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A low-cost plasmonic sensor based on a polymeric light diffusive optical fiber (LDF) has been designed, realized, and experimentally tested. The developed surface plasmon resonance (SPR) sensor has been realized by sputtering a gold nanofilm on the LDF. The work also presents a simple modal filter, realized by covering the LDF with an aqueous solution. Notably, this modal filter improves the signal-to-noise ratio (SNR) of the SPR sensor thanks to the filtering of the higher modes, without losing its sensitivity.

In this paper, we propose a dual wavelength scheme for the detection of liquids based on optically absorbing (Co2+-doped) optical fibers. The proposed configuration makes use of a Coherent-Optical Time Domain Reflectometer (C-OTDR) operating with standard fibers at 850 nm. Besides vibration measurements over all the sensing fiber, the proposed scheme performs liquid detection in short sections of Co2+-doped fibers, heated by a modulated optical pump at 1550 nm. We demonstrate that the proposed sensor detects the liquids surrounding the doped fiber, such as water or acetone.

Optical chemosensors with surface plasmon resonance (SPR) transduction are widely employed, even in complex environments, such as those outside the laboratory. In this context, not only the chemical nature but also the physical form of the receptor layer is particularly relevant. Synthetic receptors as molecularly imprinted polymers (MIPs) are well suited. This is demonstrated here in the case of an SPR sensor platform based on a multimode plastic optical fiber, which is very promising for on site application due to the low dimensions and low cost. A specific MIP was used as the receptor, with high affinity for the substance to be determined, 2-furaldehyde, in water. Here, a medium of high refractive index, i.e., vegetable oil, was considered because of the high interest for its determination in industrial diagnostics. The effects of the MIP layer thickness and the washing extent on the quality of the analytical signal were investigated. Better spectra were generated at the thinner MIP layer, while a lower detection limit is reached with extended washing.

We demonstrate the use of a graded-index perfluorinated optical fiber (GI-POF) for distributed static and dynamic strain measurements based on Rayleigh scattering. The system is based on an amplitude-based phase-sensitive Optical Time-Domain Reflectometry (ϕ-OTDR) configuration, operated at the unconventional wavelength of 850 nm. Static strain measurements have been carried out at a spatial resolution of 4 m and for a strain up to 3.5% by exploiting the increase of the backscatter Rayleigh coefficient consequent to the application of a tensile strain, while vibration/acoustic measurements have been demonstrated for a sampling frequency up to 833 Hz by exploiting the vibration-induced changes in the backscatter Rayleigh intensity time-domain traces arising from coherent interference within the pulse. The reported tests demonstrate that polymer optical fibers can be used for cost-effective multiparameter sensing.

Postoperative pancreatic fistula (POPF), the major driver of morbidity and mortality following pancreatectomy, is caused by an abnormal communication between the pancreatic ductal epithelium and another epithelial surface containing pancreas-derived, enzyme-rich fluid. There is a strong correlation between the amylase content in surgically-placed drains early in the postoperative course and the development of POPF. A simple and cheap method to determine the amylase content from the drain effluent has been eagerly advocated. Here, we developed an amylase optical biosensor, based on a surface plasmon resonance (SPR) plastic optical fiber (POF), metallized with a 60 nm layer of gold and interrogated with white light. The sensor was made specific by coupling it with an anti-amylase antibody. Each surface derivatization step was optimized and studied by XPS, contact angle, and fluorescence. The POF-biosensor was tested for its response to amylase in diluted drain effluents. The volume of sample required was 50 µL and the measurement time was 8 min. The POF-biosensor showed selectivity for amylase, a calibration curve log-linear in the range of 0.8–25.8 U/L and a limit of detection (LOD) of ~0.5 U/L. In preliminary tests, the POF-biosensor allowed for the measurement of the amylase content of diluted surgically-placed drain effluents with an accuracy of &gt, 92% with respect to the gold standard. The POF-biosensor allows for reliable measurement and could be implemented to allow for a rapid bedside assessment of amylase value in drains following pancreatectomy.

The rapid spread of the Coronavirus Disease 2019 (COVID-19) pandemic, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pathogen has generated a huge international public health emergency. Currently the reference diagnostic technique for virus determination is Reverse Transcription Polymerase Chain Reaction (RT-PCR) real time analysis that requires specialized equipment, reagents and facilities and typically 3–4 h to perform. Thus, the realization of simple, low-cost, small-size, rapid and point-of-care diagnostics tests has become a global priority. In response to the current need for quick, highly sensitive and on-site detection of the SARS-CoV-2 virus in several aqueous solutions, a specific molecularly imprinted polymer (MIP) receptor has been designed, realized, and combined with an optical sensor. More specifically, the proof of concept of a SARS-CoV-2 sensor has been demonstrated by exploiting a plasmonic plastic optical fiber sensor coupled with a novel kind of synthetic MIP nano-layer, especially designed for the specific recognition of Subunit 1 of the SARS-CoV-2 Spike protein. First, we have tested the effectiveness of the developed MIP receptor to bind the Subunit 1 of the SARS-CoV-2 spike protein, then the results of preliminary tests on SARS-CoV-2 virions, performed on samples of nasopharyngeal (NP) swabs in universal transport medium (UTM) and physiological solution (0.9% NaCl), were compared with those obtained with RT-PCR. According to these preliminary results, the sensitivity of the proposed optical-chemical sensor proved to be higher than the RT-PCR one. Furthermore, a relatively fast response time (about 10 min) to the virus was obtained without the use of additional reagents.

