Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> Mode coupling at bends in optical fibers supporting one or only a few guided modes is analyzed by considering the local normal modes for the corresponding straight waveguide. Matrix elements giving the strength of coupling between guided modes at a corner bend, and for coupling between guided modes and radiation modes, are calculated as a function of guiding strength for this "geometrical" effect. The correction to these matrix elements due to the longitudinal strain in a bent fiber is also determined. The increase in propagation constant for the fundamental mode of a fiber wrapped in a coil of constant radius is calculated from information on the coupling strengths and mode propagation constants. The phase shift and attenuation of the fundamental mode caused by a spatially periodic microbending of the fiber axis are also considered. Finally, potential applications of these effects in fiber-optic devices such as mode converters, phase shifters, switches, and sensors are discussed. <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> Abstract A fiber-optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensing element of the fiber has been fabricated by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal onto the fiber core. A white-light source is used to introduce a range of wavelengths into the fiber optic. Changes in the sensed parameters (e.g., bulk refractive index, film thinkness and film refractive index) are determined by measuring the transmitted spectral-intensity distribution. Experimental results of the sensitivity and the dynamic range in the measurement of the refractive indices of aqueous solutions are in agreement with the theoretical model of the sensor. <s> BIB002 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> A fibre-optic evanescent field absorption sensor based on a U-shaped sensing probe is described. The influences of fibre core diameter, bending radius of the probe and the refractive index of the fluid on the sensitivity of the sensor are evaluated experimentally. The results are compared with the theoretical results obtained using geometrical optics and based on two-dimensional treatment. A good qualitative agreement is found between them. <s> BIB003 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> Since the introduction of optical fiber technology in the field of sensor based on the technique of surface plasmon resonance (SPR), fiber-optic SPR sensors have witnessed a lot of advancements. This paper reports on the past, present, and future scope of fiber-optic SPR sensors in the field of sensing of different chemical, physical, and biochemical parameters. A detailed mechanism of the SPR technique for sensing purposes has been discussed. Different new techniques and models in this area that have been introduced are discussed in quite a detail. We have tried to put the different advancements in the order of their chronological evolution. The content of the review article may be of great importance for the research community who are to take the field of fiber-optic SPR sensors as its research endeavors. <s> BIB004 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> Surface plasmon resonance technique in collaboration with optical fiber technology has brought tremendous advancements in sensing of various physical, chemical, and biochemical parameters. In this review article, we present the principle of SPR technique for sensing and various designs of the fiber optic SPR probe reported for the enhancement of the sensitivity of the sensor. In addition, we present few examples of the surface plasmon resonance- (SPR-) based fiber optic sensors. The present review may provide researchers valuable information regarding fiber optic SPR sensors and encourage them to take this area for further research and development. <s> BIB005 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Review of Grating Configurations Used for SPR Excitation <s> In this paper we present a fiber optic surface plasmon resonance (SPR) sensor as a reusable, cost-effective and label free biosensor for measuring DNA hybridization and DNA-protein interactions. This is the first paper that combines the concept of a fiber-based SPR system with DNA aptamer bioreceptors. The fibers were sputtered with a 50nm gold layer which was then covered with a protein repulsive self-assembled monolayer of mixed polyethylene glycol (PEG). Streptavidin was attached to the PEG's carboxyl groups to serve as a versatile binding element for biotinylated ssDNA. The ssDNA coated SPR fibers were first evaluated as a nucleic acid biosensor through a DNA-DNA hybridization assay for a random 37-mer ssDNA. This single stranded DNA showed a 15 nucleotides overlap with the receptor ssDNA on the SPR fiber. A linear calibration curve was observed in 0.5-5 microM range. A negative control test did not reveal any significant non-specific binding, and the biosensor was easily regenerated. In a second assay the fiber optic SPR biosensor was functionalized with ssDNA aptamers against human immunoglobulin E. Limits of detection (2nM) and quantification (6nM) in the low nanomolar range were observed. The presented biosensor was not only useful for DNA and protein quantification purposes, but also to reveal the binding kinetics occurring at the sensor surface. The dissociation constant between aptamer and hIgE was equal to 30.9+/-2.9nM. The observed kinetics fully comply with most data from the literature and were also confirmed by own control measurements. <s> BIB006
To excite SPR on the side of an optical fiber, a physical access to the core-guided light is locally required so that it can be brought into contact with the surrounding medium. A straightforward configuration for doing this is fiber bending BIB001 BIB003 . Other solutions expose the core to the surrounding medium through a polishing or etching of the cladding, totally or in part BIB004 BIB005 BIB006   . The first reported configuration is based on this mechanism and dates back to 1993 BIB002 . More advanced configurations make use of fiber gratings permanently photo-inscribed in the fiber core that enable light coupling to the surrounding medium. Metal-coated fiber gratings have been attracting ever-growing interest over the years, as they bring specific practical benefits such as: (1) tuning of the SPR mode-excitation wavelength via selective cladding mode coupling; (2) subsequent compatibility with telecommunication-grade optical fibers and equipment; (3) temperature self-compensation; (4) fiber integrity conservation; and (5) compatibility with mass production, among others. Hence, numerous developments are nowadays obtained with this technology since it enables SPR excitation in the telecommunication wavelength window of around 1550 nm. This article will describe their operating principle and review the main achievements obtained for sensing selective proteins and cells with such devices. It will focus on recent progress in this field, which slowly but surely paves the way towards the use of these devices for minimally-invasive diagnosis.  Gratings are usually manufactured in single-mode optical fibers, made of an 8 µm thick core surrounded by a 125 µm cladding. Such fibers are widely available at low cost (less than 100 US$ per km) and are telecommunication-grade. Overall, gratings preserve the fiber integrity (only the polymer jacket is removed at the grating location) while providing a strong coupling between the core-guided light and the cladding. Different grating configurations in single-mode optical fibers can be used for SPR excitation. Their characteristics and operating principle will be summarized hereafter.