SPR chip could provide early warning of Alzheimer’s disease

Clinicians and engineers are building a diagnostic micoarray chip for Alzheimer’s disease that will provide a vital early warning of the condition.

They are hoping to make a handheld or a small desktop device using surface plasmon resonance (SPR) — a relatively new technology — coupled with high-sensitivity complementary metal-oxide semiconductor (CMOS) imaging.

While diagnostic chips are starting to find their way into the clinic for certain applications, other conditions present a significant challenge, as project collaborator Prof Mike Somekh, an optical engineer at Nottingham University, explained.

‘With some diseases, there are single markers or chemicals that will actually give you a good indication of the diagnosis.

‘But a lot of other diseases such as Alzheimer’s and other neurodegenerative conditions are represented by a pattern of markers, so you have to see how they are interrelated to each other to get a good, accurate diagnosis. That then imposes a constraint on the engineer to develop a platform with multiple sites for analysis.’ 

With this in mind, Somekh turned to SPR — a complex process that essentially measures the adsorption of two molecules based on their evanescent wave refractive index. 

Unlike other detection techniques, it does not require the use of fluorescence or radioactive tagging, which is time consuming and cumbersome. This makes SPR suitable for the high-throughput analysis of multiple markers simultaneously.

The concept Somekh envisions involves a sandwich structure comprising a layer of gold film attached to an immobilised antibody that ‘grabs’ the disease markers when they are present in a blood sample. When such a complex forms, it produces a signature light refraction that can be picked up by a suitably sensitive CMOS imaging chip.

‘The way it will work is there’ll be the optical side with the associated detection and then the biological side,’ he said. ‘That gold layer not only acts as a medium on which the surface plasmon propagate but it’s also the interface between the biology and the engineering.’

The overall group is headed by Prof Paul O’Shea, who works in the Faculty of Medicine and Health Sciences at Nottingham. The group has just received a £670,000 grant from the Medical Research Council to develop the diagnostic chip.