Photopolymerisable glasses are holographic recording materials which provide good recording capability, improved dimensional stability, and negligible shrinkage. Recently, a novel photopolymerisable hybrid sol-gel (PHSG) for holographic recording of volume gratings has been reported. The PHSG has significantly improved gelation time and high water resistance, both of which make it an attractive material for mass production of holographic optical elements (HOEs) with no sensitivity to ambient humidity. In order to achieve full control over the performance of the material and further improve its properties, a study of grating formation under holographic patterning is essential. This paper reports characterisation of the grating recording in PHSG. The approach is based on the analysis of grating parameters during exposure and post-recording dark processes. The obtained results suggest that photopolymerisation of the methacrylate groups is the main contributor to the creation of refractive index modulation during exposure. During the dark process, the enhancement of the refractive index modulation is observed, probably due to further polycondensation. The observations made facilitate controlled and predictable diffraction efficiency of gratings recorded on the PHSG, thereby furthering the prospect of the development of HOEs with customisable specification.

This paper focuses on characterization of the sensing performance of a refractometric sensing platform based on multimode interference couplers (MMICs). Platform fabrication exploited a low-cost process using photocurable organic-inorganic hybrid sol-gel materials which were structured to form optical waveguides by direct UV laser writing. The sensing principle is based upon the high sensitivity of the optical field distribution formed in the MMIC toward changes in the refractive index of its environment. Simulations demonstrated the importance of correctly specifying the length of the MMIC section and illustrated that longer platforms are more sensitive due to a greater shift in self-image position. To characterize sensing performance, a porous sol-gel humidity sensing enrichment layer was coated on the MMIC. Relative humidity was detected by the system with a resolution of 0.097%. Refractive index resolution of the platform was determined to be ~ 2 × 10 ^-6 RIU , which is an analyte-independent value and illustrates the generic nature of this platform. As such, this platform has immense potential for future applications as a label-free and real-time biosensor platform.

This work outlines, for the first time, the fabrication of a whole hybrid sol-gel optofluidic platform by integrating a microfluidic biosensor platform with optical waveguides employing a standard photolithography process. To demonstrate the suitability of this new hybrid sol-gel optofluidic platform, optical and bio-sensing proof-of-concepts are proposed. A photoreactive hybrid sol-gel material composed of a photopolymerisable organically modified silicon alkoxide and a transition metal complex was prepared and used as the fabrication material for the entire optofluidic platform, including the optical waveguides, the sensing areas, and the microfluidic device. The most suitable sol-gel materials chosen for the fabrication of the cladding and core of the waveguides showed a RIC of 3.5 × 10⁻³ and gave thicknesses between 5.5 and 7 μm. The material was optimised to simultaneously meet the photoreactive properties required for the photolithography fabrication process and the optical properties needed for the effective optical operability of the microstructured waveguides at 532 and 633 nm with an integrated microfluidic device. The optical proof-of-concept was performed using a fluorescent dye (Atto 633) and recording its optical responses while irradiated with a suitable optical excitation. The biosensing capability of the platform was assessed using a polyclonal primary IgG mouse antibody and a fluorescent labelled secondary IgG anti-mouse antibody. A limit of detection (LOD) of 50 ug/mL was achieved. A correlation between the concentration of the dye and the emission fluorescence was evidenced, thus clearly demonstrating the feasibility of the proposed hybrid sol-gel optofluidic platform concept. The successful integration and operability of optical and microfluidic components in the same optofluidic platform is a novel concept, particularly where the sol-gel fabrication material is concerned.

This study centers on the development and characterization of an innovative electrochemical sensing probe composed of a sensing mesoporous functional sol–gel coating integrated onto a glassy carbon electrode (sol–gel/GCE) for the detection of NH₃ and/or NH₄⁺ in water. The main interest for integrating a functional sol–gel coating onto a GCE is to increase the selective and sensing properties of the GCE probe towards NH₃ and/or NH₄⁺ ions. The structure and surface morphology of the newly developed sol–gel/GCE probe were characterized employing scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and Fourier-transform infrared (FTIR), while the electrochemical sensing properties were evaluated by Berthelot’s reaction, cyclic voltammetry (CV), and adsorptive square wave–anodic striping voltammetry (Ads SW–ASV). It is shown that the newly developed sol–gel coating is homogeneously deposited on the GCE with a sub-micron and uniform thickness close to 630 nm and a surface roughness of 25 nm. The sensing testing of the sol–gel/GCE probe showed limits of detection and limits of quantitation of 1.7 and 5.56 nM of NH₄⁺, respectively, as well as a probe sensitivity of 5.74 × 10⁻¹ μA/μM cm⁻². The developed probe was fruitfully validated for the selective detection of NH₃/NH₄⁺ in fresh and sea water samples. Computed Student t_exp (0.45–1.25) and F_exp (1.69–1.78) (n = 5) tests were less than the theoretical t_tab (2.78) and F_tab (6.39) at 95% probability.

Simulations and experimental results for novel refractometric-sensing platforms are presented here. The first platform is based on a multi-mode interference coupler (MMIC) in which the top and sidewalls of the coupler are exposed to a humidity-sensing enrichment layer. Sensor operation is based on the creation of self-images of the input field into the coupler, at regular intervals along the coupler. This phenomenon is due to interference between the optical modes in MMICs. Changes in the refractive index of the sensing layer cause predictable shifts in the position of the output image, which in turn affects the amount of light coupled into the output waveguide. Sensitivity enhancement has been demonstrated by fabricating longer MMICs capturing higher-ranking self-images, which are shifted more than the first self-image. Consequently, more significant changes in the amount of light coupled to the output are observed for a given refractive index change. The second platform demonstrated is a Multi-Channel Directional Coupler sensor (MCDC). It differs from the MMIC in that the sensing region now consists of multiple single-mode waveguides, which are in close enough proximity to allow light to transfer between the waveguides. Sensitivity dependance on platform length has been investigated and compared with that of the MMIC. The devices have been fabricated by the direct laser writing process on UV curable hybrid sol-gel materials. Such materials allow implementation of planar technology enabling integration on a silicon substrate. Future applications of these platforms include chemical and bio-chemical sensing is the areas of process, environmental and bio-diagnostic monitoring.