This work describes the design and fabrication of a novel multianalyte biosensor platform for medical diagnostic applications. The sensor platform consists of a photonic waveguide-based optical circuit used to deliver excitation light to multiple sensor windows on the platform. The platform is fabricated by UV-photopatterning of photocurable hybrid organic-inorganic sol-gel materials. The sensing mechanism is based upon the detection of fluorescently labelled antibodies, in order to determine the concentration of specific analytes in a test solution. Fluorescence is excited by means of the evanescent wave in each sensor window. It is shown that the sensing properties of the platform can be dramatically enhanced by increasing the intensity of the evanescent field of the light propagating in the optical waveguide by a precise design of a high refractive index layer deposited at the waveguide surface. This work proved the concept of employing a waveguide-based photonic platform for the detection of fluorescently labelled antibodies, with mu g/ml detection levels, and as such, we believe this system has immense potential for future applications as a medical diagnostic platform. (C) 2015 Elsevier B.V. All rights reserved.

This paper focuses on the development and characterization of a waveguide-based photonic sensing platform for the detection of biofilm. This integrated photonic platform is based upon the high sensitivity of an optical field distribution formed in optical waveguides and the resulting changes in the refractive index and absorption of this environment.The sensor platform and materials formulations were established from simulation studies conducted with the Olympios software. These simulations demonstrated the importance of correctly specifying the material refractive index to achieve single-mode waveguides. They also highlighted the necessity to deposit a high refractive index layer (HRIL) on top of the optical waveguides in order to increase the intensity of the evanescent field responsible for the sensing performance of the platform.Platform fabrication exploited a low-cost process using photocurable organic-inorganic hybrid sol-gel materials, which were microstructured by UV-photolithography to form channel optical waveguides. A tantalum-based material was synthesized using the sol-gel process with refractive index as high as 1.87. This material was developed, optically characterized and applied as an evanescent field enhancement layer, deposited at the surface of the waveguide to increase the sensitivity of the sensing platform.The sensor characterization was performed by monitoring the output intensity of the optical waveguide while contaminated water was monitored in a quasi-static flow-rate (0.5 ml/s) on the platform. It is shown that our biosensor platform was able to detect the biofilm formation after 10 min of reactions, demonstrating the early stage biofilm formation in quasi-static flow-rate. Furthermore, the sensing performances of our photonic platform were found to be strongly dependent on the thickness of the HRIL, confirming the simulations studies.This work proved the concept of employing a waveguide-based photonic platform for the early detection of biofilm formation, including the induction phase, and as such, we believe this system has immense potential for future applications as a label-free and real-time biosensor platform. (c) 2012 Elsevier B.V. All rights reserved.

This work reports for the first time the development of enhanced-conductivity, graphene-doped photo-patternable hybrid organic-inorganic ionogels and the effect of the subsequent materials condensation on the conductivity and mechanical stability of three-dimensional microstructures fabricated by multi-photon polymerisation (MPP). Ionogels were based on photocurable silicon/zirconium hybrid sol–gel materials and phosphonium (trihexyltetradecylphosphonium dicyanamide) [P6,6,6,14][DCA] ionic liquid (IL). To optimise the dispersion of graphene within the ionogel matrices, aqueous solutions of graphene were prepared, as opposed to the conventional graphene powder approach, and employed as catalysts of hydrolysis and condensation reactions occurring in the sol–gel process. Ionogels were prepared via a two step process by varying the hydrolysis degree from 25 to 50%, IL content between 0–50 w/w%, and the inorganic modifier (zirconate complex) concentration from 30 to 60 mol.% against the photocurable ormosil and they were characterised via Raman, Electrochemical Impedance Spectroscopy and Transmission Electron Microscopy. MPP was performed on the hybrid ionogels, resulting in three-dimensional microstructures that were characterised using scanning electron microscopy. It is clearly demonstrated that the molecular formulation of the ionogels, including the concentration of graphene and the zirconate network modifier, plays a critical role in the conductivity of the ionogels and influences the resulting mechanical stability of the fabricated three-dimensional microstructures. This work aims to establish for the first time the relationship between the molecular design and condensation of materials in the physico-chemistry and dynamic of ionogels.

