Search

The use of in-fiber core-to-cladding coupling components for thermal heating purposes has been well assessed in the last decades within the development of fiber optic devices for flow measurements and water thermal conductivity calculation. In these devices, light travelling in the fiber core is transferred into the cladding and absorbed by a metallic layer surrounding the fiber, with the consequent resistive heating generation. Here we demonstrate for the first time the use of a Turn-Around-Point (TAP) Long Period Grating (LPG) as resonant core-to-cladding light coupling mechanism for the fabrication of a highly efficient heating device based on metallic coated Fiber Bragg Grating (FBG). A properly designed TAP LPG was fabricated by means of point-to-point UV laser and spliced to a 150 nm thick Au-coated FBG. The heating efficiency characterizations of the final device were analyzed, in both air and water, by evaluating the temperature increase in the gold layer surrounding the FBG at incremental values of the injected power. Collected results confirm that the use of LPGs involving the excitation of higher order cladding modes provides an excellent transferring mechanism of the fiber core light into the cladding, which in turn guarantees very high thermal heating efficiency to the final device. Moreover, by comparing such results with the performance of other in-fiber core-to-cladding coupling components already presented in literature, it was found that the TAP LPG-based device exhibits an actuation efficiency 2.5 times greater, thus resulting the most effective and highly performing solution for energy transfer to the metallic overcoat.

In-fiber core-to-cladding coupling components for heating purposes have been well assessed in the last decades. Here we demonstrate the use of Turn-Around-Point Long Period Grating as coupling mechanism for highly efficient heating devices fabrication.

In this contribution, we provide an overview of our recent results concerning the proton radiation-induced effects of a bare Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser. Experimental data collected during an extensive irradiation campaign performed at the European Organization for Nuclear Research (with a fluence of 4.4·1015 p∙cm-2) have been combined with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the high dose proton exposure. A maximal radiation-induced variation of the core effective refractive index of ~1.61·10-4, responsible for a resonance wavelength red shift of ~44 nm, was retrieved at the maximal absorbed dose of 1.16 MGy. At the same time, a relevant decrease of ~0.93·10-4 in the grating refractive index modulation was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The spectral response of the LPG and the optical fiber parameters were analyzed also during the relaxation phase, showing a partial recovery of the wavelength shift due to a decrease of the core refractive index, without any relevant change in the dip visibility as a consequence of the constant grating modulation.

Mercury is a pollutant extremely toxic to the environment and human health. Although numerous methods have been reported for the analysis of Hg2+ ions in water, the development of simple, rapid, inexpensive, and sensitive sensors still represents a challenge. Here, we describe the design, synthesis and spectral characterization of a set of dansyl-amino acids able to recognize Hg2+ ions via different fluorescence emission modes. The analysis of the binding features of the different chemosensors shows that the stoichiometry of the sensor-Hg2+ complex depends on the concentration of the sensor and Hg2+ since it plays an important role in the type of response for Hg2+ ions. Among those studied here N-dansylated methionine is the best performing chemosensor in terms of sensitivity with a LOD of 140 nM. To improve the LOD of this chemosensor, we evaluated the response of a portable experimental set-up based on optical fiber probes. The new device shows an increase of LOD from 140 nM to about 5 nM, which can meet the requirements imposed by the Environmental Protection Agency for monitoring Hg2+ in drinkable water. We also show that the chemosensors are not applicable to marine water-based matrices because of the significant coordinating ability of chloride anions with Hg2+. (C) 2017 Elsevier B.V. All rights reserved.

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.

Radiochromic film dosimetry has been widely employed in most of the applications of radiation physics for over twenty years. This is due to a number of appealing features of radiochromic films, such as reliability, accuracy, ease of use and cost. However, current radiochromic film reading techniques, based on the use of commercial densitometers and scanners, provide values of dose only after the exposure of the films to radiation. In this work, an innovative methodology for the real-time reading of radiochromic films is proposed for some specific applications. The new methodology is based on opto-electronic instrumentation that makes use of an optical fiber probe for the determination of optical changes of the films induced by radiation and allows measurements of dose with high degree of precision and accuracy. Furthermore, it has been demonstrated that the dynamic range of some kinds of films, such as the EBT3 Gafchromic films (intensively used in medical physics), can be extended by more than one order of magnitude. Owing to the numerous advantages with respect to the commonly used reading techniques, a National Patent was filed in January 2018.

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 0.67x10(16) protons/cm(2), 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 similar to 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.

