Development of a high-sensitivity immunoassay for amyloid-beta 1-42 using a silicon microarray platform

In this work, we present a highly sensitive immunoassay for the detection of the Alzheimer's disease (AD) biomarker amyloid-beta 1-42 (Aβ42) based on a label/label-free microarray platform that utilises silicon/silicon oxide (Si/SiO2) substrates. Due to constructive interference, Si/SiO2 layered slides allow enhancement of the fluorescence intensity on the surface with significant improvements in sensitivity of detection. The same substrate allows the label-free multiplexed detection of targets using the Interferometric Reflectance Imaging Sensor (IRIS), a platform amenable to high-throughput detection of mass changes on microarray substrates. Silicon chips are coated with copoly(DMA-NAS-MAPS), a ter-copolymer made from dimethylacrylamide (DMA), 3-(trimethoxysilyl)propyl methacrylate (MAPS) and N-Acryloyloxy succinimide (NAS). Aβ42 aggregation was studied by circular dichroism (CD), and an optimal antibody pair was selected based on specificity of recognition, binding yield and spot morphology of the capture antibody on the coated silicon surface as analysed by IRIS. Finally, incubation conditions were optimised, and an unprecedented Aβ42 detection sensitivity of 73pg/mL was achieved using an artificial cerebrospinal fluid (CSF) sample. Because of their multiplexing capability, low volume sample consumption and efficient sample-to-result time for population-wide screening, microarrays are ideal tools for the identification of individuals with preclinical AD who are still cognitively healthy. The high sensitivity of this assay format, potentially coupled to a pre-concentration step or signal-enhancing modifications, could lead to a non-invasive, inexpensive diagnostic tool for population-wide screening of AD biomarkers in biological fluids other than CSF, such as serum or plasma.