Long-range surface plasmon resonance and its sensing applications: A review

Optical biosensors based on refractometric sensing schemes: A review.

Silicon photonics is an enabling technology that provides integrated photonic devices and systems with low-cost mass manufacturing capability. It has attracted increasing attention in both academia and industry in recent years, not only for its applications in communications, but also in sensing. One important issue of silicon photonics that comes with its high integration density is an interface between its high-performance integrated waveguide devices and optical fibers or free-space optics. Surface grating coupler is a preferred candidate that provides flexibility for circuit design and reduces effort for both fabrication and alignment. In the past decades, considerable research efforts have been made on in-plane grating couplers to address their insufficiency in coupling efficiency, wavelength sensitivity and polarization sensitivity compared with out-of-plane edge-coupling. Apart from improved performances, new functionalities are also on the horizon for grating couplers. In this paper, we review the current research progresses made on grating couplers, starting from their fundamental theories and concepts. Then, we conclude various methods to improve their performance, including coupling efficiency, polarization and wavelength sensitivity. Finally, we discuss some emerging research topics on grating couplers, as well as practical issues such as testing, packaging and promising applications.

https://www.mdpi.com/2072-666X/11/7/666/pdf

Grating Couplers on Silicon Photonics: Design Principles, Emerging Trends and Practical Issues.

Plasmonic biosensing has been demonstrated to be a powerful technique for quantitative determination of molecular analytes and kinetic analysis of biochemical reactions. However, interfaces of most plasmonic biosensors are made of noble metals, such as gold and silver, which are not compatible with industrial production technologies. This greatly limits biosensing applications beyond biochemical and pharmaceutical research. Here, we propose and investigate copper-based biosensor chips fully fabricated with a standard complementary metal–oxide–semiconductor (CMOS) process. The protection of thin copper films from oxidation is achieved with SiO2 and Al2O3 dielectric films deposited onto the metal surface. In addition, the deposition of dielectric films with thicknesses of only several tens of nanometers significantly improves the biosensing sensitivity, owing to better localization of electromagnetic field above the biosensing surface. According to surface plasmon resonance (SPR) measurements, the copper bi...

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Superior Sensitivity of Copper-Based Plasmonic Biosensors.

Surface plasmon resonance-based sensors have emerged as commercially fostering portable biodetectors. The scientific community is engaged in extensive research to improve their performance in terms...

Grating-Coupled Surface Plasmon-Polariton Sensing at a Flat Metal-Analyte Interface in a Hybrid-Configuration.

A novel, cost effective, label free and real time biosensor based on straight gold waveguides supporting long range surface plasmon polaritons (LRSPPs) is used to measure the kinetics constants of protein–protein interactions. Bovine serum albumin (BSA) and anti-bovine albumin antibody (anti-BSA) produced in rabbit are used as the bio-pair for the purposes of demonstrating and investigating the extraction of binding kinetics. BSA protein is immobilized on the surface using thiol coupling. The output power of the system is recorded continuously over time, and then converted into surface mass concentration. The kinetics constants are extracted from binding curves using the integrated rate equation. Linear least squares and non-linear least squares analysis are employed to obtain the constants and the results are compared.

Biomolecular kinetics analysis using long-range surface plasmon waveguides

A long-range surface plasmon polariton waveguide composed of a gold stripe embedded in CYTOP with an etched microfluidic channel has been used as a label-free real-time biosensor to demonstrate enhanced assay formats capable of very low detection limits. Specifically, sandwich and inhibition (competitive) assays were developed and demonstrated using Bovine Serum Albumin (BSA) and anti-BSA produced in rabbit as a model bio-specific pair. Carbodiimide coupling to a self-assembled COOH-terminated alkanethiol monolayer on the gold stripe was used to immobilize biomaterial to its surface. The optical output power from the biosensor was measured continuously over time and converted into surface mass density. Titration curves were extracted for both immunoassays. We demonstrate that protein concentrations in solution of 10 pg/ml can be detected with a signal-to-noise ratio of 20 using this new optical biosensor technology.

Low detection limits using sandwich and inhibition assays on long-range surface plasmon waveguide biosensors

Long-range surface plasmon polariton waveguides consisting of Au stripes integrated with input and output grating couplers embedded in thick Cytop claddings are proposed and demonstrated experimentally. Under the right conditions, grating couplers enable broadside (top) coupling with good efficiency while producing a low level of background light. The scheme does not require high-quality input and output edge facets, and it simplifies optical alignments. We demonstrate coupling using a cleaved bow-tie fiber and a lensed fiber, and we determine the grating coupling efficiencies in both cases over a broad operating wavelength range. The lensed fiber produces a better overlap with the long-range surface plasmon mode of interest and thus results in a better coupling efficiency with essentially no background light as observed on an infrared camera. The measurements are compared with theoretical results obtained using a realistic model of the structures, including out-of-plane curvature in the grating profile resulting from our fabrication process. The coupling scheme along with the surface plasmon waveguides hold strong potential for biosensing applications.

Grating couplers fabricated by e-beam lithography for long-range surface plasmon waveguides embedded in a fluoropolymer.

Gratings capable of incoupling an incident Gaussian beam into long-range surface plasmon polaritons (LRSPPs), propagating along a thin narrow Au stripe on a low-index cladding (fluoropolymer), or on a truncated 1D photonic crystal as a Bloch LRSPP, are investigated for potential biosensing application. The gratings are optimized, initially, through 2D modeling using the vectorial finite element method. Different 3D grating designs are then investigated through 3D modeling using the vectorial finite difference time domain method, including wide gratings on adiabatic and nonadiabatic flared stripes. Wide gratings on flared stripes have a larger area enabling size matching and coupling to larger incident beams, which facilitates optical alignments. We also investigate the effects of changing the size of the beam incident on the structures. Incoupling efficiencies of up to 25% at λ0=1310 are predicted for optimal gratings—such coupling efficiencies are among the highest reported to date for a structure of this kind. Similar grating designs are also examined as outcoupling structures, capable of coupling (Bloch) LRSPPs into a perpendicularly emerging Gaussian beam. The absorptance, reflectance, and transmittance of the structure were also calculated. Structures were fabricated on a multilayer wafer supporting Bloch LRSPPs to verify design concepts.

Maryam Khodami

Papers

Biomolecular kinetics analysis using long-range surface plasmon waveguides

Low detection limits using sandwich and inhibition assays on long-range surface plasmon waveguide biosensors

Grating couplers fabricated by e-beam lithography for long-range surface plasmon waveguides embedded in a fluoropolymer.

Grating couplers for (Bloch) long-range surface plasmons on metal stripe waveguides

Fabrication of long-range surface plasmon-polariton Bragg gratings with microfluidic channels in Cytop claddings