SWNT sensors for monitoring the oxidation of edible oils

Abstract Several methods are available to measure the oxidation of edible oils, such as their acid, peroxide, and anisidine values. However, thesemethods require large quantities of reagents and are time-consuming tasks. Therefore, a more convenient and time-saving way to measurethe oxidation of edible oils is required. In this study, an edible oil-condition sensor was fabricated using single-walled nanotubes(SWNTs) made using the spray deposition method. SWNTs were dispersed in a dimethylformamide solution. The suspension was thensprayed using a spray gun onto a prefabricated Au/Ti electrode. To test the sensor, oxidized edible oils, each with a different acid value,were prepared. The SWNT sensors were immersed into these oxidized oils, and the resistance changes in the sensors were measured. Wefound that the conductivity of the sensors decreased as the oxidation level of the oil increased. In the case of the virgin oil, the resistancechange ratio in the SWNT sensor S(%) = {[(Rf _ Ri)]/Ri}(%) was more than 40% after immersion for 1 min. However, in the case of theoxidized oil, the resistance change ratio decreased to less than that of the response of the virgin oil. This result suggests that the change inthe oil components induced by the oxidation process in edible oils is related to the conductivity change in the SWNT sensor.