A review on bio-chemical label-free sensing applications based on receptors combined with multimode plastic optical fibers (POFs) is carried out. In particular, this work focuses on different kinds of POF intrinsic sensors used in transmission mode, exploiting various types of receptors and useful in several application fields. The sensor structures and the sensing mechanisms of different simple, highly sensitive, and low-cost POF probes are reported and compared. Moreover, different kinds of chemical and biological receptors combined with POF probes, highlighting the advantages and disadvantages of each receptor, are presented in detail. More specifically, the chosen POF sensing platforms, including low-cost and simple interrogation setups, are described showing their ability to monitor specific receptors exploiting intensity variation techniques and plasmonic phenomena, as well. Finally, a prospect of future developments of biochemical sensors with multimode POFs is discussed.

Several surface plasmon resonance (SPR) sensors in optical fibers have been presented for the detection of magnetic fields. These SPR sensors measure the variation of the refractive index of a magnetic fluid in contact to the metal film, when the magnetic field changes. In this work, we have presented a different approach to monitor a magnetic field exploiting SPR optical fiber sensors and ferrofluids. More specifically, we have inserted a patch of multimode plastic optical fiber (POF) covered with ferrofluids between a light source and an SPR-POF sensor connected to a spectrometer. The magnetic field in the region near the patch covered by ferrofluids exerts a bending force on the patch changing the light in input to the SPR sensor and modifying the SPR phenomenon, in terms of resonance’s shape and wavelength.

Nowadays, the development of simple, fast, and low-cost selective sensors to detect substances of interest is of great importance in several application fields. Among this kind of sensors, those based on surface plasmon resonance (SPR) represent a promising category, since they are highly sensitive, versatile, and label-free. In this work, an SPR probe, based on a poly(methyl methacrylate) (PMMA) slab waveguide covered by a gold nanofilm, combined with a specific molecularly imprinted polymer (MIP) receptor for bovine serum albumin (BSA) protein, has been realized and experimentally characterized. The obtained experimental results have shown a limit of detection (LOD) equal to about 8.5 × 10−9 M. This value is smaller than the one achieved by another SPR probe, based on a D-shaped plastic optical fiber (POF), functionalized with the same MIP receptor; more specifically, the obtained LOD was reduced by about three orders of magnitude with respect to the POF configuration. Moreover, concerning the D-shaped POF configuration, no manufacturing process is present in the proposed sensor configuration. In addition, fibers are used only to connect the simple sensor chip with a light source and a detector, promoting a bio-chemical sensing approach based on disposable, low-cost, and removable chips.

In a specific biosensing application, a nanoplasmonic sensor chip has been tested by an experimental setup based on an aluminum holder and two plastic optical fibers used to illuminate and collect the transmitted light. The studied plasmonic probe is based on gold nanograting, realized on the top of a Poly(methyl methacrylate) (PMMA) chip. The PMMA substrate could be considered as a transparent substrate and, in such a way, it has been already used in previous work. Alternatively, here it is regarded as a slab waveguide. In particular, we have deposited upon the slab surface, covered with a nanograting, a synthetic receptor specific for bovine serum albumin (BSA), to test the proposed biosensing approach. Exploiting this different experimental configuration, we have determined how the orientation of the nanostripes forming the grating pattern, with respect to the direction of the input light (longitudinal or orthogonal), influences the biosensing performances. For example, the best limit of detection (LOD) in the BSA detection that has been obtained is equal to 23 pM. Specifically, the longitudinal configuration is characterized by two observable plasmonic phenomena, each sensitive to a different BSA concentration range, ranging from pM to µM. This aspect plays a key role in several biochemical sensing applications, where a wide working range is required.

In this work, we present a novel biochemical sensing approach based on a plasmonic sensor chip, combined with a specific receptor, excited and interrogated via a custom 3D-printed holder through a transmission-based experimental setup, exploiting polymer optical fibers. The setup is designed to measure a disposable plasmonic chip based on a gold nanograting fabricated on a polymethylmethacrylate substrate. The examined sensor configurations here presented are simulated, realized, and experimentally tested. More specifically, first, a numerical analysis is carried out by changing several sensor parameters, then an experimental optical characterization of different sensor configurations is reported. Finally, to test the biosensing capabilities of the proposed method, as a proof of concept, we deposit on the best sensor configuration a biomimetic receptor specific for bovine serum albumin detection. The experimental results demonstrate that the proposed sensor shows an ultra-low limit of detection, equal to about 37 pmol/L.

