Researchers from MIT have created a food sensor made of silk microneedles. The sensor pierces through plastic packaging to detects if it is spoiled and bacterial contamination. A smart food sensor could prevent contamination outbreaks and excess food waste due to a lack of proper labeling.

The microneedles are molded from a solution of edible proteins found in silk cocoons and designed to draw fluid back into the sensor. The sensor is printed with two kinds of bio-ink. One changes color when it comes into contact with food that has a pH range that indicates spoilage, and the other changes color when it detects contaminating bacteria.

The team started by creating a solution of silk fibroin, a protein from moth cocoons. The solution is poured into a silicone microneedle mold. Once it is dried, the solution creates an array of microneedles of about 1.6 mm long and 600 microns wide. Pores embedded in the microneedles allow the arrays to draw fluid up with capillary action.

The Velcro-like food sensor, made from an array of silk microneedles, can pierce through plastic packaging to sample food for signs of spoilage and bacterial contamination.Source: MIT/Felice Frankel

Next is they created the solutions for the bio-ink. They mixed one bio-ink with an antibody sensitive to E. coli that changes shape and physically pushes on the surrounding polymer, ultimately changing the way bio-ink absorbs light. The second bio-ink is sensitive to pH levels associated with spoilage. The bacteria sensitive bio-ink printed on the surface of a microneedle array in an E shape. The pH-sensitive bio-ink is printed in a C shape. Both appeared blue initially.

To test the new sensor, the team bought several fish fillets from a local grocery store. The filets were injected with a fluid that contained either E. coli, salmonella or nothing and loaded with sensors. After 16 hours, the E turned from blue to red in the E. coli contaminated fillet. A few hours later, the E and C in all of the contaminated samples turned red.

This sensor finds contamination and spoilage faster than existing sensors. Existing sensors often only detect pathogens on the surface of foods.

The team says that the sensor’s reliability of detection and absorption of fluid needs to be improved. But they envision that one day the sensor can be used in all areas of the supply chain.

A paper on this research was published in Advanced Functional Materials.