We have investigated the surface-supported 2D periodic array of gold nanorings and found that the sensing figure of merit can be significantly improved by coherent interactions. The experiments on the periodic nanostructures fabricated on glass substrate have shown that the sensing characteristics depend on the lattice constant and the character of the substrate grating order at a grazing angle. In the evanescent grating order range, as the lattice constant increases, the plasmon peak red-shifts, line shape strongly narrows and sensitivity decreases, but the figure of merit increases. The reason for the decrease in sensitivity is found to be the decreased field confinement and enhanced substrate effects caused by the coherent interactions. In the radiative grating order range, as the lattice constant increases, the plasmon peak blue-shifts, the line shape significantly broadens and the figure of merit decreases. The experimental results were confirmed by numerical calculations using 3D finite difference time domain method. The simulation results predict that, compared to the single nanoparticle, the bulk sensing figure of merit of the periodic array can be improved by more than three times and the surface sensing figure of merit can be improved by around 2.5 times. The grating-induced modes related to the substrate grating order found only in simulations are also discussed and show strongly suppressed sensitivity and low figure of merit.

Surface plasmon resonance sensors of the nanohole array type provide a promising platform for label-free biosensing on surfaces. For their extensive use, an efficient fabrication procedure to make nanoscale features on metallic films is required. We develop a simple and robust template-transfer approach to structure periodic nanohole arrays in optically thick Au films on poly(dimethylsiloxane) substrates. This technique significantly simplifies the process of sensor fabrication and reduces the cost of the device. A spectral analysis approach is also developed for improving the sensor performance. The sensitivity of the resulting sensor to refractive index change is 522 nm/RIU (refractive index unit) and the resolution is improved to 2 × 10(-5) RIU, which are among the best reported values for localized surface plasmon resonance sensors. We also demonstrate the limit of detection of this sensor for cardiac troponin-I.

A hydrogel-based chemiresponsive sensor for monitoring H(+) (pH) has been developed by coating the surface of a gold nanocrescent array structure with a thin film of a poly(2-hydroxylethyl methacrylate)-based (poly-HEMA) hydrogel. The transmission measurement results of the close-packed gold nanocrescent array fabricated via electron beam lithography demonstrate near-infrared localized surface plasmon resonance peaks with sensitivities up to 332 nm/RIU in detecting refractive index change. Measurements of the hydrogel under solutions of increasing pH show the plasmon peak blueshifts by 17 nm and the integrated transmission increases by 1.8 in the operating range of 4.5 - 6.4 pH, which is ideal for biochemical sensor applications.

A simple fluid detection scheme, based on light propagation through linear defect waveguides in photonic crystals, is demonstrated with isopropanol and xylene. The two-channel photonic crystal waveguide sensor is made from a GaAs-based heterostructure. The preferential channeling of light is controlled by the change in the refractive index of the corresponding waveguide branch due to the presence of the inserted fluid in the guide regions only.

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