The sticker part of the system contains a tiny sliver of metallic glass. The side touching the food is coated with phage E2, a virus engineered to stick only to Salmonella typhimurium bacteria.
In the handheld scanner, a small wire coil creates an oscillating magnetic field, which makes the glass sliver in the sticker vibrate in sympathy. The coil can measure that rate of vibration.
If salmonella is present under the sticker, it gets snagged by the phage and makes the sticker a touch heavier—enough to change its vibration frequency. The scanner could pick up the shift and sound an alarm. The work appears in the Journal of Applied Physics. [Yating Chai et al., Design of a surface-scanning coil detector for direct bacteria detection on food surfaces using a magnetoelastic biosensor]
The system should work on most produce—but probably not on chicken or eggs, because they can harbor salmonella on the inside.
—Wayt Gibbs
[The above text is a transcript of this podcast.]
