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This paper presents a smart sensor patch with flexible strain sensor and a printed temperature sensor integrated with a Near Field Communication (NFC) tag to detect strain or temperature in a semi-quantitative way. The strain sensor is fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) in a polymer Polydimethylsiloxane microchannel. The temperature sensor is fabricated by printing silver electrodes and PEDOT:PSS on a flexible polyvinyl chloride (PVC) substrate. A custom-developed battery-less NFC tag with an LED indicator is used to visually detect the strain or temperature by modulating the LED light intensity. The LED shows maximum brightness for relaxed or no strain condition, and also in the case of maximum temperature. In contrast, the LED is virtually off for the maximum strain condition and for room temperature. Both these could be related to food spoilage. Swollen food packages can be detected with the strain sensor, serving as beacons of microbial contamination. Temperature deviations can result in the growth or survival of food-spoilage bacteria. Based on this, the potential application of the sensor system for smart food packaging is presented.
Escobedo et al. (2021) studied this question.