We have exploited a laser-based integration process of ultrathin metal-oxide (MO) films to improve the plasmonic effect in sensors based on D-shaped plastic optical fibers (POFs). More specifically, using ultrathin MO films, the performances of the surface plasmon resonance (SPR) phenomenon improve and a lossy mode resonance (LMR) can occur. Although the role of this kind of materials has been already presented, when they are deposited as overlayer (upside the thin metal film), we have used a different approach by depositing MOs, especially zirconium oxide (ZrO2) and titanium oxide (TiO2), as flexible intermediate layers between the exposed core of POFs and the gold film. The MO layer is prepared from sol-gel solution, and deep-UV laser curing allows us to densify the thin film and tune the refractive index, with a room-temperature process fully compatible with the flexible polymer substrates. In a preliminary step, we have carried out numerical results, based on transfer matrix formalism, to predict the SPR response. Subsequently, we have experimentally characterized the developed sensor configurations. Numerical and experimental results have shown above all an enhancement of the sensor performances, in terms of SPR sensitivity, with respect to a reference sensor based on a polymer instead of MOs. Moreover, in some proposed sensor configurations, together with the SPR phenomenon, an LMR phenomenon was observed. It occurred in a different wavelength range, for a typical refractive index range present when considering receptors for biochemical sensing applications. Therefore, both resonances (SPR and LMR) could be used in several application fields.

Nowadays there is an increasing request to realize green, eco-friendly, and biodegradable electronic devices for biosensor implementation. In this context, we have conceived and realized a green sensor based on localized surface plasmon resonance (LSPR) phenomenon in a thin-slab waveguide of bacterial cellulose (BC). These LSPR sensors can be obtained simply by gold sputtering on the slab BC waveguides. The performances have been studied investigating the presence of ionic liquids (ILs) inside and in absence of ILs with various thicknesses of the BC substrate. Depending of the thickness of the BC layer, the ILs effect on the LSPR can be constructive or destructive. In this work, we present a study of the sensor performances, in terms of bulk sensitivity and resolution by changing the aforementioned parameters. Analyses in terms of BC geometry are pursued in order to improve the interaction between the light and the LSPR phenomenon. The experimental setup used for this kind of extrinsic optical fiber LSPR sensor is based on two optical fibers used to connect a white light source and a spectrometer with the green LSPR sensor chip. Results evince the suitability of the proposed approach in order to realize sensors and biosensors with several intriguing properties and features. In fact, these LSPR platforms could be used to realize disposable biosensors, when a specific bioreceptor is covalently bonded to the gold.

A surface plasmon resonance (SPR) platform, based on a D-shaped plastic optical fiber (POF), combined with a biomimetic receptor, i.e., a molecularly imprinted polymer (MIP), is proposed to detect 2-furaldheide (2-FAL) in fermented beverages such as wine. The determination of 2-FAL in food samples is becoming a very crucial task, on the one hand for its role in the flavor and on the other in relation to its toxic and carcinogenic effects on human beings. The proposed sensing device is easy to use and cheap; it has been tested successfully for the detection and quantification of substances of interest in different fields, such as health, the environment and industry. The possibility of performing single-drop measurements is a further favorable aspect for practical applications. As an example, the use of an SPR-MIP sensor for the analysis of 2-FAL in wine, in a concentration range useful for practical applications, is here described.

In this work, we have compared several configurations of surface plasmon resonance (SPR) sensors based on D-shaped tapered plastic optical fibers (TPOFs). Particularly, the TPOFs used to obtain the SPR sensors are made by a lab-built system based on two motorized linear positioning stages and a heating plate. Preliminarily, a comparative analysis has been carried out between two different configurations, one with and one without a thin buffer layer deposited between the core of TPOFs and the gold film. After this preliminary step, we have used the simpler configuration, obtained without the buffer layer, to realize different SPR D-shaped TPOF sensors. This study could be of interest in SPR D-shaped multimode plastic optical fiber (POF) sensors because, without the tapers, the performances decrease when the POF&rsquo, s diameter decreases, whereas the performances improve in SPR D-shaped tapered POF sensors, where the diameter decreases in the D-shaped sensing area. The performances of the SPR sensors based on different taper ratios have been analyzed and compared. The SPR-TPOF sensors have been tested using water&ndash, glycerin mixtures with refractive indices ranging from 1.332 to 1.381 RIU. According to the theory, the experimental results have demonstrated that, as the taper ratio increases, the sensitivity of the SPR sensor increases as well, while on the contrary the signal-to-noise ratio (SNR) decreases.

In this paper, frequency dielectric spectroscopy (FDS) and an innovative optical sensor for the detection of 2-furaldehyde (2-FAL) are used to check the degree of ageing of differently processed oil-paper specimens when exposed to thermal stress. The analysis of the trend of moisture content and of 2-FAL concentrations confirms the influence of drying pre-treatment of the specimens on their ageing conditions. FDS elucidated the nature of the drying process of the specimens and the optical sensor correctly assesses a lower 2-FAL production for the vapour phase dried specimens during thermal exposure.

We have studied how the optical property of a multimode plastic optical fiber (POF) can be used to monitor a magnetic field, exploiting a Surface Plasmon Resonance (SPR) POF sensor. To realize the sensor system, we have deposited a magnetic fluid on the cladding of a multimode POF connected in input to an SPR D-shaped POF sensor platform. The target magnetic field exerts a bending force on the POF covered with magnetic fluid, thus producing a change of light in input to the SPR POF sensor and modifying the SPR phenomenon. This work presents preliminary experimental results to demonstrate that this novel principle of sensing can be used for highly sensitive measuring of the magnetic field. Preliminary results have demonstrated the viability of this approach showing the possibility to obtain higher sensitivities, compared with the state of the art on SPR optical fiber magnetic field sensors exploiting magnetic fluids.

