Reduced Graphene Oxide/Polyaniline pH Sensor Based on Hybrid Microfabrication and Flexible Electronics Processes

Official URL: https://research.sabanciuniv.edu/id/eprint/47571/

Over the past few years, measuring pH levels has become essential in understanding chemical and biological interactions in various fields such as agriculture, food safety, industrial processes, the environment, and healthcare. However, traditional glass electrode sensors have limitations in terms of stability and size, making them unsuitable for in situ pH measurements that require flexibility in application. To address this issue, there has been rapid progress in making miniaturized, flexible, and low-cost pH sensors through hybrid microfabrication techniques. In this research, the potential of graphene oxide (rGO) and polyaniline (PANI) composite lithographically patterned in the form of interdigitated electrodes (IDEs) is investigated for pH sensing applications. Here the IDE structure acts both as the pH sensitive material and at the same time as electrodes through which electrical measurements can be recorded. This unique design potentially eliminates the requirement for additional contact electrodes such as silver which usually adds onto sensor cost. To this end, thermally reduced graphene oxide and PANI composite sensing material is deposited on a flexible polyethylene terephthalate (PET) substrate with a facile and scalable dip-coating method followed by thermal reduction to achieve reduced GO (rGO)/PANI films. During this process, different concentrations of rGO/PANI films (up to 20% PANI) are prepared to optimize the material. Specifically for material optimization, inkjet-printed silver (Ag) electrodes are deposited on the rGO/PANI material and a conductimetric measurement is performed to investigate the effect of different ratios of the material toward pH changes. After optimizing the material, the sensor topology is switched to IDE type, which is patterned on the rGO/PANI/PET by photolithography and oxygen plasma etching enabling precise geometry control in an arrayed format. The developed process technology demonstrates that both flexible rGO and rGO/PANI composite-coated PET films are compatible with common microfabrication processes such as photolithography and oxygen plasma etching. Diverse IDEs structures are created with the selected composite to analyze the impact of electrode size on the sensor's performance and sensor response to different pH solutions is characterized by I-V measurements.