Publications

Abstract Optical fibers have been extensively applied in optical sensing platforms for their large bandwidth, stability, light weight and accessibility. This work presents a theoretical analysis of an optical fiber surface plasmon resonance system for refractometric sensing applications. The device consists of a multilayer hyperbolic metamaterial (HMM) composed of concentric Au/TiO2 alternate layers in optical fiber matrix. HMMs exhibit hyperbolic dispersion (HD) and the interaction of different plasmonic modes at each interface of the HMM is reported to enhance light-matter coupling, leading to an increased refractometric sensitivity. The HD and its effects on sensor performance are numerically investigated by effective medium theory (EMT) and backed by the exact transfer matrix method (TMM). The maximum sensor performance was attained for a configuration with 2 bilayers with 30 nm thickness for a metal fill fraction (rho) of 0.7, achieving a figure of merit (FOM) of 18.45. A direct comparison with a plasmonic Au optical fiber sensor returned an optimized FOM of 5.74, therefore achieving over a three-fold increase in sensor performance, assessing the potential of HMM as highly refractometric sensitive platforms.

Abstract Hydrogen (H-2) infrastructure is the focus of many initiatives for the planned energetic transition, but its volatility and flammability require extensive safety measures to prevent leakages and explosions. Magnesium thin films have been investigated not only for H-2 storage but also as switchable mirrors, which drastically change their optical properties when hydrogenated. Due to their lower cost compared to other hydride-forming or plasmonic metals commonly used in optical sensing, Mg-based H-2 fiber sensors have the potential to be both affordable and effective for scalable deployment in industrial settings. To this end, multilayer thin-film structures with Mg and palladium as adsorption catalyst were deposited on single-mode fiber tips, and H-2 loading/unloading processes were tested in a controlled flow gas setup. In parallel, an optical interrogation system prototype was developed, enabling fast data acquisition of fiber-tip reflectivity across multiple sensing probes at a wavelength of 1550 nm. Preliminary testing suggests fast response times of a few seconds for significant drops in reflectivity, facilitating straightforward detection of H-2 leaks using thresholding methods. Planned future work includes performance comparison with simpler sensing structures, durability and contaminant testing, and response time optimization.

Abstract Hyperbolic Metamaterials (HMM) are a class of photonic metamaterials exhibiting hyperbolic dispersion due to strong anisotropy. This work presents a numerical analysis and experimental characterization of a hyperbolic multilayer structure supporting surface plasmon polaritons for refractometric sensing applications. The device consists of a multilayer HMM composed of alternate Au and TiO2 layers, and the interaction of different plasmonic modes at each interface of the HMM is reported to enhance light- matter coupling, leading to an increased refractometric sensitivity. The hyperbolic dispersion and its effects on sensor performance are numerically investigated using the Effective Medium Theory (EMT) and validated through the Transfer Matrix Method (TMM). A fair match was obtained between EMT and TMM simulated spectra, validating the EMT approach for simulation of the optical properties of multilayer HMMs. Despite not predicting figures of merit (FOM) accurately, both the TMM and EMT approaches closely replicated the obtained experimental refractometric sensitivity.

Abstract Concrete structures require precise temperature and humidity monitoring during curing to ensure optimal strength and prevent defects like cracking. A compact optical sensing system was developed using a single fiber that can be embedded directly within the concrete. The system functions as both a temperature and humidity sensor when paired with a spectral interrogation unit operating in the 1500-1600 nm range. Temperature monitoring is achieved through a Fiber Bragg Grating, while humidity sensing is facilitated by a Fabry-Perot interferometer at the fiber tip. The interferometer cavity is formed with a layer of polyvinylpyrrolidone (PVP). Initial air humidity sensor tests showed a significant change in the interference period with RH, demonstrating low hysteresis and high reproducibility. Calibration of one sensor revealed an approximately 3 nm period decrease when RH increased from 55% to 95%, with results suggesting a quadratic relationship between the interference period and RH values.

