Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> The use of self-assembled monolayers (SAMs) in various fields of ::: research is rapidly growing. In particular, many biomedical fields apply ::: SAMs as an interface-layer between a metal surface and a solution or ::: vapour. This review summarises methods for the formation of SAMs upon the ::: most commonly used materials and techniques used for monolayer ::: characterisation. Emphasis will lie on uniform, mixed and functionalised ::: monolayers applied for immobilisation of biological components including ::: (oligo-)nucleotides, proteins, antibodies and receptors as well as ::: polymers. The application of SAMs in today’s research, together with ::: some applications will be discussed. <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> Food quality and safety is a scientific discipline describing handling, preparation and storage of food in ways that prevent food borne illness. Food serves as a growth medium for microorganisms that can be pathogenic or cause food spoilage. Therefore, it is imperative to have stringent laws and standards for the preparation, packaging and transportation of food. The conventional methods for detection of food contamination based on culturing, colony counting, chromatography and immunoassay are tedious and time consuming while biosensors have overcome some of these disadvantages. There is growing interest in biosensors due to high specificity, convenience and quick response. Optical biosensors show greater potential for the detection of pathogens, pesticide and drug residues, hygiene monitoring, heavy metals and other toxic substances in the food to check whether it is safe for consumption or not. This review focuses on optical biosensors, the recent developments in the associated instrumentation with emphasis on fiber optic and surface plasmon resonance (SPR) based biosensors for detecting a range of analytes in food samples, the major advantages and challenges associated with optical biosensors. It also briefly covers the different methods employed for the immobilization of bio-molecules used in developing biosensors. <s> BIB002 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> Surface bioconjugation of biomolecules has gained enormous attention for developing advanced biomaterials including biosensors. While conventional immobilization (by physisorption or covalent couplings using the functional groups of the endogenous amino acids) usually results in surfaces with low activity, reproducibility and reusability, the application of methods that allow for a covalent and uniformly oriented coupling can circumvent these limitations. In this study, the nanobody targeting Vascular Cell Adhesion Molecule-1 (NbVCAM1), an atherosclerotic biomarker, is engineered with a C-terminal alkyne function via Expressed Protein Ligation (EPL). Conjugation of this nanobody to azidified silicon wafers and Biacore™ C1 sensor chips is achieved via Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry to detect VCAM1 binding via ellipsometry and surface plasmon resonance (SPR), respectively. The resulting surfaces, covered with uniformly oriented nanobodies, clearly show an increased antigen binding affinity, sensitivity, detection limit, quantitation limit and reusability as compared to surfaces prepared by random conjugation. These findings demonstrate the added value of a combined EPL and CuAAC approach as it results in strong control over the surface orientation of the nanobodies and an improved detecting power of their targets-a must for the development of advanced miniaturized, multi-biomarker biosensor platforms. <s> BIB003 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> Biosensors that depend on a physical or chemical measurement can be adversely affected by non-specific interactions. For example, a biosensor designed to measure specifically the levels of a rare analyte can give false positive results if there is even a small amount of interaction with a highly abundant but irrelevant molecule. To overcome this limitation, the biosensor community has frequently turned to antibody molecules as recognition elements because they are renowned for their exquisite specificity. Unfortunately antibodies can often fail when immobilised on inorganic surfaces, and alternative biological recognition elements are needed. This article reviews the available non-antibody-binding proteins that have been successfully used in electrical and micro-mechanical biosensor platforms. <s> BIB004 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> Abstract: Accurate identification and quantification of allergens is key in healthcare, biotechnology and food quality and safety. Celery (Apium graveolens) is one of the most important elicitors of food allergic reactions in Europe. Currently, the golden standards to identify, quantify and discriminate celery in a biological sample are immunoassays and two-step molecular detection assays in which quantitative PCR (qPCR) is followed by a high-resolution melting analysis (HRM). In order to provide a DNA-based, rapid and simple detection method suitable for one-step quantification, a fiber optic PCR melting assay (FO-PCR-MA) was developed to determine different concentrations of celery DNA (1 pM–0.1 fM). The presented method is based on the hybridization and melting of DNA-coated gold nanoparticles to the FO sensor surface in the presence of the target gene (mannitol dehydrogenase, Mtd). The concept was not only able to reveal the presence of celery DNA, but also allowed for the cycle-to-cycle quantification of the target sequence through melting analysis. Furthermore, the developed bioassay was benchmarked against qPCR followed by HRM, showing excellent agreement (R2 = 0.96). In conclusion, this innovative and sensitive diagnostic test could further improve food quality control and thus have a large impact on allergen induced healthcare problems. <s> BIB005 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> Quantification of cancer biomarker microRNAs (miRs) by exquisitely designed biosensors with a short time-to-result is of great clinical significance. With immobilized capture probes (CPs) and fluorescent-labeled signal probes (SPs), surface-involved sandwich-type (SST) biosensors serve as powerful tools for rapid, highly sensitive, and selective detection of miR in complex matrices as opposed to the conventional techniques. One key challenge for such SST biosensors is the existence of false-negative signals when the amount of miRs exceeds SPs in solution phase for a surface with a limited number of CP. To meet this challenge, a dynamic lock/open DNA assembly was designed to rationally program the pathway for miR/SP hybrids. Based on secondary structure analysis and free-energy assessment, a “locker” strand that partially hybridizes with target miR by two separated short arms was designed to stabilize target miR, preventing possible false-negative signals. The strategy was