Tips for Using the MicroRT™ System for Room- and Low-Temperature Crystallography
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To prepare a sample, start by injecting your environment-stabilizing solution into the polyester tube using a syringe needle. Try to inject the solution all the way down to the sealed end, so there's no gas bubble between the end and the liquid plug. This will help the liquid plug to stay put even if the sample is roughly handled, and eliminate plug motion caused by temperature changes.
Be generous with your plug size (say, 10-40 μl), especially if you want the crystal to remain fully hydrated for several hours. There is some evaporation (roughly 80 nl/hour) through the very thin polyester wall.
Mount your crystal on a MicroMount or MicroMesh that's been inserted into a goniometer base. Remove excess liquid, but don't let the crystal dry out entirely or it may fall off the mount.
Working under a magnifier or microscope, draw the polyester tubing down over the crystal and mount and onto the goniometer base, being careful not to bump the crystal. To make a better seal, apply a tiny amount of grease (e.g., Dow-Corning #976V high vacuum grease) or oil to the tube-capturing tip of the goniometer base.
Align the crystal manually or using an autoalignment system, just as you would for a MicroMount without the tube.
After you've collected a desired number of frames, slide the polyester tubing off. You can then soak the crystal in any desired solution or replace the liquid plug with another solution (e.g., to vapor diffuse in a small molecule or to dehydrate the crsytal), and then draw the tubing back over the crystal and take more frames.
Once you've collected your room temperature frames, just pop off the tubing, plunge the MicroMount in your favorite liquid cryogen, and you're ready to collect a low-temperature data set.
If you want store your crystals for longer than 12-24 hours, replace the polyester tube with any 2 mm ID glass or thick-walled plastic tubing.The MicroRT system can also be used with conventional nylon loop mounts. However, since the loops can have random positions and orientations relative to the pin and tube axis, the chance of bumping the loop and crystal while drawing the tubing is much greater.