16 BIOTECHNOLOGY
➠
antiferromagnetically exchange-coupled layers, separated by a thin non-magnetic conducting layer, can be altered by changing the moments of the ferromagnetic layers from anti-parallel to parallel. This change decreases the spin-dependent interfacial scattering of charge carriers resulting in a decrease in the resistance of the GMR material. He realised this very sensitive phenomenon could have potential in the development of sensors for biological materials which are naturally biochemically specific, but are not usually magnetic. By attaching tiny paramagnetic particles to biomolecules, such as proteins or single-stranded DNA, scientists could then perform standard sandwich-type immuno or nucleic acid hybridization assays over the GMR sensors. The GMR sensors, each covered with complementary protein or single-stranded DNA (the probe), could then detect the magnetically labelled biomolecules (the target) the assays were designed to identify. In a second development, NRL researchers have
developed what they describe as a forceful new method to sensitively detect proteins. The researchers report the detection of toxins with unprecedented speed, sensitivity, and simplicity. The approach can sense as few as a few hundred molecules in a drop of blood in less than ten minutes, with only four simple steps from sample to answer.
NEW S-Live 1/2 page 11/20/06 12:27 PM Page 1 The sensitive new test builds on NRL’s patent-pending
fluidic force discrimination (FFD) assay. In a FFD assay, a chip has arrays of receptor molecules such as antibodies that capture toxins or other target molecules that have been labelled with micrometre-sized beads. By encapsulating the chip in a microflow chamber, the fluid flow can be controlled to apply just enough force to remove beads that are resting on the array but not truly labelling a toxin. “In this way,” explains lead author Shawn Mulvaney, “very few molecules can be detected, because there is almost no background signal. And because we can get the background so low, FFD assays are very specific, with very few false positives.” The NRL researchers have adapted FFD assays to
detect a protein toxin at concentrations as low as 35 attomolar - over 1000 times more sensitive than existing commercial tests for proteins. In the new assay, dubbed ‘semi-homogeneous fluidic
force discrimination,’ the antibody-coated microbeads are mixed directly with the sample and rapidly collect the dilute toxin molecules. The toxin-coated beads are then injected into the microflow chamber where they are captured by the receptor designed for that target. Finally, beads that don’t belong are removed with fluid forces. The remaining beads are all attached by the toxin
to the surface and may be counted to indicate the toxin concentration. NRL has developed both electronic and optical systems to count the beads, along with reusable plastic test cartridges. u
News and reports on all the latest scientific discoveries, brought straight to your desktop
☛ Top stories of the day ☛ In depth reporting ☛ Latest product news ☛ Free e-mail newsletter
www.scientistlive.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44