How Oxygen Sensors Work
Certain organometallic molecules exhibit fluorescence when excited by particular wavelengths of light, and some of these molecules are able to have this fluorescence quenched by other entities in the immediate environment.
Ocean Optics’ oxygen sensors utilize both ruthenium and platinum based fluorescent molecules whose fluorescence is quenched by the presence of molecular oxygen. We embed these molecules into various thin-films that can be applied to the tips of fiber optic probes or to peel-and-stick patches for non-invasive measurement.
A fiber optic bundle sends the blue excitation light to the sensor chemistry, and the resulting fluorescence is relayed back down the bundle to the detector. The blue excitation LED flashes as a square wave at 10 Hz, and each time the LED turns off the fluorescence decay of the chemistry is seen by the detector.
The chemistry changes its decay profile based on the partial pressure of oxygen it feels; these sensors are strictly measuring the partial pressure of molecular oxygen, and do not consume oxygen in the process.
Calibration is performed by exposing the sensor to known oxygen concentrations and temperatures and characterizing the resulting fluorescence decay response with either linear or polynomial curve fits.