Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> The spectral characteristics of a fiber Bragg grating (FBG) with a transversely inhomogeneous refractive index profile, differs con- siderably from that of a transversely uniform one. Transmission spectra of inhomogeneous and asymmetric FBGs that have been inscribed with focused ultrashort pulses with the so-called point-by-point technique are investigated. The cladding mode resonances of such FBGs can span a full octave in the spectrum and are very pronounced (deeper than 20dB). Using a coupled-mode approach, we compute the strength of resonant coupling and find that coupling into cladding modes of higher azimuthal order is very sensitive to the position of the modification in the core. Exploiting these properties allows precise control of such reflections and may lead to many new sensing applications. <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> This paper presents the design and fabrication of a fiber-optic refractive index (RI) sensor. The novel concept employs a long-period fiber grating (LPG) to achieve surface plasmon resonance (SPR) of a single cladding mode at the gold-coated tip of a single-mode fiber. The sensor combines a high level of sensitivity, a miniaturized sensing area and simple intensity-based interrogation, and is intended for biosensing using portable point-of-care devices or highly integrated lab-on-chip systems. <s> BIB002 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> Abstract A novel fiber optical fiber hydrogen sensor based on etched fiber Bragg grating coated with Pd/Ag composite film is proposed in this paper. Pd/Ag composite films were deposited on the side-face of etched fiber Bragg grating (FBG) as sensing elements by magnetron sputtering process. The atomic ratio of the two metals in Pd/Ag composite film is controlled at Pd:Ag = 76:24. Compared to standard FBG coated with same hydrogen sensitive film, etched FBG can significantly increase the sensor’s sensitivity. When hydrogen concentrations are 4% in volume percentage, the wavelength shifts of FBG-125 μm, FBG-38 μm and FBG-20.6 μm are 8, 23 and 40 pm respectively. The experimental results show the sensor’s hydrogen response is reversible, and the hydrogen sensor has great potential in hydrogen’s measurement. <s> BIB003 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> Recent research has shown that the transmission spectrum of a long period grating (LPG) written into an optical fiber is sensitive to the thickness and the refractive index (RI) of a thin layer deposited on it, a concept which forms the basis of a number of optical fiber sensors. The research reported herein is focused, in particular, on sensors of this type to create a design with an optimized thickness of the deposited layers of polyvinyl alcohol (PVA) on LPGs forming the basis of a highly sensitive probe. In creating such sensors, the dip-coating technique is used to minimize deleterious effects in the attenuation bands resulting from the inhomogeneity of the coated surface. In this paper, LPGs with different coating thicknesses are uniformly coated with thin layers of PVA and submerged in oils of known RI over the range from 1.30 to 1.70, to create effective RI probes. It is observed that when the coating thickness reaches a particular value that enables a substantial redistribution of the optical power within the overlay, a maximum sensitivity of the sensor can be achieved, even when the overlay has a RI higher than that of the cladding. The experimental results obtained through the characterization of the devices developed are shown to be in good agreement with the results of a theoretical model. <s> BIB004 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> We demonstrate that etched fiber Bragg gratings (eFBGs) coated with single walled carbon nanotubes (SWNTs) and graphene oxide (GO) are highly sensitive and accurate biochemical sensors. Here, for detecting protein concanavalin A (Con A), mannose-functionalized poly(propyl ether imine) (PETIM) dendrimers (DMs) have been attached to the SWNTs (or GO) coated on the surface modified eFBG. The dendrimers act as multivalent ligands, having specificity to detect lectin Con A. The specificity of the sensor is shown by a much weaker response (factor of similar to 2500 for the SWNT and similar to 2000 for the GO coated eFBG) to detect non specific lectin peanut agglutinin. DM molecules functionalized GO coated eFBG sensors showed excellent specificity to Con A even in the presence of excess amount of an interfering protein bovine serum albumin. The shift in the Bragg wavelength (Delta lambda(B)) with respect to the lambda(B) values of SWNT (or GO)-DM coated eFBG for various concentrations of lectin follows Langmuir type