We report an innovative fiber optic nano-optrode based on Long Period Gratings (LPGs) working in reflection mode for the detection of human Thyroglobulin (TG), a protein marker of differentiated thyroid cancer. The reflection-type LPG (RT-LPG) biosensor, coated with a single layer of atactic polystyrene (aPS) onto which a specific, high affinity anti-Tg antibody was adsorbed, allowed the label-free detection of Tg in the needle washouts of fine-needle aspiration biopsies, at concentrations useful for pre- and post-operative assessment of the biomarker levels. Analyte recognition and capture were confirmed with a parallel on fiber ELISA-like assay using, in pilot tests, the biotinylated protein and HRP-labeled streptavidin for its detection. Dose-dependent experiments showed that the detection is linearly dependent on concentration within the range between 0 and 4 ng/mL, while antibody saturation occurs for higher protein levels. The system is characterized by a very high sensitivity and specificity allowing the ex-vivo detection of sub ng/ml concentrations of human Tg from needle washouts of fine-needle aspiration biopsies of thyroid nodule from different patients.

The full width at half maximum (FWHM) of lossy mode resonances (LMRs) in the optical spectrum depends on the homogeneity of the thin film deposited. In this Letter, a method for improving the FWHM is applied for an LMR generated by a D-shaped optical fiber in reflection configuration. For this purpose, three samples with different attenuation were deposited with DC sputtering thin films of S n O 2 − x , and a further controlled immersion of the samples in water was performed. A laser-cleaner method was used to improve the FWHM characteristics of one of the samples from 106 to 53 nm. This improvement can be applied to thin-film-based sensors where there is a problem with the inhomogeneity of the coating thickness. Moreover, with this technique, it was proved that a coated length of just 3–4 mm permits the generation of an LMR, with implications for the miniaturization of the final device.

Recent results in the field of film dosimetry demonstrated that the Green–Saunders equation, a solution of the logistic equation describing phenomena of kinetics of chemical reactions, is the absolute calibration function for all radiochromic film types. Taking advantage of the new opto-electronics-based radiochromic film reading method, which allows real-time measurements of the spectral response of radiochromic films, we confirm that the film darkening is ruled by the Green–Saunders equation independently both from the reading instrument or the choice of the observable used for the calibration. In order to demonstrate it, we exposed an XR-QA2 Gafchromic film to 90Sr/90Y beta rays up to 1400 mGy. Film spectra are recorded in real-time. The calibration is performed by means of two analytic methods: evaluation of the integral under the curves from 500 nm to 645 nm and evaluation of the intensity at 570, 600 and 643 nm. Experimental data fit to the Green–Saunders equation for both methods.

In this work, we report on a novel approach for measuring the dose absorbed by the EBT3 Gafchromic™ films exposed to 1 MeV electron beam and 250 kV X-rays in the range 0.5–100 Gy. Although EBT3 is specifically designed to obtain best performance for applications where the maximum dose is less than 10 Gy, there are certain clinical applications requiring dose ranges well above this value. In order to cover wider dose ranges, further models characterized by a thinner sensitive layer and/or different chemical composition have been released. Another method exploiting the three-channel flatbed scanner to delay the saturation point of EBT3 has been also reported. The technique proposed here, aimed at extending the sensitivity of the EBT3 film to high doses up to 100 Gy while ensuring a low dose uncertainty, is based on a broadband analysis of the absorption spectrum of the film in response to irradiation. By combining a wavelength-based approach with the monitoring of two characteristic peaks of the EBT3 absorption spectrum, we demonstrated the capability of measuring the dose in the range 0.5–100 Gy with an experimental uncertainty below 4% for doses lower than 5.52 Gy and below 2% for higher dose levels. Finally, through a dynamic fitting procedure integrating the two aforesaid approaches, a total uncertainty lower than 4%, including both the experimental and fitting errors, was achieved in the whole range 0.5–100 Gy. These results are promising in view of a potential application of this technique in the field of clinical dosimetry at high dose levels.

In this work, we report on the first demonstration of 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 0.67 × 1016 protons/cm2, corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrated the “radiation resistance” feature of the LOF devices and a clear dependence of the reflected spectrum versus 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. The numerical analysis carried out to correlate the experimental results with the dimensional and physical properties of the resonator, expected to be tightly connected to the absorbed dose, suggests that the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness, which is also consistent with past literature in the field. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for high energy physics experiments.

Radiochromic film dosimetry is a technique particularly suitable for dose measurements of radiation hardness assurance tests. The main characteristics of radiochromic films are the precise, accurate and permanent dose values, ease of handling and data analysis, high spatial resolution and wide range of dose. However, measurements of the trend of the dose in time with radiochromic films are very difficult by means of commercial read-out tools. In this work we propose a new method, for which a National Patent was filed, for the determination of the dose in real-time and by remote control with radiochromic films. This method based on optoelectronic instrumentation, makes radiochromic film dosimetry an ideal technique for radiation hardness quality assurance tests.

