Virus-Tethered Magnetic Gold Microspheres with Biomimetic Architectures for Enhanced Immunoassays

In immunoassays, non-specific bindings to biosensing surfaces can be effectively prevented by formation of biocompatible and hydrophilic self-assembled monolayer (SAM) on the surfaces. A thin gold (Au) layer on magnetic microspheres, 15 m in diameter, enables facile SAM formation and thereby accepts second layer of filamentous virus scaffolds for the immobilization of functional proteins. The merger of the virus and SAM-Au protected microspheres not only provides exceptionlly dense antibody loading, but also resembles biological cellular structures that enhance ligand-receptor interactions. Site-specific biotinylation of filamenous viruses allows formation of free-standing virus threads (>1.0 x 1010) on streptavidin-modified SAM-Au microspheres. The augmented yield of antibody loading, due to the increased surface to volume ratio, on virus-modified Au microspheres is confirmed by measuring fluorescence intensities. The bead-based immunoassays for the detection of cardiac marker proteins exhibit increased sensitivity of virus-Au microspheres, as low as 20 pg mL1 of cardiac troponin I in serum, and extremely low non-specific adsorption when compared with bare polymer beads. This increased sensitivity due to filamentous morphology and SAM-Au layer demonstrates the feasibility of merging viruses with non-biological materials to yield biomimetic tools for the enhanced bead-based immunoassays.