The ability to make an accurate diagnosis at the time of treatment is crucial for many diseases. However, current standard diagnostic procedures can only be performed in specialised healthcare facilities. To bring diagnostic methods from a specialised laboratory to the point of treatment, many alternative methods have been proposed. One of them is surfaceenhanced Raman scattering (SERS), which offers advantageous features such as high sensitivity in biotarget detection and higher accuracy. Here, we have developed an advanced SERS platform for the ultrasensitive, rapid and highly specific identification of tumour biomarkers in liquid biopsies. Our particular focus is on the detection of Thyroglobulin (Tg), the most important tumour biomarker for the diagnosis and prognosis of thyroid cancer. Specifically, SERS-active substrates fabricated by nanosphere lithography on chip or on tips of optical fiber (OF) were functionalized with Tg Capture antibodies. Gold nanoparticles were functionalized with Detection antibodies and conjugated with a Raman reporter. The sandwich assay platform was validated in the planar configuration and a detection limit of only 7 pg/ml was successfully achieved. The same approach has been successfully demonstrated on washout fluids from fine needle aspiration biopsies of cancer patients. Finally, the functionalization strategy was translated to the LOF-SERS platform and successfully used to detect Tg concentration. The proposed SERS-assisted immunoassay platform has proven to be highly versatile and can be used with both microfluidic chip POC devices and SERS-OF-based optrodes to perform sensitive, specific and rapid ex vivo assays for Tg detection in liquid intraoperative biopsies.
We investigated the creation of SERS-active hierarchical substrates based on self-assembled nanospheres (HSNs). We demonstrate how the “hierarchical” approach could be systematically exploited to extend the SERS hotspots into the third dimension, by enhancing the hot-spots spatial density and intensity. The proposed hierarchical substrates take advantage of the single layer hexagonal closed packed array nanospheres (CPA). An additional layer of upper nanospheres to obtain dense and intense hot spots pattern is employed. To predict the SERS performance and to identify the promising architectures, a numerical analysis is carried out, offering design criteria, an overview of the operating mechanisms and conditions that affect the SERS behavior of substrates. We fabricated HSNs by using a self-assembling approach and the preliminary results reported. The results highlight that HSNs can be used as cost-effective SERS substrates with better performance than simpler single-layer CPA configurations.
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.
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.
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.
In this work, we propose a novel immunoassay platform for the detection of human Thyroglobulin (Tg) to be integrated with fine-needle aspiration biopsy for early identification of lymph node metastases in thyroid cancer patients. The sensing platform detects Tg (a well-known biomarker for the classification of metastatic lymph nodes related to thyroid cancer) by a sandwich immunoassay involving a self-assembled surface-enhanced Raman scattering (SERS) substrate assisted and empowered by functionalized gold nanoparticles enabling additional Raman signal amplification and improved molecular specificity. The sandwich assay platform was preliminary validated in a planar configuration and a detection limit as low as 7 pg/mL was successfully achieved. The sandwich assay was successfully demonstrated on washout fluids of fine needle aspiration biopsies from cancer patients and confirmed the high specificity of the proposed methodology when complex biological matrices are considered. Finally, optical fiber SERS optrodes were fabricated and successfully used to detect Tg concentration by applying the same bio-recognition strategy. This opens the possibility of transferring the Tg detection approach to the optical fiber tip to develop point-of-care platforms that can be directly integrated into fine needle aspiration biopsies.
In this work, we propose new Lab-on-Fiber SERS optrodes, realized directly on the optical fiber tip with different SERS active substrates, to detect biological targets of different sizes (bovine serum albumin and red blood cells membrane).
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.
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.
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 4×105 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 metallodielectric spheres) and the analysis of the probes response against different molecules.
This paper reports on the assessment of a simple and economical self-assembly methodology to obtain reproducible substrates 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.
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.
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.
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 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.
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.
