0.1 g Uranyl-Formate powdwer. Always keep container in dark and minimize exposure to light!
10 ml ddH2O
5 μL 5M NaOH
0.2 μM syringe filter
10 ml syringe
12 ml falcon tubes (2x)
1.5 ml eppendorf tubes
Brind the ddH2O to boiling. Keep boiling for 2-3 minutes to de-oxygenate.
weigh out 0.1 g UFo into a 12 ml falcon tube
Add 5 ml of still-hot ddH2O to the UFo powder. Tightly close lid, wrap in aluminum foil and shake/vortex rigourously for 10 minutes. If the UFo powder was rather fresh, you should obtain a turbid-yellowish solution. As the UFo ages the solutions typically appear more brownish.
Filter solution through the 0.2 μM syringe filter. It should be clear now.
Aliquot 1 ml of the solution into four separate eppendorf tubes.
Centrifuge at max speed for 5 minutes in a table top centrifuge.
Wrap three of the four tubes in aluminum foil and freeze for later use.
Add 5 μL of 5M NaOH to the remaining tube with 1 ml of stain solution and vortex immediately for two to three minutes.
Spin again at top-speed for 3 minutes in a table top centrifuge.
Wrap tube in aluminum foil, keep lid clear
Stain solution is now ready for use!
Comment: UFo solution can be stored at RT for ~10 days in the dark if no NaOH is added. After longer periods of storeage precipitates/little crystales begin to appear, rendering the stain unusable for TEm. NaOH speeds up the degradation process, thus only add NaOH for immediate use.
Whatman filter paper No 1. or No 2.
2% UFo staining solution
carbon-coated TEM grids(e.g. EFCF400-Cu-50, Science Services, Munich Germany)
Glow-discharge grids(e.g. glow discharger EMS 100, Electron Microscopy Sciences). Once may have to test different exposure settings in order to make the surface hydrophilic and sticky for DNA origami objects. LEt the grids cool to RT again.
Put some water droplets on hte bench and stick a 10x10 parafilm piece to it. This is now your clean working area.
Grab a TEM grid with forceps
Apply ~3 μL sample solution onto the carbon-coated side of the TEM grid. Let absorb for a while (3 to 4 minutes are good for ~ 1nM dilute sample solutions).
Meanwhile, apply a 25 μL stain solution droplet onto the parafilm
Use filter paper edge to drain excess liquid from the edge of hte grid. DO not touch the grid surgace.
Remaining liquid film will evaporate in a few seconds, so act quickly.
Immerse grid sample-side first into the stain-solution droplet. Incubate for 40 seconds.
Use filter paper edge to dap off excess liquid from the edge of the grid. Don't touch grid surface.
Let the grid dry completly before injecting the TEM! (~30 minutes).
Ready for imaging!
Comments: Depending on the carbon quality, sample concentration/composition, incubation times may have to be varied. Washing hte grid with 0.5 MgCl2 prior to applying the sample can influence orientations on the grid (more views).