The oxygen measurement technique is based upon the fluorescence quenching of a metal organic fluorescent dye immobilized in a gas permeable hydrophobic polymer. The dye absorbs light in the blue region and fluoresces within the red region of the spectrum. The presence of oxygen quenches the fluorescent light from the dye as well as its lifetime. The quenching process is a purely collisional dynamic where the energy from the excited fluorescent dye is transferred to the oxygen molecule during a collision, hence, reducing the emission intensity as well as the fluorescent lifetime of the dye.
Fluorescence without oxygen Quenching of Fluorescence with oxygen
The O2xyDot TM is the oxygen sensor that is placed in the package before it is filled and sealed. This dot is addressed from the outside of the package via the fiber optic pen to make oxygen measurements without penetrating the package.
O2xyDotTM :
- Is 5 mm in diameter with a thickness of 0.2 mm.
- Allows multiple measurements on the same package.
- Has detection limits of 15 ppb in water and 0.03% in gas.
- Is totally passive, it does not interfere with contents of the package and does not consume oxygen.
- Is suitable for measuring oxygen both in the gas and liquids.
- Is a robust low cost sensor that can be used on a disposable basis.
- Is mechanically stable and can be sterilized and go through pasteurization process without losing calibration.
- Can be used in oil water or gas.
- Is independent of pH (2-12) and salt concentrations.
- Is not affected by other gases.
To sense oxygen within a package, an oxydot is attached to the inside of the package. The dot is illuminated with a pulsed blue light from an LED. The blue light is absorbed by the dot and red light is emitted. The red light is detected by a photo-detector and the fluorescence lifetime is measured. Different lifetimes indicate different levels of oxygen within the package.
The change in the emission intensity and lifetime is related to the oxygen partial pressure and can be calibrated to determine the oxygen concentration. The measurement is passive, totally reversible and no oxygen is consumed in the process. The fluorescence lifetime is reduced due to the presence of oxygen; this change can be calibrated to make a powerful sensor that has a large dynamic range.
OxySense® is the world's first truly non-invasive oxygen measurement system for sealed packages. It is tailored for the needs of the food, beverage, pharmaceutical, medical and electronics industries. The system is unique not only for its ability to measure oxygen non-invasively, but also for its ability to measure oxygen in headspace as well as in dissolved liquids. It is an optical system that can measure oxygen within packages that are transparent, semi-transparent and translucent, and as long as the packaging material can transmit light as 470 nm and 610 nm, a measurement can be made.
The non-invasive sensor was developed by TNO in the Netherlands and is being manufactured/marketed by OxySense in the United States.
