Flow-through microfluidic immunosensors with refractive index-matched silica monoliths as volumetric optical detection elements.

A sensitive and rapid absorbance based immunosensor that utilizes ex situ functionalized porous silica monoliths as volumetric optical detection elements is demonstrated in this study. The porous monolith structure facilitates high capture probe density and short diffusion length scales, enabling sensitive and rapid assays. Silica monoliths, synthesized and functionalized with immunocapture probes off-chip before integration into a sealed thermoplastic microfluidic device, serve to capture target antigens during perfusion through the porous structure. Gold nanoparticle immunoconjugates are combined with silver enhancement to create microscale silver clusters, followed by perfusion of an aqueous sucrose solution to limit light scattering and enhance optical signal. Using this approach, detection limits as low as 1 ng/mL are achieved for a sandwich assay, with a dynamic range of at least 4 logs. The results confirm that the combination of on-chip index matching with functionalized porous silica monoliths can enables simple and practical flow-through immunoassays for the sensitive and rapid detection of target antigens.