Signal enhancement of protein arrays using particles

Microarrays are a widely used bioanalytical tool in diagnostics, drug discovery and life science research. However, most microarrays suffer from insufficient sensitivity at low probe and target concentration and from a sometimes poor signal-to-noise ratio. This problem can be overcome by the development of 3-dimensional surfaces that provide increased immobilization capacities, by applying more sensitive detection techniques (e.g. evanescent wave technology, surface enhanced fluorescence techniques) or by using alternative labels (e.g. metal particles, quantum dots) that show a brighter luminescence and are more photostable. In our strategies for signal enhancement of protein arrays, we focus on particle arrays and Au-particles as alternative labels. Microparticles coated with IgG (immunoglobulin G) or streptavidin-IgG were arrayed in a print buffer, e.g. PBS or betaine, or a hydrogel, e.g. poly(vinyl alcohol) or pluronic polymers, on to various chip surfaces providing multiple assay replicates. 5, 10, and 40 nm Au-particles were used as labels in antibody arrays. When processing the array with fluorophor (Dy633) and Au labelled targets in different ratios, surface enhanced fluorescence was observed. The enhanced fluorescence was not only a result of the particles' size and the ratio and distance of the Dy633 and Au particles, but also the density of reactive surface groups and thus the density of bound IgG. When comparing both approaches to usual planar arrays, far higher signal-to-noise ratios could be achieved.