A nanoparticle test reported in the Proceedings of the National Academy of Sciences could herald the advent of a living diagnosis for Alzheimer's disease (AD). The test detects the prevalence of amyloid-β-derived diffusible ligands (ADDLs), and is a million times more sensitive than other approaches.

ADDLs are “...invisible to conventional neuropathology, but their presence or absence may be the real determinants of memory loss,” according to William L. Klein, a member of the research team (Science News Online, 5 February 2005), and they have been shown to target synapses well before symptoms can be spotted at present. At the moment, a firm diagnosis of Alzheimer's requires an autopsy, and other forms of diagnosis, such as memory tests and brain scans, fall short of 100% accuracy.

Although ADDLs were suspected to be present in the cerebrospinal fluid, no tests were sensitive enough to detect their presence there. The approach taken by Dimitra Georganopoulou and colleagues used antibodies directed against ADDL. Some of the antibodies were attached to iron particles, and could therefore be extracted using a magnetic field. Other antibodies, which were attached to gold nanoparticles, could also hitch a lift in the extraction process. Along with the gold were 'barcode' DNA strands, which, when released by dehybridization, bound to complementary DNA on a glass plate and were detected using a highly sensitive scanometric method.

Faced with the challenge of trying out the technique on easier-to-obtain blood and urine samples, in which ADDL concentrations are expected to be far lower, the team remains confident. “We're nowhere near the limits of the test's sensitivity.” (NewScientist.com , 31 January 2005.)