Lab-on-Fiber (LoF) technology is a research field aimed at transforming a simple optical fiber into a multifunctional probe, which exploits enhanced light-matter interaction for a variety of applications, with special aptitude for biosensing. An attractive thread in this scenario is the integration of plasmonic metasurfaces onto an optical fiber tip, known as optical fiber “meta-tips”, leading to the development of a new generation of highly sensitive optrodes. Here we report on the latest achievements concerning the investigation of LoF probes assisted by plasmonic phase-gradient metasurfaces for the detection of small molecules as well as clinically relevant cancer biomarkers in the picomolar range. The high biosensing performance, joined with huge potential for miniaturization and integration, makes this platform an excellent candidate for the development of Point-of-Care (PoC) devices aimed at real-time and label-free detection of clinically relevant biomarkers offering several advantages over conventional procedures.
We developed a miniaturized optical probe, based on a customized Fiber Bragg Grating, for mechanical characterization of biological tissues with sub-millimeter spatial resolution. The probe is integrated inside a metallic cannula (16 gauge) used for clinical applications, and it is driven by a robotic arm (KUKA LBR Med 7). The optical sensor has a resolution of less than 1 mN and measures the force on controlled tissue indentations. The functionality of the sensor was assessed by means of different tests carried out on real prostates obtained from radically surgeries of patients at different stages of the carcinoma (Gleason score from 6 to 8). Specifically, in this work, we demonstrate that our system provides results that are on line with to the biopsy analysis performed before and the surgery. Our findings lay the foundation for the development of compact optical fiber probes, with size compatible with needle/catheter, able to perform in vivo mechanical characterizations of the prostatic tissue with high sensitivity and spatial resolution.
The demand for highly sensitive, fast and low-cost biosensors for reliable quantification of small biomolecules or cancer biomarkers is leading to the development of a new class of devices able to change the techniques currently used for diagnosis in oncology. Lab‐on‐fiber (LoF) optrodes offer several advantages over conventional techniques for point‐of‐care platforms aimed at real‐time and label‐free detection of clinically relevant biomarkers. Moreover, the easy integration of LoF platforms in medical needles, catheters and nano-endoscopes offers unique potentials for in vivo biopsies and tumor microenvironment assessment. Here, we demonstrate the capability to improve the immobilization strategies through the use of hinge carbohydrates by involving homemade antibodies that demonstrated a significantly improved recognition of the antigen with ultra‐low detection limits. In order to create an effective pipeline for the improvement of biofunctionalization protocols to be used in connection with the LoF platform, here we first, optimized the protocol using a microfluidic Surface Plasmon Resonance device. Then we transferred the optimized strategy on LoF platform, based on Optical Fiber Meta‐tip (OFMT), for the final validation. As a clinically relevant scenario, we focused on a serological biomarker, Cripto‐1, for its ability to promote tumorigenesis in breast and liver cancer. Reported results demonstrate that the proposed approach based on oriented antibody immobilization is able to significantly improve Cripto‐1 detection with a ten‐fold enhancement versus the random approach. Therefore, our work opens new avenues in the development of high‐sensitivity LoF biosensors for the detection of clinically relevant biomarkers in the sub‐ng/mL range.
The need for miniaturized biological sensors which can be easily integrated into medical needles and catheters for in vivo liquid biopsies with ever-increasing performances has stimulated the interest of researchers in Lab-on-Fiber (LOF) technology. In this framework, the integration of Metasurfaces (MSs) on the tip of the optical fiber (Optical Fiber Meta- Tip, OFMT) has represented a major breakthrough. Indeed, we showed that a suitably designed plasmonic OFMT biosensor significantly outperforms standard plasmonic ones due to the advanced light wave manipulation of MSs. Here, to further improve the sensing performances, we propose a novel class of LOF optrodes for labelled biosensing based on dielectric fluorescence enhancing OFMT. We envision a single fiber probe with integrated a Silicon MS on its tip as a light coupled substrate that illuminates the sample and simultaneously collects the enhanced emission from the dye molecules labeling the biological target. We present a numerical environment to compute the fluorescence enhancement factor collected by a multi-mode-fiber, when on its tip a Silicon MS is laid, consisting of an array of cylindrical nanoantennas. According to the numerical results, a suitable design of the dielectric MS allows for a fluorescence enhancement up to three orders of magnitudes. Moreover, a feasibility study is carried out to verify the possibility to fabricate the designed MSs on the termination of multimode optical fibers using electron beam lithography followed by reactive ion etching. This work provides the main guidelines for the development of advanced LOF devices based on the fluorescence enhancement for labeled biosensing.
