Machine learning unveils surface refractive index dynamics in comb-like plasmonic optical fiber biosensors

peer reviewedThe precise measurement of surface refractive index changes is crucial in biosensing, providing insights into bioreceptors–analytes interactions. However, correlating intricate spectral features, with these refractive index variations remains a persistent challenge, particularly in optical fiber gratings-based Surface Plasmon Resonance sensing. Here, we introduce a machine learning-based approach to address this ongoing issue. We integrate a regression model with gold-coated tilted fiber Bragg grating sensors. This enhances signal stability and precision, enabling a correlation between spectral shifts and refractive index changes. Our approach eliminates the need for individual sensor calibration, thereby bolstering the effectiveness and efficiency of the sensing layer. We demonstrate the model’s versatility by showcasing its efficacy across two data acquisition systems with different resolutions, allowing for comparative analysis and robustness enhancement. Its application in a biosensing experiment for insulin functionalization and detection, demonstrates how this breakthrough approach marks an advancement in real-time refractive index monitoring

Performance théorique d'un neurone à spikes Integrate-and-Fire

International audienceThis paper focuses on the theoretical performance of a neuro-inspired digital communication, where the input signal is below the activation threshold of the neuron, making the noise crucial for the detection. We first derive the error probability of a neuro-inspired detector build upon a single Integrate-and-Fire (IF) neuron and then extend this result to a IF-based detector build upon multiple neurons. In this case, we propose to optimize the number of neurons in parallel, leading to an error probability below 10 −4 for a large noise range, proving the strength of such an IF-based detector.Ce papier se concentre sur les performances théoriques d'un détecteur neuro-inspiré pour une communication numérique où le signal d'entrée est inférieur au seuil d'activation du neurone, rendant le bruit crucial pour la détection. Nous caractérisons dans un premier temps la probabilité d'erreur d'un tel détecteur basé sur un neurone Integrate-and-Fire (IF), puis étendons ce résultat à un détecteur utilisant plusieurs neurones IF en parallèle. Dans ce cas, nous proposons d'optimiser le nombre de neurones en parallèle, permettant d'atteindre une probabilité d'erreur inférieure à 10 −4 pour une large plage de bruit, prouvant ainsi la puissance d'un tel détecteur IF

Partially gold-coated tilted FBGs for enhanced surface biosensing.

peer reviewedTo date, there is clear experimental evidence that gold-coated tilted fiber Bragg gratings (TFBGs) are highly sensitive plasmonic biosensors that provide temperature-compensated detection of analytes at concentrations in the picomolar range. As most optical biosensors, they bring an evanescent wave in the surrounding medium, which makes them sensitive to both surface refractive index variations (= the useful biosensing signal) and to bulk refractive index changes (= the non-useful signal for biosensing). This dual sensitivity makes them prone to drift. In this work, we study partially gold-coated TFBGs around their cross-section. These gratings present the ability to discriminate both volume and surface refractive index changes, which is interesting in biosensing to enhance the signal-to-noise ratio. The effects induced in the TFBGs transmitted amplitude spectra were analyzed for surrounding refractive index (SRI) changes in the range 1.3360-1.3370. Then, the gold film was biofunctionalized with human epidermal growth factor receptor (HER2) aptamers using thiol chemistry. The detection of HER2 proteins (a relevant cancer biomarker) at 10-9 g/mL, 10-8 g/mL and 10-6 g/mL demonstrated the advantage to identify environmental perturbations through the bare area of the TFBGs, which is left not functionalized. The non-specific drifts that could exist in samples are eliminated and a wavelength shift only related to the surface modification is obtained

