Friday, December 9, 2022

Researchers turn discarded CDs into flexible and stretchable biosensors

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As digital music files become more popular, CDs are falling into disuse. Sadly, discarded CDs end up in landfills with negative environmental consequences. However, some of them can still be used since the gold foil in them can be used in the production of wearable biosensors.

Researchers from Binghamton University’s Thomas J. Watson College of Engineering and Applied Science are offering a second life for CDs: Turn them into flexible biosensors that are inexpensive and easy to manufacture. In their research published in Nature Communications, the researchers show how a gold CD’s thin metallic layer can be separated from the rigid plastic and fashioned into sensors for numerous applications.

The CD was initially soaked in 40 mL of acetone for 1.5 minutes, releasing the metal layer by breaking down the polycarbonate substrate. The metal from the CD was easily harvested with polyimide tape, which also serves as the substrate layer in the new device integration to improve the mechanical durability and robustness of the thin metal film.

By removing the gold layer of a CD from the plastic underneath, Binghamton University researchers have created flexible biosensors for numerous applications.
By removing the gold layer of a CD from the plastic underneath, Binghamton University researchers have created flexible biosensors for numerous applications. Credit: Binghamton University

“When you pick up your hair on your clothes with sticky tape, that is essentially the same mechanism,” said Assistant Professor Ahyeon Koh, who led the research. “We loosen the layer of metals from the CD and then pick up that metal layer with tape, so we just peel it off. That thin layer is then processed and flexible.”

Researchers created the sensors utilizing a commercially available Cricut cutter, an off-the-shelf machine for crafters that generally cut designs from materials like paper, vinyl, card stock, and iron-on transfers. The flexible circuits then would be removed and stuck onto a person. The whole fabrication process was completed in 20-30 minutes, without releasing toxic chemicals or needing expensive equipment, and it costs about $1.50 per device.

Combined with other electronics, these biosensors can be used to monitor electrical activity in the human heart and muscles as well as lactose, glucose, pH, and oxygen levels. These sensors can communicate with a smartphone via Bluetooth.

“We used gold CDs, and we want to explore silver-based CDs, which I believe are more common,” the Ph.D. student Matthew Brown said. “How can we upcycle those types of CDs with the same kind of process? We also want to look at if we can utilize laser engraving rather than using the fabric-based cutter to improve the upcycling speed even further.”

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