I have a solution of TBS (pH=7.4) and 30nm gold nanoparticles coated with NHS polymer. I want to read the absorbance of such molecules but I cannot seem to fully resuspend the particles, there is always a precipitate. The absorbance readings are very low, and I believe it is due to the fact that the particles are not in solution, they precipitate. Is there a protocol for best resuspending gold np's and measuring its absorbance?
I think they are aggregated, that's why I see the precipitate. The solution is transparent. But i see a very low peak at around 520 nm. Could sonicating my solution help?
The particles were sold coated with the polymer already. All I did was resuspending the solid in PBS buffer. (sorry i wrote tbs at the beginning but it really is PBS) that's the buffer that the company nanopartz recommends. What would be a better buffer?
Your problem maybe rather interaction with (coating of) the container walls than larger aggregates. The latter are expected to cause a related change in appearance.
That could be the problem. I have my nps in a 15 ml plastic centrifuge tube. The solution looked light pink but when i transferred it to a new tube I saw it was clear with black aggregate at the bottom. The walls of the old plastic tube, however, remained pink.
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