Microneedle patch changes color to indicate food spoilage
We've already heard about so-called "microneedle patches" that are used for the painless and sustained release of medication through the skin. Now, MIT scientists have adapted the technology for the detection of spoiled food.
Ordinarily, microneedle patches consist of a small polymer square, the underside of which is covered in an array of tiny medication-filled spikes that are made of a water-soluble, biocompatible material. When that patch is pressed against the patient's body, the spikes painlessly penetrate the top layer of skin. They then dissolve, releasing the medication into the bloodstream via the interstitial fluid that surrounds the skin cells.
Created by a team led by Asst. Prof. Benedetto Marelli and Prof. A. John Hart, the new MIT patch is made from silk fibroin – which is an edible protein extracted from moth cocoons – along with two types of "bioink" polymers. One of these is sensitive to a molecule in E.coli bacteria, while the other is sensitive to pH levels that are typically associated with food spoilage. In both cases, the polymer will change color if the targeted molecule or pH values are present.
When the patch is pressed against the surface of a piece of fresh produce, its needles (each measuring about 1.6 mm long by 600 microns wide) will draw in fluids from within that item. This is reportedly a more accurate approach than those which just test the surface of the food, as such surfaces may contain nooks and crannies in which pathogens can hide from sensors.
In lab tests, the scientists injected raw fish fillets with a solution containing either E. coli bacteria, Salmonella bacteria, or no contaminants at all. The patches were then applied to all of the samples. Each patch had the E. coli-reactive bioink applied in a letter E pattern, and the pH-reactive bioink applied in a C.
After approximately 16 hours of sitting at room temperature, the E's turned from blue to red, but only on the samples in which the E. coli bacteria were present. Several hours later, though, the E's and C's on all of the samples turned red, indicating that they had all spoiled after sitting unrefrigerated for too long.
The scientists are now working on speeding up the reaction time, and making the patches sensitive to a wider range of contaminants. Ultimately it is hoped that the technology could be used by workers to monitor produce while it's in transit, and by consumers to check foods in the store and at their homes.
A paper on the research was recently published in the journal Advanced Functional Materials.