Continuation of the work with the Borkholder group (see this post). We put together a couple of videos of EO flow in the streaming potential cell today. Runs were performed using Ag/AgCl painted wires at ~2.5 V. Lower voltages weren’t producing very convincing flow rates. Here’s the best video of pumping we obtained: Rec0003_comp The…
Today I brought membranes and the streaming potential device to David Borkholder’s lab at RIT. His students and I set up an initial low voltage experiment. They will continue to test the device for flow rates and back pressures. Here is a list of methods and results from today: SC 214, RTPed but not oxidized,…
In this post I look at our membrane resistance and compare it to the best performing alumina membrane. Here is the resistance figure I made for the paper: This figure shows the device resistance with and without a membrane. The membrane resistance would be the difference between the white and grey bars. We would like…
We ordered quantum dots from Invitrogen. These QDs have a PEG coating that terminates in COOH and should cause the dots to be negatively charged. They are about 12.6 nm in diameter: They exhibit a -40mV zeta potential by zetasizer measurements, however the particles appear to aggregate a great deal (under microscope and visibly turn…
Small DNA oligomers behave like stiff cylindrical rods. They have both rotational and translational diffusion, and this is of interest when considering how such a rod will diffuse through a nanopore. In this post I briefly consider the effects of rotational and translational diffusion of cylinders of different lengths. The rotational diffusion coefficient can be…
This is an update of the research on the on-chip EO pump. Due to a mistake in determining the direction of particle flow, it now looks like the particles in this post were moving by electrophoresis rather than electroosmosis. The particles were negatively charged (-40 mV zeta potential) because of a COOH group on the…
For the charge model, we would like to know the surface charge density and size of our experimental molecules. I’ve attempted to use the Zetasizer for both measurements, but as mentioned in my diffusion paper, DLS gives sizes that deviate from the expected or crystal sizes. Since zeta potential measurements require large amounts of highly…
I recently performed an experimental separation with 4 proteins in 100 and 10 mM KCl. All proteins are negatively charged at the pH of the experiments, and we would expect that less would pass through the membrane in the 10 mM KCl solution. Here’s the gel: You can see that the beta-gal in particular does…
Charles developed a new microEO chamber, and I did some quick particle tracking experiments. The fluid in front of the membrane was filled with 200nm fluorescent polymer beads, and the power supply was used to cause the fluid to flow within the chamber. Bead speed was measured with Henry’s particle tracking programs. Picture of microEO:…
Diffusion based separation theory uses a hindrance model to explain how the pores affect the diffusion of molecules of different sizes. The simplest and most well known hindrance model is given by the Renkin Equation: where Dm is the diffusion coefficient within the membrane, D0 the free diffusion coefficient, and α the ratio of molecule…