A team of engineers at the University of California (UC) Berkeley has developed a new flexible sensor that can map blood oxygen levels, potentially monitoring oxygenation of skin grafts and oxygen levels in transplanted organs. With this new sensor, doctors may be able to gather real-time information about a patient’s healing. This healing cannot occur without oxygen, carried in the blood stream.
Yasser Khan, a graduate student in electrical engineering and computer sciences at UC Berkeley, said the team wanted to get away from the bulky, rigid fingertip sensors currently in use and show that oximeters can be lightweight, thin and flexible.
Fingertip oximeters use light-emitting diodes (LEDs) to shine near-infrared and red light through skin. They then record how much light is received on the other side. Oxygen-rich blood absorbs more infrared light; oxygen-poor blood absorbs more red light.
Analysis of the ratio of transmitted light determines the oxygen content of the blood. Because the light needs to travel through the skin to complete the analysis, current oximeters need to be placed on partially transparent parts of the body, like fingertips or earlobes. And they are limited to measuring blood oxygen levels where they are placed.
New flexible sensor array
The team created a sensor that can be placed on skin anywhere on the body and detects blood oxygen levels using a nine-point grid. The new sensor uses organic photodiodes printed on a flexible material and an array of alternating near-infrared and red organic LEDs.
In tests, the sensor was placed on a volunteer’s forehead to track blood oxygen levels as the person breathed air with lower and lower concentrations of oxygen, simulating a climb in altitude. The results matched those of the standard fingertip oximeter used in the experiment. The sensor was also put to work to map blood oxygen levels in a three-square-inch grid on the forearm of a volunteer wearing a pressure cuff.
“After transplantation, surgeons want to measure that all parts of an organ are getting oxygen,” Khan said. “If you have one sensor, you have to move it around to measure oxygenation at different locations. With an array, you can know right away if there is a point that is not healing properly.”
The report appeared in Printed Electronics World. More information about the sensor can be found in Proceedings of the National Academy of Sciences.