Abstract This study investigates the fabrication of plasmonic optical fiber sensors for glyphosate detection, employing silver thin film coatings deposited via the Tollens' reaction and further enhanced with protective gold plating. Silver films were produced through electroless deposition, forming rough plasmonic surfaces with localized hotspots that amplify the electromagnetic field. Surface roughness effects on the creation of hotspots were first evaluated numerically using the finite element method (FEM) and later experimentally assessed the impact on optical response. Furthermore, to address the inherent susceptibility of silver to oxidation and corrosion, a gold plating was applied using the Kirkendall effect, selectively replacing surface silver atoms with gold. This approach significantly improved the chemical stability of the sensors while preserving their plasmonic properties. This configuration was applied in developing a biosensor, using aptamers, for detecting glyphosate in concentrations ranging from 10(-1) to 10(4) mu g/L. The results demonstrated a sensitivity of 25.08 +/- 0.22 nm/(mu g/L) and a limit of detection (LOD) of 0.04 mu g/L, nearly ten times lower than the European Union's safety limit for glyphosate. Experimental results highlight the potential of this fabrication approach for developing sensitive, stable, and scalable plasmonic sensors tailored for environmental and agricultural monitoring applications.

Abstract Reinforced concrete structures form the backbone of civil infrastructure due to their durability, longevity, affordability, and availability. However, aging concrete poses challenges, with decay often beginning internally and becoming visible only at advanced stages, leading to costly repairs, restricted functionality, and safety risks. To address these challenges, sensors are crucial for enhancing infrastructure resilience and optimizing repairs. This study employs multimode optical fibers to monitor concrete curing, water ingress, relative humidity (RH), cement paste carbonation, and rebar corrosion. Four sensors monitor changes in reflection at the fiber tip of a 600 mu m multimode fiber (MMF) using LEDs and photodiodes, connected via a fiber bundle containing two 200 mu m MMF. Variations in the refractive index around the fiber tip are used to monitor water throughout the concrete lifecycle, including curing, RH changes and water intrusion. Colorimetric changes in a cement paste layer and an iron-thin film are used to monitor carbonation and corrosion. The curing sensor is temperature-independent and correlates strongly with cumulative heat release from cement hydration (R=0.95). The RH sensor monitors up to and beyond 100% RH, detecting water intrusion. The corrosion sensor detects early corrosion stages and distinguishes between reflection losses from corrosion and mechanical changes. The layer of cement paste for carbonation monitoring increases reflected intensity by 17% due to carbonation, with 63% of the increase occurring in 80 minutes in a 3% CO2 atmosphere. The broad monitoring scope and low implementation cost make this sensor a unique option among commercially available solutions for structural health monitoring of reinforced concrete.

Abstract The phase-matching conditions for exciting surface plasmon resonances (SPR) in plasmonic films are typically satisfied via prism, optical fibers or grating-assisted coupling. We recently showed that plasmonic nanospheres can act as local emitters, exciting SPR waves on thin films-termed nanoparticle-induced SPR (NPI-SPR). This structure holds promise for sensing, but the effects of optical fiber geometry and nanoparticle anisotropy on the response were unexplored. This study examines these factors, showing that an etched multimode fiber with a 200 mu m core diameter, taper ratio of 4, and etching angle of 20 degrees optimizes interaction with plasmonic nanoparticles. Tuning the nanoparticle aspect ratio from 1 to 3 shifts the NPI-SPR band from 780 to 1580 nm, with excitation highly dependent on the incident light angle. Notably, for light incident parallel to the film plane, a refractive index sensitivity exceeding 1000 nm/RIU is achieved. This efficient light emission combines the field locality enhancements of plasmonic nanoparticle-on-film structures with the emission efficiency of plasmonic nanoantennas, advancing plasmonic optical fiber chemical and biosensors.

