Using a pair of exotic techniques including a molecular-scale version of ice fishing, a team of researchers working at the National Institute of Standards and Technology (NIST) have developed methods to measure accurately the length of "nanopores," the miniscule channels found in cell membranes. The "molecular rulers" they describe in a recent paper* could serve as a way to calibrate tailor-made nanoporeswhose diameters on average are nearly 10,000 times smaller than that of a human hairfor a variety of applications such as rapid DNA analysis.
Studies at NIST and other research institutions have shown that a single nanometer-scale pore in a thin membrane can be used as a "miniature analysis laboratory" to detect and characterize individual biological molecules such as DNA or toxins as they pass through or block the passage. Such a system could potentially fit on a single microchip device, for a wide variety of applications. However, making the mini-lab practical requires an accurate definition of the dimensions and structural features of the nanopore.
In new experiments, researchers from NIST and the University of Maryland first built a membranea bilayer sheet of lipid moleculessimilar to that found in animal cells. They "drilled" a pore in it with a protein** designed specifically to penetrate cell membranes. When voltage is applied across the membrane wall, charged molecules such as single-stranded DNA are forced into the nanopore. As the molecule passes into the channel, the ionic current flow is reduced for a time that is proportional to the size of the chain, allowing its length to be easily derived.
If a chain is long enough to reach the narrowest part of the nanoporeknown as the pinch pointthe force of the electrical field behind it will push the molecule on through the rest of the channel. Exploiting this characteristic, the NIST/Maryland team developed a DNA probe method to measure the distances from the openings on each si
|Contact: Michael E. Newman|
National Institute of Standards and Technology (NIST)