Oxygen Sensors -- Fluorescence Quenching

Our oxygen sensors use the quenching of fluorescence by collision of molecular oxygen with a fluorophore that is trapped in an oxygen permeable polymer. This technique is superior to electrodes, in that O2 is not consumed. The sensing material can be put on the tip of an optical fiber, or made as a thin film on flat substrates (patches). We have a variety of sizes and shapes but they all work by the same principle.  The NEOFOX "reader" is a phase fluorometer, which pulses a blue LED and measures the red fluorescence lifetime (tau) of the return signal. There are two chemistries available, ZERO-DRIFT AP for general purpose use in gases and aqueous based samples, and HCR for use in agressive hydrocarbon solvents.

ZERO-DRIFT AP Chemistry    This is our best sensor yet! Our breakthrough multilayered formulation has virtually no drift due to photobleaching. It is not influenced by water vapor, and so it can be calibrated in gases and used without error in liquids. It is very resistant to prolonged exposure to elevated storage and operating temperatures.

HCR Chemistry  HCR is formulated to work in organic solvents, which interfere with standard formnulations. It features excellent adhesion in alcohols, jet fuels, and many other hydrocarbons. We can test our probe in your solvent to validate its use. Just give us a call.

SEOX-PT38-A  and SEOX-PT38-HCR

The PT38 probe is an industrial style 3/8" stainless steel probe with integrated fibers.  The sensor material is housed in a replaceable screw on cap and is available in ZERO DRIFT AP chemistry or the HCR chemistru for hydrocarbons. The probe has a built in thermister.

SEOX-PT38-A      $499
SEOX-PT38-A      $600
replaceable sensor caps
SEOX-38CAP-A         $99
SEOX-38CAP-HCR    $150

SEOX Dip Coated Fiber Probes in Stainless Steel Ferrules
Fibers (1000um diamter) are mounted in stainless steel tubes for mechanical strength, polished and then coated with AP or HCR chemistry. The other end is terminated with an SMA connector.  The probe is coupled to the NEOFOX electronics using a bifurcated fiber assembly. The 1/16" probe is for general purpose while the 1/4" is made especially for high pressure applications. It is rated against leaks to 55 bar (800 psi).

SEOX-F116-A              1/16" probe with Zero Drift AP chemistry    $300
SEOX-F116-HCR         1/16" probe with HCR chemsitry                  $410

SEOX-F250-A           1/4" probe, 55 bar, with Zero Drift AP             $600
SEOX-F250-HCR      1/4" probe, 55 bar, with HCR chemistry          $710





We can dip coat other sizes and styles of probes, so call us if you need something special.

SEOX POF Plastic Fiber Almost Disposable probes
These probes are very inexpensive, almost disposable! They are made with PMMA plastic fibers and low cost plastic connectors. They are not as rugged as the stainless steel variety, but work just as good in terms of the signal. The probes are 6" long and come in a variety of diameters.

SEOX-AP-POF-500   500 micron plastic fiber oxygen sensor/6" long     $39
SEOX-AP-POF-750   750 micron plastic fiber oxygen sensor/6" long     $39
SEOX-AP-POF-1000 1000 micron plastic fiber oxygen sensor/6" long   $39
SEOX-AP-POF-1500 1500 micron plastic fiber oxygen sensor/6" lonng $39
SEOX-AP-POF-2000 2000 micron plastic fiber oxygen sensor/6" long   $39  

SEOX-BB-1000-POF  Bifurcated fiber for plastic fibers     $260



SEOX-G Borosilicate Glass Fiber Almost Disposable probes
These probes are unjacketed borosilicate glass fibers, 6" long with an SMA connector. They are inexpensive, like the plastic fibers but can be used where plastic won't work.The come in a variety of diameters:

SEOX-AP-G-OX-1000 1000 micron glass fiber oxygen sensor/6" long  $45
SEOX-AP-G-OX-1500 1500 micron glass fiber oxygen sensor/6" long  $45
SEOX-AP-G-OX-2000 2000 micron glass fiber oxygen sensor/6" long  $45
SEOX-AP-G-OX-2500 2500 micron glass fiber oxygen sensor/6" long  $45
SEOX-AP-G-OX-3000 3000 micron glass fiber oxygen sensor/6" long  $45

SEOX Sensor Patches and Discs
Sensor discs are clear acrylic coated with sensing chemistry on the front side. They can be glued in place and read by pointing a a bifurcated probe at the back side of the disc. If they are mounted on a clear container wall, you can read pO2 in the inside of the container from the outside, without disturbing the sample. This is very useful for measuring respiration, monitoring O2 in sterile environments and bioreactors, and other sealed systems such as glove boxes, incubators or products packaged in modified air. The drawing below shows an installation with a PT38 probe installed in a compression fitting, and an SEOX patch being read through the wall of the container.

