Frequently Asked Questions

What is the material used to make your oxygen sensors?
The material composition is a ruthenium molecule entrapped in a silica “sol-gel” matrix.

What is "sol-gel"?
The sol-gel is a matrix made up of silicon, ethanol and water. By controlling the ratio of those constituents, we can control the pore size to ensure that the chemically sensitive dye does not leak out.

How is the ruthenium  dye entrapped in the sol-gel used as an oxygen sensor?
When the ruthenium  dye molecule is excited by a blue (470 nm) LED, it becomes sensitive to oxygen and the amount of fluorescence released by the molecule is decreased by the amount of collision between the oxygen molecule and the ruthenium dye.

What are the different formulations that we sell?
A. FOXY – ruthenium
B. HIOXY – ruthenium
C. FOSPOR – platinum porphrin

What’s the difference between FOXY and HIOXY?
The sol-gel matrix that entraps the ruthenium molecule for HIOXY has a proprietary chemical that allows it to survive in hydrocarbon environments.

The FOSPOR sensor is based on a platinum porphrin compound. What is that?
Platinum is surrounded by porphrin molecules.

What is the oxygen sensing mechanism called?
The formal name of the process described is called “collisional quenching.”

Can you define collisional quenching?
Collisional quenching is the process in which molecules physically “collide” into a fluorescent molecule. There is a transfer of energy from the fluorescent molecule to the colliding molecule (oxygen), thus the amount of fluorescence emitted is less intense.

How is collisional quenching related to partial pressure?
Consider a sealed vessel; as you increase the amount of oxygen molecules in a vessel the pressure applied on the dye by oxygen increases and the amount of the collisional events increase.

What do you mean when you say, “We measure partial pressure of oxygen?”
At 1 atm (typical conditions we live in), we breathe many molecules such as nitrogen, helium, hydrogen and oxygen. All these molecules make up the total pressure in the environment. The ruthenium in our sensors is sensitive only to oxygen, which is just one part of the total pressure in the environment. So, when we determine the percentage of oxygen present in the environment at 1 atm, we’re measuring part of the total pressure – hence the term “partial pressure.”

Does temperature play a role in measuring oxygen?
Yes. Collisional rates increase non-linearly with temperature. As temperature increases and partial pressure of oxygen remains the same, compensating for temperature mitigates the risk of a false partial pressure reading.

What are the units of pressure and how do they relate to each other?
ATM- atmosphere; Torr; mm Hg

1 atm = 760 Torr =760 mm Hg
At 1 atm oxygen is 20.9% of the total pressure in the environment
At 760 Torr oxygen is 152 Torr of the total pressure
At 760 mm Hg oxygen is 152 mm Hg of the total pressure

What technique is used to measure oxygen?
The formal name for the measurement is called phase fluorometry.

What is the generic name of equipment used to measure phase?
Phase fluorometer.

What parameter is measured by a phase fluorometer?
The phase shift between excitation (blue LED) and emission (ruthenium  fluorescence), which is used to calculate the excited state lifetime (tau).

How do the electronics measure tau?
The blue LED and the fluorescence signal received by the APD is sent to a microprocessor in which a proprietary algorithm calculates the shift in time.

What is the purpose of the reference LED in the diagram?
The reference LED accounts for any electronic changes that may have occurred during an experiment. This is proprietary to Ocean Optics and no other company has this design.

How is lifetime calculated from the phase shift?
The formula below shows the basic formula for reporting Tau (lifetime):

How is partial pressure of oxygen calculated from tau (lifetime)?
We use a modified Stern Volmer relation to calculate oxygen partial pressure:

Can we measure oxygen in solutions such as water?
Yes. Because we measure the partial pressure of oxygen, the oxygen molecules (though they are dissolved in water) still apply pressure on the sensor. We use a Henry’s Law coefficient to convert O2 partial pressure in gas to concentration of dissolved oxygen in water.

P02 = k C
pO2 = partial pressure of the solute above the solution
C = Concentration of the solute in the solution
K = Henry’s Law constant

Can we measure dissolved (D0) oxygen in any other liquid such as fuel, salt-water or blood?
No. We cannot measure the DO of other solutions because we do not know Henry’s coefficient for those solutions. We can only report the partial pressure of oxygen.

How does the NeoFox communicate to our NeoFox Viewer software?
The NeoFox reads data out via USB to the NeoFox Viewer.

Does NeoFox Viewer make all the calculations shown above to report oxygen values?
No. The NeoFox electronics system itself performs all the mathematical calculations and reports the values to the software.

