THE ACT of buying fresh produce is arguably a full theatrical presentation composed of several scenes, often starting with the visual inspection. There?s the bit that involves sniffing the juncture where the stem that connected fruit to branch has been severed, and the part where the item is handled and even thumped.

Now Canadian scientists propose adding another scene, one where the prospective buyer pulls out a chemically treated slip of paper to check the pesticide levels in the fruits and vegetables being sold. The study appeared in the Nov. 1 issue of the journal Analytical Chemistry.

Researchers from McMaster University have developed a paper-based test for pesticide levels in food samples without needing a laboratory setup.

Test strips

Using paper specially treated with chemicals printed by a modified inkjet printer, the test strips change color based on the amount of pesticide present and are said to be sensitive enough to detect even tiny amounts of common pesticides. Among those used in the tests was malathion, a chemical that is used to control pest infestations on agricultural crops, residential gardens and even flea infestations on family pets.

The team led by chemist John Brennan tested the strips on liquids and solids. They dipped the strips into samples of milk and apple juice laced with pesticides, and then checked the results of test strips swiped over apples and lettuce heads that had been sprayed with the chemicals a week earlier and then washed.

?These portable colorimetric biosensing papers could be extremely useful in remote settings or developing countries where simple bioassays are essential in the first stages of detecting disease and for monitoring environmental- and food-based toxins in the field,? wrote the team led by chemist John Brennan in their study.

Latests to subscribe

Brennan and his colleagues are among the latest to subscribe to the simplicity of the dipstick test. Perhaps the fascination lies in the low-tech, low-maintenance requirements of dipping a stick or a strip of paper into a liquid, waiting a few moments and then eyeballing the results.

For example, a few years ago, researchers from the Washington University School of Medicine in St. Louise incorporated heat-resistant antibodies from camels and llamas into a dipstick test designed to allow coffee drinkers to find out how much caffeine was actually in their beverage, whether it be hot or cold.

Another dipstick test was described last year by researchers from Israel?s Tel Aviv University in an issue of the Soil Science Society of America Journal. The team?s assay doesn?t involve paper but rather a simple adaptor attached to a common piece of field equipment so farmers can analyze soil health and local pollution levels and find out if their crops are receiving the proper amount of nutrients to flourish.

Known as the optical soil dipstick, the device is expected to also help researchers identify arable land, and is already being used in some parts of the world to note which so-called organic farms offer produce that is truly chemical-free.

Last but not least on the varied list of dipstick tests, a more recent report indicates sheep farmers might soon be able to purchase a test kit to find out if their sheep need to be treated for outbreaks of the barbers pole worm disease, said to be the most expensive ovine disease to treat, in part because tolerance to treatment builds up every year.

E-mail the author at massie@massie.com.