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 (A beta 42) 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). A beta 342 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 A beta 42 detection sensitivity of 73 pg/mL was achieved using an artificial cerebrospinal fluid (CSF) sample.