We report on the use of Fiber Bragg Grating (FBG) sensors integrated onto an aircraft landing gear for remote and realtime load monitoring. Several FBGs strain sensors, both in a linear and tri-axial configuration, have been integrated on different locations of true landing gears (both Main and Nose gears) based on their load condition derived from FEM numerical analysis and exposed to numerous qualification lab tests where the load applied to the gears was varied in the range 0-20kN. To this aim, the gears were mounted on a 25kN hydraulic press, that changed the shock absorber route from 0 mm up to 200 mm (corresponding to the maximum take-off weight,~4600 kg). Obtained results are in good agreement with those provided by reference electrical strain gauges located very close to their optical counterparts, and demonstrate the great potentialities of FBG sensors technology to be employed for remote and real time load measurements on aircraft landing gears.
We report on a innovative Lab on Fiber (LOF) dosimeter for ionizing radiation monitoring at ultra-high doses. The new dosimeter consists in a metallo-dielectric resonator at sub-wavelength scale supporting localized surface plasmon resonances realized on the optical fiber (OF) tip. The resonating structure involves two gold gratings separated by a templated dielectric layer of poly(methyl methacrylate) (PMMA). Two LOF prototypes have been manufactured and exposed, at the IRRAD Proton Facility at CERN in Geneva, to 23 GeV protons for a total fluence of 0.67x1016 protons/cm2 , corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrate the "radiation resistance" feature of the LOF devices and a clear dependence of the reflected spectrum on the total dose, expressed by a cumulative blue-shift of ~1.4 nm of the resonance combined with a slight increase of 0.16 dBm in the reflected spectrum. According to the numerical analysis and the literature, the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for High Energy Physics (HEP) experiments.
In this work we review the concept of optical fiber meta-tips, recently introduced by the authors. Optical fiber meta-tips come from the integration of plasmonic optical metasurfaces and the fiber optics technology. In particular, this integration is a major breakthrough in the recently emerged “Lab-On-Fiber” technology, where nanostructured platforms with special capabilities of light manipulation are integrated onto the tip of an optical fiber. Optical fiber meta-tips can, on one side, boost the real world applicability of optical metasurfaces, and, on the other side, bring about more advanced capabilities of on-fiber control and manipulation of light wavefront and polarization. With a view towards possible practical applications to label-free chemical and biological sensing, we inspect the potentialities of optical fiber meta-tips to work as sensors of local refractive index variations, and aim at studying the effect that the phase gradient impressed by the metasurface has on the surface sensitivity of proposed devices.
We realize the first optical-fiber “meta-tip” that integrates a metasurface on the tip of an optical fiber. In our proposed configuration a Babinet-inverted plasmonic metasurface is fabricated by patterning (via focused-ion-beam) an array of rectangular aperture nanoantennas in a thin gold film. Via spatial modulation of the nanoantennas size, we properly tune their resonances so as to impress abrupt arbitrary phase variations in the transmitted field wavefront. As a proof-of-principle, we fabricate and characterize several prototypes implementing in the near-infrared the beam-steering with various angles. We also explore the limit case where surface waves are excited, and its capability to work as refractive index sensors. Notably, its sensitivity overwhelms that of the corresponding gradient-free plasmonic array, thus paving the way to the use of metasurfaces for label-free chemical and biological sensing. Our experimental results, in fairly good agreement with numerical predictions, demonstrate the practical feasibility of the meta-tip concept, and set the stage for the integration of metasurfaces, and their exceptional capabilities to manipulate light, in fiber-optics technological platforms, within the emerging “lab-on-fiber” paradigm.
