The O2 sensors consist of quenchable fluorescence dyes embedded in sol gels and polymers that are deposited on the tips of optical fibers, or coated as thin films on flat substrates. Our AP chemistry is ideal for stable operation and immunity from interference from water vapor. Our HCR chemistry works in the harshest organic solvents including jet fuels, kerosene, acetone and toluene. Our newest sensor is the MR series, fast response and totally hydrophobic -- ideal for measuring O2 in gases.
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Zero Drift Optical O2 Sensors, drift free fiber optic Oxygen Sensors
Zero Drift Sensors are the most stable, optical based oxygen sensors available anywhere. 
Call us!  727-230-1697  or email info@zerodriftsensors.com with your application challenge.

*** Zero Drift Sensors work with Neofox electronics and all fiber assemblies from Ocean Optics ***

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Dissolved Oxygen (DO)  SensorsProcess Oxygen Sensors | pO2 SensorsOptical O2 Sensors for Fuels
 Phase Fluorometer Electronics| Optical O2 Sensor Application Notes | ZeroDrift Sensors Story | Technical Documentation & Software Downloads |

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Oxygen Sensors -- Fluorescence Quenching

Our O2 (molecular oxygen) sensors use the quenching of fluorescence by collision of molecular oxygen with a fluorophore that is trapped in an oxygen permeable sol gel or polymer. This technique is superior to polarographic electrodes in that O2 is not consumed. The sensing material can be coated on the tip of an optical fiber, or deposited as a thin film on flat substrates (patches and probe caps). 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 decay lifetime (tau) of the return signal. There are three chemistries available, ZERO-DRIFT AP for general purpose use in gases and aqueous based samples, MR hydrophobic sensor designed for fast response in gases, and HCR for use in aggressive hydrocarbon solvents such as toluene, alcohol, acetone and aviation fuels.

ZERO-DRIFT AP Chemistry

This is our best optical O2 sensor yet! Our breakthrough multi-layered formulation has virtually no drift due to photo-bleaching. It is not influenced by water vapor, and It is very resistant to prolonged exposure to elevated storage and operating temperatures. The matrix is polystyrene which provides excellent adhesion to plastic optical fibers and acrylic substrates. Zero-Drift AP optical O2 sensors are ideal for monitoring bio-reactors, fermentations, respiration experiments, soil pO2 levels, tissue pO2 levels and many other applications.

HCR Chemistry

HCR is our breakthrough optical O2 sensor material that works in aggressive hydrocarbon  organic solvents. These materials dissolve and or poison all other sensor materials in the market. It features excellent adhesion and resistance to alcohols, jet fuels, toluene, acetone, transformer oil, and many other hydrocarbons. We can test our probe in your solvent to validate its use. Just give us a call.

MR Chemistry

 MR sensors are based on  very hydrophobic sol gels, so the influence of water vapor on readings is eliminated without any degradation in response rate. It is ideal for measuring pO2 in gas mixtures where fast response is required.

 

AP formulation

Polystyrene matrix

HCR formulation

Sol Gel matrix

MR formulation

Sol Gel matrix

Response Rate

T90 = 3 sec

T90 = 1 sec

T90 = 1 sec

Dynamic Range (gas)

0 – 760 mmHg

0 – 100% (at 1 atm)

0 – 760 mmHg

0 – 100% (at 1 atm)

0 – 760 mmHg

0 – 100% (at 1 atm)

Dynamic range (DO)

0 – 40 ppm in H2O

0 – 40 ppm in H2O

0 – 40 ppm in H2O

Resolution (gas)

0.04 mmHg

0.005% (at 1 atm)

0.4 mmHg

0.05% (at 1 atm)

0.4 mmHg

0.05% (at 1 atm)

Resolution (DO)

0.002 ppm in H2O

0.002 ppm in H2O

0.002 ppm in H2O

Accuracy

5% of reading

5% of reading

5% of reading

LDL (gas)

0.04 mmHg

0.005% (at 1 atm)

0.4 mmHg

0.05% (at 1 atm)

0.4 mmHg

0.05% (at 1 atm)

LDL (DO)

0.002 ppm in H2O

0.002 ppm in H2O

0.002 ppm in H2O

Drift rate

No measureable long term drift, continuous operation

0.0001 % /hr in gas

0.0001 % /hr in gas

Sensor Operating Temperature

-50 to 100C

-50 to 200C

-50 to 200C

Useful Lifetime

3 years

3 years

3 years

Compatibility

General purpose gases and aqueous solutions

Organic solvents

General purpose gases and aqueous liquids

Water Vapor Interference

no

yes

no

Formats

Dip coated fibers

Spin coated patches & probes

Dip coated fibers

Spin coated patches & probes

Dip coated fibers

Spin coated patches & probes

Review

Best general purpose probe, longer fluorescence decay yields more resolution, zero drift means stable calibrations

Used for organic solvents and gases with organic vapors.  This sensor does respond to water vapor as well as O2

General purpose but with faster response rate than AP chemistry. Does exhibit long term photo-bleaching drift and has less resolution.




Sensing chemicals with Light, how optical O2 sensors work

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Oxygen sensor ZeroDrift fluorescence decay

Oxygen (O2) is sensed optically 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 or polymer 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 absence 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(0) 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.

Stern Volmer equation for zero drift O2 sensors

Calibrating optical oxygen sensors

In practice, the linear form of the Stern-Volmer equation above is not accurate over a large range of pO2 values. Instead the calibration data is fit to a quadratic equation, and at least 3 calibration points are required.

If temperature compensation is required, then a calibration matrix at at least 3 pO2 levels and two temperatures are required.

We offer factory calibrations for the probes, or you can do the calibrations yourself. Generally you will need a source of gases with known O2 concentrations, and a water bath, incubator or some other means to control temperature. We can help you design your calibration apparatus, so feel free to call us.

Our chemistries are extremely stable, and once calibrated should maintain calibration for a long time period. However, damage to the probe material, switching to a new set of optical fibers or other pertubations could cause a "shift" in calibration. When that happens a simple single point "reset" can be performed.



All of Zero Drift Products are available from our online store.  

727-230-1697  info@spectrecology.com