Abstract Biosurfactants/bioemulsifiers (BSs/BEs) can be defined as surface-active biomolecules produced by microorganisms with a broad range of applications. In recent years, due to their unique properties like biodegradability, specificity, low toxicity, and relative ease of preparation, these biomolecules have attracted wide interest as an eco-friendly alternative for several industrial sectors, escalating global microbial BS/BE market growth. Recently, Gordonia alkanivorans strain 1B, a bacterium with significant biotechnological potential, well known for its biodesulfurizing properties, carotenoid production, and broad catabolic range, was described as a BS/BE producer. This study focuses on the characterization of the properties of the lipoglycopeptide BSs/BEs produced by strain 1B, henceforth referred to as gordofactin, to better understand its potential and future applications. Strain 1B was cultivated in a chemostat using fructose as a carbon source to stimulate gordofactin production, and different purification methods were tested. The most purified sample, designated as extracted gordofactin, after lyophilization, presented a specific emulsifying activity of 9.5 U/mg and a critical micelle concentration of 13.5 mg/L. FT-IR analysis revealed the presence of basic hydroxyl, carboxyl, ether, amine/amide functional groups, and alkyl aliphatic chains, which is consistent with its lipoglycopeptide nature (60% lipids, 19.6% carbohydrates, and 9% proteins). Gordofactin displayed remarkable stability and retained emulsifying activity across a broad range of temperatures (30 degrees C to 80 degrees C) and pH (pH 3-12). Moreover, a significant tolerance of gordofactin emulsifying activity (EA) to a wide range of NaCl concentrations (1 to 100 g/L) was demonstrated. Although with a great loss of EA in the presence of NaCl concentrations above 2.5%, gordofactin could still tolerate up to 100 g/L NaCl, maintaining about 16% of its initial EA for up to 7 days. Furthermore, gordofactin exhibited growth inhibition against both Gram-positive and Gram-negative bacteria, and it demonstrated concentration-dependent free radical scavenging activity for 2,2-diphenyl-1-picrylhydrazyl (IC50 approximate to 1471 mg/L). These promising features emphasize the robustness and potential of gordofactin as an eco-friendly BS/BE alternative to conventional surfactants/emulsifiers for different industrial applications.

Abstract Polypore mushrooms have been widely recognized for centuries for their use in food and medicine due to their strong capacity to produce numerous biomolecules with beneficial effects on human health. Fomes fomentarius is one such species that remains poorly explored, particularly when growing in Morocco. Herein, this study aimed to characterize the bioactive compounds of F. fomentarius and evaluate its pharmacological properties. Spectrophotometric analysis showed that F. fomentarius revealed high levels of total phenolics (75.83 mg GAE/g dme) and flavonoids (37.62 mg CE/g dme). Gas chromatography-mass spectrometry (GC-MS) analysis identified 109 volatile and non-volatile compounds, primarily sugars (24), fatty acids (23), alcohols (10), organic acids (9), and terpenoids (6). In addition, liquid chromatography-mass spectrometry (LC-MS) analysis allowed the identification of 24 phenolic compounds, with isorhamnetin (2734.00 mu g/g), p-hydroxybenzoic acid (409.00 mu g/g), and kaempferol (351.10 mu g/g) as the most abundant. Regarding pharmacological properties, F. fomentarius extract demonstrated strong antioxidant activity, with the DPPH radical-scavenging assay showing the highest potency, followed by beta-carotene bleaching inhibition and ferric ion-reducing power, with EC50 (half maximal effective concentration) values of 114.40, 174.50, and 250.70 mu g/mL, respectively. Additionally, it exhibited broad-spectrum antimicrobial activity against all seven human pathogenic microorganisms, with Epidermophyton floccosum being the most susceptible ((minimum inhibitory concentration (MIC)) = 2 mg/mL and minimal fungicidal concentration (MFC) = 4 mg/mL) and A. fumigatus the most resistant (MIC = 26.67 mg/mL and MFC >= 64 mg/mL). Overall, the result indicated that Moroccan F. fomentarius is a rich source of diverse bioactive compounds with potent antioxidant and antimicrobial activities, supporting its potential for various applications.

Abstract The multifaceted nature of the neurodegenerative diseases, as Alzheimer's disease (AD) and Parkinson's disease (PD) with several interconnected etiologies, and the absence of effective drugs, led herein to the development and study of a series of multi-target directed ligands (MTDLs). The developed RIV-IND hybrids, derived from the conjugation of an approved anti-AD drug, rivastigmine (RIV), with melatonin analogues, namely indole (IND) derivatives, revealed multifunctional properties, by associating the cholinesterase inhibition of the RIV drug with antioxidant activity, biometal (Cu(II), Zn(II), Fe(III)) chelation properties, inhibition of amyloid-/3 (A/3) aggregation (self- and Cu-induced) and of monoamine oxidases (MAOs), as well as neuroprotection capacity in cell models of AD and PD. In particular, two hybrids with hydroxyl-substituted indoles ( 5a2 and 5a3) ) could be promising multifunctional compounds that inspire further development of novel anti-neurodegenerative drugs.