Biology Reference
In-Depth Information
Fig. 7. Digital STEM system detector geometry. Standard values for 100 kV opera-
tion for the illumination angle (
α
) and the angular collection range (
θ
1
to
θ
2
) of the
ADF detector are:
α
= 12,
θ
1
= 25 and
θ
2
= 75 (mrad).
6.
Correct
pi'
for the image magnification
mag
(
see
Note 16
).
pi''
=
pi
×
mlc
/ (
bf
-
zp
)
×
cfi
(3)
7.
Determine the mean
pi''
for 20-30 TMV particles.
8.
Calculate the mass per unit length correction factor (
mlc)
for TMV (assuming
TMV = 131 kDa/nm).
mlc
= 131 /
pi'
(4)
9.
Capture successive STEM images of the sample of interest adjusting the speci-
men height to maintain an invariant objective lens setting.
10.
Calculate the mass per unit length using
Eqs. 1-3
, substituting the calculated
mlc
value.
4. Notes
1.
Fixing the tissue in 2% formaldehyde prior to homogenization may help to mini-
mize loss of associated macromolecules during the extraction procedure.
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