NFC tags check food freshness
In December last year, researchers at the Massachusetts Institute of Technology (MIT) had designed simple gas sensors relying on nanotubes-based chemiresistors (electrical circuits whose resistance changes when exposed to a particular chemical).
In their implementation, the carbon nanotubes were chemically modified so that their ability to carry an electric current changed in the presence of a particular gas. This chemiresistive property was then integrated into the powering circuit of commercial near-field communication (NFC) tags.
The team first disrupted the electronic circuit by punching a hole in it before reconnecting the circuit with a linker made of the modified carbon nanotubes. Hence, the modified NFC tags can only remain operational and can only be read if the chemiresistors conduct normally, that is without the target chemical in sight.
Now, the researchers have modified the carbon nanotubes with metal-containing compounds called metalloporphyrins, known to be very good at binding to nitrogen-containing compounds such as amines. Of particular interest to the researchers were the so-called biogenic amines, such as putrescine and cadaverine, which are produced by decaying meat.
When the cobalt-containing porphyrin binds to any of these amines, it increases the electrical resistance of the carbon nanotube, which can be easily measured. The researchers tested the sensor on four types of meat: pork, chicken, cod, and salmon. They found that when refrigerated, all four types stayed fresh over four days. Left unrefrigerated, the samples all decayed, but at varying rates.
Designed within NFC-readable RFID labels, the sensors could allow consumers to determine whether the meat in their grocery store or refrigerator is safe to eat. Such sensors could be designed in smart packaging that would offer much more accurate safetyClass X capacitors are used in “across-the-line” applications where their failure would not lead to electric shock. Class X safety caps are used between the “live” wires carrying the incoming AC current. In this position, a capacitor failure should not cause any electrical shock hazards, rather, a capacitor failure “between-the-lines” would usually cause a fuse or circuit breaker to open. information than the expiration date on the package, according to Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT who had already proven similar sensors to detect ethylene, a gas that signals ripeness in fruit.