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In this paper a new low-cost fiber Bragg grating (FBG) interrogation technique for static applications is demonstrated. The idea is based on the multiplication between the FBG reflectivity profile and the emission of a sawtooth modulated distributed feedback (DFB) laser source. The variation of the FBG wavelength generates a modification in the shape, in time domain, of the reflected light signal. The concept has been proven, using simulation, to cover FBG wavelength shift up to 1.7 nm. Experimental validation was performed for FBG temperature ranging from 6 °C to 50 °C (equivalently 440 pm) with a modulation frequency of 1 kHz. Sensitivity higher than 3.5 mV/pm is achieved in all circumstances with an estimated resolution of 8 pm.

Surface-enhanced Raman scattering (SERS) has established itself as powerful tool for molecular sensing in biology and medicine. The integration of SERS systems with optical fiber is a challenging but potentially very rewarding endeavour. However, efforts to transfer the technology from the laboratory to the clinic have been frustrated by the lack of robust stable and sensitive substrates on the fiber tip, as well as the complexity of interfacing between sample and the substrate itself. Here, we propose the Lab-on-Fiber SERS optrodes, realized on the optical fiber tip by nanosphere lithography. Three types of highly ordered and reproducible SERS-active substrates have been realized: close-packed array (CPA); CPA after sphere removal (SR) and sparse array (SA) of polystyrene nanospheres, covered by a gold thin layer. To optimize the SERS probes, we compared the SERS performances in terms of Enhancement Factor (EF) and reproducibility pertaining to different patterns with different nanosphere diameters and gold thicknesses using the biphenyl-4-thiol (BPT), as target molecule. Moreover, we analysed and compared the SERS spectra of two representative biological probes, bovine serum albumin (BSA, medium molecule) and red blood cells (RBCs), in order to correlate the SERS response to the morphology and hysteric hindrance of the biological target. The SERS analysis indicated that the CPA substrate amplifies the BPT Raman intensity twice as well as the SR and SA substrates, while BSA and RBCs, with the CPA substrate, provide signals comparable to those of SR and SA substrates. Finally, we have optimized a Raman system for SERS optrode operation with efficient lighting and collection via optical fiber.

This review presents an overview of the “lab-on-fiber technology” vision and the main milestones set in the technological roadmap to achieve the ultimate objective of developing flexible, multifunctional plug and play fiber-optic platforms designed for specific applications. The main achievements, obtained with nanofabrication strategies for unconventional substrates, such as optical fibers, are discussed here. The perspectives and challenges that lie ahead are highlighted with a special focus on full spatial control at the nanoscale and high-throughput production scenarios. The rapid progress in the fabrication stage has opened new avenues toward the development of multifunctional plug and play platforms, discussed here with particular emphasis on new functionalities and unparalleled figures of merit, to demonstrate the potential of this powerful technology in many strategic application scenarios. The paper also analyses the benefits obtained from merging lab-on-fiber (LOF) technology objectives with the emerging field of optomechanics, especially at the microscale and the nanoscale. We illustrate the main advances at the fabrication level, describe the main achievements in terms of functionalities and performance, and highlight future directions and related milestones. All achievements reviewed and discussed clearly suggest that LOF technology is much more than a simple vision and could play a central role not only in scenarios related to diagnostics and monitoring but also in the Information and Communication Technology (ICT) field, where optical fibers have already yielded remarkable results.

In this paper, we studied the influence of the geometrical configuration of surface-enhanced Raman scattering (SERS)-active self-assembling gold nanostructures on the interaction with biological targets of different sizes, aiming at large-scope SERS lab-on-fiber optrodes composed of highly efficient SERS substrates integrated onto optical fibre tips. By using nanosphere lithography, we fabricated three types of highly ordered and reproducible SERS-active substrates. To correlate the SERS response to the steric hindrance of the biological target, we experimentally analysed and compared the SERS spectra of three representative biological probes, i.e., ultralow-molecular-weight molecules of biphenyl-4-thiol (BPT, small molecule, 186.27 Da), bovine serum albumin (BSA, medium molecule, 66.5 kDa) and red blood cells (RBCs, diameter

In this paper, we report the in-field demonstration of an intrusion detection system implemented using Fiber Bragg Grating (FBG) sensors. The system is conceived to protect the perimeter of an area from unauthorized accesses to railways assets. As a case study, we installed and tested the system in a real scenario, and several field trials were performed to validate the system’s ability to recognize any human intrusion within the protected area. The proposed sensing system is a powerful tool to detect intruders, especially in real scenarios where protection fences are not practicable. The proposed intrusion detection system represents a valuable solution to improve railway security.

