Biology Reference
In-Depth Information
caused by rearrangements in the thickness of the gold layer that are related to
impurities present on the glass before evaporation of the gold. Gold substrates
that are stamped immediately after evaporation are generally more stable over
time (about 3 mo) perhaps because the SAM acts as a resist against impurities
(29)
.
4.
Wafers: Rinse only with water and avoid all contact with organic solvents.
5.
PDMS Stamp: Pouring and curing: Often small air bubbles form in the PDMS
after it is poured on the master. Cover the dish and gently tap it to allow the
bubble to diffuse out of the prepolymer. Typically, stamps are 0.5-1 cm tall.
6.
PDMS Stamp: Peeling off of silicon: During curing, a layer of PDMS forms
underneath the wafer and holds it to the dish. Invert the dish and gently press on
the bottom side of it until the cured PDMS dewets from the surface of the dish.
Invert the dish and use a dull edge to trace the contour of the PDMS so as to lift it
off the dish. Often the PDMS remains attached to the wafer. Carefully cut the
layer of PDMS found under the wafer and gently peel the two surfaces away
from each other.
7.
Thiol Storage: Typically, alkanethiols that are kept in ethanolic solutions for more
than three month become oxidized and form significant amounts of disulfides.
Disulfides of EGT are detected by TLC as spots with an R
f
of approx 0.15,
whereas the thiol has an
R
f
of 0.25 (using 98:2 CH
2
Cl
2
:CH
3
OH as the eluant). By
NMR, disulfides can be distinguished from alkanethiols by the presence of a
triplet of peaks (from the methylene group adjacent to the sulfur atom) at approx
2.6 ppm instead of a quartet at 2.5 ppm. Although disulfides are known to form
SAMs with interfacial properties similar to those formed with alkanethiols, their
assembly is 75 times slower
(30)
.
8.
Thiol Stamping: Over and understamping. Observe the play of light, at an angle,
on the micropattern to ensure that the stamp has fully adhered to the substrate.
Usually, a pink color will ensure that full adhesion has occurred. Both under and
overstamping results in a loss of this interference pattern. Make sure that no
patches of nonadhesion remain. Always stamp the hexadecanethiol; stamping the
EGT results in less efficient pattern transfer, incomplete formation of SAM, and
nonspecific adsorption of proteins in the EGT regions.
9.
Protein coating: When adding the BSA solution to bring the substrates out of
fibronectin coating, the slides sink onto the dish and adhere to it; since the sub-
strates face the bottom of the dish, the pattern may be damaged. To avoid this,
add the BSA solution around the edges of the substrate so that the slides
remain afloat.
10.
Cell culture: For cell culture, cells should ideally be plated without serum (at
least for 1 h), before washing serum media back in. The serum activates certain
cell types to attach where they should not. This is cell-type specific, so some
exploration may be necessary.
11.
Cell culture: The actual surface area that is adhesive on patterned slides is a frac-
tion of that of a regular substrate; therefore, cells should be accordingly seeded at
seemingly very low concentrations.
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