The findings could help scientists better understand the underlying mechanisms of the disease and lead to the development of new treatments that could slow or possibly arrest its progression. The findings also could potentially be used to diagnose Alzheimer’s disease in living people instead of during an autopsy, says Amanda J. Haes, Ph.D., working at Northwestern University. At present, Alzheimer’s can only be accurately diagnosed after death.

Haes, in cooperation with Van Duyne, Northwestern professor William Klein and research associate Lei Chang developed a method to detect small harmful proteins in cerebrospinal fluid using nanoscale optical biosensors. The proteins, known as ADDLs (amyloid-derived diffusible ligands) are so small that they can’t be detected by conventional diagnostic tests. They are usually less than five nanometers wide and are found in extremely low concentrations.

Discovered by Klein in 1998, ADDLs accumulate in the brain tissue of individuals with Alzheimer’s disease at levels up to 70 times higher than found in people who don’t have the disease.

The biosensors developed by the Northwestern team are based on tiny, triangular silver particles that absorb and scatter light. On the outside surfaces of nanoparticles is a layer of ADDL-specific antibodies. These antibodies bind specifically to any ADDL molecules found in cerebrospinal fluid. When this happens, the colour of the silver nanoparticles shifts slightly.

The researchers detected these colour shifts using a specialised light detector called ultraviolet-visible spectrometer. In a small sample pool, comparing cerebrospinal fluid extracted from two people diagnosed with Alzheimer’s disease and two people who weren’t, Haes found that ADDL levels were elevated in the diseased patient samples in comparison to control patient samples.; Source: American Chemical Society (ACS)