Imagine shrinking the beakers, eyedroppers, chemicals and heaters of a chemistry lab onto a little microchip that could dangle from a key chain. A growing number of companies and universities are claiming to have devised such marvels, ready to perform vital analyses from detecting biological warfare agents in a soldier’s bloodstream to identifying toxins in a tainted package of hamburger meat. Almost all the new devices are surprisingly far from portable, however. The sensor that examines a drop of blood or speck of beef might indeed fit in one’s hand, but the equipment required to actually move a fluidized sample through the chip’s tiny tubes often occupies a desktop or more.