Silver nanowire wearable sensors match hospital ‘wet electrode’ accuracy

Researchers from North Carolina State University have developed a new, wearable sensor that uses silver nanowires to monitor electrophysiological signals, such as electrocardiography (EKG) or electromyography (EMG).

The new sensor is claimed to be as accurate as the ‘wet electrode’ sensors used in hospitals, but can be used for long-term monitoring and is reportedly more accurate than existing sensors when a patient is moving.

Long-term monitoring of electrophysiological signals can be used to track patient health or assist in medical research, and may also be used in the development of new powered prosthetics that respond to a patient’s muscular signals.

Electrophysiological sensors used in hospitals, such as EKGs, use wet electrodes that rely on an electrolytic gel between the sensor and the patient’s skin to improve the sensor’s ability to pick up the body’s electrical signals. However, this technology poses problems for long-term monitoring, because the gel dries up, which can cause skin irritation and make the sensor less accurate.

According to NC State, the new nanowire sensor is comparable to the wet sensors in terms of signal quality, but is a ‘dry’ electrode in that it doesn’t use a gel layer, so doesn’t pose the same problems that wet sensors do.

‘People have developed other dry electrodes in the past few years, and some have demonstrated the potential to rival the wet electrodes, but our new electrode has better signal quality than most – if not all – of the existing dry electrodes. It is more accurate,’ said Dr Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State and senior author of a paper describing the work. ‘In addition, our electrode is mechanically robust, because the nanowires are inlaid in the polymer.’

The sensors stem from Zhu’s earlier work to create highly conductive and elastic conductors made from silver nanowires, and consist of one layer of nanowires in a stretchable polymer.

The new sensor is also more accurate than existing technologies at monitoring electrophysiological signals when a patient is in motion.

‘The silver nanowire sensors conform to a patient’s skin, creating close contact,’ Zhu said in a statement. ‘And, because the nanowires are so flexible, the sensor maintains that close contact even when the patient moves. The nanowires are also highly conductive, which is key to the high signal quality.’

The new sensors are also compatible with standard EKG- and EMG-reading devices.

‘I think these sensors are essentially ready for use,’ said Zhu. ‘The raw materials of the sensor are comparable in cost to existing wet sensors, but we are still exploring ways of improving the manufacturing process to reduce the overall cost.’

The paper, Wearable Silver Nanowire Dry Electrodes for Electrophysiological Sensing, was published online on January 14 in RSC Advances.