Optical near-field enhancement at a surface where a total internal reflection occurs is an effective phenomenon that can enhance optical signals from markers conjugated with biological materials on the surface. The enhanced signal can be an effective tool to detect trace amounts of a biological substance. An external force-assisted near-field illumination biosensor is based on a sandwich assay that uses magnetic particles instead of a sensor surface to capture the targets. This sensing method detects light signals from targets sandwiched between magnetic particles and optical markers. The signal of the sandwiched target can be easily distinguished from optical noise by observing the movement of the signal induced by an external magnetic field. In this study, we improved the detection ability by using 60 nm ∅ gold nanoparticles as markers. Norovirus virus-like particles were added to a buffer or a contaminated water sample and successfully detected using this system.
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