Metasurface-assisted Lab-on-fiber optrode for highly sensitive detection of vitamin D.

The increasing demand for vitamin D status assessment has highlighted the need for rapid, sensitive, and user-friendly methods for its detection in biological samples potentially integrated in Point-of-Care (PoC) diagnostic devices. Detection of the major circulating form of vitamin D, 25-hydroxyvitamin D3-25(OH)D3, is particularly challenging due to the laborious procedures for sample preparation and its low molecular weight (∼400 Da), which requires highly sensitive detection methods. In this study, we developed a novel label-free Lab-on-Fiber biosensing platform for highly sensitive detection of 25(OH)D3 based on the integration of plasmonic metasurfaces (MSs) on the tip of a single-mode optical fiber (OF). A dedicated pipeline was carefully designed and developed to optimize the bio-functionalization of the plasmonic sensor tip to specifically detect the target biomolecule. The resulting MS-assisted Lab-on-fiber platform enables direct and highly sensitive detection of 25(OH)D3 in clinically relevant ranges (4-160 ng/mL), both in buffer solution and complex matrix, with limits of detection (LOD) of 1.40 ng/mL in saline buffer and 0.85 ng/mL in complex matrix. Overall, these results demonstrate that our platform can successfully and specifically detect small molecules in label-free configuration, with performances comparable to those of conventional methods used in clinical practice. The high degree of miniaturization combined with its high sensitivity makes our platform an exceptional building block for realizing valid diagnostic alternatives for label-free detection of clinically relevant analytes, which can be transformed into new low-cost, fast, simple, and ready-to-use PoC diagnostic devices with improved processability and performance compared to current methods.

SERS assisted sandwich immunoassay platforms for ultrasensitive and selective detection of human Thyroglobulin.

We developed an immunoassay platform for the detection of human Thyroglobulin (Tg) to be integrated with fine-needle aspiration biopsy for early detection of lymph node metastases in thyroid cancer patients. The sensing platform detects Tg by a sandwich immunoassay involving a self-assembled surface-enhanced Raman scattering (SERS) substrate assisted by functionalized gold nanoparticles that provide additional Raman signal amplification and improved molecular specificity. Specifically, the SERS-active substrates were functionalized with Tg Capture antibodies and fabricated either on-chip or on optical fiber tips by nanosphere lithography. Gold nanoparticles were functionalized with Detection antibodies and conjugated with 4-mercaptobenzoic acid, which serves as a Raman reporter. The sandwich assay platform was validated in the planar configuration and a detection limit as low as 7 pg/mL was successfully achieved. Careful morphological examination of the SERS substrates before and after Tg measurements further assessed the effective capture of nanoparticles and correlated the average nanoparticle coverage with the Tg concentration obtained by SERS measurements. 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, SERS optrodes were fabricated and successfully used to detect Tg concentration by applying the same bio-recognition strategy and Raman interrogation through an optical fiber. 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.

Self-assembly on optical fibers: a powerful nanofabrication tool for next generation "lab-on-fiber" optrodes.

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.

Light-microgel interaction in resonant nanostructures.

Combination of responsive microgels and photonic resonant nanostructures represents an intriguing technological tool for realizing tunable and reconfigurable platforms, especially useful for biochemical sensing applications. Interaction of light with microgel particles during their swelling/shrinking dynamics is not trivial because of the inverse relationships between their size and refractive index. In this work, we propose a reliable analytical model describing the optical properties of closed-packed assembly of surface-attached microgels, as a function of the external stimulus applied. The relationships between the refractive index and thickness of the equivalent microgel slab are derived from experimental observations based on conventional morphological analysis. The model is first validated in the case of temperature responsive microgels integrated on a plasmonic lab-on-fiber optrode, and also implemented in the same case study for an optical responsivity optimization problem. Overall, our model can be extended to other photonic platforms and different kind of microgels, independently from the nature of the stimulus inducing their swelling.

Microgel assisted Lab-on-Fiber Optrode.

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.