SEOX-PATCH-A Zero Drift AP sensor discs, 1/4", 5/pack                 $479
SEOX-PATCH-HCR Hydrocarbon resistant O2 discs, 1/4" 5/pk          $600

SEOX-RB-125   Bifurcated bundle with 1/8" ferrule for reading sensor discs      $320

Electronics - NeoFox Phase Fluorometer 

NEOFOX is our new phase fluorometer for measuring fluorescence quenching in our
optical oxygen sensors. The NEOFOX couples via USB to your PC.

Use any of our fiber optic probes or patches with the NEOFOX for real time drift free O2 measurements. 

NEOFOX comes in several versions:

NEOFOX           USB based lab system, couples to your PC        $2624
NEOFOX-GT     USB and RS232 for lab or process installations   $2624
NEOFOX-SPORT  Portable version with display & battery           $3359

Sensing chemicals with Light, how it works!

Oxygen is sensed from the fluorescence decay rate of a trapped metal-organic fluorphore. A blue LED pulse is sent down the fiber to the tip, or to a patch with a polymer or sol-gel matrix encapsulated fluorophore. The blue light causes a red fluorescence. The red fluorescence decays over micro-seconds of time. Collision with O2 molecules causes quenching, and a faster decay rate. If the LED is modulated, the fluorescence signal is also modulated but with a phase delay that is related to the lifetime.  In the basence of O2 the lifetime is long, as the partial pressure of O2 increases, the lifetime gets shorter.  The relationship between lifetime and pO2 follows a Stern Volmer relationship. Tau(o) is the lifetime in the absence of O2, Tau is the lifetime in the sample, pO2 is the partial pressure of O2 and Ksv is the sensor calibration coefficient.



The calibration, calculation of pO2 in various units, data logging and real time display are provided by the application software NEOFOX VIEWER, which comes with the NEOFOX unit.

 

New version of Neofox Viewer!
Version 2.55 uses the Neofox onboard pressure sensor to allow for accurate calibrations and measurements of gaseous O2 concentration. The O2 sesnors respond to partial pressure of O2, which is 0.209 atmospheres only when total atmosphereic pressure is exactly 1 atmoisphere. 

Download the new version here. Please be aware it will not work with 64bit versions of Windows 7.

 Neofox Viewer ver 2.55

Here is a screen shot showing the choices in display offered for gases and liquids. The new addition is gas concentration (v/v) which is calculated from pO2 and ambient pressure.  The screen shot shows readings taken on a rainy day in the Georgia mountains -- hence the low pressure!



The calibration algorithms have also been updated to automatically calculate pO2 from entered O2 concentration values.





Applications Support

• There are many tricks and techniques that can help you obtain quality data from your system. We are pleased to discuss your application with you, and are prepared to offer suggestions. Here are a few general tips.

• The probe responds to the partial pressure of O2, not concentration. To calculate concentration in gases, you need to know the total pressure. In liquids you need to know the Henry's Law coefficient.

• Air is 20.9% O2 by concentration, but you need to know total pressure to calculate O2 partial pressure if you are using air as one of your standard gases. NEOFOX has an onboard pressure monitor for ambient pressure. If your probe is not at ambient pressure (if its deployed in a tank or pipe for example) then you will need to measure the pressure independently.

• Temperature is critical. The probe is slightly more sensitive to temperature than pO2.  You can use the NEOFOX-TP probe to measure temperature, or enter temperature by hand. We need to know temperature to about 0.1C

• NEOFOX provides for a "single point reset"  This will change the intercept of the calibration so that the system will read the correct value at a single O2 level (for example air). This is only an approximation. Your single point reset is by definition perfect at the reset point, but the error grows the further from this point that you get.

• Our AP chemistry is not affected by water vapor. The older FOXY chemistry is affected by water vapor. This will lead to errors if you calibrate in dry gases, and then use the probes in moist environments.

• If you don't have access to calibration gases, you can use chemicals to create O2 free samples. Sodium hydrosulfite added to water will scavenge all O2.  If you are in a bind, room temperature carbonated beverages are pretty near zero as well, at least when you first open them. 

• The sensor is more sensitive to changes in O2 at low O2 values.  Sensitivity decreases as pO2 increases, and as temperature increases.

• Dissolved O2 concentration is a little tricky. pO2 and concentration are directly related for a liquid at a set temperature, but Henry's Law coefficient changes with temperature as well as media.

• The HCR probe stands up well to most organic solvents. However, many solvents also have an effect on the sensor signal. This is a reversible, reproducible quenching that can be removed from consideration by calibrating the probe in the solvent.

• Signal to noise varies with the intensity of the fluorescence signal. Bigger fibers are bettet than smaller fibers in terms of signal strength.

• The fluorescence decay is in principle not affected by changes in intensity from fiber bending, ambient light, LED aging etc. Phtobleaching does affect the observed tau in sol gel coatings such as FOXY.  Our new AP formulation has reduced photobleaching drift to near zero.