This paper reports the experimental assessment of an automated optical assay based on label free optical fiber optrodes for the fast detection of class C β-lactamases (AmpC BLs), actually considered as one of the most important sources of resistance to β-lactams antibiotics expressed by resistant bacteria. Reflection-type long period fiber gratings (RT-LPG) have been used as highly sensitive label free optrodes, while a higher affine boronic acid-based ligand was here selected to enhance the overall assay performances compared to those obtained in our first demonstration. In order to prove the feasibility analysis towards a fully automated optical assay, an engineered system was developed to simultaneously manipulate and interrogate multiple fiber optic optrodes in the different phases of the assay. The automated system tested in AmpC solutions at increasing concentrations demonstrated a limit of detection (LOD) of 6 nM, three times better when compared with the results obtained in our previous work. Moreover, the real effectiveness of the proposed optical assay has been also confirmed in complex matrices as the case of lysates of Escherichia coli overexpressing AmpC.

We report here on a reflection-type long period fiber grating (RT-LPG) biosensor for the fast detection of class C (AmpC) β-lactamases (BLs), actually considered as one of the most important source of resistance to β-lactam antibiotics expressed by resistant bacteria. A standard LPG working in transmission configuration is first transformed in a more practical probe working in reflection mode and successively coated with a primary high refractive index (HRI) overlay of atactic polystyrene (aPS) in order to increase its surrounding refractive index sensitivity (SRI) in biological solutions. The aPS-coated RT-LPG is then coated by a secondary layer of poly(methylmethacrylate)- co -methacrylic acid (PMMA- co -MA) in order to provide the necessary surface functionalities to promote a stable covalent bioreceptors immobilization. The BLs detection has been performed by using the 3-aminophenylboronic acid (3-APBA) as biorecognition element, due to its excellent inhibition properties against class C BLs and specificity. Results here provided demonstrate that the proposed label free biosensor is capable of reliable detection of purified AmpC BLs in phosphate buffer solutions (PBS) with concentrations as low as one hundred nM, with a lowest limit of detection (LOD) of the order of a few tens of nM. The real effectiveness of the proposed biosensor has been also confirmed in lysate samples, which contain Escherichia coli bacteria overexpressing AmpC BLs.

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.

In this paper, we report the experimental results on the fabrication and validation 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 practical probe working in reflection mode, then it is coated by two layers: atactic polystyrene (aPS) and (methyl methacrylate-co-methacrylic acid) (PMMA-co-MA). This multilayer strategy allow, at same time, to increase the surrounding refractive index sensitivity of the standard LPG and create the necessary conditions for a correct bio-functionalization. Standard linkage chemistry has been applied to anchor the bioreceptors on the probe surface. The experimental results demonstrate the capability of our LPG biosensor to successfully monitor all the biological steps of the biomolecular experiments, with β-lactamase AmpC binding detection tests obtained using two different ligands characterized by two different β-lactamase affinities.

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.

We report an innovative fiber optic biosensor based on Long Period Gratings (LPGs) working in reflection configuration for real time monitoring of human Thyroglobulin (Tg), a protein marker of differentiated thyroid cancer. A standard LPG is first transformed in a practical probe working in reflection mode, and then it is coated with a single layer of atactic polystyrene (aPS) in order to increase its surrounding refractive index sensitivity and to provide, at the same time, the desired interfacial properties for a stable anti-Tg antibody. The functionalized reflection-type LPG biosensor clearly demonstrates the effectiveness and sensitivity of the developed biosensing platform, allowing the real time and label-free detection of Tg in the needle washouts of fine-needle aspiration biopsies, at concentrations useful for pre- and post-operative assessment of the biomarker levels. Analyte recognition and capture were confirmed with a parallel on fiber ELISA-like assay using, in pilot test s, the biotinylated protein and HRP-labeled streptavidin for its detection. Dose-dependent experiments showed that the detection is linearly dependent on concentration within the range between 0 and 4 ng/mL, while antibody saturation occurs for higher protein levels.

In this contribution, the response of a Long Period Grating (LPG) inscribed in a B/Ge co-doped optical fiber exposed to proton irradiation is presented for the first time to the best of our knowledge. The experiment was performed in the proton irradiation facility at the European Organization for Nuclear Research (CERN) and lasted 146 hours. A proton fluence of ~ 4.4×1015 p/cm2 was applied during the experiment, corresponding to a total absorbed dose by the sample of ~ 1.16 MGy. From the on-line measurements, we evaluated a maximum radiation induced shift of ~ 44 nm and no saturation was observed at the maximal accumulated dose. A post-irradiation recovery shift of ~ 7 nm was measured after 7.5 days. Collected off- line results demonstrated that the LPG temperature sensitivity is not significantly affected by irradiation.

Radiochromic film dosimetry is a well-established technique particularly suitable for off-line dose measurements. We propose an innovative method for the determination of the dose in real-time with radiochromic films based on optoelectronic instrumentation.

In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·1015 p∙cm−2 is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10−4, responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10−4 in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.