In this paper, we investigated the realization of Lab on fiber accelerometers based on micro-opto-mechanical cavities on the optical fiber tip. Two alternative approaches have been pursued. In the former one, the opto-mechanical cavity includes a simple cantilever suspended on the optical fiber end facet. In the latter, the opto-mechanical structure consists of a membrane sustained by four cantilevers. The mechanical response of the sensors has been predicted by numerical simulations based on the finite element method. Cantilever based accelerometers have been realized by using a ferrule top approach, whilst membrane based accelerometers have been realized through a photolithographic process followed by a transferring step for the final integration on the optical fiber tip. Different accelerometers have been fabricated with different geometrical features and characterized by using a shaking table. Either cantilever and membrane based Lab on fiber accelerometers exhibited a sensitivity of about 0.1 nm/(m/s2) on a 3 dB-bandwidth of 5 kHz with a resolution down to 100 μg/(Hz)1/2. Overall, the performance comparison with the actual state of the art confirms the potentiality and the versatility underlying the integration of micro-opto-mechanical (MOM) structures with the optical fibers towards a novel class of opto-mechanical lab on fiber accelerometers.

We report on our activities related to the development of surface enhanced Raman scattering (SERS) probes realized onto the optical fiber tip (OFT) through nanosphere lithography. In the first stage of our research, we adapted the nanosphere lithography to operate on the optical fiber tip, by assessing the process and demonstrating either the potentiality or the repeatability of the proposed nanopatterning approach. Successively, we investigated the ability of the manufactured structures on the fiber tip to act as SERS probes by measuring the SERS spectra in presence of a Biphenyl Thiol (BPT) monolayer. Firstly, we focused the attention on the samples shaped as closed packed array of nanospheres covered by gold. The analysis allowed us to identify the most promising SERS platform, exhibiting an Enhancement Factor (EF) of 4x10(5) and a SERS measurements variability lower than 10%. We addressed also the limitations related to the use of the same optical fiber for both illumination and light collection by selecting a commercial optical fiber exhibiting a suitable trade-off in terms of high excitation/collection efficiency and low silica background. Current activities are devoted to the investigation of other nanopatterns on the optical fiber tip (namely, Sparse Array of metallo-dielectric spheres) and the analysis of the probes response against different molecules.

This review presents an overview of “Lab on Fiber” technologies and devices with special focus on the design and development of advanced fiber optic nanoprobes for biological applications. Depending on the specific location where functional materials at micro and nanoscale are integrated, “Lab on Fiber Technology” is classified into three main paradigms: Lab on Tip (where functional materials are integrated onto the optical fiber tip), Lab around Fiber (where functional materials are integrated on the outer surface of optical fibers), and Lab in Fiber (where functional materials are integrated within the holey structure of specialty optical fibers). This work reviews the strategies, the main achievements and related devices developed in the “Lab on Fiber” roadmap, discussing perspectives and challenges that lie ahead, with special focus on biological sensing applications.

