Biomolecular sensing using near-null single wavelength arrayed imaging reflectometry.

We use reflectivity changes at an interface functionalized with molecular probes to detect label-free biomolecular binding. Attachment of the target molecules to the surface alters the effective thickness of an antireflective coating formed by thermal oxidation of a silicon wafer to remove destructive interference of the reflected waves. The thermal oxide thickness is adjusted for precise interference using electrostatic layer-by-layer self-assembly of polyelectrolytes to which the molecular probes can be bound covalently. Reflectivity increases of over a factor of 100 are observed for binding of 2.5 nm of streptavidin to biotinylated polyelectrolytes, considerably more sensitive than surface plasmon resonance detection. Theoretical modeling is in agreement with the experimentally observed reflectivity increases and suggests the sensitivity is at present limited by the roughness of the oxide.