With more than nine billion music CDs having been shipped in the U.S. since 1999, many discarded CDs have ended up in landfills with negative environmental consequences. Now, say Binghamton University researchers, they have discovered an easy, inexpensive recycling method to turn discarded CDs into flexible biosensors that are inexpensive and easy to manufacture.
Their research shows how 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 lactose, glucose, pH and oxygen levels. The sensors can communicate with a smartphone via Bluetooth.
The fabrication is completed 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 an advantageous research-based waste stream that does not require cutting-edge microfabrication facilities, expensive materials or high-caliber engineering skills,” say the researchers in a paper published this month in Nature Communications.
The researchers investigated previous research on biosensors made from CDs, but found that those sensors retained a rigid structure and had a limited number of applications. To address this, the first step in their method is to remove 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,” says Assistant Professor Ahyeon Koh from the Department of Biomedical Engineering. “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, the researchers used a Cricut cutter, an off-the-shelf machine for crafters that generally cuts designs from materials like paper, vinyl, card stock and iron-on transfers. The flexible circuits then would be removed and stuck onto a person. With the help of a smartphone app, medical professionals or patients could get readings and track progress over time.
The researchers say they have ideas about how the CD-to-sensor technology could be improved.
“We used gold CDs, and we want to explore silver-based CDs, which I believe are more common,” says Matthew Brown, PhD ’22. “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.”
Koh adds, “We also could have more generalized step-by-step instructions on how to make them in a day, without any engineering skills. 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.”