Self-assembly offers a unique resource for the preparation of discrete structures at the nano- and microscale, which are either not accessible by other fabrication techniques or require highly expensive and technologically demanding processes. The possibility of obtaining spontaneous organization of separated components, whether they are molecules, polymers, nano- or micro-objects, into a larger functional unit, enables the development of ready-to-use plug and play devices and components at lower costs. Expanding the applicability of self-assembly approaches at the nanoscale to non-conventional substrates would open up new avenues towards multifunctional platforms customized for specific applications. Recently, the combination of the amazing morphological and optical features of self-assembled patterns with the intrinsic properties of optical fibers to conduct light to a remote location has demonstrated the potentiality to open up new intriguing scenarios featuring unprecedented functionalities and performances. The integration of advanced materials and structures at the nanoscale with optical fiber substrates is the idea behind the so-called lab-on-fiber technology, which is an emerging technology at the forefront of nanophotonics and nanotechnology research. Self-assembly processes can have a key role in implementing cost-effective solutions suitable for the mass production of technologically advanced platforms based on optical fibers towards their real market exploitation. Novel lab-on-fiber optrodes would arise from the sustainable integration of functional materials at the nano- and microscale onto optical fiber substrates. Such devices are able to be easily integrated in hypodermic needles and catheters for in vivo theranostics and point-of-care diagnostics, opening up new frontiers in multidisciplinary technological development to be exploited in life science applications. This work is conceived to provide an overview of the latest strategies, based on self-assembly processes, which have been implemented for the realization of lab-on-fiber optrodes with particular emphasis on the perspectives and challenges that lie ahead. We discuss the main fabrication techniques and strategies aimed at developing new multifunctional optical fiber nanoprobes and their application in real scenarios. Finally, we highlight some of the other self-assembly processes that have not yet been applied to optical fiber sensors, but have the potentiality to be exploited in the fabrication of future lab-on-fiber devices.

In this paper we report on the engineering of repeatable surface enhanced Raman scattering (SERS) optical fiber sensor devices (optrodes), as realized through nanosphere lithography. The Lab-on-Fiber SERS optrode consists of polystyrene nanospheres in a close-packed arrays configuration covered by a thin film of gold on the optical fiber tip. The SERS surfaces were fabricated by using a nanosphere lithography approach that is already demonstrated as able to produce highly repeatable patterns on the fiber tip. In order to engineer and optimize the SERS probes, we first evaluated and compared the SERS performances in terms of Enhancement Factor (EF) pertaining to different patterns with different nanosphere diameters and gold thicknesses. To this aim, the EF of SERS surfaces with a pitch of 500, 750 and 1000 nm, and gold films of 20, 30 and 40 nm have been retrieved, adopting the SERS signal of a monolayer of biphenyl-4-thiol (BPT) as a reliable benchmark. The analysis allowed us to identify of the most promising SERS platform: for the samples with nanospheres diameter of 500 nm and gold thickness of 30 nm, we measured values of EF of 4 × 105, which is comparable with state-of-the-art SERS EF achievable with highly performing colloidal gold nanoparticles. The reproducibility of the SERS enhancement was thoroughly evaluated. In particular, the SERS intensity revealed intra-sample (i.e., between different spatial regions of a selected substrate) and inter-sample (i.e., between regions of different substrates) repeatability, with a relative standard deviation lower than 9 and 15%, respectively. Finally, in order to determine the most suitable optical fiber probe, in terms of excitation/collection efficiency and Raman background, we selected several commercially available optical fibers and tested them with a BPT solution used as benchmark. A fiber probe with a pure silica core of 200 µm diameter and high numerical aperture (i.e., 0.5) was found to be the most promising fiber platform, providing the best trade-off between high excitation/collection efficiency and low background. This work, thus, poses the basis for realizing reproducible and engineered Lab-on-Fiber SERS optrodes for in-situ trace detection directed toward highly advanced in vivo sensing.