The luminosity upgrade of the Large Hadron Collider (HL-LHC) planned at the European Organization for Nuclear
Research (CERN) requires the development of a new generation of superconducting magnets based on Nb3Sn technology.
The instrumentation required for the racetrack coils needs the development of reliable sensing systems able to monitor the
magnet thermo-mechanical behavior during its service life, from the coil fabrication to the magnet operation. With this
purpose, Fiber Bragg Grating (FBG) sensors have been embedded in the coils of the Short Model Coil (SMC) magnet
fabricated at CERN. The FBG sensitivity to both temperature and strain required the development of a solution able to
separate mechanical and temperature effects. This work presents for the first time a feasibility study devoted to the
implementation of an embedded FBG sensor for the measurement of the "true" temperature in the impregnated Nb3Sn coil
during the fabrication process.
Maria Principe, Alberto Micco, Alessio Crescitelli, Giuseppe Castaldi, Marco Consales, Emanuela Esposito, Vera La Ferrara, Vincenzo Galdi, Andrea Cusano
We report on the first example of a “meta-tip” configuration that integrates a metasurface on the tip of an optical fiber. Our proposed design is based on an inverted-Babinet plasmonic metasurface obtained by patterning (via focused ion beam) a thin gold film deposited on the tip of an optical fiber, so as to realize an array of rectangular aperture nanoantennas with spatially modulated sizes. By properly tuning the resonances of the aperture nanoantennas, abrupt variations can be impressed in the field wavefront and polarization. We fabricated and characterized several proof-of-principle prototypes operating an near-infrared wavelengths, and implementing the beam-steering (with various angles) of the cross-polarized component, as well as the excitation of surface waves. Our results pave the way to the integration of the exceptional field-manipulation capabilities enabled by metasurfaces with the versatility and ubiquity of fiber-optics technological platforms.
Distributed and multi-point fiber-optic based measurements of cryogenic temperature down to 30 K are presented. Measurements have been performed along the cryostat of a superconducting power transmission line, which is currently being tested at CERN over a length of about 20 m. Multi-point measurements were based on two kinds of FBG with different coatings (epoxy and PMMA). In addition, distributed measurements exploited optical frequency-domain reflectometry to analyze the Rayleigh scattering along two concatenated fibers with different coatings (acrylate and polyimmide). Results confirm the viability of these approaches to monitor cryogenic temperatures along a superconducting transmission line.
We report the development of a reflection-type long period fiber grating (LPG) biosensor able to perform the real time detection of thyroid cancer markers in the needle washout of fine-needle aspiration biopsy. A standard LPG is first transformed in a practical probe working in reflection mode, then it is coated by an atactic-polystyrene overlay in order to increase its surrounding refractive index sensitivity and to provide, at the same time, the desired interfacial properties for a stable bioreceptor immobilization. The results provide a clear demonstration of the effectiveness and sensitivity of the developed biosensing platform, allowing the in vitro detection of human Thyroglobulin at sub-nanomolar concentrations.
This work deals with a novel Lab-on-Fiber biosensor able to detect in real time thyroid carcinomas biomarkers. The device is based on a gold nanostructure supporting localized surface plasmon resonances (LSPR) directly fabricated on the fiber tip by means of electron beam lithography and lift-off process. Following a suitable chemical and biological functionalization of the sensing area, human Thyroglobulin has been detected at nanomolar concentrations. Also, compatibility with full baseline restoration, achieved through biomarkers/bioreceptors dissociation, has been demonstrated.
