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 lactate, glucose, pH and oxygen levels. Credit: Matthew Brown
Flexible biosensors allow for real-time health monitoring through wearable, disposable and non-invasive devices that can be stuck to the skin to measure metrics like heart and muscle activity, lactate, glucose and oxygen levels, and more. However, these novel sensors rely on expensive materials like gold and silver to fabricate sensitive biocompatible electrodes, and the fabrication process can be lengthy and involve environmentally harmful chemicals, limiting the technology’s widespread use. Researchers from Binghamton University, State University of New York, have now developed an inexpensive, rapid and sustainable method for fabricating flexible biosensors, which is achieved through the upcycling of gold CDs.
The team was able to produce the sensors by separating the thin metallic layer from the CD’s rigid plastic. This involved soaking the CDs in acetone and harvesting the gold using polyimide (PI) tape. The PI-gold layer could then be cut into a precise circuit shape using a relatively inexpensive, off-the-shelf mechanical cutter. This simple method takes only 20-30 minutes and costs about $1.50 for each device, the researchers wrote. Fourier-transform infrared spectroscopy (FTIR) analysis showed that a protective layer of polymethylmethacrylate (PMMA) remains on the metal after the acetone soak, which improves the durability of the thin gold layer and does not require removal to produce the biosensors. However, the metal layer could be further stripped down to pure gold by soaking in nitric acid, making the sensors more biodegradable, the researchers found.
The patterned devices were mechanically tested and shown to have suitable flexible and stretchable properties for use on human skin as soft bioelectronics. The sensors and tape can be laminated to the skin using a liquid bandage or incorporated into a silicone-based bandage. The fully-fabricated device consisted of two biopotential electrodes, a heater or temperature sensor, a reference electrode, a counter electrode, a pH electrode, an oxygen electrode, a lactate electrode and a glucose electrode, the authors wrote. The performance of the biopotential electrodes, which can record ECG signals to a smartphone using a microcontroller unit and Bluetooth module, was found to be similar to that of commercially available gel electrodes. The temperature sensor was found to have analogous sensitivity to that of a laboratory-based infrared camera, and the electrochemical sensors showed suitable dynamic ranges and sensitivity for health monitoring applications. The biocompatibility of the sensors with skin keratinocyte cells (HaCaT) was also confirmed for those produced by both acetone and nitric acid soaking methods. This research was published in Nature Communications.
“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,” the authors wrote.
The researchers are considering further optimizing the process using laser engraving rather than mechanical cutting methods to create the circuits, as well as applying the same method to silver-based CDs, said first author Matthew Brown.