Compact Discs Get a New Lease on Life as Flexible Biosensors

Every year, consumers generate 50 million tons of electronic waste—amounting to more weight than all commercial airplanes ever made. Less than 20% of e-waste is recycled every year. In many circumstances, the reasons behind the low rates of e-waste recycling come down to device complexity. Highly-integrated electronic products are difficult to recycle because of the complicated process to separate the fine materials in these devices. 

Among the mountains of e-waste worldwide, millions of compact discs (CDs) are thrown away every year and end up in landfills and incinerators, damaging the environment and wasting significant energy.

 

CDs can be responsibly recycled through several mail-in programs. Image used courtesy of Treehugger/Lexie Doehner

 

When disposed of improperly, CDs are known to depolymerize from polycarbonate into their toxic monomer, Bisphenol A (BPA). Part of the problem with CD disposal is that these discs require a specific recycling process: they must be left at a local drop-off recycling center that accepts them or recycled through a mail-in process.

 

Upcycling CDs for Bioelectronics

Now, researchers at Binghamton University have discovered a new way to repurpose the materials in CDs for biomedical use. The team's study, published in Nature Communication, outlines how a gold CD's thin metallic layer can be separated and used in flexible biosensors that can monitor electrical activity in the human heart and measure lactate, glucose, pH, and oxygen levels—all in real-time. The sensor can also communicate with a smartphone via Bluetooth.

 

Binghamton researchers hope to give CDs a new lease on life—this time, as flexible and inexpensive biosensors that are easy to manufacture. Image used courtesy of Binghamton University

 

The Binghamton researchers achieved this by transforming rigid electronic metal strips into soft mechanics with thin polymeric substrates. They transferred the rigid metal materials into stretchable components by patterning deterministic architectures, which enables deformation and lower contact impedance. These characteristics also make the material more comfortable to wear. 

 

An Affordable Fabrication Technique

Stretchable electronic devices are usually fabricated using costly and time-consuming printing or lithography technologies. Here, the researchers demonstrate a fast and low-cost fabrication technique, where the metal is patterned with an affordable craft mechanical cutter.

 

Components of the upcycled sensor. Image used courtesy of Nature Communication

 

To harvest the metal from CDs, the CD is first soaked in acetone to break down the polycarbonate substrate and release the metal layer. After that, polyimide tape extracts the metal and is also used as a temporary substrate through the patterning process. Polyimide tape also serves as a substrate for patterning the insulation layer. The researchers claim that fabrication takes around 20 to 30 minutes without releasing toxic chemicals or requiring expensive equipment.

 

Researchers Set Their Sights on Silver-based CDs

A fully-fabricated upcycled sensor consists of biopotential electrodes, a heater or a temperature sensor, a reference electrode, a counter electrode, a pH electrode, an oxygen electrode, a lactate electrode, and a glucose electrode.

Beyond scalable bioelectronics, the researchers have been unable to demonstrate the mechanical durability of their sensors for wearable applications. In future research, the researchers intend to upcycle silver-based CDs (which are more common) and explore if engraving can be used to improve the patterning speed.