We report on the engineering of repeatable surface enhanced Raman scattering (SERS) optrodes realized through nanosphere lithography on optical fiber (Figure 1). In particular, the Lab-on-Fiber SERS optrode consists of polystyrene nanospheres in close-packed arrays (CPA) configuration covered by a thin film of gold onto the optical fiber tip. The SERS surfaces were fabricated by using a nanosphere lithography approach that already demonstrated to be able to produce highly repeatable patterns on the fiber tip [1]. Starting from the promising pristine results, in order to engineer and optimize the SERS probes, we first evaluated and compared the SERS performances in terms of Enhancement Factor (EF) pertaining to different patterns with different nanospheres diameters and gold thicknesses. To this aim, the EF of SERS surfaces with a pitch of 500, 750 and 1000 nm, and gold films of 20, 30 and 40 nm have been retrieved, adopting the SERS signal of a monolayer of biphenyl-4-thiol (BPT) as a reliable benchmark (Figure 2). The analysis allowed us the identification of the most promising SERS platform: for the samples with nanospheres diameter of 500 nm and gold thickness of 30 nm, we measured values of EF of 4×105, which is comparable with state-of-the-art SERS EF achievable with highly performing colloidal gold nanoparticles [2]. The reproducibility of the SERS enhancement was thoroughly evaluated. Finally, in order to determine the most suitable optical fiber probe, in terms of excitation/collection efficiency and Raman background, we selected several commercially available optical fibers and tested them towards a BPT solution used as benchmark. A fiber probe with pure silica core of 200 µm diameter and high numerical aperture (i.e. 0.5) was found to be the most promising fiber platform providing the best trade-off between high excitation/collection efficiency and low background (Figure 3). Ongoing activities are devoted to use our Lab-on-Fibre SERS optrodes for cancer cell identification with the ambitious aim to achieve a highly advanced in-vivo sensor.

We present a comparative study on numerical models used to predict the absorption enhancement in thin-film solar cells due to the presence of structured back-reflectors exciting, at specific wavelengths, hybrid plasmonic-photonic resonances. To evaluate the effectiveness of the analyzed models, they have been applied in a case study: starting from a U-shaped textured glass thin-film, µc-Si:H solar cells have been successfully fabricated. The fabricated cells, with different intrinsic layer thicknesses, have been morphologically, optically and electrically characterized. The experimental results have been successively compared with the numerical predictions. We have found that, in contrast to basic models based on the underlying schematics of the cell, numerical models taking into account the real morphology of the fabricated device, are able to effectively predict the cells performances in terms of both optical absorption and short-circuit current values.

We present a fiber optic magnetic field sensor conceived for magnetic resonance imaging (MRI) applications. The sensor is based on the integration of fiber optic strain sensors (fiber Bragg gratings—FBGs) with a sensing material (Terfenol-D). The response of an FBG integrated with a block of Terfenol-D was preliminarily investigated by taking into account the dependence of the Terfenol-D magnetostrictive response on both the longitudinal and transversal magnetic fields, with different preloads. Based on the performed characterizations, a triaxial magnetic field sensor was designed, characterized, and fabricated. An algorithm enabling the demodulation of the magnetic field from the readout of the three FBGs was also implemented, by taking into account the interdependence among the different sensor responses. Experimental results demonstrate the ability of the triaxial sensor to measure the magnetic field. Performance assessment and critical analysis are reported as well, elucidating both the abilities and limitations of the implemented sensing configuration. Finally, as proof of principle, a sensing system constituted of 20 triaxial sensors has been fabricated and used to map the magnetic field strength distribution in an MRI diagnostic centre.

This paper reports on the assessment of a simple and economical self-assembly methodology to obtain reproducible infstrates onto the optical fiber tip for surface-enhanced Raman spectroscopy (SERS) applications. The method relies on the use of the nanosphere lithography of the optical fiber end facet. A careful analysis has been carried out to investigate the capability of the proposed procedure to realize repeatable pattern on the optical fiber tip. Finally, we demonstrate the effective application of the patterned OFTs as SERS nanoprobes. © 2017 SPIE.

We report on the fabrication and repeatability assessment of patterned substrates onto the optical fibre tip for surface-enhanced Raman spectroscopy (SERS) applications. In the route of "Lab on Fiber" Technology, indeed, we developed a simple an inexpensive self-assembly technique to create ordered and regular nanostructures on the optical fibre tip. The fabrication technique is borrowed from nanosphere lithography and it is adapted to operate on the cleaved end of standard optical fibre tips. This technique has been used to create different nanostructures with completely different morphological features on the fibre tip. The repeatability of the fabricated structures is here analyzed by using Focused Ion Beam Microscopy (FIBM) and Atomic Force Microscopy (AFM). The morphological analysis allowed to assess the nanospheres pattern regularity by systematically measuring the nanostructures features sizes and the number of defect for unit area. The analyzed samples have been also characterized spectrally to quantify the effective impact of the defect formation on the samples spectral response. Finally, the capability of the samples to act as SERS probes has been verified by detecting low concentrations (1 μM) of Crystal Violet diluted in an aqueous solution.

