Compact CDs are progressively becoming outdated as digital music files grow in popularity. However, some old CDs might still be valuable since the gold foil they contain can be utilized to make wearable biosensors. CDs are mostly polycarbonate but have a small layer of reflective foil. Most CDs use aluminum for that foil, but the aptly named gold compact discs utilize gold for (arguably) superior performance.

Typically, the gold foil from abandoned gold CDs is dumped with the remainder of the disc in a landfill. Instead, scientists at Binghamton University in New York wondered if they could use the gold from the CDs for skin-adhered flexible biosensors, which also require thin layers of gold.

Asst. Prof. Ahyeon Koh and Ph.D. student Matthew Brown created a method in which gold CDs were first submerged in acetone for 90 seconds, breaking down the polycarbonate and weakening the binding with the foil. The foil was then covered with a sheet of polyimide sticky tape, and both the foil and the gold were then removed off the polycarbonate substrate.

The gold foil and the tape substrate were cut into flexible circuits using a commercially accessible Cricut fabric-cutting machine (customarily used by crafters). These circuits can be repeatedly attached to and removed from a person’s skin. These biosensors can measure oxygen levels, lactose, glucose, pH, and electrical activity in the wearer’s heart and muscles when combined with additional electronics. Finally, a smartphone can receive all the information via Bluetooth.

According to reports, the recycling and manufacturing process takes only 20 to 30 minutes, doesn’t call for expensive equipment, and costs about US$1.50 per sensor. Additionally, even though acetone is used in the process, no hazardous chemicals are discharged into the waste stream.

“We used gold CDs and want to explore silver-based CDs, which I believe are more common. We also want to see if we can utilize laser engraving rather than using the fabric-based cutter to improve the upcycling speed even further.”

The findings are detailed in a paper that appeared in the issue of Nature Communications on June 28, 2022.