Edible sensors may indicate bacterial contamination

Demand for products that can help processors ensure their goods are safe has grown in the wake of a number of high profile food recalls and scares in the US with researchers looking increasingly to nanotechnology in this regard.

Edible silk lenses as biosensors could be one such means of effectively monitoring the level of dangerous bacteria in food packaging, according to researchers from the School of Engineering at Tufts University in the US.

“For example, at a low cost, we could potentially put a bioactive silk film in every bag of spinach, and it could give the consumer a readout of whether or not E. coli bacteria were in the bag before the food was consumed,”​ claims David Kaplan, chair of the biomedical engineering department at Tufts.

E. coli​

Microbiological safety is a key issue for fruits, vegetables and ready-to-eat prepared vegetable tissues, because all are intended for consumption raw, without further preparation or cooking.

An outbreak of E. coli in September 2006 was traced back to packaged cut spinach originating from California. The outbreak killed three people and sickened more than 200 people across the US.

Biodegradable sensor​

Edible nanoparticles can be made of materials that react with the body's heat or chemistry, such as polymers. Silk optic sensors would have the advantage of the strong, flexible, benign, and biodegradable nature of silk, claim findings from the Tufts University study, published in the American Journal of Chemistry​.

The researchers boiled silk cocoons in water to produce a purified silk solution that was poured onto glass moulds to create the edible sensors in the form of lenses, microlens arrays and holograms, according to the report.

Innovation ​

Significantly, the researchers claim that the part of the process which enables the embedding of biological agents can be done at room temperature, thus enabling the integration into the silk optics of proteins, enzymes and organic pH indicators, which normally would be destroyed by heat.

“We have optical devices embedded with enzymes that are still active after almost a year of storage at room temperature,” ​claims researcher Fiorenzo Omenetto.

The project was funded by the US Defense Department through its Defense Advanced Research Projects Agency (DARPA). Tufts University claims it has filed patent applications on silk-based optics and is looking at developing commercially available products.