Near-field coupled RFID tag for carbon dioxide concentration sensing

Measuring carbon dioxide (CO2) concentration plays an important role in environmental sciences, agri-food, medicine, packed food, and oil and chemical industry (R. Ali, T. Lang, S.M. Saleh, R.J. Meier and O.S. Wolfbeis, Analytical Chemistry, 83, 2846–2851, 2011). Spoilage of grain can be 3–10% in developed countries and as high as 30% in developing countries. Increased levels of CO2 in a stored grain bulk indicate that insects, mould, or excessive respiration is present. A wireless sensor that is able to monitor the evolution of excessive CO2 from a stored grain mass would be an inexpensive reliable indicator of deteriorating grain and lead to significant reduction in food loss. Conducting polymer, colorimetric pH indicator and metal-oxide based sensors have previously been applied to sense CO2. These approaches require custom electronics in order to be integrated with RFID technology. In this work we present a new CO2 sensor based on a hydrogel pH-sensitive electrode pair. This sensor provides a direct voltage measurement depending on the CO2 concentration in the surrounding environment. We have integrated this sensor into a chipless near-field coupled RFID tag.