Abstract Monitoring the real-time status of food products using pH sensors is important to determine if pathogens are present and growing, which in turn affects food quality. A promising material for pH sensors is ruthenium dioxide (RuO2) due to its chemical stability and excellent performance. Furthermore, graphene oxide (GO) provides an electrode with large surface area and good electrical properties. Here, in situ sol-gel deposition of RuO2 nanoparticles on the surface of GO as a facile, cost-effective, and environmentally friendly approach is used for the fabrication of a flexible pH sensor. As-synthesized GO-RuO2 nanocomposites with a low volume were applied on the surface of screen printed carbon paste. The obtained GO-RuO2 nanocomposite pH sensor achieved high pH sensitivity (55.5 mV/pH) in the pH range of 4-10, up to 4 times higher compared to the unmodified carbon electrode. The increased sensitivity is due to the positive role of RuO2 nanoparticles densely anchored across the GO sheets. It also shows low drift (0.36 mV/hr) and low hysteretic width. Considering this novel method and material with the cost-effective green synthesis approach, as well as excellent pH sensing properties, GO-RuO2 can be considered as a promising material for production of high-performance electrochemical pH sensors.

Food wastage is a critical and world-wide issue resulting from an excess of food supply, poor food storage, poor marketing, and unstable markets. Since food quality depends on consumer standards, it becomes necessary to monitor the quality to ensure it meets those standards. Embedding sensors with active nanomaterials in food packaging enables customers to monitor the quality of their food in real-time. Though there are many different sensors that can monitor food quality and safety, pH sensors and time-temperature indicators (TTIs) are the most critical metrics in indicating quality. This review showcases some of the recent progress, their importance, preconditions, and the various future needs of pH sensors and TTIs in food packaging for smart sensors in food packaging applications. In discussing these topics, this review includes the materials used to make these sensors, which vary from polymers, metals, metal-oxides, carbon-based materials; and their modes of fabrication, ranging from thin or thick film deposition methods, solution-based chemistry, and electrodeposition. By discussing the use of these materials, novel fabrication process, and problems for the two sensors, this review offers solutions to a brighter future for the use of nanomaterials for pH indicator and TTIs in food packaging applications.