A gigapan

Monday, October 25, 2010

A DIY Microtome

"microtome (from the Greek mikros, meaning "small", and temnein, meaning "to cut") is a sectioning instrument that allows for the cutting of extremely thin slices of material, known as sections." (from Wikipedia)

They also cost actual cash money...from an economical $69.75 for this 'Hand Microtome' from The Science Company.  Which says that one turn of the base will create a 0.5mm section, and is calibrated to create 10 micron sections, so 1/50th of a turn = 10 microns, a full turn = 500 microns or .5 mm.

Or you can spend $12,445 for a unit which can create,  a 0.5 micron section.

But building from the DIY philosophy, you can build a pretty nifty Microtome with with a bit of wax a 1/4" - 20 nut and bolt, and a razor blade!  With all credit, like many good DIY ideas, this one comes from an older book.  See below for details...
The parts for a homemade Microtome

Read on to learn how!

  1. Screw the nut onto just one thread of the bolt.
  2. Slice a small piece of your sample and put it into the nut.
    Subject in the microtome
  3. Fill with wax
    Wax poured into the microtome to hold the subject
  4. Use the razor blade to slice off the bulky wax plug.
    Making the first 'cleaning' slice
  5. Advance the screw enough to expose the size slice you want.
With a 1/4" 20 thread  each full turn is 1/20th of an inch, or about 1.3mm for a complete turn.  1/3rd of a turn is just over 0.4mm.

It is a little hard to get the wax evenly distributed enough to support cutting the subject when it fills much of the thickness of the nut.  You also may want to let the wax cool completely.

This slice is closer to 1 mm.
A section of plant material ready to image.

And we can take an image of the slice. 

But ick!  That is only in focus for select bits of the image!

Which brings up the importance of Focus Stacking, which is the subject of another post.  But as a teaser, here is a focus stacked version of our leaf stem.

In the Whole Earth Review I learned that the best way to learn about a new subject is to first read books about the subject directed at Junior High Students.  The writing will be simple, but mostly offer a reasonable survey of the material, and most importantly: authors writing non-textbook non-fiction directed at early adolescents know that they have to make their material interesting.  Once you are in High School and College, and even worse, in a professional career, you are more or less forced into reading whatever you are told to read.

Following this advice I found a copy of Microscope and the World of Science by Marvin F. Riemer.
 Amazon has multiple copies available used.  i got mine in Portland at Powell's :-)  It was published in 1962, and is obviously dated.

Except for where it is not.  Such as the chapter 'Sectioning Techniques for Plant and Animal Tissue.'  Which contains this excellent DIY line "A simple microtome that will serve quite adequately for the beginner can be made at virtually no cost from a large bolt and nut."

Note: Mr. Riemer advocates dipping the speciman in the paraffin multiple times to encase it in  nice wax plug.  I will do this the next time...but the hour is late, and I am now in 'writing up results' mode, rather than 'continue to try all of the variations' mode :-)

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