We have developed and characterized a surface plasmon resonance (SPR) biosensor in a plastic optical fiber (POF) to detect traces of naphthalene (NAPTHA) in water. As previously developed for perfluorinated compounds (PFAs), the gold surface of the plasmonic POF sensor has been chemically modified through the formation of specific reactive groups and functionalized with antibodies able to specifically recognize the NAPTHA. The obtained limit of detection value (0.76ng/mL) is lower than the maximum residue limit value of naphthalene (0.13µg/mL) referred as the water environmental quality standards.

We reported a low-cost optical chemical sensor for the detection of furfural (furan-2-carbaldehyde, 2-FAL) in aqueous media. This novel optical sensor platform is based on a PET (polyethylene terephthalate) substrate with a pattern of silver nanoparticles, printed on it by InkJet technology. To obtain the selective detection of the analyte, the slab waveguide has been covered by a specific molecularly imprinted polymer (MIP) for 2-FAL. The sensing device has connected to a light source and a spectrometer by two plastic optical fibers (POFs), to monitor the interaction between the MIP and 2-FAL. The performances reported in this work are comparable to those of plasmonic POF sensors combined with the same MIP.

Different lines of evidence indicate that monitoring the blood levels of therapeutic antibodies, characterized by high inter-individual variability, can help to optimize clinical decision making, improving patient outcomes and reducing costs with these expensive treatments. A surface plasmon resonance (SPR)-based immunoassay has recently been shown to allow highly reliable and robust monitoring of serum concentrations of infliximab, with significant advantages over classical ELISA. The next level of advancement would be the availability of compact and transportable SPR devices suitable for easy, fast and cheap point-of-care analysis. Here we report the data obtained with recently developed, cost-effective, optical-fibre-based SPR sensors (SPR-POF), which allow the construction of a compact miniaturized system for remote sensing. We carried out an extensive characterization of infliximab binding to an anti-infliximab antibody immobilized on the SPR-POF sensor surface. The present proof-of-principle studies demonstrate the feasibility of the proposed SPR-POF platform for the specific detection of infliximab, in both buffer and human serum, and pave the way for further technological improvements.

We have used the same biomimetic receptor, a specific molecularly imprinted polymer (MIP), on two different plasmonic plastic optical fiber (POF) sensors to measure how the optical response influences the chemical response. To obtain two surface plasmon resonance (SPR) platforms, we have used two different overlayers between the core of the POF and the gold film. These overlayers, with a refractive index higher than that of the POF’s core [poly(methyl methacrylate) (PMMA)], have been used to improve the performances of the plasmonic sensor. As overlayers, we have deposited a photoresist (Microposit S1813), in two different aging conditions, namely, before and after its expiry date. In this article, we have demonstrated how the alteration in the photoresist changes the sensor’s performances and eventually the chemical response of the MIPs. More specifically, we have compared the MIPs responses of these two SPR-POF platforms in two different refractive index ranges. For this purpose, an MIP receptor already tested in the detection of perfluorinated compounds (PFAs) in water has been exploited.

A novel low-cost surface plasmon resonance (SPR) platform has been tested, for the first time, to monitor the interaction between a molecularly imprinted polymer (MIP) and a small molecule as the substrate. As a proof of principle, the considered MIP was specific for furfural (2-FAL, MW = 96.4), so that the possibility of using the new device for detection of 2-FAL in aqueous media was investigated. For the sake of comparison a sensor based on the same MIP specific for 2-FAL deposited on an SPR platform in a D-shaped plastic optical fiber (POF), which has been previously demonstrated to well perform for different analytes, has been considered too. The experimental results showed good performances of the novel platform for chemical sensing based on MIP as receptor in terms of selectivity, sensitivity and figure of merit (FOM). The limit of detection (LOD) of this simple and low-cost SPR sensor system is about 0.03 ppm, completely comparable to that of previously proposed devices based on SPR in a D-shaped POF (about 0.05 ppm), but with the advantage of an easier and more reproducible preparation procedure.

We present a comparative study of three optical sensing platforms based on surface plasmon resonance (SPR) in plastic optical fibers (POFs). The proposed sensors consist of a D–shaped POF sensing area, where the exposed core is covered by a photoresist layer, used as intermediate layer between the fiber’s core and the metal (gold) film. The photoresist deposited on the exposed core in the D–shaped POF region, is pivotal in order to improve the performances of the sensor in terms of sensitivity. In particular, we have compared the performances of three different buffer layers based on the following photoresist: Microposit SU-8 3005, Microposit S1813 before and after the expiry date.

