Silica NP Separation
Here’s my ‘blog’ post using Google’s Picasa photo album:
A few weeks back I received nanoparticles from Ithaca startup company called Hybrid Silica Technologies (HST). They are silica particles that are infused with fluorescent dyes that are generally similar in size and coated with a PEG layer, suspended in DI H20.
I chose to work with their ~10 nm Cy5 (blue) and ~45 nm TRITC (pink) particles. I had been using membranes from w504 to perform permeability tests, so I re-used a few of those membranes to do concentration and separation experiments. The photo captions are hopefully self-explanatory.
Results:
– w504 concentrates 45 nm particles – the pink solution became significantly darker as a clear filtrate passed through
– w504 allowed the 10 nm particles to freely pass. The filtrate had nearly the same color as the retentate
– Mixing the particles ahead of time gave a clear/milky color that was neither pink nor blue. After spinning the solution using w504, the filtrate appeared to be a light blue and the retentate started turning pink.
I have not had a chance to do any quantitative work on the filtrates/retentates and hope to get to that when we get back from Boston.
Last but not least – wafer 504 after ozone treatment did not need to be wetted on the backside to push water through. This was true for the constant pressure cell as well as the centrifuge. In fact, it ran just fine in the centrifuge and passed reasonable amounts of water within 60 minutes (40-80 uL) at low speed with just the two slits. This very surprising result was the motivation to try the 45 nm particles, to make sure there were no sub-optical defects allowing the water to flow w/o PVP treatment. The fact that these membranes could separate the two particle populations and flow water without anything more than ozone treatment is great!
So JP and Dave – please do whatever you can to produce more wafers like w504.