A Micro-Centrifuge, Cheap & Easy

by Rosemarie Arbur, Oregon, US

 

In Exploring with the Microscope Werner Nachtigall tells how convenient a centrifuge is for getting the one drop of pond-water on your slide to contain the greatest possible amount of micro-life. He shows a picture of an old hand-cranked model and says inexpensive centrifuges can still be bought. My problem is that, after checking some online catalogs, I find $250+ a bit too costly. So I improvised and came up with the truly low-cost micro-centrifuge to the right, and I built it in two hours. Since I work slowly and at times needed to stop and figure out what I was doing, you can probably make one in the same time—including your trips to the hardware store and supermarket.

The only prerequisite is a hand-powered drill that will accept a 3/8" bit —in this case, the handle of the wooden spoon. (Older hand-drills generally have 1/4" chucks, but shaving the end of a spoon handle is easy.)

See how simple it is? —you make the little centrifuge, you put your pond water in the test tubes or the little plastic jars, you stick the spoon handle into your drill, and in three minutes or so you have the "good stuff" concentrated at the bottom of the containers, ready to be examined or transferred to a cosier home.

wooden-spoon micro-centrifuge

 

  • Materials:
  • 1 wooden spoon (handle 3/8" diameter)
  • 2 small plastic test tubes
  • 2 same-size 4- or 5-oz plastic jars ("vitamin C, 250 tablets")
  • 4 small eye-screws (or cup hooks to be closed)(eye 1/2" diameter)
  • 2 cotter pins (should be 1/2" longer than test tube diameter)
  • if necessary, wooden dowel that fits inside test tube easily
  • scrap of 24.
  • Tools:
  • little saw or hacksaw blade
  • piece of sandpaper
  • drill and bits
  • 2 little pliers (or hemostats or strong tweezers, to bend pins)
  • bigger saw to shape the scrap of 2 4 if you want it to look nice
  • if necessary, a knife to downsize the end of the spoon.

 

Young people should get a more experienced person to do the sawing, the drilling, and the whittling. All people should be careful making the little holes.

 

How to do it:

Cut the dowel or spoon handle to make "stoppers" an inch long. Sand where you sawed. Open two of the eye-screws, slip the other two inside, and close the opened ones. Drill tiny guide-holes for the eye-screws, to keep the thin wood from splitting. (Don't use smaller eye-screws than I listed above because the threads have to be big enough to get a good purchase in the wood.) Drill little holes in the plastic test tubes, 1/2" from the top, and be careful that the second hole is 180 away from the first. Then put the stoppers in the test tubes and drill about half way through the stopper; stick a pin or pencil-tip in that first hole and then drill just a little way into the stopper from the second hole in the test tube. Then remove the stoppers and very carefully re-align the bit and the holes to get the second hole to meet the first one (this is touchy, but if you do it my silly slow way, you'll probably get it right and be happy). Then you can make the holes a little bigger if they need to be in order for the cotter pin to fit.

The only non-routine thing you need to do is to bend the longer stem of the cotter pin as shown, to make it a neat lock pin. The size of your test tubes determines the bend. Next, drill a hole into the middle of the cap of each plastic jar, just big enough to accept the same wooden stoppers as go into the test tubes. When you want to centrifuge more water than your test tubes hold, you simply use the cotter pin and stopper on the jar-lids. No redundancy, no extra parts to lose!

The rest is easy. Screw the eye-screws into the stoppers, then screw them into the sides of the spoon. Make a nice hole in the scrap of 2 4 for the spoon handle to fit in when you need a third hand attaching and detaching water-filled containers. Sand what needs to be sanded, and you're all set.

details of lock pin and jar lid



How to use it:
(See safety footnote.)

 Carefully!

 Please notice only hand-driven drills are recommended for this design.

 Don't use glass test tubes or jars; what it lacks in shock value glass makes up for in potential for blood. Messy. Too saline for your little pond-dwellers, too.

 Practice once or twice with both test tubes and little jars. With the hand-drill you'll need to discover a steady pace. You'll need to develop a firm hold on the drill, resting it on a table or floor, but preferably mounted in a vice.

 Fill both containers, even if one is only ballast. I tried using just one jar, and even a half-filled little jar develops surprising momentum; when I thought of something else for an instant, the whole contrivance almost got away from me.

 Remember that your micro-centrifuge isn't exactly a high-end piece of equipment when you're using the little jars instead of the test tubes. The jars don't have tapered bottoms, so they don't concentrate the "good stuff" nearly so well as the test tubes do. But, low-end or not, the jars work quite satisfactorily for setting up micro-aquaria, where a little extra "empty" water isn't a problem.

 

Fruits of my labor:

I have a pint jar of water and algae from a temporary irrigation pond. Daphnids, copepods, annelids, and vorticellae are easy to find at the bottom, but at the middle level the algae is rather dense, and drops of water from the midst of it don't contain many critters. Just the situation for a micro-centrifuge, I thought, so I pipetted mid-level water from the pint jar into my little centrifuge jars, spun it for about 3 minutes, drew out the bottom half-inch of water, and put it into a 25-mm-diameter "aquarium." After it settled a bit, I put two drops from the bottom on a well slide and took a look.

shelled amoeba
That mid-level water was an entirely different habitat! —and I could easily spend two weeks identifying the more noticeable "new" organisms I found. Free-swimmers and smaller algae predominated. The diatoms were more numerous and more mobile. There were more gastrotrichs, different (as well as familiar) rotifers, and all kinds of "new" green algae. What looked like a beautiful vorticella swam about without an anchor for 45 minutes (I had to add a drop of water next to the coverglass to extend my viewing time). There were 15 shelled amoebae (they looked like Difflugia, but most had only one thick pseudopod), all on the move, on the one slide, and several elegant heliozoa, maybe Actinosphaeria. Now I must order some methyl cellulose to slow down the swimmers, and then I can try to identify some of the quick flagellants and ciliates. In the meantime, I can work on the green algae. (I'm using Thomas H. Aungst's "tea" to keep the critters alive; it works wonderfully, providing food for the bacteria at the bottom of the food chain without clouding the water.) The little centrifuge has more than justified my two hours' work already.

Comments to the author Rosemarie Arbur are welcomed.

 

Micscape safety notice: It is emphasised that this design should only be used with a well supported, preferably clamped, hand-drill. Electrically driven drills (cordless or mains powered) could spin this design too fast for safety. Even with a hand-drill, take care and spin at a steady pace away from eye level; a protective screen and/or face visor is strongly advised.

Disclaimer: This article is offered in good faith by the author. It is up to the reader using this design to construct and operate in a safe manner. The author, Microscopy-UK, Micscape, Onview.net, site administrators and contributors assumes no responsibility for damage to persons or property incurred by building and using the project described.

 

Microscopy UK Front Page
Micscape Magazine
Article Library


Microscopy UK or their contributors.

Published in the July 2000 edition of Micscape Magazine.

Please report any Web problems or offer general comments to the Micscape Editor,
via the contact on current Micscape Index.

Micscape is the on-line monthly magazine of the Microscopy UK web
site at Microscopy-UK



© Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.