As digital music files become increasingly popular, compact discs are likewise becoming obsolete. There may still be a use for some existing CDs, however, as the gold foil in them could be used in the production of wearable biosensors.
Although CDs are made mainly of polycarbonate, they do contain a thin layer of reflective foil. That foil is aluminum in most CDs, although gold is used for (debatably) better performance in aptly named gold compact discs.
Ordinarily, when gold CDs are discarded, that gold foil goes into the landfill along with the rest of the disc. Because thin layers of gold are also used in skin-adhered flexible biosensors, scientists at New York's Binghamton University wondered if they could salvage the gold from the CDs for that purpose.
Led by PhD student Matthew Brown and Asst. Prof. Ahyeon Koh, they developed a technique in which gold CDs were initially soaked in acetone for 90 seconds – this broke down the polycarbonate, loosening the bond between it and the foil. Next, a sheet of polyimide adhesive tape was applied to the foil, after which both it and the gold were peeled off the underlying polycarbonate.
Utilizing a commercially available Cricut fabric-cutting machine (typically used by crafters), both the gold foil and its tape substrate were then cut into flexible circuits that can be repeatedly applied to and removed from a person's skin. Combined with other electronics, these biosensors can be used to monitor electrical activity in the wearer's heart and muscles, plus they're capable of measuring lactose, glucose, pH and oxygen levels. All the data can be relayed to a smartphone via Bluetooth.
The whole recycling/fabrication process reportedly takes just 20 to 30 minutes, doesn't require expensive equipment, and costs approximately US$1.50 per sensor. And while acetone is used in the process, no toxic chemicals are released into the waste stream.
"We used gold CDs, and we want to explore silver-based CDs, which I believe are more common," said Brown. "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."
The research is described in a paper that was recently published in the journal Nature Communications.
Source: Binghamton University
