Engineers at the Massachusetts Institute of Technology (MIT) have developed a novel sensor designed to sample food through plastic packaging for signs of spoilage — using ultra-tiny silk-based microneedles and color-changing "bioink."
"Food quality monitoring, particularly, the detection of bacterial pathogens and spoilage throughout the food supply chain, is critical to ensure global food safety and minimize food loss," the paper's abstract reads. "Incorporating sensors into packaging is promising, but it is challenging to achieve the required sampling volume while using food‐safe sensor materials."
"Here, by leveraging water‐based processing of silk fibroin, a platform for the detection of pathogenic bacteria in food is realized using a porous silk microneedle array; the microneedle array samples fluid from the interior of the food by capillary action, presenting the fluid to polydiacetylene‐based bioinks printed on the backside of the array."
"There is a lot of food that’s wasted due to lack of proper labeling, and we’re throwing food away without even knowing if it’s spoiled or not," explains Assistant Professor Benedetto Marelli, of the team's work. "People also waste a lot of food after outbreaks, because they’re not sure if the food is actually contaminated or not. A technology like this would give confidence to the end user to not waste food."
The patches — made from silk proteins, which Marelli points out is "completely edible, non-toxic, and can be used as a food ingredient, and it’s mechanically robust enough to penetrate through a large spectrum of tissue types, like meat, peaches, and lettuce" — are covered in microneedles just 1.6mm (around 0.06in) long and 600 microns wide. The patch is printed with two bioinks, one sensitive to pH levels and the other to the presence of E. coli bacteria. If the food is spoiled, a letter on the patch changes color with better accuracy and in less time than surface-based sensors.