http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2843992/pdf/rsif20090526.pdf

http://rsif.royalsocietypublishing.org/content/7/42/143

I assume that the nanoparticles are in pure water? If not, then there might be some other chemical that is attractive. The nanoparticles may have some chemical that helps prevent them from settling out of solution.

Centrifuge the nanoparticles. Expose ants to liquid.

Take the nanoparticles, and wash them with DI water. Are the ants still attracted to the nanoparticles?

Yes Timothy!! sterile DI water, as I told, I had two cuvettes, first one is DI as a control to calibrate apparatus and in same water make nanoparticles, there were no ways of water to be contaminated, method is highly septic and prevent  any kind of external contamination, if water was contaminated ants were go also into DI water cuvette, anyway I will repeat experiment next week and post a video and pictures if this occurs again, thank you very much,

Do you think it is because of paramagnetism? 

We know that the invasive red imported fire ant, Solenopsis invicta, at least here in the U.S. is attracted to electric boxes and electrical equipment where they build their nests. For what you describe these ants may be attracted to the magnetic field similar to the fire ants here. I do not think anybody knows how they do this, how they detect the magnetic field (if this is what they are detecting). There is much about sensory physiology do not know. Insects have sensors for many environmental factors that we are just beginning to uncover.

Thank you Patricia, I am not entomologist, so I cannot identify which species of ant we have in Thailand. These ents are small and can be found anywhere, I read that paramagnetic particle were found in antennas and abdomen of ant. Red color of ants, is it due to Fe in ants or some pigments ?

So this might be a great chance to do a fun experiment. If the article by Oliveira that Stephan cites is correct, then it should be possible to rear the ants in an artificial environment that lacks small particles of iron. One can then redo the microscopy to show that the ants in this colony lack the iron particles. One can do a behavioral study to show if the ants still retain their 13 degree shift in migration pattern.

Another alternative. Try using nanoparticles made of an isotope of iron that is not found naturally (or is very rare). If the ants are after the nanoparticles, then you should be able to find the rare isotope in their bodies. Maybe something like EDAX or AES could be used to identify the isotope from such a small sample. I haven't used these techniques in decades and for all I know the modern versions are sensitive enough.

Another alternative is to use nanoparticles that are paramagnetic but not iron. Do they replace the iron particles in the ants?

I could hypothesize an adaptive advantage to this ability if it exists. By being able to travel in a direction (say always 13 degrees off of due north), I insure that after migration the new nesting site will be in a different spot than the previous one.

That said, if I am silly and always migrate at 13 degrees off of due north, then there will come a time when all the colonies are crammed up tight against the ocean at the northern edge of the continent. So something must redistribute the colonies (mating flights?) back to the south to start the process over. It would also work if migrations at 13 degrees were frequent but travel less distance, while migrations at other angles were less frequent but travel further.

@kenneth Hematite

Yes, using Raman spectroscopy I obtained data that it is hematite, in original post I didnt know since I didn't have results from Raman,

I am going to create magnetite NP, however I think I maybe contaminated sample with oxygen when baking solution, and now I repeated experiment and wait for results of next raman analysis 

As I said, according to Raman spectrometry and XRD, it was hematite, be aware that I am in process of repairing experiment again in more hermetic conditions, and without baking part ( I annealed at 500 600 degree) but also starting solution is hematite, I will repeat again, currently I am waiting data for second repeat, I will let you know when I get results, 

Yes Kenneth, I agree with you, please sorry for not providing you what was my starting material, I didnt read properly question. Let me explain now,

Starting materials for synthesis of MNP was pure Iron wire, DI water, electric current, everything was hermetic, all process was done in tube so there is little evidence of contamination, except oxygen contamination, which is why repeat experiment.

In the second experiment, all production of MNP was carried in argon flow, although I dont have results yet, I assume that this will be magnetite, do you know how? because observing of wave formation when magnetic stirrer is turned on , solution start to behave similar to ferrofluid, "waving" I don't know if this is appropriate english expression, I hope you understand what I mean.

I notice that ants are quite attracted by this solution, no matter what position in experiment was, is it possible somehow this be connected?

Why would you like to know? It is not important or related to my question, and it is independently going on, with no connection to ants behaviour,  

As I wrote, this situation occurred while I was measuring OD,  in cuvettes, separate location from where I made MNP

Something odd happened in the lab. Curiosity took over. An excellent trait for a graduate student. There is a great deal that can be learned from this task even if there is no clear goal. If nothing else, I got to read a paper on magnetic particles in ants that might be associated with an apparent ability to detect the Earth's magnetic field. Another bit of (probably) useless information that a good scientist stores against the remote chance that it suddenly fits with other bits of equally useless information leading to a huge discovery.