This work deals with the development of fiber optic sensors for the measurement of soil moisture and temperature over large areas. It has been carried out within the Regional Project "Sensoristica in Fibra Ottica per il Risparmio Idrico - SFORI". The sensor system is based on the fiber Bragg gratings (FBGs) technology and is aimed at optimizing the irrigation practice in order to guarantee a sustainable water resources management. Two sensors networks, each one based on FBG thermo-hygrometers, have been realized and installed in two experimental sites. Preliminary results envisages good perspectives for a massive usage of the proposed technology.
The design, fabrication and tests of a new generation of superconducting magnets for the upgrade of the LHC require the support of an adequate, robust and reliable sensing technology. The use of Fiber Optic Sensors is becoming particularly challenging for applications in extreme harsh environments such as ultra-low temperatures, high electromagnetic fields and strong mechanical stresses offering perspectives for the development of technological innovations in several applied disciplines.
New generation of superconducting magnets for high energy applications designed, manufactured and tested at the European Organization for Nuclear Research (CERN) require the implementation of reliable sensors able to monitor the mechanical stresses affecting the winding from fabrication to operation in magnetic field of 13 T. This work deals with the embedding of Fiber Bragg Grating sensors in a short model Nb3Sn dipole magnet in order to monitor the strain developed in the coil during the cool down to 1.9 K, the powering up to 15.8 kA and the warm up, offering perspectives for the replacement of standard strain gauges.
This work investigates the performances and the radiation hardness capability of optical thermo-hygrometers based on Fiber Bragg Gratings (FBG) technology for humidity monitoring in the Compact Muon Solenoid experiment (CMS) at CERN, in Geneva. Extensive characterizations in terms of sensitivity, repeatability and accuracy on 80 specially produced polyimide-coated FBG sensors and 80 commercial temperature FBG sensors are presented. Progressive irradiation campaigns with γ- ionizing radiations were also performed. Results showed that the sensors sensitivity is unchanged after each radiation exposure; while the wavelength peak exhibits a radiation-induced shift. The saturation properties of this shift are discussed.
We report on the development of a multilayer coated reflection-type long period fiber grating (LPG) biosensor, useful for the detection of antibiotic resistance bacteria. A standard LPG is first transformed in a more practical probe working in reflection mode, then it is coated by a primary layer of aPS and a secondary layer of PMMA in order to increase its surrounding refractive index sensitivity and at the same time provide the necessary conditions for a correct biofunctionalization. Standard linkage chemistry has been applied to anchor the bioreceptors on the probe surface. We show some preliminary results demonstrating the capability of our LPG biosensor to successfully monitor all the biological steps of the biomolecular experiments, including β-lactamase binding detection tests.
This contribution deals with a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN).In particular, due to the wide investigations carried out in the last years aimed to assess the radiation hardness capability of fiber optic technology in HEP environments, our multidisciplinary research group has been recently engaged in the development of high-sensitivity TiO2-coated Long Period Fiber Gratings (LPGs) sensors for relative humidity (RH) monitoring at temperatures below 0°C as well as in presence of strong ionizing radiations.
This contribution deals with a feasibility analysis for the development of radiation tolerant fiber optic humidity sensors based on long period grating (LPG) technology to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN). In particular, here we propose a high-sensitivity LPG sensor coated with a finely tuned titanium dioxide (TiO2) thin layer (~100 nm thick) through the sol gel deposition method. The sensor characterization in the relative humidity (RH) range [0-75] % at four different temperatures (in the range -10°C - 25°C) was carried out to assess sensor performances in real operative conditions required in typical experiments running at CERN. Experimental results demonstrate the very high RH sensitivities of the proposed device (up to 1.4 nm/%RH in correspondence of very low humidity levels), which turned out to be from one to three orders of magnitudes higher than those exhibited by fiber Bragg grating (FBG) sensors coated with micrometer thin polyimide overlays. The radiation tolerance capability of the TiO2-coated LPG sensor is also investigated by comparing the sensing performances before and after its exposure to 1Mrad dose of γ-ionizing radiation. Collected results demonstrate the strong potentialities of the proposed technology in light of its future exploitation in HEP applications as robust and valid alternative to currently used commercial hygrometers.
