Combined SERS-Raman screening of HER2-overexpressing or silenced breast cancer cell lines.

BACKGROUND: Breast cancer (BC) is a heterogeneous neoplasm characterized by several subtypes. One of the most aggressive with high metastasis rates presents overexpression of the human epidermal growth factor receptor 2 (HER2). A quantitative evaluation of HER2 levels is essential for a correct diagnosis, selection of the most appropriate therapeutic strategy and monitoring the response to therapy. RESULTS: In this paper, we propose the synergistic use of SERS and Raman technologies for the identification of HER2 expressing cells and its accurate assessment. To this end, we selected SKBR3 and MDA-MB-468 breast cancer cell lines, which have the highest and lowest HER2 expression, respectively, and MCF10A, a non-tumorigenic cell line from normal breast epithelium for comparison. The combined approach provides a quantitative estimate of HER2 expression and visualization of its distribution on the membrane at single cell level, clearly identifying cancer cells. Moreover, it provides a more comprehensive picture of the investigated cells disclosing a metabolic signature represented by an elevated content of proteins and aromatic amino acids. We further support these data by silencing the HER2 gene in SKBR3 cells, using the RNA interference technology, generating stable clones further analysed with the same combined methodology. Significant changes in HER2 expression are detected at single cell level before and after HER2 silencing and the HER2 status correlates with variations of fatty acids and downstream signalling molecule contents in the context of the general metabolic rewiring occurring in cancer cells. Specifically, HER2 silencing does reduce the growth ability but not the lipid metabolism that, instead, increases, suggesting that higher fatty acids biosynthesis and metabolism can occur independently of the proliferating potential tied to HER2 overexpression. CONCLUSIONS: Our results clearly demonstrate the efficacy of the combined SERS and Raman approach to definitely pose a correct diagnosis, further supported by the data obtained by the HER2 gene silencing. Furthermore, they pave the way to a new approach to monitor the efficacy of pharmacologic treatments with the aim to tailor personalized therapies and optimize patients' outcome.

Optrode-Assisted Multiparametric Near-Infrared Spectroscopy for the Analysis of Liquids.

We demonstrate a sensing scheme for liquid analytes that integrates multiple optical fiber sensors in a near-infrared spectrometer. With a simple optofluidic method, a broadband radiation is encoded in a time-domain interferogram and distributed to different sensing units that interrogate the sample simultaneously; the spectral readout of each unit is extracted from its output signal by a Fourier transform routine. The proposed method allows performing a multiparametric analysis of liquid samples in a compact setup where the radiation source, measurement units, and spectral readout are all integrated in a robust telecom optical fiber. An experimental validation is provided by combining a plasmonic nanostructured fiber probe and a transmission cuvette in the setup and demonstrating the simultaneous measurement of the absorption spectrum and the refractive index of water-methanol solutions.

An Innovative Fiber-Optic Hydrophone for Seismology: Testing Detection Capacity for Very Low-Energy Earthquakes.

An innovative fiber-optic hydrophone (FOH) was developed and investigated via an experiment at sea; it is capable of operating at a very low frequency of the seismic spectrum and detecting small magnitude earthquakes. The FOH exploits an optical fiber coil wrapped around a sensitive mandrel in a Michelson interferometric configuration. The FOH operated for about seven days at a water depth of 40 m, in the Campi Flegrei volcanic area (Southern Italy), and a few meters from a well-calibrated PZT hydrophone used as a reference. Thirty-three local earthquakes occurred during the simultaneous operation of the two hydrophones, allowing a straightforward comparison of the recordings. The local earthquakes occurred at an epicentral distance less than 2.5 km from the site of recording, and were estimated to be in the range of magnitude from -0.8 to 2.7. The analysis of the recorded earthquake waveforms in the frequency and time domains allowed retrieving the response function of the FOH in the frequency range from 5 to 70 Hz. The FOH responsivity in terms of acoustic pressure reached about 230 nm/Pa and was flat in the studied frequency range. Due to the high quality of the FOH recordings, this equipment is suitable for applications addressing submarine volcanic activity and the background seismicity of active faults in the ocean.

Innovative Photonic Sensors for Safety and Security, Part II: Aerospace and Submarine Applications.