adsorption isotherm, giving an affinity constant of similar to 4 x 10(7) M-1 for SWNTs coated eFBG and similar to 3 x 10(8) M-1 for the GO coated eFBG. (C) 2014 Elsevier B.V. All rights reserved. <s> BIB005 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> A novel fiber optical refractive index sensor based on gold nanoshells immobilized on the surface of an etched single-mode fiber including a Bragg grating is demonstrated. The nanoparticle coating induces refractive index dependent waveguide losses, because of the variation of the evanescently guided part of the light. Hence the amplitude of the Bragg reflection is highly sensitive to refractive index changes of the surrounding medium. The nanoshell functionalized fiber optical refractive index sensor works in reflectance mode, is suitable for chemical and biochemical sensing, and shows an intensity dependency of 4400% per refractive index unit in the refractive index range between 1.333 and 1.346. Furthermore, the physical length of the sensor is smaller than 3 mm with a diameter of 6 μm, and therefore offers the possibility of a localized refractive index measurement. <s> BIB006 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> A graphene-based long-period fiber grating (LPFG) surface plasmon resonance (SPR) sensor is proposed. A monolayer of graphene is coated onto the Ag film surface of the LPFG SPR sensor, which increases the intensity of the evanescent field on the surface of the fiber and thereby enhances the interaction between the SPR wave and molecules. Such features significantly improve the sensitivity of the sensor. The experimental results demonstrate that the sensitivity of the graphene-based LPFG SPR sensor can reach 0.344 nm%-1 for methane, which is improved 2.96 and 1.31 times with respect to the traditional LPFG sensor and Ag-coated LPFG SPR sensor, respectively. Meanwhile, the graphene-based LPFG SPR sensor exhibits excellent response characteristics and repeatability. Such a SPR sensing scheme offers a promising platform to achieve high sensitivity for gas-sensing applications. <s> BIB007 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> The tilted fiber Bragg grating (TFBG) is a new kind of fiber-optic sensor that possesses all the advantages of well-established Bragg grating technology in addition to being able to excite cladding modes resonantly. This device opens up a multitude of opportunities for single-point sensing in hard-to-reach spaces with very controllable cross-sensitivities, absolute and relative measurements of various parameters, and an extreme sensitivity to materials external to the fiber without requiring the fiber to be etched or tapered. Over the past five years, our research group has been developing multimodal fiber-optic sensors based on TFBG in various shapes and forms, always keeping the device itself simple to fabricate and compatible with low-cost manufacturing. This paper presents a brief review of the principle, fabrication, characterization, and implementation of TFBGs, followed by our progress in TFBG sensors for mechanical and biochemical applications, including one-dimensional TFBG vibroscopes, accelerometers and micro-displacement sensors; two-dimensional TFBG vector vibroscopes and vector rotation sensors; reflective TFBG refractometers with in-fiber and fiber-to-fiber configurations; polarimetric and plasmonic TFBG biochemical sensors for in-situ detection of cell, protein and glucose. <s> BIB008 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> A compact and label-free optical fiber sensor based on a taper interferometer cascaded with a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for detection of a breast cancer biomarker (HER2). The tapered fiber-optic interferometer is extremely sensitive to the ambient refractive index (RI). In addition, being insensitive to the RI variation, the FBG can be applied as a temperature thermometer due to its independent response to the temperature. Surface functionalization to the sensor is carried out to achieve specific targeting of the unlabeled biomarkers. The result shows that the proposed sensor presents a low limit-of-detection (LOD) of 2 ng/mL, enabling its potentials of application in early diagnosis on the breast cancer. <s> BIB009 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> A compact and low-power consuming fiber-optic anemometer based on single-walled carbon nanotubes (SWCNTs) coated tilted fiber Bragg grating (TFBG) is presented. TFBG as a near infrared in-fiber sensing element is able to excite a number of cladding modes and radiation modes in the fiber and effectively couple light in the core to interact with the fiber surrounding mediums. It is an ideal in-fiber device used in a fiber hot-wire anemometer (HWA) as both coupling and sensing elements to simplify the sensing head structure. The fabricated TFBG was immobilized with an SWCNT film on the fiber surface. SWCNTs, a kind of innovative nanomaterial, were utilized as light-heat conversion medium instead of traditional metallic materials, due to its excellent infrared light absorption ability and competitive thermal conductivity. When the SWCNT film strongly absorbs the light in the fiber, the sensor head can be heated and form a "hot wire". As the sensor is put into wind field, the wind will take away the heat on the sensor resulting in a temperature variation that is then accurately measured by the TFBG. Benefited from the high coupling and absorption efficiency, the heating and sensing light source was shared with only one broadband light source (BBS) without any extra pumping laser complicating the system. This not only significantly reduces power consumption, but also simplifies the whole sensing system with lower cost. In experiments, the key parameters of the sensor, such as the film thickness and the inherent angle of the TFBG, were fully investigated. It was demonstrated that, under a very low BBS input power of 9.87 mW, a 0.100 nm wavelength response can still be detected as the wind speed changed from 0 to 2 m/s. In addition, the sensitivity was found to be -0.0346 nm/(m/s) under the wind speed of 1 m/s. The proposed simple and low-power-consumption wind speed sensing system exhibits promising potential for future long-term remote monitoring and on-chip sensing in practical applications. <s> BIB010 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> In this study, we propose a tilted fiber Bragg grating (TFBG) humidity sensor fabricated using the phase mask method to produce a TFBG that was then etched with five different diameters of 20, 35, 50, 55 and 60 μm, after which piezoelectric inkjet technology was used to coat the grating with graphene oxide. According to the experimental results, the diameter of 20 μm yielded the best sensitivity. In addition, the experimental results showed that the wavelength sensitivity was −0.01 nm/%RH and the linearity was 0.996. Furthermore, the measurement results showed that when the relative humidity was increased, the refractive index of the sensor was decreased, meaning that the TFBG cladding mode spectrum wavelength was shifted. Therefore, the proposed graphene oxide film TFBG humidity sensor has good potential to be an effective relative humidity monitor. <s> BIB011 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> The Karhunen–Loeve transform (KLT) is used to retrieve the wavelength information of several fiber Bragg gratings (FBGs) that are acting as a multiplexed sensor. The modulated light of a broadband source is launched to the FBG cascade in order to capture the electrical frequency response of the system. Thanks to dispersive media, the wavelengths of the FBGs are mapped in radio-frequency delays. Wavelength changes are determined by the amplitude change of the samples in the impulse response, a change which is followed by the eigenvalue calculated by the KLT routine. The use of the KLT routine reduces by three orders of magnitude the amount of points needed to have a subdegree resolution in temperature sensing, while keeping the accuracy almost intact. <s> BIB012 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> This work presents the development of an innovative plasmonic optical fiber (OF) immunosensor for the detection of cytokeratin 17 (CK17), a biomarker of interest for lung cancer diagnosis. The development of this sensing platform is such that it can be assessed in non-liquid environments, demonstrating that a surface plasmon resonance (SPR) can be excited in this case. For this purpose, detections have been first carried out on CK17 encapsulated in gel matrix in the aim of mimicking tissue samples. Gold-coated OF immunosensors were embedded in a specifically designed packaging providing enough stiffness to penetrate into soft matters. Resulting reflected spectra have revealed, for the first time, the presence of a stable SPR signal recorded in soft matters. Experiments conducted to detect CK17 trapped in a porous polyacrylamide gel matrix have highlighted the specific and selective biosensor response towards the target protein. Finally, the packaged OF immunosensor has been validated by a preliminary test on human lung biopsy, which has confirmed the ex-vivo CK17 detection. Consequently, this work represents an important milestone towards the detection of biomarkers in tissues, which is still a clinical challenge for minimally-invasive in vivo medical diagnosis. <s> BIB013 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> Abstract A novel immunosensor for detecting