Vital signs on the run

For fitness enthusiasts interested in tracking their vital signs while engaged in pursuits such as running, hiking or playing tennis, a newly designed pulse oximeter sensor could be a welcome and wearable accessory. The all-organic optoelectronic sensor – used for measuring pulse rate and blood oxygen saturation levels – could be sported like an adhesive bandage while mountain climbing, bicycle riding or walking the dog, to name a few examples. Importantly, the sensor could also be useful in medical clinics.

 The new device is flexible, which sets it apart from the rigid, electronics-based pulse oximeters that typically are clipped onto fingertips or earlobes in hospitals and doctors’ offices.

“Our prototype uses polymeric materials as semiconductors,” said Ana Arias, head of the University of California, Berkeley, team that created the new sensor. “These materials are flexible by nature and when processed on flexible substrates can lead to electronic devices that conform better to the human body than conventional electronics.”

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A new, all-organic optoelectronic sensor can be worn like a Band-Aid to measure pulse rate and blood oxygen saturation. OLED = organic LED. Courtesy of Yasser Khan.

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A switch to the organic, carbon-based design could enable inexpensive fabrication of the new devices. Because the components of conventional silicon-based oximeters are relatively costly, health care providers choose to disinfect contaminated oximeters, Arias noted. In contrast, she said, “organic electronics are cheap enough that they are disposable, like a Band-Aid.”

The prototype, interfaced with electronics at 1 kHz, incorporates a green (532 nm) and a red (626 nm) organic LED, and the optical signal is detected by an organic photodiode to perform blood-oxygenation measurement. To calculate the pulse, it detects the pattern of arterial blood flow. In contrast, a conventional pulse oxi meter uses LEDs to send red and infrared light through a fingertip or earlobe to obtain the blood-oxygenation measurement. Oxygen-rich blood absorbs more infrared light, while oxygen-poor blood absorbs more red light.

According to Arias, integration aspects always are challenging and, in this case, using organic materials brought an additional challenge because they are not very stable when emitting infrared light. Researchers had to modify the measurement to use green and red light instead of red and infrared. The sensor’s LEDs and detector were deposited from solution-processed materials onto a flexible piece of plastic using spin-coating and printing techniques.

The researchers found that the organic sensor measures pulse rate and oxygenation with errors of 1 and 2 percent, respectively, providing similar measurement capabilities to a commercially available pulse oximeter.

“We showed that if you take measurements with different wavelengths, it works, and if you use unconventional semiconductors, it works,” said Arias.

Arias said the team is talking to companies that are interested in commercializing the new sensor.