High sensitive and direct fluorescence detection of single viral DNA sequences by integration of double strand probes onto microgels particles.

A novel class of probes for fluorescence detection was developed and combined to microgel particles for a high sensitive fluorescence detection of nucleic acids. A double strand probe with an optimized fluorescent-quencher couple was designed for the detection of different lengths of nucleic acids (39 nt and 100 nt). Such probe proved efficient in target detection in different contests and specific even in presence of serum proteins. The conjugation of double strand probes onto polymeric microgels allows for a sensitive detection of DNA sequences from HIV, HCV and SARS corona viruses with a LOD of 1.4 fM, 3.7 fM and 1.4 fM, respectively, and with a dynamic range of 10(-9)-10(-15) M. Such combination enhances the sensitivity of the detection of almost five orders of magnitude when compared to the only probe. The proposed platform based on the integration of innovative double strand probe into microgels particles represents an attractive alternative to conventional sensitive DNA detection technologies that rely on amplifications methods.

Optical fiber tip templating using direct focused ion beam milling.

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.

Simple technique for integrating compact silicon devices within optical fibers.

In this work, we present a simple fabrication process enabling the integration of a subwavelength amorphous silicon layer inside optical fibers by means of the arc discharge technique. To assess our method, we have fabricated a compact in-line Fabry-Perot interferometer consisting of a thin (<1 µm) a-Si:H layer completely embedded within a standard single-mode optical fiber. The device exhibits low loss (1.3 dB) and high interference fringe visibility (~80%) both in reflection and transmission, due to the high refractive index contrast between silica and a-Si:H. A high linear temperature sensitivity up to 106 pm/°C is demonstrated in the range 120°C-400°C. The proposed interferometer is attractive for point monitoring applications as well as for ultrahigh-temperature sensing in harsh environments.

Long period grating working in transition mode as promising technological platform for label-free biosensing.

We present the development of a platform for label-free biosensing based on overlayered Long Period Gratings (LPGs) working in transition mode. Nano-scale layers of Polystyrene (PS) with different thicknesses were deposited onto the same LPG to test the performances of the device in different working points of its modified sensitivity characteristic. Adsorption dynamic of biotinylated bovine serum albumin (BBSA) onto the PS overlays was on-line monitored as well as a subsequent streptavidin (SA) binding dynamic on the biotinylated sites of the protein ad-layer. Experimental results show that overlayered LPGs are among the most sensitive refractive index transducers to be employed in label-free biochemical detection and that wide margins of further optimization exist.

Spectral behavior of thin film coated cascaded tapered long period gratings in multiple configurations.

In this work the spectral response of cascaded tapered long period gratings coated by nano-sized polymeric films has been investigated as function of the surrounding medium refractive index (SRI). The investigation was aimed to identify the best configuration in terms of coated/not coated areas in order to fully benefit of the SRI sensitivity enhancement due to the modal transition mechanism of nano-coated long period gratings while preserving the fringes visibility.

Near field behavior of SnO(2) particle-layer deposited on standard optical fiber by electrostatic spray pyrolysis method.

We report the emergent optical near field profiles from standard single mode optical fibers on the cleaved end of which were deposited particle layers of SnO(2). The layers, composed of micron and sub-micron sized particles, were deposited by means of Electrostatic Spray Pyrolysis (ESP) technique. Powerful analytical tools such as Atomic Force Microscopy (AFM) and Scanning Near-field Optical Microscopy (SNOM) were used to obtain simultaneously the SnO(2) layers topography and the related optical near field intensity distribution, when the fiber-substrate is illuminated by a light radiation in NIR range. We show that isolated microstructures, positioned in correspondence of the fiber core, reveal highly unusual capability of locally enhancing the collected optical near field. The observed phenomenon leads to new concepts of fiber optic chemical sensors and in fiber microsystems as well.

Micro-structured fiber Bragg gratings: optimization of the fabrication process.

