Reproducible Results!

So many dilutions! Endless labelling...

Last week, I repeated the equilibrium dialysis two separate times and prepared calibrations and dilutions for ICP.

I wasn't able to run ICP until Monday since we ran out of Argon gas. I ran the ICP on Monday and Tuesday (only 2 runs because my samples were limited). After analyzing the data, we found that both dialysis runs showed 1 Na/S and nearly 1 K/S! I found a calculation error in the data analysis from last week which, when corrected, indicated that both Na and K samples had 1 ion for every 4 S. That dialysis was a "quick and dirty" experiment so we are more confident in the most recent data which has proven to be reproducible.

One thing that looks interesting is that the hydrodynamic radius of the nanoparticles goes down after salt dialysis and back up after water dialysis. After the water dialysis is can be up to 30 nm bigger than after the salt dialysis! Since the amount of PSS/NP is remaining constant, this data indicates that the conformation of the PSS is changing in response to the salt concentration.

Aggregated Nanoparticles

Going forward, we are going to run some tests with varying salt concentration. Today I did a titration of NaCl into the PSS coated NPs and took samples at a range of salt concentrations. I found that the nanoparticles aggregated (due to instability) partially at 100mM salt and completely at above 200 mM salt. This will give us an idea of what range we can dialyze the nanoparticles at.