XPS Confirmation of Exosome Purity
So this is basically an update of my post from a couple of weeks ago (and a figure from the poster that I just put up), but it is a very good status update of the contamination experiments that I have been running with XPS. Basically, I ran the sample that had been purified by ultracentrifugation and then normalized everything to a C:Si ratio to compare the results. What it showed was actually really cool.
For the SepCon sample I basically observed an “infinite” (to the XPS) layer of carbon while the ultracentrifuged sample had a 14:1 C:Si ratio, the TF sample had a 4.32:1 C:Si ratio and the blank control had a 0.69:1 C:Si ratio. What we can immediately tell is that our samples are approximately 4 times more pure than those purified by ultracentrifugation. This is an argument that is critical to our research and one that I will be pursuing further. The next steps in this are actually quantifying protein layer thicknesses using angle resolved XPS and also checking in triplicate that this result is what we get each time. I also want to run multiple blank chips from the same wafer and from different wafers to get a good idea of the chip to chip variation in Si and N ratios.
Hi Kilean: From my limited understanding, doesn’t the XPS data here just show you absorbed carbon from any source? For example, observed C could be from absorbed abundant proteins (serum albumin, immunoglobulins) or exosomes? Isn’t the low C signal just as indicative of low exosome yield as it is low non-specific protein yield? I agree this latter point is encouraging though.