User:Brian P. Josey/Notebook/2010/05/26

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Serious Thinking
I am scouring the web, looking for ideas that could help me solve an issue that I have with my salad dressing idea. This idea is to suspend ferritin, which is water soluble, in a water. I then want to add hydrophillic quantum dots to the water and suspend droplets of this combination in an oil, or other hydrophobic/organic liquid creating a flow cell. Then when I place this on a microscope and introduce a magnetic field, I should hopefully be able to track the ferritin moving across the flow cell by watching the flashes from the quantum dots. There are a couple of problems that I am thinking about, and trying to solve, but there is one that sticks out that I am working on: will ferritin be drawn out of the water droplets by the magnet? If not, how can I calculate the speed of the droplet (measured by tracking the quantum dots) from the number of ferritin in the droplet, and the size of the droplet?

Generally, I am convinced that a ferritin won't pop out of a drop of water and continue along in oil. It is hydrophilic (assumed since it freely floats inside of cells and I have a reference that mentions its water solubility), so chemically it would prefer to be in water and not the oil. There is a greater pressure in small droplets that I believe will keep the ferritin in, but I don't know quite how this pressure will affect the force a ferritin will contribute to moving the water droplet.

Interfacial Tension for Ferritin
I've managed to learn a lot about surface tension today. For the sake of being brief, I will not write up all of my notes here. With what I've learned, I've managed to find a way to calculate the speed at which a droplet of water, suspended in an oil or another hydrophobic liquid, would travel under the influence of the magnetic force ferritin experiences.

As I described above, my plan is to suspend droplets of water containing both ferritin and quantum dots in a sample of some oil. I haven't picked one yet, but Andy suggested mineral oil, which is one of the oils that I am looking at. When I apply a magnetic field to sample, the ferritin will undergo a force and will move. They will move until they come in contact with the water and oil interface. When this happens, there is a chance that the magnetic force will pull them out, which I doubt but I want to prove. To prove that it doesn't get pulled out, I am balancing the force of the magnet with the pressure due to the surface tension and if the necessary surface tension is much greater than the magnetic force, then I know that it won't be pulled out. The issue is that I don't know the interfacial tension, the term for surface tension between two liquids. I am still looking for them.

After this, I can use the viscosity of the oil, and treat the droplet of water as a sphere to calculate the speed of the droplet as a function of its radius and number of ferritin in it. I fortunately have all the values for viscosity that I need, but I am still searching for the the interfacial tensions.


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