We recently introduced a reliable fabrication process enabling the integration of dielectric and metallic nanostructures directly on the tip of optical fibers1. It involves conventional deposition and nanopatterning techniques (typically used for planar devices fabrication) suitably adapted to directly operate on the fiber tip. By using this approach, and with a view towards possible applications, here we demonstrate the realization of different technological platforms based on the integration on the fiber facet of periodic and quasi-periodic metallo-dielectric nanostructures supporting localized surface plasmon resonances, that can be used for chemical and biological sensing as well as polarization sensitive devices.
We report on a feasibility analysis for the development of fiber optic humidity sensors to be applied in high-energy physics applications and in particular in experiments actually running at the European Organization for Nuclear Research (CERN). Due to the stringent sensors requirements concerning radiation hardness capability and low temperature operation, we focus our attention on the investigation of fiber optic humidity sensors based on polyimmide (PI)-coated Fiber Bragg Gratings (FBGs). Data here reported, obtained during a wide experimental campaign carried out in the laboratories of CERN, demonstrate that the selected technological platform is able to perform relative humidity (RH) measurements with percent resolution in the temperature range -15-20°C as well as in presence of ionizing radiations up to 10KGray, largely outperforming conventional humidity sensors, currently employed within CERN environment.
We recently introduced a reliable fabrication process enabling the integration of dielectric and metallic nanostructures directly on the tip of optical fibers, involving conventional deposition and nanopatterning techniques suitably adapted to directly operate on the fiber tip1. By using this approach, we also demonstrated a first technological platform based on the integration, on the optical fiber tip, of 2D hybrid metallo-dielectric nanostructures supporting localized surface plasmon resonances, that can be efficiently used for label free chemical and biological sensing. In this contribution we want to emphasize the versatility of the proposed technological platform. In particular, we demonstrate how by acting on the numerous degrees of freedom it provides, we are able to improve the performances of our nanoprobes for label-free chemical and biological sensing applications. Finally, the possibility to create novel advanced devices by breaking the circular symmetry of the crystal nanostructure is also demonstrated.
We introduce a reliable fabrication process enabling the integration of dielectric and metallic nanostructures on the tip of
optical fibers. It involves conventional deposition and nanopatterning techniques typically used for planar devices, but
here adapted to directly operate on optical fiber tip. Following this approach, we demonstrate a first technological
platform based on the integration, onto the optical fiber tip, of two-dimensional (2D) hybrid metallo-dielectric
nanostructures supporting localized surface plasmon resonances (LSPR), that can be efficiently used for label free
chemical and biological sensing and as a microphone for acoustic wave detection.
We report the evidence of plasmonic-photonic resonances in hybrid metallo-dielectric quasi-crystal nanostructures
composed of aperiodically-patterned low-contrast dielectric slabs backed on a metal layer. Via both experimental and
numerical studies, we characterize these resonant phenomena with specific reference to the Ammann-Beenker (quasiperiodic,
octagonal) tiling lattice geometry, and investigate the underlying physics. In particular, we show that, by
comparison with standard periodic structures, a richer spectrum of resonant modes may be excited. Such modes are
characterized by a distinctive plasmonic or photonic behavior, discriminated by their field distribution. Concerning the
possible applications, we also explore the structure functionalization via nanosized high refractive index overlays (for
resonance tuning and quality-factor enhancement), as well as its surface sensitivity to deposition of nanolayers of
materials mimicking bio-molecular binding. Overall, our results indicate the possibility of exciting a wealth of resonant
modes with state-of-the-art quality factors and sensing/tuning efficiencies, of potential interest for the development of
high-performance optical devices for communications, energy and sensing applications.