Phase interrogation of plasmonic tilted fiber Bragg grating biosensors through the Jones formalism

peer reviewedGold-coated tilted fiber Bragg gratings (TFBG) are refined plasmonic biosensors, highly sensitive to surrounding refractive index (RI) changes. Their interrogation usually relies on insertion loss measurements for single input polarized light, limiting the set of exploitable features. To overcome this limitation, we trigger the Jones formalism to retrieve the polarization enabling optimized plasmonic excitation for both phase and amplitude measurements. We present an experimental phase shift with a sensitivity as high as 45835°/RIU and further assess this approach to HER2 proteins sensing at 1µg/ml. We compare this angular modality with the one relying on the insertion loss using a quality factor that takes the shift as well as the dispersion into account. This strengthens its relevance in terms of precision for ultra-small RI variations

Optical Fiber Gratings Immunoassays

peer reviewedOptical fibers are of growing interest for biosensing, especially for point-of-care and biomedical assays. Their intrinsic properties bestow them sought-after assets for the detection of low concentrations of analytes. Tilted fiber Bragg gratings (TFBGs) photo-inscribed in the core of telecommunication-grade optical fibers are known to be highly-sensitive refractometers. In this work, we present different strategies to use them for label-free immunoassays. Bare, gold-sputtered, gold-electroless-plated (ELP) and hybrid configurations are biofunctionalized with antibodies, aiming at the detection of cancer biomarkers. We discuss the relative performances of the tested configurations and show that each leads to singular key features, which therefore drives their selection as a function of the target application. The most sensitive configuration presents a limit of detection of 10-12 g/mL in laboratory settings and was successfully used ex vivo in freshly resected lung tissues

Towards sensitive and precise plasmonic fiber biosensors through phase analysis

A gold-coated tilted fiber Bragg grating (TFBG) can detect the surrounding refractive index (SRI) change by surface plasmon resonance (SPR) shift following a similar principle as in commercial devices based on the Kretschmann prism. Although information from optical fiber sensors only rely on spectral characteristics. Using phase analysis, we are able to detect HER2 protein (an oncogene overexpressed in breast cancer cells) at 1 μg/mL

Plasmonic Optical Fiber-Grating Immunosensing: A Review

peer reviewedPlasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis

Evaluation of gold layer configuration for plasmonic fiber grating biosensors

peer reviewedGold-coated fiber Bragg gratings (FBGs) are nowadays a mature technology for lab-on-fiber sensing based on surface plasmon resonance (SPR) excitation. Tilted FBGs bring valuable assets such as easy light injection, remote operation in very small volumes of analytes and immunity to temperature fluctuations. Different gold configurations have been reported to date, without considering their relative performances in terms of biochemical sensing. In this work, we experimentally study the impact of the gold coating on the cladding mode distribution in the tilted FBG amplitude spectrum and subsequently on its sensitivity to cytokeratins used as biomarkers for cancer diagnosis. Some relevant configurations of gold coatings are produced and tested, relying on both the sputtering and electroless plating (ELP)processes. The obtained results confirm that the coating thickness and its roughness drive the biosensing performances. The experimental limit of detection for cytokeratins 17 sensing reaches 14 fM for the most sensitive configurations

Mode-division and spatial-division optical fiber sensors

peer reviewedThe aim of this paper is to provide a comprehensive review of mode-division and spatial-division optical fiber sensors, mainly encompassing interferometers and advanced fiber gratings. Compared with their single-mode counterparts, which have a very mature field with many highly successful commercial applications, multimodal configurations have developed more recently with advances in fiber device fabrication and novel mode control devices. Multimodal fiber sensors considerably widen the range of possible sensing modalities and provide opportunities for increased accuracy and performance in conventional fiber sensing applications. Recent progress in these areas is attested by sharp increases in the number of publications and a rise in technology readiness level. In this paper, we first review the fundamental operating principles of such multimodal optical fiber sensors. We then report on the theoretical formalism and simulation procedures that allow for the prediction of the spectral changes and sensing response of these sensors. Finally, we discuss some recent cutting-edge applications, mainly in the physical and (bio)chemical fields. This paper provides both a step-by-step guide relevant for non-specialists entering in the field and a comprehensive review of advanced techniques for more skilled practitioners