Near cut-off wavelength operation of resonant waveguide grating biosensors.

Numerical simulations and analytical calculations are performed to support the design of grating-coupled planar optical waveguides for biological sensing. Near cut-off and far from cut-off modes are investigated, and their characteristics and suitability for sensing are compared. The numerical simulations reveal the high sensitivity of the guided mode intensity near the cut-off wavelength for any refractive index change along the waveguide.

Intensity interrogation near cutoff resonance for label-free cellular profiling.

We report a method enabling intensity-based readout for label-free cellular assays, and realize a reader device with the same footprint as a microtiter plate. For unambiguous resonance intensity measurements in resonance waveguide grating (RWG) sensors, we propose to apply resonances near the substrate cutoff wavelength. This method was validated in bulk refractive index, surface bilayer and G protein-coupled receptor (GPCR) experiments.

Handheld imaging photonic crystal biosensor for multiplexed, label-free protein detection.

We present a handheld biosensor system for the label-free and specific multiplexed detection of several biomarkers employing a spectrometer-free imaging measurement system. A photonic crystal surface functionalized with multiple specific ligands forms the optical transducer. The photonic crystal slab is fabricated on a glass substrate by replicating a periodic grating master stamp with a period of 370 nm into a photoresist via nanoimprint lithography and deposition of a 70-nm titanium dioxide layer.

Enhanced sensitivity of photonic crystal slab transducers by oblique-angle layer deposition.

Photonic crystal slabs (PCS) are one of the major transducers for label-free, optical biosensing applications. In this paper we present oblique-angle layer deposition of the high index slab material as a method to improve the PCS sensitivity. In simulations and experiments we consider PCSs composed of a high index silicon monoxide layer on a nanostructured resist layer on a glass substrate.

Visual device for pressure measurement using photonic crystal slabs.

We propose and demonstrate a visual, all-optical pressure-measuring device composed of a flexible membrane dilating toward a photonic crystal slab. Due to its transparency and capability to be miniaturized, it may be integrated on the inner side of an artificial lens and directly measure the eye's intraocular pressure. Using crossed polarization filters for the readout process, we obtain a contrast enhancement for the circular contact area of the membrane with the photonic crystal slab.

Photonic crystal slabs for surface contrast enhancement in microscopy of transparent objects.

In optical microscopy the contrast of transparent objects achieved with conventional methods is often not satisfactory, for example for the automated recognition of cells. In this paper we present a nano-optical label-free approach for contrast enhancement based on photonic crystal slabs (PCS) as the specimen holder. Quasi-guided modes inside these structures cause an intrinsic color of the PCS, which strongly depends on the wavelength and the quality factor of the optical mode.

Photonic crystal biosensors towards on-chip integration.

Photonic crystal technology has attracted large interest in the last years. The possibility to generate highly sensitive sensor elements with photonic crystal structures is very promising for medical or environmental applications. The low-cost fabrication on the mass scale is as advantageous as the compactness and reliability of photonic crystal biosensors.

Low-cost label-free biosensors using photonic crystals embedded between crossed polarizers.

There is a strong need for low-cost biosensors to enable rapid, on-site analysis of biological, biomedical, or chemical substances. We propose a platform for label-free optical biosensors based on applying the analyte onto a surface-functionalized photonic crystal slab and performing a transmission measurement with two crossed polarization filters. This dark-field approach allows for efficient background suppression as only the photonic crystal guided-mode resonances interacting with the functionalized surface experience significant polarization rotation.

Optical characterization of photonic crystal slabs using orthogonally oriented polarization filters.

We present an experimental method for direct analysis of guided-mode resonances in photonic crystal slab structures using transmission measurements. By positioning the photonic crystal slab between orthogonally oriented polarization filters light transmission is suppressed except for the guided-mode resonances. Angle resolved transmission measurements with crossed polarizers are performed to obtain the band structure around the Gamma-point.