This study reports on the first development of high refractive index thin film materials processed at temperatures not greater than 100 degrees C. Three materials were synthesised by the sol-gel technique, each employing different transition metal precursors (niobium, tantalum and vanadium alkoxides). The optical properties of these materials were characterised by ellipsometry and the propagation losses at 638 nm were measured by the prism coupling method. It is shown that refractive indices as high as 1.870, 2.039 and 2.308 are obtained from niobium-, tantalum- and vanadium-based materials respectively, attributed to the influence of the transition metal atomic size on the condensation reactions. (C) 2012 Elsevier B.V. All rights reserved.

This work describes the development of photopatternable ionogels based on a hybrid organic/inorganic sol–gel material and both phosphonium (trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][dca], trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)-amide [P6,6,6,14][NTf2]) and imidazolium (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [emIm][FAP]) room temperature ionic liquids (RTILs). Ionogels were prepared via a two step process with the RTIL content varied between 40 and 80 w/w%, and characterised via Raman and Electrochemical Impedance Spectroscopy. 1 and 2 photon polymerisation was performed on the hybrid ionogels using photolithography, resulting in three dimensional structures that were characterised using scanning electron microscopy. Electrochromic ionogels were prepared by addition of ethyl viologen dibromide (EV) to an ionogel containing [emIm][FAP] and hybrid sol–gel material. This composition was photo-polymerised on ITO electrodes by UV irradiation and subsequentially characterised viaUV/Vis spectroelectrochemistry. It was also possible to fabricate a solid state electrochromic device based on EV and switch between the colourless (oxidised) and blue (reduced) forms using a perturbation signal of 1 V.

We describe the synthesis of optical quality thin film materials with high refractive index, employing zirconium based hybrid sol-gel precursors. As the zirconium propoxide precursor is unstable in the presence of a strong nucleophilic agent such as water, two synthesis routes have been performed employing a chelating agent and an organosilane precursor to avoid the formation of any undesired ZrO2 agglomerates, leading to organo-zirconate complexes and silicato-zirconate copolymers, respectively. The prepared hybrid sol-gel materials were deposited by spin-coating to form a transparent thin film on silicon substrates, and heat treated at 100 °C for the final stabilisation of the layer. The effect of the two synthesis routes on the optical properties of zirconium based hybrid sol-gel material is discussed. It was found that the nature and concentration of the organosilane precursor can significantly affect the structural properties of the deposited films. A correlation was also demonstrated between the concentration of the organosilane precursor and the refractive index of the material. By reducing the concentration of organosilane precursor, high refractive index materials were obtained. Similar behaviour was observed for the materials synthesised via chelating agent. The synthesis employing an organosilane precursor produces films with higher refractive index. A maximum refractive index of 1.746 was measured at 635nm for the deposited thin films.

In this work, we report the fabrication of single-mode Nb2O5 based hybrid sol–gel channel waveguides. Nb2O5 based hybrid sol–gel material has been deposited by spin-coating on silicon substrate and channel waveguides have been fabricated by a UV direct laser writing process. Optical guided modes have been observed to confirm single-mode conditions and optical propagation loss measurements have been performed using the cut-back technique. Optical propagation losses were measured to be 0.8dB/cm and 2.4dB/cm at 1.31μm and 1.55μm respectively. These experimental results demonstrate low loss optical waveguiding within the infrared range and are very promising in view of material choice for the development of integrated optical devices for telecommunication.

