SPR Imaging With White Light

A new surface plasmon resonance (SPR) sensor that is optimized for visible and near-infrared wavelengths could make SPR imaging cheaper and easier to use, according to a study led by chemistry professor Ralph G. Nuzzo and materials science professor John A. Rogers of the University of Illinois, Urbana-Champaign (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200800501). In SPR, polarized light strikes a layer of metal at the interface between media with different refractive indexes, exciting electromagnetic waves called surface plasmons that are sensitive to changes at the interface. The researchers devised an SPR crystal made of an array of gold-coated nanowells. The new device, which is more sensitive at visible and near-IR wavelengths than previous SPR sensors, depends on the diameter, depth, and spacing of the wells and on the thickness of the gold layer. The researchers tested it by using white-light illumination to image 1-octadecanethiol monolayers on the sensor surface. The improved performance in the visible and near-IR spectral regions suggests that such SPR optics could be used with standard laboratory optical microscopes and low-cost charge-coupled device cameras.