Development of Easily Visualized Immunoassays for Diagnostic Applications

Abstract

Microarray-based immunoassay is an important technique employed in screening proteins at low volumes and high throughputs. In this study, the ability of adapting a fluorescence based microarray system for detecting human immunoglobulin G (IgG) to a liquid crystal microarray system was investigated. Here, we built an immunoassay on silanized glass slide coated with protein G that was then cross-linked for grafting the capturing protein, anti-immunoglobulin G (anti-IgG), for screening immunoglobulin G (IgG). We have proven that after cross-linking, protein G maintains its capability of orientating and capturing anti-human IgG that was grafted onto it. Results also suggest that Cy3-tagged human IgG spotted on the abovementioned decorated surface interacts specifically with anti-human IgG. The specificity of the interaction was cross checked with cy3-tagged murine IgG. Limit of detection of this system was found to be 0.4 ?g/mL, with signal to noise ratio at 3. The dynamic range was 0.4 ?g/mL to 5.0 ?g/mL towards human IgG. Subsequently, the fluorescence immunoassay was adapted to liquid crystal, 4-cyano-4?-pentylcyanobiphenyl (5CB), read out format. This change of read out remains a challenge because the immunoassay designed based on fluorescence study was found to exceed the critical concentration at which liquid crystal works. As such, alternatives such as usage of ferromagnetic and ferroelectric nanoparticles are discussed in this work.