Lab on a sheet of paper
Call it litmus paper for the 21st century. Paper with lines of chemicals printed on it can direct fluids across its surface, allowing basic chemical tests to occur right on the paper, a new Harvard study shows. This extremely low-cost “lab on paper” could make chemical tests feasible in less-industrialized countries.
Researchers are working on so-called lab-on-a-chip devices, which have tiny channels etched into small blocks of glass or plastic. These chips move nanoliters of liquid through the channels to bring about controlled chemical reactions. But these chips can cost hundreds of dollars each and often require expensive equipment to operate them.
As a low-tech, cheaper alternative, George Whitesides’ group of chemists at Harvard laid down a pattern of water-repellent chemicals, which act like walls to channel liquids, on the surface of chromatography paper. This paper is designed to separate out different molecules, but is cheap and readily available.
Their prototype has one inlet for loading a sample (at the bottom in the photo below). Capillary action draws the liquid up into each of three separate lobes (at the top in the photo below), which are laced with chemicals that react with the fluid. In this test, the left lobe showed the presence of glucose in the fluid, the right lobe showed the presence of proteins, and the center was a control.
This “lab on paper,” about five centimeters across, could be a cheap, portable way of running chemical tests.
Credit: Scott Phillips, Harvard University
The researchers showed that the paper could also act as a filter. When they loaded it with a liquid sample containing dirt, pollen, and graphite powder, they found that the contaminants stayed put while only the fluid moved up into the lobes. Each piece of patterned paper might cost less than a penny to mass-produce, they estimate. Mason Inman
Reef-dwelling fish smell their way home
Tiny fish larvae follow their noses home in Australia’s Great Barrier Reef, according to research by Gabriele Gerlach and colleagues from the Marine Biological Laboratory in Woods Hole and Boston University.
Half-inch-long cardinal fish larvae are washed from the reef soon after their birth and spend two weeks drifting on ocean currents. Researchers have thought that larvae from one reef spread widely to other nearby reefs. But DNA testing of fish from different but closely spaced reefs showed that each location hosted its own genetically distinct adult groups.
Cardinal fish (Ostorinchus doederleini)
Credit: Gabriele Gerlach
That discovery suggested that the dispersed baby fish eventually made their way back to the same spot where they were born. The investigators hypothesized that the larvae might be able to smell their home reef, in the same way that salmon follow odor cues to return to their spawning grounds.
To demonstrate this, coauthor Jelle Atema devised a flow chamber where fish could choose to swim in water collected from their home reef or from a different reef. Consistently, they chose their home water.
The behavior looks like a form of olfactory “learning”; the odors the fish encounter upon hatching are the same ones they seek out later in life. The researchers don’t know what the odor is—the fish might detect the smell of its own community or local variations in reef life. Only a few species of fish have known sniffing abilities.
This homing instinct supports the formation of genetically distinct clans of cardinal fish on reefs just a few miles apart. This contributes to the rich biodiversity of reefs, the researchers say.
The work was published in this week’s online edition of the Proceedings of the National Academy of Sciences. Pat McCaffrey
Defending and protecting your gut
Our intestines teem with bacteria, an environment that calls for an aggressive immune response. Fortunately, normal intestinal cells rarely get attacked, but the reason has remained a mystery. Now, local researchers have identified a new class of protective cells that help the immune system distinguish friend from foe in this immunological war zone.
Previously thought to have no function in regulating the immune system, the so-called stromal cells sit in the lymph nodes where other immune cells reside. There, the researchers found, they produce intestinal proteins, which they display to passing T cells. The T cells that recognize these proteins as foreign are picked out and eliminated before they can reach the intestine and cause trouble.
The stromal cells make up a large of part of lymph nodes throughout the body and may play a role in suppressing autoimmune responses in other tissues, too. They could point out new ways of preventing or treating autoimmune diseases.
The findings, from Shannon Turley and colleagues at the Dana-Farber Cancer Institute, were published in Nature Immunology. Pat McCaffrey
