E coli sensors using silk

Researchers at Georgia Tech in Atlanta, have made electronic biosensors that identify bacteria in poultry plants. Scientists at Texas A&M University, Georgia Tech and other schools are experimenting with "electronic noses" and other types of semiconductor-based sensors designed for food safety. Printed electronics is often involved and even purely visual testers can be combined with printed optical sensors where useful.

 

For example, two years ago the US Food and Drug Administration urged millions of Americans to stop eating bagged spinach until its safety could be assured due to an outbreak of E. coli which killed 5 people and infected more than 205 others, leaving them vulnerable to future health problems.

 

Now scientists at Tufts University School of Engineering have developed and demonstrated an edible optical sensor made from fibers from silkworms that could be placed in bags of spinach providing the consumer with a read-out of whether or not E. coli bacteria were present - before the food was consumed.

 

To form the devices, the team boiled cocoons of the Bombyx mori silkworm in a water solution and extracted the glue-like sericin proteins. The purified silk protein solution was ultimately poured onto negative molds of ruled and holographic diffraction gratings with spacing as fine as 3600 grooves/mm. The cast silk solution was air dried to create solid fibroin silk films that were cured in water, dried and optically evaluated. A similar process was followed to create lenses, microlens arrays and holograms. Film thicknesses from 10 to 100 µm; were characterized for transparency and optical quality.

 

The variety and quality of the optical elements compared favorably with conventional platforms and outperformed other commonly used biopolymers.

 

The elements are prepared, processed and optimized in all-aqueous environments and at ambient temperature. This makes possible the inclusion of sensitive biological 'receptors' within the solution that stay active after the solution has hardened into a free-standing silk optical element.

 

The Tufts team embedded three very different biological agents in the silk solution: a protein (hemoglobin), an enzyme (horseradish peroxidase) and an organic pH indicator (phenol red). In the hardened silk optical element, all three agents maintained their activity for long periods when simply stored on a shelf.

 

Sophisticated optical devices that are mechanically robust yet fully biodegradable, biocompatible and implantable don't exist today," said principal investigator Fiorenzo Omenetto, associate professor of biomedical engineering and associate professor of physics. "Such systems would greatly expand the use of current optical technologies in areas like human and livestock health, environmental monitoring and food quality."

 

According to experts silks spun by spiders and silkworms represent the strongest and toughest natural fibers known. They offer many opportunities for functionalization, processing and biological integration when compared to conventional polymers.

 

The scientists suggest that the optical sensor could be implanted to monitor glucose in the blood for a year and then dissolve.

 

The Tufts research was published in a recent paper in "Biomacromolecules."

 

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