Bio-barcode amplification (BCA) is a new technique that can search for biological markers of Alzheimer's disease, which may lead to earlier diagnosis.

One of the first examples of nanotechnology being put to use in the service of medicine is a new, extremely sensitive technique for finding minute amounts of certain disease proteins in bodily fluids. Bio-barcode amplification, or BCA, is the work of a research team led by Chad Mirkin of Northwestern University. In the February 15 Proceedings of the National Academy of Sciences, Mirkin and a Northwestern colleague, neuroscientist William Klein, describe how the BCA technique employs nanoparticles, each one smaller than a single human cell, to search for markers of disease in human cerebrospinal fluid. In Alzheimer’s disease, the marker is known as ADDL, for amyloid-betaderived diffusible ligand. This is a subunit of the protein that aggregates into the nerve-entangling amyloid plaques that come to riddle the brain in the late stages of the disease. For decades, the presence of these plaques and neurofibrillary tangles in the brain has been the only definitive evidence of Alzheimer’s disease, and this evidence is available only in a postmortem examination. But because the BCA technique can detect the presence of small ADDL molecules even at the lowest levels, it raises the exciting possibility of an accurate diagnosis years earlier, even before the onset of disease. Early diagnosis would, in turn, allow much more time for treatments aimed at attenuating or at least delaying later symptoms. “This is an exciting development, not only for neurodegenerative diseases like Alzheimer’s disease but also for many forms of cancer and for infectious diseases such as HIV-AIDS, in which the ability to study and validate new markers for these ailments requires extraordinarily sensitivity,” Mirkin says.

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