PART ONE:
The "Lab on Fiber" concept envisions novel and highly functionalized technological platforms completely
integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems
to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated
optical fiber devices requires that several structures and materials at nano and micro scale are constructed, embedded and
connected all together to provide the necessary physical connections and light-matter interactions.
This paper reviews the strategies, the main achievements and related devices in the "Lab on Fiber" roadmap
discussing perspectives and challenges that lie ahead.
PART TWO:
After having reviewed, in the previous part, the main results achieved in the "Lab o Fiber" roadmap through the
development of several wavelength-scale devices and components based on the lab on fiber concept, here we focus the
attention on new trends involving innovative nano-fabrication strategies enabling to exploit further intriguing photonic
and/or plasmonic phenomena at the forefront of optical research.
Novel complex fabrication techniques of "Lab-on-fiber" device at the nanoscale are here presented and discussed,
from advanced multi material stacks and drawing technique up to the use of nanotechnologies, including standard
lithographic tools as well as new nano-imprinting approaches.
In particular, for the first time, we report some preliminary results obtained by our multidisciplinary research group
concerning the design and fabrication of a 2D hybrid metallo-dielectric photonic crystal (PC) nanostructure, directly
realized by innovatively applying the electron beam lithography technique on the cleaved end of standard single mode
optical fibers.
Here, we report on recent experimental results obtained with Fiber Bragg Grating (FBG) hydrophones for underwater
sound pressure detection. Investigated optical hydrophones consist of FBGs coated with ring shaped polymers of
different size. Coating material has been selected to provide mechanical amplification through a low elastic modulus
combined with acoustic impedance matching. Underwater acoustic measurements carried out in the range 4-35KHz
reveal a resonant behaviour depending on the coating size. This behaviour is consistent with numerical analysis
performed using finite element method and presented in part I. In addition, good linearity was observed versus local
sound pressure demonstrating a minimum detectable sound pressure of few Pascal.
Long-period fiber gratings (LPFGs) represent an attractive fiber grating-based technological platform because of their
selective spectral features together with the intrinsic sensitivity to surrounding refractive index (SRI). Unfortunately,
their main limitation relies on the necessity to opportunely coat the glass substrate when sensitivity enhancement and/or
specific functionalization are required. Here, we investigate the possibility to realize a self-functionalized and high-sensitivity
LPFG by evanescent-wave interaction of the propagating light with a periodically patterned overlay. In
particular, a D-shaped optical fiber is considered because of its peculiar geometrical features. First chemical etching is
used to allow the evanescent-wave interaction of the propagating light with the surroundings with the desired sensitivity.
Successively a uniform atactic polystyrene overlay is deposited onto the flat surface of the structure by dip-coating
technique. Finally the overlay is opportunely patterned by laser-micromachining techniques in order to create a LPFG-like
structure. The reported results demonstrate the spectral features of the realized device and confirm the LPFG-like
behavior with high SRI-sensitivity. The flexibility of the adopted fabrication method could allow the realization of
innovative LPFGs to be adopted for a multitude of sensing applications, depending on the nature of the material
deposited onto the flat surface of the etched D-fiber.
In this paper we present the activity that our research group is making on Fiber Optic Sensors (FOS) applications to
monitor high-energy physics (HEP) experiments. Starting from the consideration that Fiber Optic radiation hardness has
been widely proven, we have applied the technology of Fiber Optic Sensors to this very relevant field of interest. Here,
we give the experimental evidences of the possibility to use such a class of sensors also in these very complex
environmental side conditions. In particular, regarding the Compact Muon Solenoid (CMS) experiment at the CERN, we
have monitored temperatures and strains in different locations by using Bragg Grating sensors, and we are now starting
the development of a new class of Relative Humidity sensor based on Fiber Optic technology. Preliminary results are
very encouraging, letting us consider the use of FOS technique as a robust and effective solution for monitoring
requirements in HEP detectors for other physical and environmental parameters.