The employability of photonics technology in the modern era's highly demanding and sophisticated domain of aerospace and submarines has been an appealing challenge for the scientific communities. In this paper, we review our main results achieved so far on the use of optical fiber sensors for safety and security in innovative aerospace and submarine applications. In particular, recent results of in-field applications of optical fiber sensors in aircraft monitoring, from a weight and balance analysis to vehicle Structural Health Monitoring (SHM) and Landing Gear (LG) monitoring, are presented and discussed. Moreover, underwater fiber-optic hydrophones are presented from the design to marine application.

Innovative Photonic Sensors for Safety and Security, Part I: Fundamentals, Infrastructural and Ground Transportations.

Our group, involving researchers from different universities in Campania, Italy, has been working for the last twenty years in the field of photonic sensors for safety and security in healthcare, industrial and environment applications. This is the first in a series of three companion papers. In this paper, we introduce the main concepts of the technologies employed for the realization of our photonic sensors. Then, we review our main results concerning the innovative applications for infrastructural and transportation monitoring.

Innovative Photonic Sensors for Safety and Security, Part III: Environment, Agriculture and Soil Monitoring.

In order to complete this set of three companion papers, in this last, we focus our attention on environmental monitoring by taking advantage of photonic technologies. After reporting on some configurations useful for high precision agriculture, we explore the problems connected with soil water content measurement and landslide early warning. Then, we concentrate on a new generation of seismic sensors useful in both terrestrial and under water contests. Finally, we discuss a number of optical fiber sensors for use in radiation environments.

Liquid Resin Infusion Process Validation through Fiber Optic Sensor Technology.

In the proposed work, a fiber-optic-based sensor network was employed for the monitoring of the liquid resin infusion process. The item under test was a panel composed by a skin and four stringers, sensorized in such a way that both the temperature and the resin arrival could be monitored. The network was arranged with 18 Fiber Bragg Gratings (FBGs) working as temperature sensors and 22 fiber optic probes with a modified front-end in order to detect the resin presence. After an in-depth study to find a better solution to install the sensors without affecting the measurements, the system was investigated using a commercial Micron Optics at 0.5 Hz, with a passive split-box connected in order to be able to sense all the sensors simultaneously. The obtained results in terms of resin arrival detection at different locations and the relative temperature trend allowed us to validate an infusion process numerical model, giving us better understanding of what the actual resin flow was and the time needed to dry preform filling during the infusion process.

Improving the width of lossy mode resonances in a reflection configuration D-shaped fiber by nanocoating laser ablation.

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 SnO2-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.

Detection of small DNA fragments by biolayer interferometry.

Small molecular weight species such as miRNAs and other nucleic acid fragments are gaining an increased interest as biomarkers for relevant diseases. Also, cheap and rapid assays for their routine detection are becoming an urgent need. We have investigated the usability and convenience of a price affordable, label free and fast technique for their detection on a laboratory scale small device based on Bio-Layer Interferometry. Using a model DNA fragment (7 kDa), we have found that the technique is effectively fast and sensitive enough for the detection of nucleic acid fragments having a MW below the stated molecular size detection limit (10 kDa). The test molecule has been detected in solution at 100 nM in a direct capture experiment and up to about 10 nM following an improved approach where an enhancing probe is used to increase the apparent molecular dimensions of the analyte. The technique, following further optimizations, can be applied for the routine, cheap and fast analysis of small nucleic acid fragments that have a relevance in diagnosis and in therapy.

Lab-On-Fiber Technology: A Roadmap toward Multifunctional Plug and Play Platforms.

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

Smart Optical Catheters for Epidurals.

Placing the needle inside the epidural space for locoregional anesthesia is a challenging procedure, which even today is left to the expertise of the operator. Recently, we have demonstrated that the use of optically sensorized needles significantly improves the effectiveness of this procedure. Here, we propose an optimized configuration, where the optical fiber strain sensor is directly integrated inside the epidural catheter. The new design allows the solving of the biocompatibility issues and increases the versatility of the former configuration. Through an in vivo study carried out on a porcine model, we confirm the reliability of our approach, which also opens the way to catheter monitoring during insertion inside biological spaces.

Nanosphere Lithography on Fiber: Towards Engineered Lab-On-Fiber SERS Optrodes.

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

Optimization Strategies for Responsivity Control of Microgel Assisted Lab-On-Fiber Optrodes.

Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications.

Fiber Optic Thermo-Hygrometers for Soil Moisture Monitoring.

