetic wound also provides the information about whether the wound is infected. In addition, the sensing of other parameters like glucose and lactate typically rely on enzymatic reactions which are affected by the pH of the wound exudate. Also, the pH of a wound can give an idea of how well it is healing. Thus, pH sensing is important by itself and also to calibrate the other readings of biosensors in the wound environment. The reliance on pH to determine the outcomes of processes and to establish baselines for sensors is the motivation behind the development of the flexible miniature pH sensor reported here. Due to the small size and flexibility of the pH sensor it can easily be integrated for use in many different situations.<br/>In this work, an electrochemical pH sensor was developed using polyaniline (PANI) as the pH sensitive material. PANI was selected due to its ability to reversibly undergo protonation and deprotonation from its emeraldine base (EB) form to the emeraldine salt (ES) form and back, in the presence of acidic or basic media. This is utilized as the sensing mechanism as the EB form is less conductive than the ES form. Thus, based on the pH of the sample the conductivity of the PANI thin film will change. Another reason that PANI was chosen is that it is sensitive to the physiologically relevant pH range of 4 - 9.[1] One issue with PANI is that pristine PANI thin films are very fragile - therefore, polyvinyl alcohol (PVA) is added to increase the mechanical durability and flexibility of the pH sensor. The sensors were fabricated using an Optomec Aerosol Jet 5X printer to print gold electrodes on a flexible Kapton substrate, followed by a passivation layer of polyimide (PI) to prevent shorting of the device. Next the device was treated with oxygen plasma to enhance the adhesion of the PANI/PVA film to the Kapton substrate. Finally, a PANI/PVA thin film is spin coated on the device to create the pH sensitive film. Devices will be optimized by varying the geometry and composition. Results of pH measurements in different artificial buffers will be presented. To improve the signal to noise quality the developed PANI/PVA thin films will be used in organic electrochemical transistors (OECT) as the gate or channel material.<br/> <br/>References<br/>[1] L. A. Schneider, A. Korber, S. Grabbe, and J. Dissemond, “Influence of pH on wound-healing: A new perspective for wound-therapy?,” <i>Archives of Dermatological Research</i>, vol. 298, no. 9, pp. 413–420, Feb. 2007, doi: 10.1007/S00403-006-0713-X.