[3dem] reflections from gold fiducials

[Jaap Brink]

Hi,

These are bright-field reflections arising from Bragg diffraction of the gold lattice in the nanogold. They should disappear at exact or Gaussian focus. But, you don't want to do that. The way to remove them should be to dial in a smaller OL aperture that cuts off everything beyond 3Å resolution.

Jaap
----
Jacob Brink Ph.D.
TEM Product Manager Life Sciences
JEOL USA, Inc., Peabody MA 01960
(978) 317-9561

Sent from mobile device. Please excuse typos and this reply's brevity as I'm using all thumbs to type :-)

On Nov 6, 2017, at 4:18 PM, "vojta at strubi.ox.ac.uk<mailto:vojta at strubi.ox.ac.uk>" <vojta at strubi.ox.ac.uk<mailto:vojta at strubi.ox.ac.uk>> wrote:

Hi Lars,

To my knowledge coloidal gold particles are almost always polycrystalline.  At higher magnifications you will start to see lines corresponding to different spacing of the crystal lattices and if you crank the magnification all the way up to something like 0.3 Apix you can see individual columns of atoms (attached below is an image of a wurtzite crystal I took on an F30 some time ago).  The reflections you see move closer to each gold bead as you get nearer to focus which I think is an amazing example of high resolution information being delocalised with defocus.

Only rarely do we see reflections like these in tomograms, I would also like to know what dethermines if they show up or not!

If you're interested in this topic I strongly recommend watching the supplemental videos in Lu et al. (2010, https://www.nature.com/articles/nnano.2010.4) and you can also find plenty of publications on the structure of gold nanoparticles.

Best,

Vojta

Vojtěch Pražák
Graduate Student
Department of Structural Biology
The Wellcome Trust Centre for Human Genetics
Roosevelt Drive, Oxford, OX3 7BN UK
University of Oxford

Email: vojta at strubi.ox.ac.uk<mailto:vojta at strubi.ox.ac.uk>
Web: https://www.strubi.ox.ac.uk/research/kay-grunewald


---- Original message ----
Date: Mon, 6 Nov 2017 21:13:14 -0000
From: "3dem" <3dem-bounces at ncmir.ucsd.edu<mailto:3dem-bounces at ncmir.ucsd.edu>> (on behalf of "Lars-Anders Carlson" <lars-anders.carlson at umu.se<mailto:lars-anders.carlson at umu.se>>)
Subject: [3dem] reflections from gold fiducials
To: <3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>>

Dear community,
We encountered something during tilt series acquisition recently that I
hadn't seen before: several 10 nm gold fiducials gave clear reflections,
see attached image (compressed snapshot - it looks stronger in the
original images).

The reflections were often symmetrically arranged around a fiducial and
would then disappear at the next tilt ange. We used a 100 um objective
aperture at a Krios at 300kV. Admittedly I never worried about the
crystalline arrangement of gold fiducials before, so I took some higher
mag images of the fiducials, and some of them look mosaic, others more
monocrystalline (see image), which could explain why some cause more
reflections than others.

Is this something people have encountered before? Are some batches of
fiducials better ordered than others at the atomic level? I'm curious to
hear what people think of this since it fascinated me...

Cheers,
Lars

--
Lars-Anders Carlson
Assistant Professor
Dept of Medical Biochemistry and Biophysics
Wallenberg Centre for Molecular Medicine
Umeå University
901 87 Umeå, Sweden

lab website including OPEN POSITIONS:
http://www.carlsonlab.se/
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