Soft molecularly imprinted nanogels (nanoMIPs), selective for human transferrin (HTR), were prepared via a template assisted synthesis. Owing to their soft matter, the nanoMIPs were observed to deform at binding to HTR: while no relevant changes were observed in the hydrodynamic sizes of HTR-free compared to HTR-loaded nanoMIPs, the HTR binding resulted in a significant increment of the nanoMIP stiffness, with the mean Young's modulus measured by AFM passing from 17 ± 6 kPa to 56 ± 18 kPa. When coupled to a plastic optical fibre (POF) plasmonic platform, the analyte-induced nanoMIP-deformations amplified the resonance shift, enabling to attain ultra-low sensitivities (LOD = 1.2 fM; linear dynamic range of concentrations from 1.2 fM to 1.8 pM). Therefore, soft molecularly imprinted nanogels that obey to analyte-induced deformation stand as a novel class of sensitivity-gain structures for plasmonic sensing.

Authors recall two high sensitive, small size, and low-cost surface plasmon resonance (SPR) sensors based on plastic optical fibers (POFs): the first one, a D-shaped SPR intrinsic POF sensor, the second one an SPR extrinsic POF sensor. These plasmonic POF sensors, intrinsic and extrinsic, combined with different kinds of specific receptors can be directly connected to an online platform by a software interface, allowing storing, analyzing and displaying the sensor's data, to realize low-cost biochemical sensors for several applications. The simple experimental setup, used for both these SPR POF sensor configurations, was arranged to measure the light spectrum transmitted through the plasmonic platform, exploiting a halogen lamp and a spectrometer connected to a PC.

The COVID-19 pandemic has emphasized the need for portable, small-size, low-cost, simple to use, and highly sensitive sensors able to measure a specific substance, with the capability of the transmission over the Internet of statistical data, such as in this specific case on the spread of the SARS-CoV-2 virions. Moreover, to resolve the COVID-19 emergency, the possibility of making selective SARS-CoV-2 measurements in different aqueous matrices could be advantageous. Thus, the realization of rapid and innovative point-of-care diagnostics tests has become a global priority. In response to the current need for quick, highly sensitive and on-site detection of the SARS-CoV-2 virions in different aqueous solutions, two different nanolayer biorecognition systems separately combined with an adaptable optical fiber sensor have been reported in this work. More specifically, two SARS-CoV-2 sensors have been developed and tested by exploiting a plasmonic plastic optical fiber (POF) sensor coupled with two different receptors, both designed for the specific recognition of the SARS-CoV-2 Spike protein; one is aptamer-based and the other one Molecular Imprinted Polymer-based. The preliminary tests on SARS-CoV-2 virions, performed on samples of nasopharyngeal (NP) swabs in universal transport medium (UTM), were compared with data obtained using reverse-transcription polymerase chain reaction (RT-PCR). According to these preliminary experimental results obtained exploiting both receptors, the sensitivity of the proposed SARS-CoV-2 optical fiber sensors proved to be high enough to detect virions. Furthermore, a relatively fast response time (a few minutes) to detect virions was obtained without additional reagents, with the capability to transmit the data via the Internet automatically.

In this work, a novel approach to realize a plasmonic sensor is presented. The proposed optical sensor device is designed, manufactured, and experimentally tested. Two photo-curable resins are used to 3D print a surface plasmon resonance (SPR) sensor. Both numerical and experimental analyses are presented in the paper. The numerical and experimental results confirm that the 3D printed SPR sensor presents performances, in term of figure of merit (FOM), very similar to other SPR sensors made using plastic optical fibers (POFs). For the 3D printed sensor, the measured FOM is 13.6 versus 13.4 for the SPR-POF configuration. The cost analysis shows that the 3D printed SPR sensor can be manufactured at low cost (∼15 €) that is competitive with traditional sensors. The approach presented here allows to realize an innovative SPR sensor showing low-cost, 3D-printing manufacturing free design and the feasibility to be integrated with other optical devices on the same plastic planar support, thus opening undisclosed future for the optical sensor systems.

We present a hybrid Brillouin/Rayleigh sensor for multiparameter sensing in optical fibers. The system makes use of a single laser pulse to excite both Rayleigh and Brillouin backscattering in the same optical fiber. In the detection path, the backscattered signals are separated based on their different wavelengths. The system is capable of determining simultaneously the Brillouin frequency shift (BFS) of the fiber, as well as the frequency contents of any vibration acting on the same fiber as recovered by phase sensitive OTDR (ϕ-OTDR) measurements. The reported experiments show the possibility to perform simultaneous temperature and vibration measurements, as well as to perform dynamic strain measurements combining the information provided by slope-assisted Brillouin scattering measurements, with those provided by amplitude-based ϕ-OTDR measurements.

In this work, an unconventional light-diffusing fiber (LDF) plasmonic platform is exploited to efficiently monitor a bio-interaction. The surface plasmon resonance (SPR)-LDF sensor is used to detect the immunoglobulin G (IgG)/anti-IgG interaction as exemplifying bioassay. The IgG bioreceptor was deposited on the gold surface of the SPR-LDF platform, and the biological target was transported through a customized thermo-stabilized flow cell by means of a buffer fluid. Moreover, to test the usability of the proposed SPR-LDF biosensor also for immunosensing in complex matrices, a second assay was conducted by immobilizing anti-C-reactive protein (CRP) and detecting different concentrations of CRP in human serum. An innovative data analysis approach for the extraction of the best value of the resonance wavelength was developed and applied. The obtained results reveal that the unconventional platform represented by the LDF can be successfully exploited for the implementation of SPR-based biosensors with very good performances, also when compared to more common SPR systems.

