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I've been trying, for some time, to image nanoparticles (iron oxide, citrate-coated silver, and PVP-coated gold particles) in water in order to determine their size, without a great success so far. Often images show few if not no particles at all, when the same sample is dried and scanned in air afterwards, lots of particles are observed. Does anyone have some ideas or tips for imaging and sizing of nanoparticles in water? Is it doable?
It sounds like the particles are not affixing to the substrate in water. It is probably a matter of finding the right substrate and might also depend on how the water is filtered. What type of substrate(s) have you tried so far?
Mike is right. You first need to strongly attach the nanoparticles to your substrate. Otherwise you just drag the particles away while you are scanning. Other tip: you HAVE TO use tapping mode rather than contact mode for imaging under liquid environment. And as you may know, the tapping oscillation can be greatly disturbed by the surface charges. never image in pure water. Always use a buffer containg counter-ions that can screen your surface charges. To answer your question, yes, it's doable. I already successfully imaged polystyrene nanoparticles under liquid conditions, as well as virus nanoparticles and liposomes (30 to 100 nm in diameter).
Good luck,
Alex.