MIT chemists developed simple food related gas sensor which can be interfaced to a smartphone. These sensors can detect ammonia, hydrogen peroxide, and cyclohexanone and such gases which help in detecting spoiled food both in homes and commercial food serving/storage places.
These sensors are designed to cost less and connect to the smart phones wirelessly without using wires. Some of the good examples include getting alerts in the smart phones when the food in the fridge get spoiled. By using the sensors, spoiled food can be detected without smelling or tasting.
The sensors are basically called chemiresistors, which consist of simple electrical circuits whose resistance changes when exposed to a particular chemical. Measuring that change in resistance reveals whether the target gas is present.
These gas sensors are integrated with near Field communication tags (NFC) tags. Not as a separate module but as part of the NFC's circuitry, where these sensors becomes a resistor, whose resistance varies based on the gas presence.
MIT researchers have used carbon nanotubes specialized to detect a particular gas. When carbon nanotubes bind to the target gas, their resistance changes and that changes the frequency at which power can be transferred to the device which in turn used to detect gas.
When these sensors can get NFC-fied, they can also get IoT-fied by embedding further hardware to this.