Just because a food item may be frozen when you buy it, that doesn't mean it wasn't thawed and refrozen somewhere along the line. A new self-powered sensor, however, would change color to let you know if that had happened.
Developed by a team from the Istituto Italiano di Tecnologia (Italian Institute of Technology), the food-safe device is currently in functional proof-of-concept form.
It incorporates two electrodes – a magnesium anode and a gold cathode – which are separated by a frozen electrolyte solution. In various versions of the sensor, that solution has contained salts and electrolyte-rich grape, apple and melon matter.
As long as the electrolyte solution remains frozen, nothing happens. If it thaws, however, it allows electrons to flow from the anode to the cathode, causing the sensor to generate an electrical current. That current in turn causes a red-cabbage-juice-based solution to change from a reddish-purple to blue color. It then stays blue, even if the sensor is refrozen.
The temperature at which the electrolyte thaws can be tuned within a range of 0º C to -50º C (32º F to -58º F).
All of the components are currently contained within a beeswax body. It is hoped that once developed further, the technology could take the form of a thin, inexpensive, single-use, edible material that could be applied directly to the food items.
A paper on the research, which is being led by Ivan Ilic and Mario Caironi, was recently published in the journal ACS Sensors.
Source: American Chemical Society