This work has been devoted to present and demonstrate a novel approach for the fabrication of micro-structured fiber Bragg gratings (MSFBGs) with enhanced control of the geometric features and thus of the spectral properties of the final device. The investigated structure relies on the localized stripping of the cladding layer in a well defined region in the middle of the grating structure leading to the formation of a defect state in the spectral response. In order to fully explore the versatility of MSFBGs for sensing and communications applications, a technological assessment of the fabrication process aimed to provide high control of the geometrical features is required. To this aim, here, we demonstrate that the optimization of this device is possible by adopting a fabrication process based on polymeric coatings patterned by high resolution UV laser micromachining tools. The function of the polymeric coating is to act as mask for the HF based chemical etching process responsible for the cladding stripping. Whereas, UV laser micromachining provides a valuable method to accurately pattern the polymeric coating and thus obtain a selective stripping along the grating structure. Here, we experimentally demonstrate the potentiality of the proposed approach to realize reliable and cost efficient MSFBGs enabling the prototyping of advanced photonics devices based on this technology.

Mode transition in high refractive index coated long period gratings.

In this work, the numerical and experimental investigation of the cladding modes re-organization in high refractive index (HRI) coated Long Period Gratings (LPGs) is reported. Moreover, the effects of the cladding modes re-organization on the sensitivity to the surrounding medium refractive index (SRI) have been outlined. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the SRI. In particular, if layer parameters are properly chosen, the transition of the lowest order cladding mode into an overlay mode occurs. As a consequence, a cladding modes re-organization can be observed leading to relevant improvements in the SRI sensitivity in terms of wavelength shift and amplitude variations of the LPGs attenuation bands.

Contactless optoelectronic technique for monitoring epoxy cure.

We describe a novel noninvasive optical technique to monitor the refractive-index variation in an epoxy-based resin that is due to the polymerization process. This kind of resin is widely used in polymer matrix composites. It is well known that the process of fabricating a thermoset-based composite involves mass and heat transfer coupled with irreversible chemical reactions that induce physical changes. To improve the quality and the reliability of these materials, monitoring the cure and optimization of the manufacturing process are of key importance. We discuss the basic operating principles of an optical system based on angle deflection measurements and present typical cure-monitoring results obtained from optical characterization. The method provides a flexible, high-sensitivity, material-independent, low-cost, noninvasive tool for monitoring real-time refractive-index variation.

Hypouricemia in acquired immunodeficiency syndrome.

Clinical evaluations of hypouricemia in patients with the acquired immunodeficiency syndrome (AIDS) have shown that it is a common disorder resulting from defective renal handling of uric acid. We prospectively studied renal urate handling in 23 patients and reviewed the records of 73 consecutive patients with AIDS or AIDS-related complex (ARC), who were seen in our AIDS clinic between March 1985 and April 1988, to determine the incidence, significance, and, when possible, the cause of hypouricemia. Hypouricemia was defined as serum urate less than or equal to 0.18 mmol/L (3 mg/dL). Renal clearance studies were performed in 23 patients, 10 hypouricemic and 13 nonhypouricemic. Eight patients (six with hypouricemia) underwent central venous pressure (CVP) monitoring, which was performed for clinical signs and symptoms of extracellular volume depletion. Fourteen (eight with hypouricemia) had daily urine urate measured. Hypouricemia was found in 21 (21.9%) of 96 patients. It was more common in females and intravenous (IV) drug abusers, and was associated with more opportunistic illnesses, particularly mycobacterium avium intracellulare (MAI) and cytomegalovirus (CMV) infections. Hypouricemia occurred in three patients with ARC and 18 patients with AIDS and was associated with cerebral atrophy in all 12 hypouricemic and 14 of 28 nonhypouricemic patients who had cranial computed tomography (CT) scans. During a comparable follow-up period, 71.4% of the hypouricemic as compared with 38.7% of nonhypouricemic patients died. Eleven developed hypouricemia as outpatients. Fractional excretion of uric acid (FEua) was elevated in the eight patients with CVP less than 1 cm of water, and in 10 of 10 with and nine of 13 without hypouricemia, despite CVP less than 1 cm water in eight.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyponatremia in patients with acquired immune deficiency syndrome.

