One of Christine’s projects was to determine if pinholes affected electrical resistance (TEER) measurements. She summarized her work here. I collected her data and did some negative controls to finish this work up. Here’s the graph: The “no membranes” data is from Sepcon transwells with pnc-Si chips but without membranes (I broke them before assembling…
Separations were performed at 2 different salt concentrations with equal volume filtrate and retentate (to avoid dilution problem). Separation time was 40hrs rather than the usual 24. The lower salt concentration run has a lower cutoff – which is just like what we see in the DNA separations. Remember though that proteins have different charges…
Christine and I have been looking into whether the O-ring position affects transport through pnc-Si transwells. The hypothesis was that the unstirred water layer under the Sepcon might be diminished by switching the O-ring from its normal position (“O-ring bottom”) at the bottom of the Sepcon to above pnc-Si (“O-ring top” or “pnc-Si bottom”). This…
UPDATED: More sizing characterization (see chart and figure below). We recently purchased our own gold ladder, and today I’ve done some of the initial characterization. Particles come in 5, 10, 15, 20, 30, and 40nm. Here are the absorbance scans in both water and 10mM KCl: The scans look similar, so none of these particles…
Anant and I have been doing long-term discoloration experiments for the past few weeks. We set up samples in “ideal” conditions – pnc-Si in transwells with pnc-Si side down, autoclaved samples and in the incubator (lower OH-). The only non-ideal component is the use of DMEM+10%FBS with high NaHCO3 (3.7 mg/mL). Chips were RTP’ed at…
PDMS/membrane deflection was measured on Veeco profiler by JP and me. The main problem with this kind of measurement is that it is taken form the backside of the membrane and the walls need to be excluded from the measurement. Using 20x objective helps but still has some problems. PDMS was first spin-coated on the…
In my last post, I concluded that switching the o-ring position from below the membrane to the top in the sepcon produced no leaks. The reason for this switch was to reduce the 1mm “dead-space” (created by the o-ring) that adds to the unstirred water layer (UWL). The next thing that Barrett and I looked…
PES Membranes: I tested 100 and 300kD PES membranes from Pall. 5 and 20 nm particles were used in both water and 10mM KCl. I won’t show all of the data, but I didn’t see any particles in any of the filtrates by absorbance or DLS. The filters were also stained red after the experiments….
In these trials, I used TER to look at the resistance between membranes with different amounts of pinholes. Finding a trend would produce a quicker way to scan for pinholes as opposed to checking each slot on the wafer with the microscope. The table below is my raw data. Wafer Number of Pinholes Resistance (ohms)…
The new electroosmosis wafers have randomly distributed chips with 1, 3, 6, or 9 .1x.1mm freestanding pnc-Si squares. The idea is that we can use these to get a better EO rate vs. active area curve. SC125 seemed to have some sort of film on it, but I decided to give it a shot anyhow…