I think you can centrifuge it at room temperature.  If you have prepared gold nanoparticles using Turkevich  method, you must have used sodium citrate. Sodium citrate can act as both reducing as well as stabilizing agent. So your nanoparticle dispersion will be stable for long days at room temperature after centrifugation. Thanks

Room temperature is fine for it. 

Previously, roughly a decade before, I did the same and concentrated 8-10 times.  I am not remembering exactly the rpm now. You need to  optimise it first.  If you are using very high rpm means, it'll form nice mirror in the bottom of your centrifuge tube. 

Good luck to you

Thank you very much for your reply

thank you for your response

the volume you want to centrifuge will decide the total centrifugation time.. i used to centrifuge 10ml in 15ml centrifuge tubes for 90 minutes... 2 ml in eppendorf 2ml for 20-25 minutes.. citrate capped tend to aggregate on resuspension with passing time..

Use room temperature for centrifugation. As a rule use prolonged centrifugation times (20-40 min) rather than using high speed to avoid agglomeration of gold nanoparticles. Please go through the attached link. A reference table is provided by cytodiagnostics inc which shows g force and time required for centrifuging gold nanoparticles of different diameter. 

Also, while centrifuging gold nanoparticles always keep in mind that the pellet formed is not compact. So carefully remove say 800 uL of supernatant from 1 mL of sample. To achieve complete washing repeat the procedure 3-4 times. You will then be left with a 5x concentrated sample of washed gold nanoparticles.

http://www.cytodiagnostics.com/store/pc/Gold-Nanoparticle-Handling-and-Storage-d7.htm

Room temperature is fine, yes. Though some amount of loss due to aggregation is likely (centrifuge too hard, and you lose almost all of it due to aggregation. A careful optimisation process is needed.

However, that's not really what you needed to know. The problem seems to be that your centrifuge temperature rises. This is normal for high RPM centrifuges, the motor gets hot, and the rotor itself will also get heated by air friction. Some high speed centrifuges have a vacuum chamber for the rotor. Spinning under vacuum might eliminate most of your heating problem.

If your centrifuge does not have a vacuum chamber, but does have cooling, then you will have to set the cooling of the centrifuge chamber below the desired rotor temperature. How much will depend on how hot the rotor is getting, but to avoid corrosion problems I would advise staying a few degrees above the local dew point.

Hi,

We regularly centrifuge citrate-capped Au particles in our laboratory. 14,000 rpm @ 10-20 celsius generally does the job just fine. If you are still concerned about agglomeration, a small percentage of tween-20 (usually ~1% or less) in your solution can decrease the rate of this occurrance. We also sonicate our particles after centrifugation to ensure that they are sufficiently resuspended. As a rule of thumb, the temperature you want to use during this step would likely be at room temperature or below. We occasionally go as low as 4C.

There is flexibility here. You may want to aliquot some small volumes of your particles and test different conditions, if you have the time.

Thank you very much for the very very useful information.

In our experience using Turkevich Au nanoparticles a single centrifugation and re-dispersion in pure water can be done without significant loss of material and without cooling the centrifuge. Subsequent ones are likely to destabilise the particles due to the absence of stabilising agent in solution. I don't believe that cooling will make a big difference here.

Thank you for your valuable information

Thank you for your suggestion.

I used the centrifugation of Au nps at room temperature but the cycles and speed also matters here. That means 1 hour is enough for centrifugation even at high temperature.