We performed prospective and retrospective studies of 96 consecutive patients with acquired immune deficiency syndrome (AIDS) or AIDS-related complex (ARC) to determine the incidence, pathogenesis, and clinical significance of hyponatremia, defined as serum sodium levels less than or equal to 130 mmol/L on more than one occasion. Thirty (31.3%), six with ARC and 24 with AIDS, had hyponatremia, and it developed in 20 as outpatients. Age, gender, duration of illness, and weight loss did not differ between groups. The hyponatremic patient had more opportunistic illnesses, including Pneumocystis carinii pneumonia and cytomegalovirus infections, and had a mortality of 70% as compared to 36.4% of the patients without hyponatremia. The probability of 50% survival after diagnosis of human immunodeficiency virus (HIV) infection in the hyponatremic group was 11.5 months, as compared to 39 months for those without hyponatremia, p less than 0.001. The probability of 50% survival after development of hyponatremia was 4.5 months and the median length of time to development of hyponatremia was 12.5 months after diagnosis of HIV infection. Eighty-eight percent had hypovolemia and 12% normovolemia. Seventeen of 21 with hypovolemia had no evident source of fluid loss. Two had Addison's disease, and 15 had unexpectedly high urine sodium concentration without evidence of renal or adrenal insufficiency. Hyponatremia occurs commonly in ambulatory patients with ARC or AIDS, appears in patients with higher mortality and morbidity, and does not represent a terminal event. Most patients had hypovolemia and unexpectedly high urine sodium concentration, suggesting defective renal sodium conservation.

Juvenile rheumatoid arthritis with renal amyloidosis: a 23-year survival.

A 14-year-old girl with juvenile rheumatoid arthritis developed severe renal amyloidosis and presented with nephrosis and renal failure. Renal function returned to normal in a year and over 23 years, serial biopsies showed remarkable, biopsy-proven regression of amyloid deposits. Amyloid was not found in skin, gum or rectal biopsies. This case demonstrates an improved prognosis and apparent reversibility.

Ontogeny of B-lymphocyte function. IX. Difference in the time of maturation of the capacity of B lymphocytes from foetal and neonatal mice to produce a heterogeneous antibody response to thymic-dependent and thymic-independent antigens.

The ontogeny of the capacity of the B-lymphocyte population to produce a response which is heterogeneous with respect to antibody affinity was studied in a cell transfer system. Lethally irradiated mice were reconstituted with B cells from donors of various ages, together with adult thymus cells when the response to T-dependent antigens was studied. The animals were immunized with one of a variety of antigens one day after cell transfer and the distribution of their splenic plaque-forming cells (PFC) with respect to affinity was assayed, by hapten inhibition of plaque formation, 2 to 3 weeks after immunization. Mice reconstituted with B cells from neonatal donors produced a response of low affinity and restricted heterogeneity. With four different thymic-dependent antigens (DNP-BGG, F-BGG, DNP-KLH and Dan-KLH) the splenic B-cell population acquired the capacity to reconstitute irradiated mice to produce a normal adult-like, highly heterogeneous, high affinity PFC response between 7 and 10 days after birth. The capacity to produce a heterogeneous response to the thymic-dependent protein antigen BGG matured just slightly later between 10 and 14 days of age. The bone marrow matures with regard to the capacity to reconstitute irradiated mice to give a heterogeneous response several days after the spleen, possibly as a consequence of the redistribution of peripheral B cells to the bone marrow. In contrast, maturation of the capacity of the splenic B-cell population to reconstitute irradiated recipients to give a heterogeneous, adult-like PFC response to three 'thymic-independent' antigens (TNP-PA, DNP-Ficoll and TNP-BA) takes place considerably later (between 3 and 4 weeks of age). These results suggest that the population of B-cell precursors which responds to thymic-dependent antigens may represent a different subpopulation of B cells from the population that responds to thymic independent antigens. Furthermore, the results suggest that these B-cell subsets mature at different times, presumably under independent controls.