Researchers use graphene to develop the world's thinnest sensor

Not long ago, the graphene "tattoo" exhibited at the San Francisco International Electronic Components Conference (IEDM) is the world's thinnest epidermis electronic device. A graphene sensor attached to the surface of the skin like a tattoo measures electrical signals from the heart, muscles and brain, as well as the temperature and humidity of the skin. The measurement accuracy of this new sensor is the same or even higher than that of a large traditional medical device.  

Sensor developers at the University of Texas at Austin hope that the product will be used in the cosmetics market, and hope that ultra-thin sensors can replace existing medical testing equipment to provide users with a more comfortable wearing experience.

Currently, if a doctor wants to diagnose heart disease by monitoring heart rate, the patient needs to wear a large ECG monitoring device (EKG) for 24 hours. Researchers hope to develop smaller, unobtrusive surveillance devices while maintaining or even improving measurement accuracy. Deji
Akinwande) is an electrical engineer in the field of two-dimensional materials. He is working with Professor Lu Nanxun, a skin electronics expert, on the project.

Materials scientists have been promoting the superior electrical and mechanical properties of graphene for many years. In addition, this one-atom thickness two-dimensional material has an important property: transparency. When it is attached to the skin, it also deforms along the contours of the skin surface. Deji said that the transparency and softness of the graphene material makes it almost impossible to feel when it is attached to the surface of the skin.

The researchers first grown a single layer of graphene on a copper substrate, then covered a layer of elastic polymer material and etched away the copper. Next, after placing the polymer-graphene sheet on the temporary tattoo paper, the researchers etched the graphene sheet into a flexible spiral electrode by a certain method. In this way, the world's thinnest medical device can be attached to the skin like a temporary tattoo.

In the validation experiment, the researchers performed five measurements using graphene tattoos and compared the data obtained with the results of conventional sensors.

The graphene electrode can read the change in electrical resistance caused by changes in electrical activity in the epithelial tissue. When worn on the chest, the graphene sensor can detect weak fluctuations that are not visible to traditional ECG devices. In addition, the accuracy of sensors applied to electroencephalography (EEG) and electromyography (EMG, which is used to record electrical signals of muscles, which can be widely applied to the next generation of prostheses) is also very high. Deji introduced that graphene sensors can also monitor changes in skin temperature and humidity, and many cosmetic companies are very interested in this.

The high conformity of graphene to the skin is one of the reasons for its high precision. There is an air gap between the large-volume rigid electrode used in conventional medical testing equipment and the skin, which greatly reduces the signal accuracy of these instruments. Some new sensors are only a few microns thick and have a much better fit to the skin, but because they still use hundreds of nanometers thick gold electrodes, the electrodes may lose contact with the skin as the skin stretches and contracts.

In contrast, Texas Instruments researchers developed a graphene electrode with a thickness of only 0.3 nm.

Deji said that they will add a signal transmission system to the graphene tattoo to transfer data between the device and the mobile phone or computer.

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