So how do people know that there are ants associated with electrical boxes? How have they separated out the fact that it is an electrical box from other biotic and abiotic factors? How should I know that this isn't "one in a thousand nests of this ant happen to be in electrical boxes because they are warm, dry, and enclosed" as opposed to 92% of the nests of this ant are associated with electrical boxes because the electricity in the wires generates a magnetic field? Possibly there is a geospatial correlation between ant nests and electrical boxes that I am unaware of. I have heard people state the correlation many times, I just have not seen experimental proof. However, now there is a plausible mechanism for how the ants detect a magnetic field. It is not proof, but it is plausible.

I can understand ants in the kitchen, ants in the biology and microbiology lab, because there is a substances which can attract them ( food, sugars, ...) but since this experiment is conducted in nanomaterial lab, where most materials are toxic or they are metals, polymers powder, a lot of organic solvents and highly explosive gasses.

Of course there are electric appliances and high voltage power supply, but I dont think ants have nest there ( which I will check again, to make sure ).

Is there any chance to prove behaviour of ants, without killing them? How valid data can be obtained without extracting MNP from ants?

Yes is the short answer.

Maybe is a more accurate answer. It depends on how much effort you are willing to devote to this, and how much failure you can accept. I am not an ant expert, but I work with insects.

The simplest experiment would be to get a number of tubes with nanoparticles. So if I have a tube with water, several tubes with different forms of iron oxide, several with cobalt oxide, and tubes with zinc oxide, nickel oxide, chromium oxide, and titanium oxide, do the ants always choose just one tube? From this test you can eliminate questions like: do ants collect small particles? Can ants tell the difference between Fe2O3 versus FeO? Make several tests in different buildings (which hopefully will be different nests).

I would also try to see if the ants respond to magnetic fields. I might repeat the above experiment but place the tubes on some paper, and have a wire under the paper such that the ants must pass over the wire to get to the tubes. I can let the ants acquire the appropriate tubes, and see if their response changes if electricity is passed through the wire. I could set up an arena to test if it takes longer to find the correct tube if electricity is passed through the wire. The issue here is that I have no idea how much electricity would be required. Is there a difference if you use AC or DC? Can you arrange the wire in a pattern under the paper to improve an ants chance of finding the right tube? The control is always with the wire but without electricity. The problem is that it is not clear if the magnetic effect (if it exists) influences individual workers or if it is most evident when the colony migrates.

If this works, then graduate to more complex tests where you will need several colonies in laboratory culture. This can be difficult. It is easy to capture some ants, stuff them in a cage, and watch them. It is harder to find a queen and get an established nest. However, you can now control their environment. I would see if I could get a good colony in sand, or artificial media. Anything where you can be certain that there are no particles of the metals identified in the previous experiment. The experiments here can be more complex. If you get this far, I would consult an entomologist at your university. Preferably, someone interested in insect behavior.

You could also do experiments where you use a permanent magnet or electromagnet under the table. It is possible that a single wire does not generate a sufficient magnetic field for the ants to detect no matter how many kilovolts you apply.

Do nanoparticles of metallic iron work just as well as iron oxide? How about magnetized nanoparticles of pure iron?

Yes, that can be done. Experiment that you described in first answer is possible to conduct, all parts are available, however, higher degree experimental design would be difficult at the moment to achieve and create, due to lack of funding. Also I wouldnt like to force nanomaterial lab to shift to the ant physiology lab :D Anyway, simple experiment, as you describe can be organize and even if it is not publishable ( I am not familiar what kind of papers are published in entomological journals,) this can serve as preliminary study for conferences or application for funding.  Good idea Timothy, thank you very much,

Regarding your second question, other one metallic nanoparticle that exhibit magnetic properties and are used in my lab are Nickel NPs, I dont know if ants were attracted to them since I didn't do that research. Iron oxide, first one that was create-hematite, dont have magnetic properties, ants were attracted to cuvette with solution, in second repeat ants were attracted to flask with magnetite solution ( magnetite presence is concluded by observing waves on the magnetic stirrer, other techniques need to be done)

Regarding pure iron nanoparticles, honestly I never tried to create them, since it is quite expensive process for now, but that doesn't mean I will not, since I need them anyway for my original research, but thanks for question, I will observe them when I make pure Fe NPs

Yes, I used SEM and XRD, nanoparticles are all with size 10-9 nm, 

concerning magnetic nanoparticle, I think there is only certain range where they exhibit paramagnetic properties, from 5 to 20 nm.