A new type of oximeter — or blood-oxygen sensor — is made of organic electronics printed on bendable plastic that molds to the contours of the body. Unlike fingertip oximeters, it can detect blood-oxygen levels at nine points in a grid and can be placed anywhere on the skin. It could be used to map oxygenation of skin grafts, or to look through the skin to monitor oxygen levels in transplanted organs. Patients with diabetes, respiration diseases, or sleep apnea could use the sensor, worn anywhere, to monitor blood-oxygen levels 24/7.

The sensor, made of an alternating array of printed LEDs and photodetectors, can detect blood-oxygen levels anywhere in the body. The sensor shines red and infrared light into the skin and detects the ratio of light that is reflected back. (UC Berkeley photo by Yasser Khan, Arias Research Group)

Existing oximeters use light-emitting diodes (LEDs) to shine red and near-infrared light through the skin and detect how much light makes it to the other side. Red, oxygen-rich blood absorbs more infrared light, while darker, oxygen-poor blood absorbs more red light. By looking at the ratio of transmitted light, the sensors can determine how much oxygen is in the blood. These oximeters only work on areas of the body that are partially transparent, like the fingertips or the earlobes, and can only measure blood-oxygen levels at a single point in the body. Thick regions of the body — such as the forehead, arms, and legs — barely pass visible or near-infrared light, which makes measuring oxygenation at these locations very challenging.

The sensor is built of an array of alternating red and near-infrared organic LEDs and organic photodiodes printed on a flexible material. The sensor has been used to track the overall blood-oxygen levels on the forehead of a volunteer who breathed air with progressively lower concentrations of oxygen — similar to going up in altitude — and found that it matched those using a standard fingertip oximeter. It also was used to map blood-oxygen levels in a three-by-three grid on the forearm of a volunteer wearing a pressure cuff.

After transplantation, for example, surgeons could detect if all parts of an organ are receiving oxygen. With an array of sensors, they would know immediately if there is a point that is not healing properly.

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