With the growing popularity of digital music files, CDs are likewise being phased out. However, there may still be a place for some existing CDs, as the gold leaf in them can be used to produce wearable biosensors.
Although CDs are primarily made of polycarbonate, they do contain a thin layer of reflective foil. In most CDs, this foil is aluminum foil, although gold is used for (controversially) better performance and is aptly named gold discs.
Typically, when gold discs are discarded, these gold foils are landfilled with the rest of the disc. Since thin gold foil is also used in flexible biosensors that are applied to the skin, scientists at SUNY Binghamton wondered if they could obtain gold foil from CDs for this purpose.
Led by doctoral student Matthew Brown and associate professor Ahyeon Koh, they developed a technique that starts by soaking a gold CD in acetone for 90 seconds – which breaks the polycarbonate and loosens the bond between it and the gold foil. Next, a sheet of polyimide tape is applied to the foil, and the gold foil is then peeled from the polycarbonate backing.
Using commercially available Cricut fabric cutters (often used by craftspeople), gold foil and its taped substrate are cut into flexible circuits that can be repeatedly applied to and removed from a person’s skin. In combination with other electronic devices, these biosensors can be used to monitor the electrical activity of the wearer’s heart and muscles, in addition to their ability to measure lactose, glucose, pH and oxygen levels. All of the data can be forwarded to a smartphone via Bluetooth.
The entire recovery/manufacturing process reportedly takes only 20 to 30 minutes, does not require expensive equipment and costs about $1.50 per sensor. Although acetone is used in the process, no toxic chemicals are released into the waste stream.
“We used gold discs, and we wanted to explore silver discs, which I believe are more common,” Brown said. “We also wanted to see if we could use laser engraving, rather than using a fabric-based cutter, to further increase the speed of upcycling.”
The research is described in a recent paper published in the journal Nature Communications.