demonstrated on a fiber-based flu... <s> BIB006 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Surface Biofunctionalization <s> The apparent increase in hormone-induced cancers and disorders of the reproductive tract has led to a growing demand for new technologies capable of screening xenoestrogens. We reported an estrogen receptor (ER)-based reusable fiber biosensor for facile screening estrogenic compounds in environment. The bioassay is based on the competition of xenoestrogens with 17β-estradiol (E2) for binding to the recombinant receptor of human estrogen receptor α (hERα) protein, leaving E2 free to bind to fluorophore-labeled anti-E2 monoclonal antibody. Unbound anti-E2 antibody then binds to the immobilized E2-protein conjugate on the fiber surface, and is detected by fluorescence emission induced by evanescent field. As expected, the stronger estrogenic activity of xenoestrogen would result in the weaker fluorescent signal. Three estrogen-agonist compounds, diethylstilbestrol (DES), 4-n-nonylphenol (NP) and 4-n-octylphenol (OP), were chosen as a paradigm for validation of this assay. The rank order of estrogenic potency determined by this biosensor was DES>OP>NP, which were consistent with the published results in numerous studies. Moreover, the E2-protein conjugate modified optical fiber was robust enough for over 300 sensing cycles with the signal recoveries ranging from 90% to 100%. In conclusion, the biosensor is reusable, reliable, portable and amenable to on-line operation, providing a facile, efficient and economical alternative to screen potential xenoestrogens in environment. <s> BIB007
Metal-coated fiber gratings are then functionalized for biosensing purposes. The chemistry involved for the surface activation depends on the target application. For example, numerous biosensors use the antibody/antigen affinity to detect proteins of interest, but a large panel of variants exist, using for example DNA hybridization BIB005 BIB006 , enzymes and biomimetism (phage display and recombinant protein engineering, aptamers technologies, oxidative state sensing) BIB002 . New emerging technologies are also increasingly used to expand the target possibilities and enhance the sensor response, such as the immobilization of nanobodies, affimers or estrogens BIB002 BIB003 BIB004 BIB007 . Concerning the analyzed parameters, the biosensing area can be used to detect the presence of target analytes such as biomarkers for clinical measurements, but also to monitor cellular behaviour and densities, the development of biofilms, the detection of bacteria and viruses, environmental monitoring, etc. Whatever the analyte to be detected, the most common technique for immobilizing recognition molecules on the sensor is the elaboration of a self-assembled monolayer (SAM) BIB001 . For this, metal-coated optical fibers are first cleaned with absolute ethanol and immersed in a thiols solution. Practically, this can be done in a capillary tube sealed at both ends after the insertion of the fiber, to prevent solvent evaporation. After this, the functionalized fiber gratings are rinsed again and the surface is activated using the selected biomolecules. An effective blocking step is also needed after the functionalization to ensure a high specificity and a low rate of false positive responses when analyzing complex media. Generally, this yields the structure depicted in Figure 9 .  Metal-coated fiber gratings are then functionalized for biosensing purposes. The chemistry involved for the surface activation depends on the target application. For example, numerous biosensors use the antibody/antigen affinity to detect proteins of interest, but a large panel of variants exist, using for example DNA hybridization BIB005 BIB006 , enzymes and biomimetism (phage display and recombinant protein engineering, aptamers technologies, oxidative state sensing) BIB002 . New emerging technologies are also increasingly used to expand the target possibilities and enhance the sensor response, such as the immobilization of nanobodies, affimers or estrogens BIB002 BIB003 BIB004 BIB007 . Concerning the analyzed parameters, the biosensing area can be used to detect the presence of target analytes such as biomarkers for clinical measurements, but also to monitor cellular behaviour and densities, the development of biofilms, the detection of bacteria and viruses, environmental monitoring, etc. Whatever the analyte to be detected, the most common technique for immobilizing recognition molecules on the sensor is the elaboration of a self-assembled monolayer (SAM) BIB001 . For this, metal-coated optical fibers are first cleaned with absolute ethanol and immersed in a thiols solution. Practically, this can be done in a capillary tube sealed at both ends after the insertion of the fiber, to prevent solvent evaporation. After this, the functionalized fiber gratings are rinsed again and the surface is activated using the selected biomolecules. An effective blocking step is also needed after the functionalization to ensure a high specificity and a low rate of false positive responses when analyzing complex media. Generally, this yields the structure depicted in Figure 9 .  Metal-coated fiber gratings are then functionalized for biosensing purposes. The chemistry involved for the surface activation depends on the target application. For example, numerous biosensors use the antibody/antigen affinity to detect proteins of interest, but a large panel of variants exist, using for example DNA hybridization BIB005 BIB006 , enzymes and biomimetism (phage display and recombinant protein engineering, aptamers technologies, oxidative state sensing) BIB002 . New emerging technologies are also increasingly used to expand the target possibilities and enhance the sensor response, such as the immobilization of nanobodies, affimers or estrogens BIB002 BIB003 BIB004 BIB007 . Concerning the analyzed parameters, the biosensing area can be used to detect the presence of target analytes such as biomarkers for clinical measurements, but also to monitor cellular behaviour and densities, the development of biofilms, the detection of bacteria and viruses, environmental monitoring, etc. Whatever the analyte to be detected, the most common technique for immobilizing recognition molecules on the sensor is the elaboration of a self-assembled monolayer (SAM) BIB001 . For this, metal-coated optical fibers are first cleaned with absolute ethanol and immersed in a thiols solution. Practically, this can be done in a capillary tube sealed at both ends after the insertion of the fiber, to prevent solvent evaporation. After this, the functionalized fiber gratings are rinsed again and the surface is activated using the selected biomolecules. An effective blocking step is also needed after the functionalization to ensure a high specificity and a low rate of false positive responses when analyzing complex media. Generally, this yields the structure depicted in Figure 9 . 