[dainian]

I thought I should post this here instead of the "homework help"-type sections, as it's not really homework help, per se, so let me know if I should post this in another forum. I am an undergraduate chemistry student working on my final research project. For the project, I decided to reproduce previous research involving the synthesis and characterization of degradable polyacrylamide nanoparticles. Once I've prepared the NP's, I have to use gel-permeation chromatography to characterize the degradability and SEM to characterize the size distribution. The SEM used by the researchers is a Philips XL30 FEG SEM at the University of Michigan. Since the university I attend is a much smaller university, we only have an old Hitachi S-2100. Our SEM is supposed to have nanoscale resolution, but I'm told that it couldn't go down to the 15-20 nm range that I need. I may be optimistic, but I really only need a semi-blurry image of "white dots on black background," before sending it off to a larger SEM which seems possible. A professor at my school told me that it may indeed be possible by incorporating a heavy metal, such as osmium, into the matrix to increase the sensitivity. This should be simple as a hallmark of the NP's is their ability to swell and contract by pH adjustment as to incorporate drugs within the matrix. So my question is: is this feasible with or without a heavy metal? If so, is osmium a good choice or would something else be better? Any details or guidance would be much appreciated, and I can certainly attach the paper if necessary. Thank you ahead of time.

[zoork34]

The reason you cant just use the particles "as-is" is that the electron beam that is used to obtain SEM measurements will melt your particles before you can get a good look at them.  They are non-conductive, so they will undergo resistive heating when the beam is aimed at them. 

It is VERY common to coat non-conductive samples with a metal before running a sample.  Almost all biological SEM samples have to be coated before they are examined.  OSO4 is a common coating, but that stuff is super toxic.  People also use sputter coating of gold or silver.  http://en.wikipedia.org/wiki/Osmium_tetroxide  http://en.wikipedia.org/wiki/Sputter_coating 

Basically, you have to coat your samples with something conductive or they will be destroyed before you can get a good look at them.