Methods, systems, and kits are disclosed for determining the presence of a biomolecule. An assay plate may be composed of nanostructures capable of binding the biomolecule. Reporter species may be associated with the nanostructure-bound biomolecules. The assay plate may be illuminated with radiation capable of inducing plasmonic fields near the nanostructures. The fields may cause nearby reporter species to fluoresce. Nanostructures may be fabricated by illuminating nanoparticles in the presence of linker species. The induced plasmonic fields may cause the linker species to bind to the nanoparticles at field hotspots. Binder species conjugated with the linker species may form capture species capable of binding the biomolecule. A system for measuring the presence of a biomolecules may include a chamber that may be light tight, a source of illumination, and a photodetector. A kit for such a system may include an assay plate and solutions for the assay.