The possibility of developing a multichannel optical chemical sensor, based on molecularly imprinted polymers (MIPs) and surface plasmon resonance (SPR) in a D-shaped multimode plastic optical fiber (POF), is presented by two cascaded SPR-POF-MIP sensors with different thicknesses of the gold layer. The low cost, the high selectivity and sensitivity of the SPR-POF-MIP platforms and the simple and modular scheme of the optical interrogation layout make this system a potentially suitable on-line multi-diagnostic tool. As a proof of principle, the possibility of simultaneous determination of two important analytes, dibenzyl disulfide (DBDS) and furfural (2-FAL), in power transformer oil was investigated. Their presence gives useful indication of underway corrosive or ageing processes in power transformers, respectively. Preliminarily, the dependence of the performance of the D-shaped optical platform on the gold film thickness has been studied, comparing two platforms with 30 nm and 60 nm thick gold layers. It has been found that the resonance wavelengths are different on platforms with gold layer of different thickness, furthermore when MIPs are present on the gold as receptors, the performances of the platforms are similar in the two considered sensors. Keywords: Cascaded multianalyte detection, Surface plasmon resonance, Dibenzyl disulfide, Furfural (furan-2-carbaldehyde), Molecularly imprinted polymers, Plastic optical fibers

We use as optical waveguide a green composite, based on bacterial cellulose (BC). More specifically, we have sputtered a thin gold film on this innovative slab waveguide for obtaining a Localized Surface Plasmon Resonance (LSPR) sensor. Experimental results confirm the possibility of using the BC based composite as an environmental friendly optical sensor platform with plasmonic capabilities, which could be exploited for realizing disposable biosensors. The new optical sensor has been used by combining it with optical fibers. The fibers connect the green disposable optical sensor with a light source and with a spectrometer. The device has been tested by measuring the refractive index of different water-glycerin solutions.

Two sensors for the detection of the metal ion Cu(II), based on the same sensing layer, are compared. They rely on different transduction methods, i.e., electrochemistry and surface plasmon resonance (SPR). D,L-penicillamine was used as the specific receptor since it is a strong ligand for copper(II). Moreover it is easily immobilized on a gold layer by a self assembling procedure by contacting the gold layer overnight with water/EtOH (80/20) containing D,L-penicillamine, taking advantage of the spontaneous interaction of thiols with gold surfaces. Both the electrochemical and SPR platforms were derivatized in the same way. In the first case a gold disc was used as working electrode, and in the second one a thin gold layer (60 nm thick) was deposited by sputtering over the exposed core of a plastic optical fiber (POF), after removing the cladding along half circumference.

The detection of perfluorobutanesulfonic acid (PFBS) in water is presented for the first time exploiting a low-cost optical chemical sensing strategy, based on plastic optical fibers and molecularly imprinted polymers (MIPs), able to detect pollutants in water. The sensor’s response measured in this work for the detection of PFBS is similar to the one obtained with Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), already investigated. The detection limit of PFBS is considered of interest when compared to those obtained by using different expensive traditional approaches, e.g. high performance liquid chromatography-mass spectrometry (HPLC-MS). Moreover, the use of this sensing approach is a very attractive perspective for fast, in situ, and remote low-cost detection of pollutants in water for smart cities applications.

In this study the influence of the surface roughness on the transmission capacities of D-shaped plastic optical fibers (POFs) and sensors performance was investigated. Five D-shaped POF sensors were produced and characterized for refractive index sensing between 1.33 and 1.41. The sensors were characterized using a low-cost optical sensing system based on the variation of the transmitted light though the POF with refractive index changes (RI). Higher surface roughness increases the scattering losses through the POF and influences the sensors&rsquo, performance, therefore, a balance must be attained. Generally, the best performance was achieved when the sensing region was polished with P600 sandpaper as a final polishing step. Polishing with sandpapers of lower grit size resulted in lower scattering, higher linearity of the sensor response and generally lower performance for RI sensing. A sensor resolution of 10&minus, 3&ndash, 10&minus, 4 RIU, dependent on the value of the external refractive index, was obtained through simple and low-cost manufacturing procedures. The obtained results show the importance of surface roughness in the development of POF sensors which can be used in several applications, such as for water quality assessment.

We have investigated, in a numerical and experimental way, a refractive index (RI) sensor based on surface plasmon resonance (SPR) in a silver-coated light-diffusing fiber (LDF). The experimental tests were conducted using water-glycerine mixtures with refractive indices ranging from 1.332 to 1.388. In the considered refractive index range, the experimental results show a sensitivity of the SPR wavelength to the outer medium’s RI ranging from 2600 to 4700 nm/RIU, which is larger than the sensitivity recently reported for a gold-coated LDF sensor (1200 to 4000nm/RIU). The silver-coated sensor is also shown to ensure a higher signal-to-noise ratio (SNR) compared to the gold-coated sensor.

In this work we want to compare performances of different plasmonic sensors, obtained by different polishing processes of D-shaped Plastic optical fibers (POFs). Three D-shaped POF plasmonic sensor configurations, obtained by three different polishing processes, have been created and experimentally tested. The proposed devices are based on the excitation of surface plasmons at the interface between the under test medium and a thin gold layer directly deposited on plastic fiber core (D-shaped area). The experimental results have shown that the performances are influenced by surface roughness variations in the D-shaped POF region.

