Wearable graphene sensors to measure pulse rate and blood oxygen levels offer potential for health care providers. The sensors use quantum dots.

“Graphene coated with nanoparticles has been used to make wearable light sensors that measure the human pulse and blood oxygen levels from ambient light passing through tissue, offering a potential platform for health-care monitoring.
The popularity of wearable technology has risen enormously, with the US market projected to be in the tens of billions of dollars by 2022 (see go.nature.com/33tcein). However, the effectiveness of the most common wearable devices is hindered by the physical specifications of their components: although the device is often embedded in a flexible soft shell, the main parts, such as the sensors and electronics, are still rigid.
Now, writing in Science Advances, Polat et al. report a class of truly flexible, transparent wearable device that is based on graphene covered with a layer of semiconducting nanoparticles known as quantum dots. Impressively, the devices measure various vital signs using only ambient light as a signal.
Materials that are just one or a few atoms thick are said to be two-dimensional. The best-known example is graphene, which consists of single sheets of carbon atoms arranged in a hexagonal lattice. 2D materials in general, and graphene in particular, have tremendous potential for the development of next-generation wearable, soft biosensors because they combine electrical conductivity, optical transparency and mechanical flexibility with outstanding biocompatibility and stability to biological electrolytes.
So how were the sensors used to measure vital signs? Light at certain wavelengths passes easily through human skin and adjacent tissue, but is absorbed strongly by blood — more specifically, it is absorbed by haemoglobin, the molecule that transports oxygen in red blood cells. By continuously monitoring the intensity of light passing through tissue, sensors can produce read-outs called photoplethysmograms (PPGs) that contain information about volumetric changes to blood vessels, which can be correlated to heart rate….
Graphene has now been used as a sensor and as a signal transducer in various prototypes for wearable and mobile health devices. More importantly, however, graphene has paved the way for other 2D materials to be used in sensors and mobile health-monitoring devices.”

Read the full article Wearable graphene sensors use ambient light to monitor health

Source: Nature 576, 220-221 (2019). by Deji Akinwande & Dmitry Kireev
Image: A sensor that detects vital signs using light. a, Polat et al.3 have used graphene coated with semiconducting nanoparticles (not shown) to make flexible, transparent devices that can detect the light transmitted through tissue.

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