New light-sensitive 'tattoo' sensor can be used to measure blood oxygen levels

Monitoring blood oxygen levels is important when treating patients with certain illnesses, including COVID-19. Now, a new subcutaneous light-sensitive sensor offers a way to do just that, and could one day be used to measure other substances in the blood as well.

The technology is being developed in the lab of Professor David Kaplan at Tufts University in Massachusetts. It currently takes the form of a thin film disc smaller than a U.S. dime that is surgically inserted just below the surface of the skin -- a bit like a tattoo.

The film consists of a permeable gel composed mainly of cellulose, a protein extracted from silk. It is not only biodegradable and biocompatible, but also does not change the chemical properties of the substances added to it.

In this latest study, that substance is a compound called PdBMAP, which glows when exposed to near-infrared light—and the more oxygen there is in the surrounding environment, the shorter the glow. Depending on how it's made, the sensor will dissolve harmlessly in the body over a period of weeks to a year.

In testing the device, the scientists inserted the sensor into the skin of a mouse and then shone near-infrared light through the mouse's skin toward that location. The sensor responded by glowing for a duration that accurately represented the oxygen level of the interstitial fluid surrounding it -- a fluid whose oxygen level mirrors that of the blood.

Although blood oxygen levels can already be measured noninvasively using pulse oximeters, the researchers hope that further development of the sensor technology could allow it to measure other substances in the blood, such as glucose, lactate or electrolytes. Currently, such measurements can only be made through blood samples or by connecting the patient to complex equipment.

"We can envision many situations where tattoo-like sensors under the skin could be useful," said Thomas Falcucci, a graduate student in Kaplan's lab who developed the device. "This would typically be in situations where people with chronic conditions need to be monitored long-term outside of a traditional clinical setting. It could be possible to use an array of sensors under the skin to track multiple blood components."

It is reported that this research has been recently published in Advanced Materials.