A gold CD’s thin metallic layer can be separated from the rigid plastic and fashioned into sensors to monitor electrical activity in human hearts and muscles as well as lactate, glucose, pH and oxygen levels.

Researchers turn recycled CDs into flexible biosensors

Image credit: Matthew Brown

New research offers a second life for CDs: turning them into flexible biosensors that are inexpensive and easy to manufacture.

Matthew Brown, assistant professor from the Department of Biomedical Engineering at Binghamton University, State University of New York, and his team have shown how they have separated a gold CD’s thin metallic layer from the rigid plastic and fashioned it into sensors to monitor electrical activity in human hearts and muscles as well as lactate, glucose, pH and oxygen levels.

Such sensors can communicate with a smartphone via Bluetooth, according to the research team.

Experts can complete the fabrication in 20 to 30 minutes without releasing toxic chemicals or needing expensive equipment, and it costs about $1.50 per device. “This sustainable approach for upcycling electronic waste provides a helpful research-based waste stream that does not require innovative microfabrication facilities, expensive materials, or high-calibre engineering skills.”

Contributing to the research was assistant professor Yeonsik Noh from the University of Massachusetts who said she first considered the idea of converting the CDs into sensors while doing postdoctoral research at the University of Illinois.

“I had an idea: Maybe we could harvest the critical material from the CD and then upcycle to sensing systems,” she said. “I talked to Matt about my idea during the early stage of his dissertation research, and he wanted to continue this research.”

Flexible biosensor

Image credit: Matthew Brown

Brown investigated previous research on biosensors made from CDs, but he found those sensors retained a rigid structure and had a more limited number of applications than he and Koh hoped to achieve.

The first step is removing the metallic coating from the plastic beneath using a chemical process and adhesive tape.

“When you pick up your hair on your clothes with sticky tape, that is essentially the same mechanism,” Koh said. “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.”

To create the sensors, Binghamton researchers used a Cricut cutter, an off-the-shelf machine for crafters that cuts designs from materials like paper, vinyl, card stock and iron-on transfers.

Experts can then remove the flexible circuits and stick them onto an individual. With the help of a smartphone app, medical professionals or patients could get readings and track their progress over time.

Flexible biosensor on skin

Image credit: Matthew Brown

As Brown’s PhD advisor, Koh said she was thrilled to see something she speculated could be possible almost a decade ago is now a reality.

“I was so lucky to have Matt in the lab because otherwise, it would have stayed an idea from my postdoc research,” she said. “Some of my postdoc colleagues remember me talking about this idea to them, and they're so excited about it.”

Brown has ideas about how they can improve the CD-to-sensor technology: “We used gold CDs, and we want to explore silver-based CDs, which I believe are more common. How can we upcycle those types of CDs with the same process? We also want to look at if we can use laser engraving rather than using the fabric-based cutter to improve the upcycling speed even further.”

Like her former student, Koh would like to expand the CD-to-sensor research as well, possibly with the help of the campus community.

“Maybe we can create a box on campus where we could collect CDs. We also could have more generalised step-by-step instructions on how to make them in a day, with no engineering skills,” she said.

“Everybody can create those kinds of sensors for their users. We want these to become more accessible and affordable, and more easily distributed to the public.”

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