Wabash River PH Test
Back in the chemistry class days, we had pH strips that changed colour according to whether a liquid was an acid or base. Now scientists at Hamilton, Ontario's McMaster University have come up with a cheap and fast way of finding out if there are pesticides in your food and drinks, by using an inkjet printer to build up layers of "bio-ink". You just dip the strip and in minutes, the paper changes colour according to which pesticide is causing the contamination.
Most technologies for testing food require several hours and electrically powered equipment, so this would be very useful in the field, areas without power and in the developing world.
images found in full article.
Because paper moves liquids by capillary action, you can stick one end into the liquid and draw it up through different sensing areas.
They tested the strips on apples that had been sprayed with the pesticide paraoxon, and found that they were a quick solution for determining in the field if they were safe to eat, concluding that "the bioactive paper sensor could be a pivotal tool for assessment of low concentrations of pesticides, affecting both humans and animals."