Flexible sensor maps blood-oxygen levels across the body

November 09, 2018 // By Julien Happich
Researchers from the University of California, Berkeley have combined recent advances in printed electronics to sandwich OLEDs and organic photodiodes on one flexible substrate and drive them as a large-area reflectance oximeter array (ROA).

Their paper "A flexible organic reflectance oximeter array" published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) details an array composed of four red and four NIR printed organic light-emitting diodes (OLEDs) and eight organic photodiodes, all addressed sequentially using analogue switches to drive the OLEDs and read out the OPD signal. 

The reflectance oximeter array 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).

For their device, the researchers chose red (612nm) and NIR (725nm) OLEDs for which molar absorptivities of HbO2HbO2 and HbHb are significantly different, yielding good reading results for blood-oxygen levels. Taking reflectance oximetry to a large area with pixel-driven arrays means localized readings can be achieved over large skin areas for the 2D mapping of blood-oxygen levels across entire parts of the body, for example to monitor in real time the oxygenation (and healing) of tissues, wounds, skin grafts, or transplanted organs.

Another benefit of this flexible sensor approach over conventional and localized transmission-mode pulse oximetry (usually only performed at a fingertip or the ear lobe), is that oxygenation mapping can be performed even when there is poor blood circulation or no pulse.

In the case of a medical shock, low blood perfusion, or organ injury, the authors highlight, the pulsatile arterial blood signal of becomes too weak to be used for pulse oximetry. The researchers proved their setup on a forearm by occluding blood supply to the arm using a pressure cuff (as those used for measuring arterial tension).

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