We demonstrate the ability of Fiber Bragg Gratings (FBGs) sensors to protect large areas from unauthorized activities in railway scenarios such as stations or tunnels. We report on the technological strategy adopted to protect a specific depot, representative of a common scenario for security applications in the railway environment. One of the concerns in the protection of a railway area centers on the presence of rail-tracks, which cannot be obstructed with physical barriers. We propose an integrated optical fiber system composed of FBG strain sensors that can detect human intrusion for protection of the perimeter combined with FBG accelerometer sensors for protection of rail-track access. Several trials were carried out in indoor and outdoor environments. The results demonstrate that FBG strain sensors bonded under a ribbed rubber mat enable the detection of intruder break-in via the pressure induced on the mat, whereas the FBG accelerometers installed under the rails enable the detection of intruders walking close to the railroad tracks via the acoustic surface waves generated by footsteps. Based on a single enabling technology, this integrated system represents a valuable intrusion detection system for railway security and could be integrated with other sensing functionalities in the railway field using fiber optic technology.

A high-throughput and reproducible lithographic approach enables the formation of ordered nanostructures on optical fiber tips that act as efficient surface-enhanced Raman spectroscopy detectors.

In this paper, we report a fiber-optic triaxial magnetic field sensor, based on Fiber Bragg Gratings (FBGs) integrated with giant magnetostrictive material, the Terfenol-D. The realized sensor has been designed and engineered for Magnetic Resonance Imaging (MRI) applications. A full magneto-optical characterization of the triaxial sensing probe has been carried out, providing the complex relationship among the FBGs wavelength shift and the applied magnetostatic field vector. Finally, the developed fiber optic sensors have been arranged in a sensor network composed of 20 triaxial sensors for mapping the magnetic field distribution in a MRI-room at a diagnostic center in Naples (SDN), equipped with Positron emission tomography/magnetic resonance (PET/MR) instrumentation. Experimental results reveal that the proposed sensor network can be efficiently used in MRI centers for performing quality assurance tests, paving the way for novel integrated tools to measure the magnetic dose accumulated day by day by MRI operators.

In this work, we report a straightforward and cost-effective fabrication route for the development of nano-patterned optical fiber tips. The technique is based on self-assembling polystyrene microspheres at the air/water interface and on their successive transferring on the fiber tip of single mode optical fiber. By applying to the fiber further treatments like particle size reduction, metal coating and sphere removal, different periodic structures have been conveniently realized. The morphological analysis reveals indeed the successful creation on the optical fiber tip of regular metallic-dielectric spheres' arrays as well as metallic patterns with dimensional features down to a submicron scale. Finally, as proof of concept, we demonstrated the capability of the realized patterns to work as efficient Surface Enhanced Raman Spectroscopy (SERS) fiber probes. © 2016 SPIE.

In this paper, we report on recent experimental results obtained with fiber-Bragg-grating (FBG) hydrophones for underwater acoustic detection. The optical hydrophones under investigation consist of FBGs coated with ring-shaped polymers of different size and mechanical properties. The coating materials were selected and designed in order to provide mechanical amplification, via judicious choice of their acousto-mechanical properties and by exploiting selected resonances occurring in different frequency ranges. Our underwater acoustic measurements, carried out within the range 4–35 kHz, reveal the resonant behavior of these optical hydrophones, as well as its dependence on the coating size and type of material. These experimental data are also in good agreement with our previously published numerical results. By comparison with bare (i.e., uncoated) FBGs, responsivity enhancements of up to three orders of magnitude were found, demonstrating the effectiveness of polymeric coatings in tailoring the acoustic response of FBG-based hydrophones.