How many channels can NeoFox viewer monitor?
NeoFox Viewer can monitor up to 6 channels. However, you will need a USB hub in order to accommodate each unit. Each system will have its own tab within the software for monitoring.

In a multi-channel set up, does each NeoFox need to have the temperature probe connected?
Yes. Each NeoFox needs to have its own temperature sensor attached -- especially in the case of making a dissolved oxygen measurement.

Are there other methods of communication?
Yes. You can use the analog 4-20 mA output signal to report oxygen.

Is it possible for a customer to create his or her own software?
Yes. We provide drivers (DLLs) to the customer and sample VI’s to help them create their own software in LabVIEW only.

Ocean Optics is calibrating our NeoFox oxygen sensor for us. The last time I used this sensor, the calibration data came on a CD. When using the 4-20 mA analog output, how is the calibration presented?
The calibration will come on a CD. You will still need to use the same calibration procedures that you did last time. Please see User Manual Appendix C for information on setting up the analog outputs. You will need to have an external power supply to run the 4-20 mA loop as shown in Appendix C of the User Manual.

Is it possible to send commands via USB to the NeoFox without interfacing directly with the provided software?
You cannot send commands to the NeoFox via USB. However, with our assistance, you may be able to use the DLL to operate the system. This is most likely to occur with an OEM or other customer who wishes to bypass the NeoFox Viewer software to operate the system. Please contact an Applications Scientist for assistance.

I understand that there is a pressure sensor inside the NeoFox controller itself, but not on the probe. Is it possible to get pressure measurement at the site of the probe?
The NeoFox controller will likely have a slightly different pressure than the probe itself. There is a pressure sensor inside the NeoFox system; if the pressure is changing over time, there reported answers will be incorrect. Pressure is linear with reported oxygen. For example, if you double the pressure during a measurement the reported oxygen value will double. To be able to monitor this in real time, you need to send the signal from your pressure sensor to your custom software and you have to read our oxygen and temperature readings via the 4-20 mA option. It’s doable, but challenging.

Using the electronics, can you control your sample read time? And how does that affect your results?
Yes. In advanced settings, under “SENSOR CONTROL” there is the option of setting the duty cycle. Standard setting is LED duty cycle on = “1” and LED duty cycle off = “0”, meaning 1 second read time and no off time. You can change this setting. Controlling the duty cycle off and on time can manage your signal drift.

How can we calculate the new drift based on the new setting of duty cycle?
The drift we report is based on “continuous” excitation of NeoFox LED (the default continuous excitation of the LED is hard coded at 20% duty cycle). For example we report our FOSPOR drift at 0.05 O2% per hour. If a customer decides to toggle the LED by changing the settings of “duty cycle on” / “duty cycle off “under advanced settings, they should recalculate the new drift as follows.

How are the sensors manufactured?
Sensor probes are dip coated and patches are spin coated.

How reproducible are the probes and patches from batch to batch?
Probes are not reproducible; each probe gets calibrated as an independent product. However, we can apply one calibration factor to 75 patches.

How do we calibrate the probes and patches?
The sensors are calibrated within a NIST traceable oxygen and temperature regulator. The calibration is done at 1 atm.

What’s the purpose of calibration?
The oxygen sensor is sensitive to temperature, so we must calibrate the sensor performance over the range noted by the customer to ensure accurate readings over the course of the measurement.

How does range of calibration affect accuracy?
The accuracy and resolution decrease as you increase the temperature and oxygen range. The widest range in reported accuracy is noted in the specifications for each formulation.

How long does a calibration last?
Typically a calibration should last 9-12 months, depending on use. We recommend a sensor being recalibrated once per year. The 18G and 21G probes can not be recalibrated.

What is the role of the SGS test product?
The SGS is a free sensor coated on a test disk. Use it to test chemical compatibility for the formulation of choice.

Does a customer have to use our probes and patches?
No. We can apply our sensor coatings all a wide variety of substrates. If you want us to coat your current probes, they must be polished at a specific angle (45 degrees) to ensure maximal performance.

How do you know if a coated probe is working well?
In our QC process we evaluate the ratios of fluorescence intensity when the probe is in oxygen and nitrogen. For the new technology we look at the tau ratio of oxygen to nitrogen.

What options are available if I'm uncertain that my application will work?
We have tested a variety of samples under varying conditions. So, our knowledge base is strong. Nonetheless, we can perform feasibility and other testing to ensure optimal results. Be sure to contact an Ocean Optics Applications Scientists for assistance.