Readout beam coupling strategies for plasmonic chemical or biological sesnors

Abstract

Plasmonic devices are among the most sensitive contemporary sensors of chemical or biological analytes, in some cases even reaching single molecule sensitivity. These are refractometric devices making use of extreme light concentrations and offering real-time, label-free operation. For their proper operation one needs efficient coupling between the propagating interrogation beam and bound surface plasmons polaritons (SPP) whose wave vector is much larger. An external prism in Kretchmann or Otto configuration can be used for such coupling, or some kind of diffraction coupler or fiber-based endfire coupler. In this contribution we investigate theoretically and experimentally possibilities to fabricate sensor structures that simultaneously exhibit plasmonic properties and ensure diffraction-based coupling. To this purpose we fabricated different micrometer-sized two-dimensional metal-dielectric arrays that can match wave vectors of propagating beams and of SPP and at the same time show plasmonic properties tunable by design. We investigated structures functioning in reflection or in transmission mode, with gold or aluminum as the basic material and with deep subwavelength details. Our structures can be made much more compact than the conventional ones, thus being convenient for monolithic on-chip integration with light source and detector and offering a larger degree of design freedom for multianalyte CORN sensing.