Real Time Oxygen Measurement in Individual RBCs

An engineering breakthrough could eventually be used to determine oxygen metabolism in cells, or how various disease therapies impact oxygen delivery throughout the body.

Researchers at Washington University (St. Louis, MO, USA) developed single-RBC photoacoustic flowoxigraphy (FOG), which can image oxygen delivery from single flowing RBCs in vivo, with millisecond-scale temporal resolution and micrometer-scale spatial resolution. The new technology works by firing two laser pulses of different colors at a red blood cell 20 microseconds apart, receiving return signals identifying the color of the RBC at any given moment; using intrinsic optical absorption contrast from oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR), FOG then allows label-free imaging.

Although the RBCs travel very quickly, the speed of the device—200 Hz, or 20 frames per second—allows the researchers to see the cells in real time, and by watching the color shift, the researchers can determine the average oxygen delivery per unit length of capillary segment. The researchers also demonstrated that single-RBC oxygen delivery was modulated by changing either the inhalation gas or blood glucose, and that the coupling between neural activity and oxygen delivery could be imaged at the single-RBC level in the brain. The study was published early online on March 25, 2013, in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

“Photoacoustic flowoxigraphy is considered an engineering feat, enabling oximetry at the most fundamental level, namely, the single-cell level,” said lead author Professor of Biomedical Engineering, Lihong Wang, PhD. “There are many biomedical questions that this technology could answer: How would cancer or diabetes change oxygen metabolism? How would cancer therapy or chemotherapy affect oxygen level? We’d like to see if we could use this technique to monitor or predict therapeutic efficacy.”

Using FOG, the researchers were also able to watch the RBCS choose which direction to travel when encountering a capillary bifurcation. They found that RBCs tend to travel in clumps to where the oxygen is most needed in the body at a particular time.

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