I’ve been taking lots of zetapotential measurements with my current setup. Serendipitously, it appears that the more I use the electrodes, the more stable my zetapotential measurements become. Because the system seems well behaved now, I decided to move on to a more difficult problem. Sarah and I made some nanofluidic transistors a few weeks back,…
Last week Sarah and I made several standard nanofluidic transistor (NFT) stacks (3 nm Ti, 12 nm Ag over a 3-slot SiN membrane – wafer # 1024) in the cleanroom. I then measured the zetapotential of these devices at pH 7.43, and we thought that because the outer layer of the chip was Al2O3 that the…
This paper (SiN paper) by Ulrich Rant et. Al. details several experiments conducted with a single pore drilled through a SiN membrane via TEM. They measure the relationship of pH vs. zetapotential for both a model protein (avidin) and their membrane, and then see how protein moves across the membrane at different pH’s. Translocation is…
The blue line reflects measurements taken with my zetapotential setup. Each data point is the average of three independent measurements of zetapotential (a new 3-slot SiN wafer 1024 chip for each measurement) and the linear fit for the pressure vs. streaming potential was at least R^2 > 0.92. Error bars come from the standard deviation…
I’ve been going to considerable lengths to try and get reproducible zetapotential measurements from my streaming potential device. Zetapotential measurements are the closest we can experimentally get to measuring the surface charge of a membrane, and are important for three reasons. First, I need accurate surface charge data for the membranes if my electrostatic model is…
This paper (Variance of Streaming Potential) examines the sources of error in zetapotential measurements. Jess and Zydney both cite it in their EO papers as a source of experimental procedure – in particular this paper found that waiting for the pressure to equilibrate at discrete timepoints works better than a continuous ramp-up in pressure. From…
This is part three of a series of posts on constructing a mathematical model of the movement of gold through a porous membrane. In part one, I implemented William Deen’s mathematical model of the electrostatic and steric effects that contribute to whether a gold nanoparticle will translocate through a pore. The mathematica and matlab code…
Prior to my qualifying exam about a month ago, I put together a simple model of transport (detailed in this previous post) across a nanomembrane that incorporated electrostatics as well as terms describing both convective and diffusive transport across the membrane. It was a useful model, but ultimately limited, as shown by the following image:…
UPDATE: I have since ported the program into Matlab. If you open the following zip document(Archive) you can run Find_Sieving_Coefficient. You can select a results file and after ~5 minutes the expected sieving coefficient for the pore distribution is spat out. Using Wolfram Alpha’s Mathematica programming language, I’ve implemented an amalgamation of different mathematical models…
I’ve spent a long time in lab trying to optimize the protocol for streaming potential measurements. The slope of an applied pressure vs. streaming potential graph can give us the apparent zetapotential through the helmholtz-smolachowski equation. The apparent zetapotential is a good measure of the surface charge of a nanoporous membrane, and since I’ll be…