This work deals with the fabrication, prototyping, and experimental validation of a fiber optic thermo-hygrometer-based soil moisture sensor, useful for rainfall-induced landslide prevention applications. In particular, we recently proposed a new generation of fiber Bragg grating (FBGs)-based soil moisture sensors for irrigation purposes. This device was realized by integrating, inside a customized aluminum protection package, a FBG thermo-hygrometer with a polymer micro-porous membrane. Here, we first verify the limitations, in terms of the volumetric water content (VWC) measuring range, of this first version of the soil moisture sensor for its exploitation in landslide prevention applications. Successively, we present the development, prototyping, and experimental validation of a novel, optimized version of a soil VWC sensor, still based on a FBG thermo-hygrometer, but able to reliably monitor, continuously and in real-time, VWC values up to 37% when buried in the soil.

Grating-coupling-based excitation of Bloch surface waves for lab-on-fiber optrodes.

In this paper, we investigate the possibility to excite Bloch surface waves (BSWs) on the tip of single-mode optical fibers. Within this framework, after exploring an idealized, proof-of-principle grating-coupling-based scheme for on-tip excitation of BSWs, we focus on an alternative configuration that is more robust with respect to fabrication-related non-idealities. Subsequently, with a view towards label-free chemical and biological sensing, we present a specific design aimed at enhancing the sensitivity (in terms of wavelength shift) of the arising resonance with respect to changes in the refractive properties of the surrounding environment. Numerical results indicate that the attained sensitivities are in line with those exhibited by state-of-the-art plasmonic bioprobes, with the key advantage of exhibiting much narrower spectral resonances. This prototype study paves the way for a new class of miniaturized high-performance surface-wave fiber-optic devices for high-resolution label-free optical biosensing, and represents an important step forward in the "lab-on-fiber" technology roadmap.

Cryogenic-temperature profiling of high-power superconducting lines using local and distributed optical-fiber sensors.

This contribution presents distributed and multipoint fiber-optic monitoring of cryogenic temperatures along a superconducting power transmission line down to 30 K and over 20 m distance. Multipoint measurements were conducted using fiber Bragg gratings sensors coated with two different functional overlays (epoxy and poly methyl methacrylate (PMMA)) demonstrating cryogenic operation in the range 300-4.2 K. Distributed measurements exploited optical frequency-domain reflectometry to analyze the Rayleigh scattering along two concatenated fibers with different coatings (acrylate and polyimide). The integrated system has been placed along the 20 m long cryostat of a superconducting power transmission line, which is currently being tested at the European Organization for Nuclear Research (CERN). Cool-down events from 300-30 K have been successfully measured in space and time, confirming the viability of these approaches to the monitoring of cryogenic temperatures along a superconducting transmission line.

Lab-on-fiber technology: a new vision for chemical and biological sensing.

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.

Nanoscale TiO2-coated LPGs as radiation-tolerant humidity sensors for high-energy physics applications.

This Letter 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 solgel deposition method. Relative humidity (RH) monitoring in the range 0%-75% and at four different temperatures (in the range -10°C-25°C) was carried out to assess sensor performance 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 to very low humidity levels), which turned out to be from one to three orders of magnitude higher than those exhibited by fiber Bragg grating sensors coated with micrometer-thin polyimide overlays. The radiation tolerance capability of the TiO2-coated LPG sensor is also investigated by comparing the sensing performance before and after its exposure to a 1 Mrad dose of γ-ionizing radiation. Overall, the results collected demonstrate the strong potential of the proposed technology with regard to its future exploitation in HEP applications as a robust and valid alternative to the commercial (polymer-based) hygrometers currently used.

An intrusion detection system for the protection of railway assets using Fiber Bragg Grating sensors.

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

Surface sensitivity of Rayleigh anomalies in metallic nanogratings.

Sensing schemes based on Rayleigh anomalies (RAs) in metal nanogratings exhibit an impressive bulk refractive-index sensitivity determined solely by the grating period. However, the surface sensitivity (which is a key figure of merit for label-free chemical and biological sensing) needs to be carefully investigated to assess the actual applicability of this technological platform. In this paper, we explore the sensitivity of RAs in metal nanogratings when local refractive-index changes are considered. Our studies reveal that the surface sensitivity deteriorates up to two orders of magnitude by comparison with the corresponding bulk value; interestingly, this residual sensitivity is not attributable to the wavelength shift of the RAs, which are completely insensitive to local refractive-index changes, but rather to a strictly connected plasmonic effect. Our analysis for increasing overlay thickness reveals an ultimate surface sensitivity that approaches the RA bulk value, which turns out to be the upper-limit of grating-assisted surface-plasmon-polariton sensitivities.