Sketch a heart sensor with pencil drawings that become electrodes

By Donna Lu

Squiggly pencil lines on paper make inexpensive electrodes that can sense heart rate or skin temperature

Yadong Xu

Pencil sketches on paper can be configured into sensors that detect a variety of physiological signals, including heart rate, skin temperature and compounds in sweat.

Zheng Yan at the University of Missouri in the US and his colleagues have developed electrodes made from pencil sketches on paper that can pick up the body’s electrical signals when applied to the skin. The researchers believe it could be a cheaper alternative to other on-skin electrodes that cost more to produce and require materials such as copper or silicon.

The team created the electrodes by drawing mesh-like geometric sketches onto pieces of ordinary office copy paper. They then sprayed the paper with an adhesive spray to help them stick to human skin. They connected the pencil-and-paper electrodes to external data-recording hardware using a type of conductive cable.

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The lines of pencil graphite are conductive, and can convey electrical signals that are present on the surface of human skin from underlying organs. Electrocardiograms, for example, record the heart’s electrical activity based on numerous electrodes affixed to the skin.

The researchers successfully used the electrodes to record ECG signals, heart rate and respiratory rate. They say the recorded signals from their electrodes were comparable in quality to conventional methods.

The electrodes could also detect skin temperature. “Electrical resistance reduces when the temperature of the pencil electrodes increases,” says Yan.

Mesh-like geometric patterns are ideal for making electrodes that will stretch when on someone’s skin

Yadong Xu

The electrodes were drawn with serpentine designs so that they would maintain their electrical properties even when subjected to stretching or bending, says Yan. “The electrical resistance in this case is determined by the length and cross-sectional area of these conductive traces,” he says.

When treated with certain chemicals, the electrodes can also be used to detect compounds in sweat such as uric acid, glucose and pH levels.

A different design was also able to harvest electrical energy from humidity in the air, sustaining a voltage of up to 480 millivolts for more than two hours.

Next, the team plans to develop pencil-and-paper-based electrodes with wireless capabilities, says Yan.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2008422117

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