NFC-Enabled Passive Sensor for the Quality Control of Ethanol Against SARS-CoV-2

Ethanol sanitizers are crucial to fight SARS-CoV-2. Nevertheless, some products concentration and purity are not always adequate and sometimes can be toxic. Conveniently, only the desired substance should be detected, minimizing the risk of false-positive readings from ethanol mixtures or impurities like methanol. Here, we developed a passive wireless dual-sensor based on the permittivity changes of a solution. Our sensor has two capacitive interdigital transductors (IDTs) with different coupling factors (K), each coupled directly to a pair of antennas of a wireless NFC system, and explicitly tuned to assess the quality of a specific sample. The operating principle is based on the coupling frequency of the antennas and the permittivity changes of the solution that turns on or turns off the NFC chip for each antenna. The relation between the two states of the antennas allows quality control and product identification. This NFC-Enabled passive sensor is a cheap alternative to identify possible permittivity changes of a solution. Our NFC-Enabled passive sensor detects a variation of 5% v/v methanol, deionized water (DI water), and sub-optimal ethanol concentration in an antiseptic solution. Further works can be focused on identifying the frequencies of several substances, and avoiding toxic methanol mixtures and counterfeit ethanol. The quality of a liquid substance can be tested based on its chemical properties by designing sensors that can respond accurately to certain types of samples.