Abstract
A biomolecular sensor consisting of a thin metallic grating deposited on a glass prism is studied in the formalism of poles and zeros of the scattering matrix. Surface plasmon resonance is used to increase the sensitivity of the device with respect to a variation of the refractive index of the substrate. It is shown that a direct coupling between counter propagating surface plasmons using double-harmonic Fourier gratings leads to an enhancement of the sensitivity. The result of the stronger coupling is the transfer of the working point from the lower to the upper edge of the band gap in the dispersion diagram.
Highlights
The technique of surface plasmon resonance has found wide use in recent years in biosensing applications, with the principal configuration employing a prism in the frustrated or attenuated total reflection configuration associated with the name of Kretschmann [1]
A recent study [9] has shown that by placing a sinusoidal profile grating in silver of appropriate period and depth on the rear face of a substrate used in the Kretschmann configuration, the surface plasmon resonance (SPR) sensitivity may be enhanced by a factor of six when compared with an uncorrugated surface
We will show that such compound profile gratings can provide a further sixty percent increase in plasmon resonance sensitivity above that provided by the sinusoidal profile, and that this heightened sensitivity is achieved because the operating point of the sensor moves from the lower frequency edge of a minigap between two plasmon dispersion curves to the upper frequency edge
Summary
The technique of surface plasmon resonance has found wide use in recent years in biosensing applications, with the principal configuration employing a prism in the frustrated or attenuated total reflection configuration associated with the name of Kretschmann [1]. It should be stressed that gratings with profiles composed of superposed Fourier harmonics can be created by established interference techniques [11] Their fabrication offers an additional degree of complexity, they do offer the advantages of relatively large area grating format, possibility of mosaic gratings on a single substrate and precision replication through several generations from a single master in common with sinusoidal and ruled gratings. We consider the case of a sinusoidal grating used as an SPR sensor, and show how the optimization of its sensitivity may be achieved by regarding the behaviour of the trajectories of the zeros and poles of the scattering matrix We use this insight, where we study the case of a Fourier grating with two superposed surface modulations.
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