Single-walled carbon nanotubes (SWCNTs) have been infiltrated within the holes of hollow-core optical fibers (HOFs) by Langmuir-Blodgett method in order to develop new in-fiber active and passive optoelectronic devices. Far field transmission characterizations demonstrated HOF's holes successful filling and the SWCNTs' capability to modify the guiding properties of HOFs. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2729–2732, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24725

The development of fiber optic chemical sensors based on the integrated design of novel sensitive nanocoatings combined with advanced sensing configurations is reported in the present study. Different sensitive coating materials have been exploited togheter with their deposition techniques, i.e nano-porous polymers deposited by using dip coating, carbon nanotubes deposited by Langmuir-Blodgett method and metal oxides, prepared by electrostatic spray pyrolysis. In accordance to the chemo-optical properties of these materials novel sensing schemes based on nano-coated Long Period Fiber Gratings, modified Fabry-Perot interferometers involving near field effect and photonic bandgap modification in Hollow-core Optical Fibers, have been proposed, respectively, to provide the best sensing performance. Experimental results reveal the potentiality of the integated approach that simultaneously accounts for the selection of the coating materials and of the fiber optic sensing scheme in developing optical devices for a wide range of applications related to the environmental monitoring either in air and water environments.

In this paper, the surprising sensing performance of fiber-optic near-field chemical sensors, based on wavelength scale tin dioxide particle layers, against chemical pollutants in air environment at room temperature are reported. The layers were deposited upon the distal end of standard single-mode optical fibers by means of the very simple, versatile, and low-cost electrostatic spray pyrolysis technique. The morphologic and optical features of the deposited layers were characterized by means of a complex scanning probe system constituted by simultaneous atomic force microscope (AFM) and near-field scanning optical microscope (NSOM). Particle layers composed by tin dioxide grains, with wavelength and subwavelength dimensions, are very promising because they are able to significantly modify the optical near-field profile emerging from the film surface. As matter of fact, a local enhancement of the evanescent wave contribute occurs leading to a strong sensitivity to surface effects induced by the analyte interaction. Here, for the first time to our best knowledge, experimental results on the sensing capability of the proposed chemical probes in air environment are reported. Also, a preliminary study on the effects of the processing stage and the post processing thermal annealing on the film morphology and near-field behavior are presented.

In this work, we report on the integration between hollow-core optical fibers (HOF) and single walled carbon nanotubes (SWCNTs) for the development of novel opto-chemical sensors for volatile organic compounds (VOCs) detection. Here, sensing probes were obtained by coating and partially filling the termination of HOFs by multiple SWCNTs monolayers. The infiltration of SWCNTs inside the HOF holes has been accomplished by means of the Langmuir–Blodgett deposition technique. Reflectance and far field transmission characterizations have been carried out within the HOF bandwidth in order to study the influence of the carbon nanotubes on the HOF photonic bandgap. Finally the sensing capability of the proposed sensors has been proved by exposure to VOCs traces. Experimental results demonstrate the success of the SWCNTs partial filling within the HOF holes and the sensor capability to perform VOCs detection with a good sensitivity and fast response times.

We report on a method for integrating sub-wavelength resonant structures on top of optical fiber tip. Our fabrication technique is based on direct milling of the glass on the fiber facet by means of focused ion beam. The patterned fiber tip acts as a structured template for successive depositions of any responsive or functional overlay. The proposed method is validated by depositing on the patterned fiber a high refractive index material layer, to obtain a ‘double-layer’ photonic crystal slab supporting guided resonances, appearing as peaks in the reflection spectrum. Morphological and optical characterizations are performed to investigate the effects of the fabrication process. Our results show how undesired effects, intrinsic to the fabrication procedure should be taken into account in order to guarantee a successful development of the device. Moreover, to demonstrate the flexibility of our approach and the possibility to engineering the resonances, a thin layer of gold is also deposited on the fiber tip, giving rise to a hybrid photonic-plasmonic structure with a complementary spectral response and different optical field distribution at the resonant wavelengths. Overall, this work represents a significant step forward the consolidation of Lab-on-Fiber Technology.

