The Winograd lab held their annual summer party this past weekend at the Winograd/Garrison home. On the menu was beautiful weather, delicious food, great wine, and the group’s first interaction with Nick’s new drone.
Just back from a week sequestered in the Newark Hilton, testifying in a patent litigation. More on the trial later, but suffice to say, it has been a real awakening. Lawyers work a lot harder than chemists, I can certainly assert right from the start.
There were a number of requests for an index of the proceedings of the Kanazawa meeting. The organizers have gone to a great effort to produce this product. It will be very very useful. The link is either here or at the SIMSsociety.org website.
Castner, Ratner et al. have just published an important paper that discriminates amongst different cell types at the single cell level. They used C60 etching to remove the overlayer junk from the lawn of cells, and principle component analysis to look for chemical differences. The image quality was dramatically improved with the C60 treatment. The samples were freeze-dried, and the authors acknowledge this could lead to some artifacts. I am a bit concerned that they do not talk about the higher mass ions – in the lipid region from m/z 500-900. It seems to me that getting these distributions at the single cell level is the holy grail of mass spec imaging right now.
There is a nice review article (DOI: 10.1021/ac203126f) summarizing many of the most important techniques for characterizing phospholipid films on solid supports. The SIMS technique gets some nice press with the following statement:
“Imaging mass spectrometry allows label-free detection of individual sample constituents and components and area mapping of their distribution on a sample surface. Secondary ion mass spectrometry (SIMS) is the most interesting imaging technique for phospholipid film studies, as it provides high spatial resolution on the nanometer length scale”
Unfortunately, the authors have only used nanoSIMS data to illustrate their point. There is apparently some confusion about emission of molecular ions versus atomic ions. There is also an implication that MALDI is part of SIMS, which most people would not buy. However, overall, the article is an interesting study that places our method in perspective.
There is a thought provoking work published this week resulting from a collaboration between AMOLF in the Netherlands and PNNL where C60-SIMS has been coupled to a high performance FTMS. The mass resolution and accuracy are just what you would expect for this analyzer, so the experiment seems to work very well. The major stumbling block so far is in the imaging. According to the authors, spectral acquisition time is in the 1-20 sec range. For a 256×256 pixel image, an image would require 18 to 364 hours to obtain. A similar observation was made a few years ago in the Caprioli lab for imaging MALDI.
If the speed could be increased, it would be a fantastic imaging tool.
This field really seems to be taking off these days. It is especially interesting to see so many different approaches to the problem. MALDI, DESI, electrospray, fs IR laser desorption, etc etc. There is a big push these days to improve the spatial resolution from 100 microns to 10 microns to 1 micron. For us SIMS users, our main niche has been submicron spatial resolution with depth profiling capabilities – traits which none of the other methods can provide. With an effort to improve the spatial resolution, we are getting some pretty stiff competition. There is a nice recent paper where 7 micron resolution is claimed for MALDI in atmospheric pressure. Since many groups are getting serious about this sort of thing, I think they need to seriously consider more rigorous methods of evaluating spatial resolution. For SIMS, we usually look at a sharp edge and measure the 80-20 distance. So far, the other people are looking at their images and guessing. How about some better protocols for this type of thing?
The installation has gone smoothly. Only a few vacuum leaks, a loose circuit board and a loose wire or 2. Gavyn, Andy and Paul have come and gone, so we are on our own now. Our first attempt is the grid shown below. The red color is crystal violet at m/z 372. Spatial resolution of 1 micron was easy to obtain.