Newcastle disease virus (NDV) was developed using excessively tilted fiber grating (Ex-TFG) coated with gold nanospheres (AuNs). AuNs were coated on the Ex-TFG surface via Au–S bonds using 3-mercaptopropyltrimethoxysilane (MPTMS), and the activated staphylococcal protein A (SPA) was linked to AuNs by covalent bonds via cysteamine. AuNs greatly enhanced the impact of the analyte on the fiber cladding mode through the local surface Plasmon resonance (LSPR) effect, thus improving the detection limit and sensitivity of the immunosensor. Meanwhile, SPA enhanced the bioactivity of anti-NDV monoclonal antibodies (MAbs), thus promoting the effectiveness of specific binding events on the fiber surface. Immunoassays were performed by monitoring the resonance wavelength shift of the proposed sensor under NDV samples containing different particle amounts. Specificity was assessed, and clinical tests for NDV were performed by contrast experiments. Experimental results showed that the detection limit for NDV was about 5~10 times improved compared to that of reference Ex-TFG without AuN treatment. Moreover, the novel biosensor was reusable and could potentially be applied in clinic. <s> BIB014 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Spectrometer-Based Interrogation <s> Surface Plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-toimplement alternative to well established bulky prism configurations for in-situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nano-scale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface Plasmon for high accuracy interrogation. In this talk, we briefly review the principle, characterization and implementation of plasmonic TFBG sensors, followed by our recent developments of the “surface” and “localized” affinity studies of the biomolecules for real life problems, the electrochemical actives of electroactive biofilms for clean energy resources, and ultra-highly sensitive gas detection. <s> BIB015
This technique relies on the quantification of the wavelength shift induced by a refractive index change in the sensing region BIB009 . It has been the most widespread method for interrogating plasmonic FBG sensors since the early stages of this technology, and hence the majority of commercially available FBG interrogators are based on the same principle. As can be seen in Figure  11a , the classic implementation consists of a broadband source (BBS) and an optical spectrum analyzer (OSA) for interrogating the transmission response of the sensors. In the case of etched FBGs BIB003 BIB005 and LPFGs BIB004 BIB007 BIB002 , the wavelength tracking can be carried out in a wider region than the one required for TFBGs BIB010 BIB011 BIB014 BIB015 BIB008 and eccentric FBGs BIB001 , since for these configurations the most sensitive cladding mode must be carefully isolated from the rest.  This technique relies on the quantification of the wavelength shift induced by a refractive index change in the sensing region BIB009 . It has been the most widespread method for interrogating plasmonic FBG sensors since the early stages of this technology, and hence the majority of commercially available FBG interrogators are based on the same principle. As can be seen in Figure 11a , the classic implementation consists of a broadband source (BBS) and an optical spectrum analyzer (OSA) for interrogating the transmission response of the sensors. In the case of etched FBGs BIB003 BIB005 and LPFGs BIB004 BIB007 BIB002 , the wavelength tracking can be carried out in a wider region than the one required for TFBGs BIB010 BIB011 BIB014 BIB015 BIB008 and eccentric FBGs BIB001 , since for these configurations the most sensitive cladding mode must be carefully isolated from the rest. For sensor interrogation in reflection mode, an optical fiber circulator is located between the source and the sensor. The OSA is also connected so that both source and detector remain located at the same side of the optical path. For etched FBGs no additional element is required due to the nature of their reflection response BIB006 and certain algorithms can be used for increasing the resolution of the measurements BIB012 . For the rest of the summarized alternatives, a mirror is deposited on the fiber tip in order to allow back-reflection of the light modes that are sensitive to the external medium BIB013 . Practically, some FBG interrogators integrate the source, circulator and detector as one, so that the sensor can be connected to a single port of the device. In this precise case, the source can be a tunable laser, offering a very high wavelength resolution (1 pm typically) and a fast acquisition rate (most often in the range 1-10 Hz with currently available commercial FBG interrogators) over the C + L wavelength bands.