As a proof of principle, we have developed a novel surface plasmon resonance (SPR) sensor used to monitor the interaction between a molecularly imprinted polymer (MIP) and a small molecule as the substrate. This plasmonic platform is based on a removable polymethyl methacrylate (PMMA) chip with a thin gold film on the top, two PMMA plastic optical fibers (POFs) and a special holder, designed to obtain the plasmonic phenomenon. We have experimentally tested whether the optical sensitivity is sufficient for monitoring an MIP receptor. The advantage of MIPs is that they can be directly deposited on a flat gold surface by a spin coater machine, without modifying the surface, as needed for the bio-receptors. With this new sensor, it is possible to achieve remote sensing capabilities, by POFs, and also to realize an engineered platform with a removable chip sensor.

An optical sensor for transformer oil monitoring is reported. It has been implemented in a plastic optical fiber which acts as optical platform for the sensing element, that is, a Molecular Imprinted Polymer layer, which is a robust, reproducible and low-price receptor for chemical marker in the insulating oil matrix. This optical sensor has been assessed on the detection of a chemical byproduct of transformers’ paper degradation, the furfuraldehyde (2-FAL). The optical sensor performances have been tested on used insulating oil samples spilled from ex-serviced instrument transformers and compared with results of standard methods applied to the same samples. The achieved good agreement emerging by comparative analysis confirms the ability of the optical sensor of detecting low 2-FAL contents directly in mineral oil, without any treatment or dilution of the oil.

A novel optical platform has been used to monitor the interaction between a molecularly imprinted polymer (MIP) and a small molecule. The new optical sensor is made of a polyethylene terephthalate substrate with a pattern of silver nanoparticles, printed on it by inkjet technology, and two plastic optical fibers (POFs). The POFs connect the optical sensor, later covered by the MIP layer, with a light source and with a spectrometer. The detection of furfural (furan-2-carbaldehyde, 2-FAL) in aqueous media was investigated exploiting a selective MIP receptor. The experimental results show that this novel approach presents a limit of detection of about 0.03 ppm, comparable to that of plasmonic sensors combined with the same MIP, but with the advantage of an easier preparation procedure.

The development of optical biosensors for the rapid and costless determination of clinical biomarkers is of paramount importance in medicine. Here we report a fast and low-cost biosensor based on a plasmonic D-shaped plastic optical fibre (POF) sensor derivatized with an aptamer specific for the recognition of thrombin, the target marker of blood homeostasis and coagulation cascade. In particular, we designed a functional interface based on a Self Assembled Monolayer (SAM) composed of short Poly Ethylene Glycol (PEG) chains and biotin-modified PEG thiol in ratio 8:2 mol:mol, these latter serving as baits for the binding of the aptamer through streptavidin-chemistry. The SAM was studied by X-ray Photoelectron Spectroscopy (XPS) analysis, static contact angle (CA), Surface Plasmon Resonance (SPR) in POFs, and fluorescence microscopy on gold surface. The optimized SAM composition enabled the immobilization of about 112 ng/cm2 of aptamer. The thrombin detection exploiting POF-Aptasensor occurred in short times (5–10 minutes), the reached Limit of Detection (LOD) was about 1 nM, and the detection range was 1.6–60 nM, indicating the POF-Aptasensor well addresses the needs for a low-cost, simple to use and to realize, rapid, small size and portable diagnostic platform.

Highly sensitive plasmonic optical fiber platforms combined with receptors have been recently used to obtain selective sensors. A low-cost configuration can be obtained exploiting a D-shaped plastic optical fiber covered with a multilayer sensing surface. The multilayer consists of a gold film, functionalized with a specific receptor, where the surface plasmon resonance (SPR) occurs. The signal is produced by the refractive index variation occurring as a consequence of the receptor-to analyte binding. In this work, a selective sensor for copper(II) detection in drinking water, exploiting a self-assembled monolayer (SAM) of d,l-penicillamine as the sensing layer, has been developed and tested. Different concentrations of copper(II) in NaCl 0.1 M solutions at different pH values and in a real matrix (drinking water) have been considered. The results show that the sensor is able to sense copper(II) at concentrations ranging from 4 &times, 10-6 M to 2 &times, 10-4 M. The use of this optical chemical sensor is a very attractive perspective for fast, in situ and low-cost detection of Cu(II) in drinking water for human health concerns. Furthermore, the possibility of remote control is feasible as well, because optical fibers are employed.

In several application fields, plasmonic sensor platforms combined with bio-receptors are intensively used to obtain biosensors. Most of these commercial devices are based on a disposable chip. Usually a gold chip, functionalized with a specific bio-receptor, inside a costly sensor system, is used. In this work, we propose a low-cost and small-size sensor system, used for monitoring a disposable plasmonic chip, based on an innovative optical waveguide made of bacterial cellulose (BC). In particular, we have sputtered gold on the green slab waveguide that is able to excite localized surface plasmon resonance (LSPR). Experimental results are presented on the capabilities of using the BC-based composite as an eco-friendly plasmonic sensor platform, which could be exploited for realizing disposable biosensors. The sensor has been used with optical fibers and simple equipment. More specifically, the fibers connect the green disposable LSPR sensor with a light source and with a spectrometer. The novel plasmonic sensing approach has been tested using two different optical waveguide configurations of BC, with and without ions inside BC.

