Sample Prep Part 3

The concentration process is very scalable.  Still, there is a “sweet spot” of about 1000X concentration per stage.  To begin with, this is because there are tradeoffs based on the size of the concentration cells, and the size of your sample.   For a given concentration cell, the initial sample can be up to about a thousand times bigger than the final concentrated volume.  If the initial input volume is 100 liters of drinking water, the cell will be pretty big and the output volume might be 50 to 100 milliliters or so (Slide 11).
 
If you want more concentration, and the sample isn’t now too thick with muck, it can be concentrated on a second stage.  If the input volume is 50 mL to 100 milliliters, the final extracted volume could be 50 to 100 microliters. So, theoretically, you can do a Million X concentration by setting up a two-stage system.  We are currently doing that in an SBIR program for EPA and have demonstrated over 800,000 X in less than 30 minutes run time with our systems.  We plan to develop a commercial device based on this demonstrated approach.  This works well with pretty clean water, and the final samples usually look and smell like the source of the water… which can be pretty bad. 
 
Various types of extraction fluid include low concentration Tween 20 with Tris buffer, Triton X-100 with PBS or another buffer, and several other surfactants and buffers.
Finally, I should point out that when concentrating very tiny particles, like viruses, DNA, or proteins, there is a tradeoff to be made regarding the pore size of the fiber filters in the concentration cell.