US scientists are developing a "glowing" dye to help spot signs in the brain of early dementia.
The dye attaches to and shows up brain lesions
The dye works by binding to the brain areas damaged in Alzheimer's disease and giving off a fluorescent glow that can be seen with a brain scan.
The Massachusetts Institute of Technology team has made a prototype that it hopes will soon be ready to use clinically.
The team's findings appear in the journal Angewandte Chemie.
Currently, doctors make a diagnosis of Alzheimer's based on a patient's symptoms, but these normally occur much later when the condition has been present for some time.
The only way to say for sure that the cause is actually Alzheimer's is after the patient has died, by doing a post-mortem and looking for the characteristic signs the disease leaves in the brain - deposits or plaques made of the protein amyloid.
This makes it difficult for doctors looking for a cure for Alzheimer's because they cannot monitor whether candidate drugs are having a direct effect on disease progression in the brain.
This prompted Professor Timothy Swager and his team, along with colleagues from the University of Pittsburgh, to make their prototype.
When they tested their dye, called NIAD-4, in living mice they found it was able to bind to and "light up" brain amyloid plaques, similar to those seen in people with Alzheimer's.
However, to be able to do the same in humans they say they need to change the dye slightly so it glows at a slightly longer wavelength, closer to the infrared region.
Professor Swager said: "Before you can cure Alzheimer's, you have to be able to diagnose it and monitor its progress very precisely.
"Otherwise it's hard to know whether a new treatment is working or not.
"What we have is a dye that lights up when it binds to amyloids that form in the brains of people with Alzheimer's.
"Further wavelength adjustments in these dyes will allow us to perform in vivo analysis through human tissue."
Harriet Millward, deputy chief executive of the Alzheimer's Research Trust, UK, said: "If this further work is successful, this could lead to a fairly simple and practical way of detecting the plaques in the early stages of Alzheimer's, before the disease has taken hold.
"This would be major progress towards better and earlier diagnosis of the disease."
She said early diagnosis was important not only to allow prompt treatment, but also to give time for both the patient and their family to prepare and plan for the future.