In this work, the feasibility of exploiting novel Cadmium Arachidate (CdA)/single-walled carbon nanotubes (SWCNTs)
based composites as sensitive coatings for the development of robust and high performances optoelectronic chemosensors
able to work in liquid environments has been investigated and proved. Here, nano-composite sensing layers have
been transferred upon the distal end of standard optical fibers by the Langmuir-Blodgett (LB) technique. Reflectance
measurements have been carried out to monitor ppm concentration of chemicals in water through the changes in the
optical and geometrical features of the sensing overlay induced by the interaction with the analyte molecules.
Preliminary experimental results evidence that such nanoscale coatings integrated with the optical fiber technology offers
great potentialities for the room temperature detection of chemical traces in water and lead to significant improvements
of the traditional fiber optic sensors based on SWCNTs layers.
In this work, the feasibility to exploit optoelectronic chemo-sensors based on cadmium arachidate (CdA)/single-walled
carbon nanotubes (SWCNTs) composites for detection of chemical pollutants both in air and water environments has
been investigated. The nanocomposite sensing layers have been transferred upon the distal end of standard optical fibers
by the Langmuir-Blodgett (LB) technique. Single wavelength reflectance measurements (&lgr;=1310 nm) have been carried
out to monitor chemicals concentration through changes in the optical length of the Fabry-Pérot (FP) cavity induced by
the interaction of the sensitive layer with the analyte molecules. The preliminary experimental results evidence the good
potentiality of these fiber optic nanosensors to detect toluene and xylene at ppm level both in air and water environments
at room temperature.
In this work, Hollow-core Optical Fibers (HOF) functionalized with Single Walled Carbon NanoTubes (SWCNTs) are
proposed for volatile organic compounds (VOCs) detection. The sensing probe is composed by a piece of HOF with a
termination coated and partially filled by SWCNTs. The infiltration of the SWCNTs inside the HOF holes has been
accomplished by means of the Langmuir-Blodgett technique. Reflectance and far field transmission characteristics have
been carried out within the HOF bandwidth. Finally the sensing capability of the proposed sensors has been investigated
by exposure in a proper designed test chamber to traces of toluene. The experimental results obtained 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.
KEYWORDS: Sensors, Near field optics, Particles, Molecules, Optical fibers, Molecular interactions, Near field, Near field scanning optical microscopy, Biological and chemical sensing, Optical coatings
In this work, the surprising sensing performances of opto-chemical sensors based on SnO2 particles layers against
chemical pollutants either in air and water environment, at room temperature, are reported. The Electrostatic Spray
Pyrolysis (ESP) method has been used to deposit the sensing coatings upon the distal end of standard fibers. This
technique allows the fabrication of SnO2 layers composed of micron and sub-micron dimensions able to locally modify
the profile of the optical near-field collected in the close proximity of the fiber tip. Such layers morphology leads to
strong surface interactions between sensing coatings, analyte molecules and the evanescent contribute of the field,
resulting in an excellent sensors sensitivity against chemical pollutants, even at room temperature.
KEYWORDS: Near field, Sensors, Near field optics, Particles, Tin, Fiber optics sensors, Near field scanning optical microscopy, Optical fibers, Annealing, Metals
In the last decade a huge number of SnO2-based gas sensors have been proposed for environmental monitoring, automotive applications, air conditioning in houses, airplane and aircrafts. However, most of the proposed sensors work at very high temperatures in order to reach high sensitivities. Here, a SnO2-based optical fiber sensor is proposed for the room temperature detection of chemical pollutants in air. Particles layers composed by tin dioxide grains, with wavelength and subwavelength dimensions, resulted very promising because they are able to significantly modify the optical near field profile emerging from the film surface due to local enhancements of the evanescent wave contribute, and thus to improve the sensitivity to surface effects induced by the analyte interaction. The room temperature sensing performances of SnO2-based particles layers towards environmental pollutants have been investigated by the exposure to different concentrations of toluene and xylene vapors as well as gaseous ammonia. They have also been compared with the performances obtained with other optical fiber sensors in the same configuration, but coated with different sensitive materials, such as Single-Walled carbon nanotubes. The preliminary results obtained evidenced the surprising capability of the SnO2-based optical sensor to detect chemical pollutants at ppm level in air at room temperature. Finally, preliminary results on the effects of the processing parameters and post processing thermal annealing on film morphology and optical near field are presented.
