UltrAuFoil® Frequently Asked Questions
UltrAuFoil® are an exciting development in specimen support technology. As many customer would like to know more about them, we've gathered together some of the most frequently asked questions below, but if there's anything you're still not sure of please ask us or your local distributor - we're happy to help.
Why are UltrAuFoil® grids "gold on gold" with both the grid and foil being made of the same metal?
Using the same metal for both the grid and the foil improves the quality of your data because it reduces beam-induced motion caused by changes in the geometry and tension of the foil due to the elimination of the differential thermal contraction between grid and metal during plunge vitrification and sample irradiation. As discussed in Russo and Passmore, Science 346: 1377-1380 (2014) and Russo and Passmore. J. Struct. Biol. 193: 33-44 (2016).
Why is the metal chosen for both grid and foil gold?
Gold has several properties that make it ideal as a sample support in electron microscopy, including being conductive, nonoxidizing, radiation-hard. In addition, it is does not interfere with the specimens you are studying as it is chemically inert and biocompatible, as described in Russo and Passmore, 2014 and 2016.
Why is the foil 500 Å thick?
A foil thickness of 400-500 Å provides optimum data quality by balancing the need for the thinnest possible layer of ice with sufficient thickness of the gold foil to minimise beam-induced motion.
A thicker foil will not further reduce beam-induced motion, but risks degrading data quality due to thicker ice resulting in poor particle dispersion and increased background scatter. In contrast, a thinner foil might offer better particle dispersion due to the formation of a thinner layer of ice, but at <400 Å, the foil is thinner than the individual gold nano-particles it is made from and this increases beam-induced motion due to poorer conductance as the surface becomes uneven. See Russo and Passmore, 2014 and 2016 for further details.
How should I store the UltrAuFoils® and what is their lifespan?
As for our other products, UltrAuFoils® should be stored in a grid storage box in a cool, dark, low-humidity environment. While there is no date of expiry for the UltrAuFoils® we generally recommend using them within two years.
Do I need to modify the UltrAuFoils® before use?
UltrAuFoil® sample supports are ready to use straight from the box. However, as with all transmission electron microscopy grids, users may achieve better sample dispersion and improved wetting if the foils are made more hydrophillic. This can be achieved using standard glow discharge and plasma systems, as described here. UltrAuFoil grids particularly benefit from these treatments, as, lacking the more volatile carbon foil, they can be safely exposed to extended glow discharge or plasma treatment without risk of any surface degradation.
Can I add a continuous film of amorphous carbon?
Yes. We are happy to supply UltrAuFoil® with an ultrathin carbon layer at a thickness of your choice (most commonly 2 nm, but 3, 5 and even 10 nm additional carbon layers are available on request). Alternatively, you may add an additional layer of amorphous carbon yourself: standard float transfer methods, as described in Passmore and Russo, 2016, are recommended to transfer thin films of carbon onto UltrAuFoils®.
How do I set up the beam for data collection?
Data collection can be carried out as you would for holey carbon foils with similar geometries. Thus, we recommend that the electron beam geometry is circularly symmetric beam and centered on the hole. The micrograph is taken at the centre of the hole. We would recommend including a small section of the support foil in each image, as this aids with focussing (see "How do I focus using UltrAuFoils®", below)
How do I focus using UltrAuFoils®?
Since there is no amorphous material in the gold support structure, Thon rings cannot be used to focus. Russo and Passmore, 2016, present a number of different options for focussing when using UltrAuFoils, but the two simplest are:
- Oscillate the beam tilt around 0°, and the plane for which the image shift is minimized is the in focus setting. This method is most useful for automated data collection.
- The micro-crystals of gold in the foil diffract elections, with the diffraction spots occurring in a ring around the crystal image at a distance related the lattice spacing of the gold crystals, as predicted by the Bragg equation, and the defocus. As the smallest lattice spacing of the Gold crystals gives rise to diffraction at a resolution of 2.35 Å, care should be taken to ensure that any objective aperture does not block electrons at the diffracted frequencies. This method is primarily recommended for manual data collection modes.
How do I correct the astigmatism?
We recommend using a calibration specimen to correct the stigmation and beam tilt prior to collecting data on UlrAuFoils®.
Can I use automated data collection methods?
Yes, automated data collection has been successfully tested on UltrAuFoils® using beam tilt to focus.
Are UltrAuFoils® fragile?
No, they should be handled in the same way as traditional carbon foils, and are similarly robust. As with traditional carbon foils, care should be taken when handling the foils with tweezers and during plunge freezing, as if the foil is damaged in these processes, the stability of the support may be severely degraded. We recommend collecting data only from squares where the foil is uniform and intact.
In addition, the gold foil is not volatile when glow discharged or treated with plasma, so the grids may be subjected to far more extensive plasma treatments than standard carbon foils, without any risk of degrading the surface.
Who invented UltrAuFoil® sample supports?
Dr Christopher J Russo and Dr Lori A Passmore of the MRC Laboratory of Molecular Biology, Cambridge, UK invented these sample supports and they are produced under licence by Quantifoil Micro Tools, GmbH.
Where can I find more details about the properties of these grids and how they compare to traditional carbon holey foils?
Chris Russo and Lori Passmore have written two very informative papers about the characteristics of these grids and how they compare to more traditional holey carbon foils.