Electrochemical Determination of PH using Paper-Based Devices

Abstract

For the past decade, many microfluidic paper-based analytical devices have been developed and used in different research fields. These devices are low-cost, portable, flexible, sterilizable, disposable, and easy to manufacture. The microfluidic paper-based analytical devices offer good alternatives to measurements and assays commonly performed in laboratories for analytical and clinical purposes, especially in diagnostics. In this work, we developed an electrochemical paper-based pH sensor. The determination of pH is essential in applications in areas as diverse as in the food industry, agriculture, health care or water treatment. The method presented in this work is an electroanalytical method that involves quantification of pH using stencil-painted graphite electrodes. Preliminary tests showed that pH can be determined on paper-based devices, thus indicating the presence of electroactive elements sensitive to pH on the surface of our electrodes (Chapter 4). Chemical modification of the electrode by adsorption with sodium carbonate and modification of the surface of the electrode was accomplished via: oxygen (ambient air) plasma treatment and pure oxygen plasma treatment. These treatments were to attempt to improve the definition of redox peaks on the CVs (Chapter 5). The changes made to the design of the paper-based device and the addition of a conditioning step improved the definition of the redox peaks on the CVs and increased the pH-sensing ability of our method (Chapter 6). The pH-sensing ability of our method was evaluated by testing solutions over a wide pH range. Adding sodium chloride to samples adjust the solution for accurate pH determination. The pH was successfully measured for solutions with values ranging from 1 to 13 and for artificial saliva samples prepared with pH values in the cavity-prone range (Chapter 7). This work offers a method that uses electroactive elements sensitive to pH on the surface of the PBD electrodes for pH-sensing.