In this work, we report on the integration of Hollow-core Optical Fibers (HOF) and Single Walled Carbon NanoTubes (SWCNTs) in order to obtain new functionalized devices by means of the modification of the photonic bandgap (PBG) characterizing the HOF itself. The samples were obtained by coating and partially filling by SWCNTs the termination of HOFs. The infiltration of SWCNTs inside the HOF holes has been accomplished by means of the Langmuir-Blodgett technique. Far field transmission characterizations have been carried out at 1550nm in order to study the influence of the carbon nanotubes within the HOF holes on the HOF PBG. Finally, in light of the sensing features of the SWCNTs, the realized samples have been employed as opto-chemical sensors for volatile organic compounds (VOCs) detection and their sensing capability has been proved by their exposure to VOCs traces. Experimental results demonstrate the success of the SWCNTs partial filling within the HOF holes, the influence of the deposition parameters on the HOF PBG and sensing performances as well as the sensor capability to perform VOCs detection with a good sensitivity and fast response times.
In this work, the possibility to detect ppm ammonia concentrations in water environment, at room temperature, by means of Standard Optical Fibers (SOFs) sensors coated by Metal Oxides (MOXs) films has been demonstrated. Electro-spray pyrolisis technique has been used to deposit SnO2 films onto the distal end of single-mode optical fibers. This deposition technique allows the possibility to tailor the fabricated films properties by varying the deposition parameters, such as the metal chloride concentrations, the solution volume and the substrate temperature. The sensor operating principle relies on the measurement of the light intensity reflected by the fiber-sensitive layer interface: the pollutant molecules adsorption within the MOX film causes a change in its complex dielectric function and thus in the fiber-film reflectance. Spectral characterization of the obtained sensing probes has been carried out in the range 400-1750nm. Single wavelength reflectance measurements have been carried out to test the sensor performances for ppm ammonia detection. High sensitivity to the target analyte, response times of approximately 10-20 minutes and a Limit Of Detection as low as sub-ppm has been observed.
The sensing properties of Langmuir-Blodgett (LB) films consisting of tangled Single-Walled Carbon Nanotubes (SWCNTs) used as sensitive nanomaterials for Volatile Organic Compounds (VOCs) detection have been investigated by using Quartz Crystal Microbalance (QCM) 10 MHz AT-cut quartz resonators, and standard Silica Optical Fiber SOF) based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in the gas sensing applications as mass change and complex refractive index change induced by gas molecules adsorption. Highly sensitive, repeatable and very fast responses of SWCNTs sensors to ethanol and ethylacetate, with concentrations in the range 10-500 ppm, have been observed. A good inter-relationship has been found between the two different transducers, showing a good correlation of the sensing mechanisms based on the change in the mass and optical properties of the chemosensitive nanomaterial for QCM and SOF sensors, respectively.
In this work, preliminary experimental results on the capability of a Metal Oxides (MOXs) based optical sensor to perform ammonia detection in water environments, at room temperature, are presented. Electro-spray pyrolisis technique has been used to deposit the SnO2 films on the distal end of standard Silica Optical Fibers (SOFs). Reflection spectra of the sensing probes have been measured in the range 1520-1620nm by using a tunable laser and an optical spectrum analyzer. Single wavelength reflectance measurements have been carried out to test the sensing performances for ammonia detection in the range 4-20 ppm. High sensitivity to the target analyte and fast response times have been observed. From the results obtained, a Limit Of Detection (LOD) as low as sub-ppm has been achieved.
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