In this work, an ultra compact in line fiber optic Fabry-Perot interferometer is presented. The interferometric structure consists of a thin (< 1 μm) amorphous silicon layer in line integrated into a standard single mode optical fiber by means of an electric arc discharge technique. The device exhibits low loss (1.46 dB) and high interference fringe visibility (~ 30% in linear scale) both in reflection and transmission due to the high refractive index contrast between silica and α-Si. A high linear temperature sensitivity up to 75 pm/°C is demonstrated in the range 15-52 °C. The proposed device is simple, compact, cost effective and attractive for point monitoring sensing application in ultra-high temperature sensing in harsh environments.
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 present recent results on the fabrication of metallo-dielectric structures on the optical fiber tip by using a self-assembly technique. Our studies aim to attain advanced nanostructured sensors by exploiting easy and low cost fabrication processes suitable to be employed in massive production of technologically advanced devices in the roadmap of the Lab on Fiber Technology. The pursued approach basically consists in the preliminary preparation of a patterned polymeric film by the breath figure technique, directly on the optical fiber tip, and in the successive metal deposition by evaporation. The experimental results demonstrate the successful creation of a metallo-dielectric honeycomb pattern on the optical fiber tip. The experimental spectral features are in good agreement with the numerical analysis, elucidating the photonic and plasmonic interactions occurring in the Lab onto the optical fiber tip. The sensing properties of the optical fiber probes have been successfully explored in terms of sensitivity to the surrounding refractive index changes demonstrating their potentialities for chemical and biological sensing applications.
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.
The “Lab on Fiber” technology has been recently proposed as a valuable route for the realization of novel and highly
functionalized technological platforms completely integrated in a single optical fiber in communication and sensing
applications. As a follow up of the proposed technological approach, here, we present recent results on the fabrication of metallo-dielectric structures on the optical fiber tip by using a self-assembly technique. Our studies aim to attain advanced nanostructured sensors by exploiting easy and low cost fabrication processes suitable to be employed in massive production of technologically advanced devices. The pursued approach basically consists in the preliminary preparation of a patterned polymeric film by the breath figure technique, directly on the optical fiber tip, and in the successive metal deposition by evaporation. The experimental results demonstrate the successful creation of a metallodielectric honeycomb pattern on the optical fiber tip. The experimental spectral features are in good agreement with the numerical analysis, elucidating the photonic and plasmonic interactions occurring in the Lab onto the optical fiber tip. The sensing properties of the optical fiber probes have been successfully explored in terms of sensitivity to the surrounding refractive index changes demonstrating their potentialities for chemical and biological sensing applications.
In this work, we report the preliminary results on the fabrication of metallo-dielectric nanostructures on the optical fiber
tip by using a simple and low cost self-assembly approach. The fabrication process relies on the breath figure technique
here adapted to operate on unconventional substrates as the case of single mode optical fibers. The experimental results
demonstrate the successful creation of a honeycomb pattern on the optical fiber tip and the feasibility of the proposed
approach in the roadmap of "Lab on fiber" technology development. Further work is currently running aimed to the
assessment the presented fabrication procedures in order to attain advanced optical fiber sensing probes with high
fabrication throughput by exploiting a low cost technology.
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.
By now, fiber Bragg gratings (FBGs) represent a well assessed technology in both communications and sensing fields. In
particular, thanks to their small signal bandwidth and wavelength encoded information, they allow simple measurements
in reflection for sensing purposes and also easy multiplexing capability in realizing sensors arrays. Unfortunately, to
make FBGs sensitive to surrounding refractive index (SRI), hosting fiber structuring is needed. In last years, also tilted
FBGs (TFBGs) - intrinsically SRI sensitive structures - have been proposed as promising technological platform for
several sensing applications. However, complex spectral features combined with the difficulty to be configured as quasi
distributed or multi-point sensors network limit the practical exploitation of this assessed and mature technology. It
would be extremely useful to merge the peculiar spectral characteristics of both grating types. To address this issue, here,
we propose a hybrid cavity involving two unbalanced uniform FBGs written at both sides of a TFBG to form an all-fiber
interferometer. The proposed configuration provides a wavelength gated reflection signal with interference fringes
depending on the cavity features modulated by spectral dips associated to the wavelength dependent optical losses due to
cladding mode coupling occurring along the TFBG. Such a structure preserves the advantages of uniform FBGs in terms
of interrogation methods and allows the possibility to contemporarily measure multiple parameters.
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