A sensitive diagnostic assay for Alzheimer's
Alzheimer's disease (AD) is turning into a major health issue in western countries. Current diagnosis methods are time consuming and there are limited assays for monitoring disease progression. As a result, novel diagnostic and prognostic tools are required to alleviate patients from the suffering of continuous monitoring. Seeking to address this, the EU-funded 'Quantum dot-based highly sensitive immunoassays for multiplexed diagnostics of Alzheimer's disease' (NANOGNOSTICS) project set out to develop an innovative tool for identifying alterations of protein expression patterns caused by AD. The NANOGNOSTICS technology relied on a multiplex immunoassay where detection of a biomarker was performed by two differently labelled antibodies. When the two antibodies recognised the same molecule, they came into close proximity and a physical phenomenon known as fluorescence resonance transfer (FRET) occurred. This phenomenon required that the employed dyes had overlapping emission and absorption spectra, and that the antibodies were brought together on the same molecule by another level of strong binding, the biotin–streptavidin interaction. The advantage of this technology over standard immunoassays was the signal amplification it generated, making it sensitive enough to detect small amounts of protein in human blood. Importantly, researchers are confident that diagnosis would be provided in less than 10 minutes following blood sample collection. As alternatives to fluorescent dyes, project partners exploited the nanoparticles known as semiconductor quantum dots (QDs). Their unique photophysical properties combined with their size-dependent absorption and emission wavelengths render QDs ideal candidates for such purposes. To this end, a variety of QDs were studied for their suitability to be used in highly sensitive clinical FRET-bioassays. Researchers worked on the applicability of various proteins as disease biomarkers of AD, and focused particularly on vascular endothelial growth factor (VEGF), EGF and L-selectin. Additional assays based on the aggregated form of amyloid-beta peptide — the hallmark of AD — were constructed. Application of the NANOGNOSTICS assays was performed on blood and cerebrospinal fluid samples from AD patients. The highly specific and sensitive detection of VEGF demonstrated the feasibility of the assay for biomarker detection. Although the technology can deliver sensitivity in protein detection and is envisioned to improve early AD diagnosis, the reported inconsistencies on AD biomarkers still prohibit the clinical applicability of the method.
Keywords
Alzheimer's disease, biomarker, fluorescence resonance transfer, immunoassay, quantum dots, disease diagnosis