Smart or multi-functional materials are receiving more and more attention in the last decade, due to their strong potentialities to provide new and remarkable functionalities.

In this work, we demonstrate the capability of Fiber Bragg Gratings (FBGs) sensors to protect large areas from unauthorized activities in railway scenarios such as stations, depots or tunnels. In particular, we propose an integrated optical fiber sensing system, composed by FBGs strain sensors, deployed in a network, to detect human intrusion through the perimeter to be protected, combined with FBG accelerometers sensors to protect the rail track access. Several trials were carried out in indoor and outdoor environments. The experimental results demonstrated that the proposed integrated system represents a valuable intrusion detection system for railway security.

The integration of microfluidics and photonic biosensors has allowed achievement of several laboratory functions in a single chip, leading to the development of photonic lab-on-a-chip technology. Although a lot of progress has been made to implement such sensors in small and easy-to-use systems, many applications such as point-of-care diagnostics and in vivo biosensing still require a sensor probe able to perform measurements at precise locations that are often hard to reach. The intrinsic property of optical fibers to conduct light to a remote location makes them an ideal platform to meet this demand. The motivation to combine the good performance of photonic biosensors on chips with the unique advantages of optical fibers has thus led to the development of the so-called lab-on-fiber technology. This emerging technology envisages the integration of functionalized materials on micro- and nano-scales (i.e. the labs) with optical fibers to realize miniaturized and advanced all-in-fiber probes, especially useful for (but not limited to) label-free chemical and biological applications. This review presents a broad overview of lab-on-fiber biosensors, with particular reference to lab-on-tip platforms, where the labs are integrated on the optical fiber facet. Light-matter interaction on the fiber tip is achieved through the integration of thin layers of nanoparticles or nanostructures supporting resonant modes, both plasmonic and photonic, highly sensitive to local modifications of the surrounding environment. According to the physical principle that is exploited, different configurations - such as localized plasmon resonance probes, surface enhanced Raman scattering probes and photonic probes - are classified, while various applications are presented in context throughout. For each device, the surface chemistry and the related functionalization protocols are reviewed. Moreover, the implementation strategies and fabrication processes, either based on bottom-up or top-down approaches, are discussed. In conclusion we highlight some of the further development opportunities, including lab-in-a-needle technology, which could have a direct and disruptive impact in localized cancer treatment applications.

In this work, we report a fabrication route for self-assembling periodic patterns on optical fiber tips. The technique is based on self-assembling polystyrene microspheres at the air/water interface and on successive transferring of the monolayer colloidal crystal on the fiber tip. By applying to the fiber further treatments like particle size reduction, metal coating and sphere removal, different periodic structures are conveniently realized. The results obtained indicate that self-assembly technique affords opportunity to create on the optical fiber tip dielectric and metallic-dielectric spheres' arrays with a feature size down to a submicron scale or metallic patterns with a few hundred nanometers at low fabrication costs. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

In this chapter we report on the filling of the air holes of hollow-core optical fibers (HOFs) with single-walled carbon nanotubes (SWCNTs). The infiltration of SWCNTs inside the HOF holes has been accomplished through the deposition of multiple SWCNTs monolayer by means of the Langmuir–Blodgett method. The experimental results reviewed here demonstrate the success of the SWCNTs infiltration within the HOF holes. Furthermore, experimental measurements performed in a test chamber reveal that MOFs–SWCNTs sensing probes can be exploited to realize novel optochemical sensors for volatile organic compounds (VOCs) detection.

This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips. The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet. Polystyrene (PS) nanospheres are initially self-assembled in a hexagonal array on the surface of water. The created pattern is then transferred onto an optical fiber tip (OFT). The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber, such as metal coating, nanosphere size reduction and sphere removal. Ordered dielectric and metallo-dielectric sphere arrays, metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach. Furthermore, the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions. The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost. The method can be easily extended to simultaneously produce multiple fibers, opening a new route to the development of fiber-optic nanoprobes. Finally, we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes.