Mark my words: one day Eva Harris will win the Nobel Peace Prize. This visionary professor at the University of California at Berkeley will certainly deserve such recognition for her work, which could save countless lives. Harris develops inexpensive ways to conduct sophisticated biomedical tests and then brings that technology to people in the developing world. By providing the right equipment and training to local public health workers, she is building epidemiological firewalls around disease "hot spots." These preparations are now helping to contain outbreaks before they grow into epidemics.
In 1998 Harris founded the Sustainable Sciences Institute in San Francisco to carry out this mission, and already her group has achieved some stunning successes. As part of that effort, Harris recently published A Low-Cost Approach to PCR (Oxford University Press; ISBN: 0-19-511926-6), which is the definitive manual on cost-conscious biotech. Though intended for health professionals, this book is a boon for amateurs working on a budget. It explains how anyone with a bit of inexpensive equipment can carry out the polymerase chain reaction (PCR), a technique for generating large quantities of DNA.
The PCR method unzips a DNA double helix into two complementary strings, which are immersed in a soup of DNA building blocks. The proper experimental conditions induce these constituents to assemble two new copies from what was originally one DNA molecule. The steps involved take just a few minutes. And repeating the procedure doubles the number of copies each time. So 30 cycles of PCR produce a billion-fold increase of the targeted section of DNA, "amplifying" what might begin as a single molecule into enough material for easy examination.
Amateur scientists can do PCR at home, but the exercise is quite challenging. For one, the very sensitivity of PCR means that this technique is extremely vulnerable to contamination: a single wayward cell could render your experiment meaningless. The serious experimenter should purchase Harris's book and a good textbook on biochemistry. To get you started, this column describes a demonstration of PCR that avoids most of the pitfalls. And the Society for Amateur Scientists can supply the materials that are difficult to obtain.
First, you will need some of your own DNA and several sterile Pyrex test tubes with rubber stoppers--or better yet, some plastic microcentrifuge tubes with built-in caps. You can reduce the risk of contamination by washing your glassware and working surface with bleach and by wearing latex gloves at all times. To collect the DNA sample, gently scrape the inside of your cheek with a sterile cotton swab, then slosh the tip around inside a clean tube filled with a few milliliters of distilled water. Gently boil the water for two minutes to rip open the cell walls and release your genetic blueprint. The solution will now contain a few DNA fragments, as well as other large molecules and sundry leftovers from the ruptured cells.
Let this biological broth cool and then, if you can, use a blender-centrifuge [see The Amateur Scientist, January 1998] to separate and remove the larger cellular debris. Some of the dissolved molecules can interfere with PCR, so practitioners usually dilute the solution by factors of 10 and 100 to reduce the concentration of any troublesome ingredients. Once you have made these preparations, keep your samples packed in ice until you are ready to use them.
The high price of materials leads even professionals to use fantastically tiny amounts of the various reagents, often one microliter or less. Dishing out such small quantities typically requires a calibrated pipetting tool (such as part no. S346503 from Fisher Scientific, $219; you'll also need the disposable pipette tips, part no. S346501, which cost about $30 for a set). But you can instead employ translucent plastic coffee stirrers. Just dip the straw into the solution to the appropriate depth and cover the end with your thumb as you transfer the contents. The set of white stir sticks I purchased from my grocery store cost less than two cents apiece and yet deliver about 70 microliters for each centimeter of length. I found that I could transfer 70 microliters of liquid very consistently (to within about 4 percent), and I could dole out as little as five microliters with only about 40 percent error