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Airdate: Aug 08, 2007
Scientist: Michael Hochella

Science Diary: How Toxins Move-Samples

Science Diary: How Toxins Move-Samples
Preparing samples for a high-tech microscope employs a surprisingly low-tech method.


Welcome to Pulse of the Planet's Science Diaries, a glimpse of the world of science from the inside. Virginia Tech Geochemist Michael Hochella is searching for elusive, little-understood bits of matter called nanoparticles. He's in the lab with graduate student Kelly House. Kelly is preparing water samples for their new Transmission Electron Microscope, or TEM for short. It's an incredibly powerful scope that allows them to see nanoparticles, which are too small to view with traditional optical microscopes.

MH: "The thing about TEM samples is that they have to be very, very thin. The reason that they have to be thin is because electrons that are coming down the TEM column, have to penetrate and pass through the sample with very little or no energy loss. So Kelly, tell us about this particular kind of sample preparation
KH: If you don't have a good sample, you're not going to get to see what you want to see. This is basically a Plexiglas frame. And on the inside there's a little, about one-inch motor, and on top of that is a horizontal disk that the motor spins around.
MH: This transmission electron microscope we're going to use costs two million dollars. And this motor that's the key to making these samples, costs two dollars.
KH: You mix some of your river water sample with what's called an embedding resin. And you take a very, very small drop of that and place it on the grid, which is on the disk, and you spin it around for about ten seconds. And then you have a very thin coating of the sample embedded in your resin, which is now on the grid. It should be about five nanometers thick when it's finished.
MH: Five nanometers thick. That is not thick at all. So, let's give it a shot, okay?

By way of comparison, a human hair is 80,000 nanometers wide. In future programs, we'll hear if Michael finds the nanoparticles he's been looking for. Pulse of the Planet's Science Diaries are made possible by the National Science Foundation.