Re: [IAWA Forum] SEM

From: Lloyd.Donaldson@scionresearch.com
Subject: Re: [IAWA Forum] SEM
Date: Thu, 9 Mar 2006 08:54:12 +1300
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Dear Rocio

SEM preparation can be difficult. I assume the problem you have is cutting
a clean surface on the sample. Fresh - never dried samples will always cut
better than those that have been dried. However if you must use dried
samples (perhaps from a xylarium) the samples should be rehydrated before
cutting. Using 50% ethanol to rehydrate will be more effective than just
soaking in water. You can try cutting wet samples but if this still gives
poor results try fixing in FAA (90mls ethanol, 5 mls glacial acetic acid,
5mls formaldehyde) for as long as possible - the longer the fixation ie
months, the better the results. FAA will also likely remove most of the
extractives which is also important as resins and gums can easily cover up
fine detail on surfaces. If the wood you are working with has a lot of
extractive you will need to change the FAA several times until there is no
further extraction.
The second most important thing with SEM preparation is the quality of the
blades you use for cutting. Try a range of different blades to find the
best one. For viewing longitudinal surfaces fracturing or splitting can be
more useful than cutting, depending on what you want to see.
The sample usually has to be dried for SEM. You can try air drying from
ethanol.
Wood is non-conducting so mount the block with conducting adhesive (silver
paint is good). The sample should be coated in a sputter coater. Platinum
or chromium give better results than gold but it depends on what equipment
you have access to. The ideal accelerating voltage for wood is about 3kV
but only newer instruments can provide this so you may be restricted to
higher voltages. A field emission instrument has much greater resolution
than a conventional SEM but again it will depend on what equipment you have
access to.

Let me know if I can help further.

Regards -
Dr Lloyd Donaldson - Microscopist
Cellwall Biotechnology Centre
SCION - Next generation biomaterials
Te Papa Tipu Innovation Park, 49 Sala Street
Private Bag 3020, ROTORUA, New Zealand
DDI 64 7 343 5581
Fax 64 7 343 5507
email lloyd.donaldson@scionresearch.com
http://www.scionresearch.com/fluorescence+microscopy+of+wood.aspx



                                                                           
             Rocío Astrid                                                  
             Bernal                                                        
             <rocidito@hotmail                                          To 
             .com>                     "IAWA" <iawa@COF.ORST.EDU>          
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             owner-iawa@COF.OR                                             
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             09/03/06 01:20                                                
                                                                           
                                                                           
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               Rocío Astrid                                                
                  Bernal                                                   
             <rocidito@hotmail                                             
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Dear IAWA members,

I am doctoral studient from University of Porto, I am studying antomical
and molecular biology aspects of some species of Lecythidaceae. At this
moment, I am working with SEM but I did not have good results. I would like
to know how do you prepare your material for this studies.

Thanks,

Rocío Astrid Bernal Garzón
(PhD student)
Faculdade de Ciências - Universidade do Porto
Departamento de Botânica
Rua do Campo Alegre, 1191
4150-181 Porto
Portugal


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