In the present investigation a new intensity-based sensor platform for refractive index sensing is presented. It is based on a special holder, a slab waveguide and two Plastic optical fibers (POFs). In particular, we present a comparison between two different configurations: the slab waveguide with and without a buffer layer. Advantages of this new approach are the possibility of sensing with a removable chip, the easy production of an engineered platform and the use of a special holder, which is also suitable for thermo-stabilized flow cells implementation.

Authors present a very low-cost bio-sensing strategy, based on plastic optical fibers (POFs) and receptors, able to selective detection of substances in water solution. In this work several applications based on different kinds of receptors are reported, such as molecularly imprinted polymers (MIPs), chemical receptors (Deferoxamine and D,L-penicillamine) and bio-receptors (aptamers and antibodies). In particular, we have reported how, exploiting the same plasmonic platform in a D-shaped POF with these different kinds of receptors, interesting results have been achieved in medical diagnostics for cancer bio-markers detection, Celiac disease antigens monitoring, L-nicotine detection, and detection of Iron Fe(III) and copper Cu(II).

Optical chemosensors offer a decisive solution to monitor critical parameters in power transformers, as they can operate safely on electrical equipment. Surface Plasmon Resonance (SPR) is widely used as a detection principle for many sensors operating in different fields, such as bio and chemical sensing. Its use with optical fibers makes the remote SPR sensing straightforward and suitable for applications also in presence of high electromagnetic interferences, as in the case of power transformers. Additionally, a low-cost sensing device is achieved when an SPR chemical sensor is implemented in a plastic optical fiber (POF) in which an artificial receptor of chemical agents in different liquid environments is exploited. In this work, we report an overview on the main results about the feasibility of application of a developed SPR-POF sensor for the detection, in oil matrix, of two markers of the paper-oil insulating system degradation in oil-filled transformer.

A novel Molecularly Imprinted Polymer (MIP) able to bind perfluorinated compounds, combined with a surface plasmon resonance (SPR) optical fiber platform, is presented. The new MIP receptor has been deposited on a D-shaped plastic optical fiber (POF) covered with a photoresist buffer layer and a thin gold film. The experimental results have shown that the developed SPR-POF-MIP sensor makes it possible to selectively detect the above compounds. In this work, we present the results obtained with perfluorooctanoate (PFOA) compound, and they hold true when obtained with a perfluorinated alkylated substances (PFAs) mixture sample. The sensor&rsquo, s response is the same for PFOA, perfluorooctanesulfonate (PFOS) or PFA contaminants in the C4&ndash, C11 range. We have also tested a sensor based on a non-imprinted polymer (NIP) on the same SPR in a D-shaped POF platform. The limit of detection (LOD) of the developed chemical sensor was 0.13 ppb. It is similar to the one obtained by the configuration based on a specific antibody for PFOA/PFOS exploiting the same SPR-POF platform, already reported in literature. The advantage of an MIP receptor is that it presents a better stability out of the native environment, very good reproducibility, low cost and, furthermore, it can be directly deposited on the gold layer, without modifying the metal surface by functionalizing procedures.

The use of Nanostructured SPR sensors on Plastic Optical Fibers opens new challenges, because in an SPR sensor made by a continuous metal layer, the sensor’s response is basically related to the metal properties at optical frequencies and to the waveguide characteristics. On the other hand, when a Nanostructured SPR sensor is used, the behavior is also related to the geometric parameters of the Nanostructures. Working on them it is potentially possible to tune the sensor’s behavior. In this work the Authors present a numerical investigation in order to evaluate the behavior of two different SPR Nanostructured platforms, made by “long” gold Nanorods, and comparing them to an SPR sensor with a continuous gold layer. The difference between these two Nanostructured platforms is the orientation of the Nanorods, with respect to the light’s propagation direction. The numerical results seem to indicate an increase of the sensitivity, when an SPR Sensor with long Nanorods is used, with respect to the sensor made by a continuous gold film, with some benefits.

A simple approach to low-cost plasmonic sensing is obtained exploiting Plastic Optical Fibers (POFs). POFs are especially advantageous for their properties and, when receptors are used for bio/chemicals detection, are suitable for different application fields.

This paper reports preliminary results of vibration test carried out on an optical voltage sensor prototype, specially designed for monitoring Voltage parameters in Medium Voltage switchboards. These electrical components, on service, are naturally subjected to environmental noise like mechanical vibrations. Tests were carried out in a laboratory mock up, to critically assess the response of the optical sensor to an applied AC voltage in presence of vibrations. The measured good rejection to vibrations either of the sensor body and of the connecting optical fiber cable, confirmed the suitability of the exploited optical solution for next applications in Medium Voltage substation.

A new approach for the selective detection of the Perfluorinated compounds in water is presented. The low-cost sensor system is based on a Molecular Imprinted Polymer deposited on a D-shaped Plastic Optical Fiber platform.