By Paul Rincon
BBC News science reporter
A new nanotechnology-based technique could lead to a test for diagnosing the early signs of Alzheimer's disease.
A clinical assay could be ready within two years
The Bio-Barcode-Assay can recognise ADDL, a protein that accumulates in the brains of sufferers.
It is a million times more sensitive than conventional tests and could revolutionise disease detection.
In future, it might form the basis not only of a test for Alzheimer's but also for types of cancer, the human form of mad cow disease and HIV.
Details of the technique have been outlined at a one-day conference in London.
Doctors currently have no way of diagnosing Alzheimer's disease in their patients. The disease can only be confirmed after death, by studying brain tissue.
"Diagnosis [of Alzheimer's] is 100% accurate post-mortem. What you want is the ability to detect the marker so you can begin to think about new types of therapies," said Professor Chad Mirkin, of Northwestern University in Evanston, US.
Professor Mirkin and his research group at Northwestern developed the highly sensitive test by manipulating molecules at the nanometre scale (one billionth of a metre).
"We have done the first set of experiments that quantify the number of ADDLs in cerebrospinal fluid," Professor Mirkin said.
ADDLs are protein bundles which attack nerve synapses in the brains of people with Alzheimer's.
"Nobody is able to study this with the existing tools. A nanotechnology-enabled tool is allowing us to study these kinds of markers and link them to disease.
"The next exciting step would be to move to blood. If you detect it in blood, you have a huge win."
To perform a Bio-Barcode-Assay, researchers select antibodies on the basis of the biomarker they need to detect in a solution.
Some antibodies are fixed to magnetic particles while others are attached to spherical gold particles just 30 nanometres in diameter. Strands of DNA are fixed to the gold nanoparticle.
When antibodies bind to a target biomarker, it becomes sandwiched between a magnetic particle on one side, and a gold particle and its strands of DNA on the other.
Applying a magnetic field brings this entire "complex" out of solution. Researchers then release the DNA strands and use a DNA detection device to recognise their signature sequences.
A research assay could be available to scientists within a year, Professor Mirkin said. A clinical assay could be commercialised within two, he added.
Professor Mirkin said it could also lead to a test to diagnose breast cancer by detecting the faint presence of a protein called PSA, normally associated with prostate cancer in men.
It could also form the basis of a new test for HIV and other diseases in blood screening.
The test could be used in GPs' surgeries as well as hospitals, or even by members of the public at home.