This one step single component acrylic embedding resin system has many
advantages, its ultra low viscosity, only 8 cps, is almost like that of
water and will infiltrate just about any type of sample. Even large
blocks impregnate surprisingly fast. Another feature is convenience since
one can do both TEM and LM sectioning from the same block.
Polymerization is started either by heat or when the need to preserve the
sample's antigenicity is paramount, then also by a low temperature UV cure.
One characteristic of the cured block is that sections tend to be quite
hydrophilic. Actually LR White is quite a versatile embedding resin and
there are quite a few interesting
applications that have been described. So far as resins go, LR White is pretty easy to use, and
problems when they do arise, are encountered only very rarely.
This technique has been used to increase the accessibility of the antigenic
sites, or "antigen retrieve" in the section for immuno electron microscopy.
We would recommend the paper "Antigen Unmasking for Immuno electron
Microscopy: Labeling is Improved by Treating with Sodium Ethoxide or Sodium
Metaperiodate, then Heating on Retrieval Medium", Journal of Histochem. and
Cytochem., 43:115-123 (1995).
There have been numerous reports in the published literature describing various staining
techniques of immunolabeled sections. Most of them involve the use of
uranyl acetate as a negative stain.
For many workers, there is experienced some difficulty embedding plant
tissue with other embedding resin systems. LR White, with its viscosity
that is like water, can be very easily infiltrated (relatively speaking, of
course) and there has
been quite a bit published on the embedding of plant tissue.
The resin itself comes ready to
use and if intended for use at low temperature, one would need
SPI #02648-AB, accelerator which comes in a convenient dropper bottle.
Available in three grades, hard medium and soft, with hard and medium grades
for most users being much more popular than the "soft".
Despite the less rigorous processing associated with the use of LR White,
neither the appearance or the amount of the extracellular material was affected by
the different embedding protocols. We interpret this to mean that some antigenic
sites are more sensitive to alcohol disruption than others, and in this case, the
sites must have been quite resistant to such disruption. But for other systems,
the opposite is true. The point is, for a new system, it is often times worth
trying several different embedding approaches, in order to determine the one that
is the most optimum for that specific situation.
All three resin grades can be polymerized either chemically, at low
temperature using UV irradiation at 365 nm, or by elevated temperatures, either by conventional
oven or microwave techniques. Note that this resin system is not compatible with
the use of acetone, since the presence of any ketone will inhibit polymerization.
Each bottle of resin comes complete with five different monographs to provide assistance to the user of the resin:
We are addressing now the cured block, something that to most people is about as
inert of a material as one will find. But the standard practice in many laboratories
is to use a small jeweler's (or even a small hack) saw to cut the block down to the
right size, sometimes even to shape it.
We want to address the dust that is generated and how its exposure can and should be minimized.
We strongly recommend that the LR White Resins be shipped in low temperature packaging and by the most
rapid means possible. LR White accelerator may be shipped without low temperature packaging.
This acrylic resin facilitates the embedding of unfixed material at low
temperatures, enabling high-quality histochemistry and immuno-cytochemistry
of fixation-sensitive enzymes and epitopes. It is non-toxic and may be
cured with visible light and reveals high-quality morphological details
from 1-4 µm sections, providing a faster and lower-cost alternative to frozen sections.
LR Gold can be catalyzed in a number of different ways depending on the
choice of catalyst (e.g. color of light to initiate polymerization,
temperature, etc.). The resin was specifically formulated to be catalyzed
with benzil and it will work
very well with blue light and will also polymerize below 1° C, often
times needed in order to enhance antigenic preservation for experiments in immunocytochemistry.
It can also be polymerized at sub-zero° C temperatures by the addition
of benzoin methyl ether and polymerization with UV light. As this is
intrinsically less safe than the blue light/benzil regime and offers no
advantages in performance of the resin, this is not the method of choice for
LR Gold. For polymerization at room temperature, this can be achieved
readily via the addition of benzoyl peroxide.
Such a polymerization is exothermic and rapid, with the total
time needed for full polymerization on the order of ten minutes.