Ocean Optics OOISensors - Manual (Page 47)

Chapter 3
Oxygen Sensors
The following section provides information on operation of the oxygen sensors, as well as the theory
behind sensor operation.
How the Oxygen Sensors Work
Oxygen sensors use the fluorescence of a ruthenium complex in a sol-gel to measure the partial pressure
of oxygen.
► Procedure
This measurement is taken as follows:
1. An LED sends excitation light to one leg of a bifurcated optical fiber assembly.
2. The optical fiber carries the light to the oxygen probe, which is polished to a 45° angle. The distal
end of the probe tip consists of a thin layer of sensor formulation trapped in a sol-gel matrix,
immobilized and protected from the sample. FOXY and HIOXY sensors use a ruthenium
formulation, while FOSPOR sensors use a Pt-porphyrin formulation.
3. The light from the LED excites the ruthenium or porphyrin complex at the probe tip.
4. The excited complex fluoresces, emitting energy at ~600 nm (ruthenium) or 650 nm (pophyrin).
5. If the excited ruthenium complex encounters an oxygen molecule, the excess energy is transferred
to the oxygen molecule in a non-radiative transfer, decreasing or quenching the fluorescence
signal. The degree of quenching correlates to the partial pressure of oxygen in the sol-gel, which
is in dynamic equilibrium with oxygen in the sample (see
Fluorescence Quenching ).
6. The fluorescence is collected by the probe and carried to the spectrometer or MFPF unit via a
second leg of the bifurcated fiber assembly. The fluorescence intensity (for spectrometer) or
phase (for MFPF unit) is measured and related to the partial pressure of oxygen through the
Stern-Volmer equation.
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