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 similar to 2 x 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 article reports on a detailed investigation of sol–gel processed hybrid organic–inorganic materials for use in lab-on-a-chip (LoC) applications. A particular focus on this research was the implementation of integrated microfluidic circuitry in waveguide-based photonic sensing platforms. This objective is not possible using other fabrication technologies that are typically used for microfluidic platforms. Significant results on the surface characterisation of hybrid sol–gel processed materials have been obtained which highlight the ability to tune the hydrophilicity of the materials by careful adjustment of material constituents and processing conditions. A proof-of-principle microfluidic platform was designed and a fabrication process was established which addressed requirements for refractive index tuning (essential for waveguiding), bonding of a transparent cover layer to the device, optimized sol–gel deposition process, and a photolithography process to form the microchannels. Characterisation of fluid flow in the resulting microchannels revealed volumetric flow rates between 0.012 and 0.018 μl/min which is characteristic of capillary-driven fluid flow. As proof of the integration of optical and microfluidic functionality, a microchannel was fabricated crossing an optical waveguide which demonstrated that the presence of optical waveguides does not significantly disrupt capillary-driven fluid flow. These results represent the first comprehensive evaluation of photocurable hybrid sol–gel materials for use in waveguide-based photonic platforms for lab-on-a-chip applications.

This work describes the development of photopatternable ionogels based on a hybrid organic/inorganic sol–gel material and both phosphonium (trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][dca], trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)-amide [P6,6,6,14][NTf2]) and imidazolium (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [emIm][FAP]) room temperature ionic liquids (RTILs). Ionogels were prepared via a two step process with the RTIL content varied between 40 and 80 w/w%, and characterised via Raman and Electrochemical Impedance Spectroscopy. 1 and 2 photon polymerisation was performed on the hybrid ionogels using photolithography, resulting in three dimensional structures that were characterised using scanning electron microscopy. Electrochromic ionogels were prepared by addition of ethyl viologen dibromide (EV) to an ionogel containing [emIm][FAP] and hybrid sol–gel material. This composition was photopolymerised on ITO electrodes by UV irradiation and subsequentially characterised via UV/Vis spectroelectrochemistry. It was also possible to fabricate a solid state electrochromic device based on EV and switch between the colourless (oxidised) and blue (reduced) forms using a perturbation signalof 1 V.

A novel hybrid organic-inorganic photocurable sol-gel material based on tantalum ethoxide and 3-trimethoxysilylpropylmethacrylate has been developed, characterised and used in the fabrication of optical waveguides and three-dimensional woodpile structures employing the single and two-photon polymerisation techniques, respectively. Single mode waveguides operating at 1310 and 1550 nm have been fabricated, optically characterised and their performances correlated to the material formulation. Three-dimensional woodpile structures exhibiting negligible shrinkage have been developed and their remarkable mechanical stability correlated to the molecular structure of the hybrid material. The overall fabrication process of these devices is described and it is shown that the refractive indices of the materials can be tailored by a precise control of the material composition allowing the successful fabrication of performing single mode waveguides. (C) 2010 Elsevier B.V. All rights reserved.

In this letter, we report on the development of a novel camera phone-based UV-dosimeter for monitoring the solar disinfection (SODIS) of water. The dosimeter consists of a UV indicator, methylene blue, dispersed in an ethylcellulose-based polymer matrix. To provide quantitative measurement of UV dose, we demonstrate the use of a camera phone to analyze dosimeter color change in response to UV exposure. The dosimeter response exhibits excellent agreement with a polynomial model (R2) >; 0.99) over the UV exposure range tested. A notable advantage of the dosimeter described here is that it can be deposited on a variety of substrates with the potential to be incorporated into water containers. It is envisaged that use of such a dosimeter in conjunction with mobile phone technology will enhance the use of SODIS thereby impacting significantly on the challenge of providing clean drinking water in developing regions of the world.

Two-photon polymerization (2PP) is a rapid prototyping technique allowing the fabrication of complex 3D structures with submicrometer resolution. In this work, we present recent results on two-photon microstructuring of novel photocurable hybrid organic-inorganic materials developed by the sol-gel process. Sol-gel material synthesis permits the precise tailoring of material properties by appropriate selection of chemical precursors and processing conditions. The resulting materials have properties ranging from those of glass-like to pure organic polymers. The sot-gel formulations presented here have been developed from metal alkoxides, and have the advantage of low shrinkage coefficients and excellent mechanical and optical properties. In this work we have examined the minimum feature size of structures fabricated by 2PP as a function of the concentration of inorganic components within the sol-gel material.

Recent interest in photolithographic processes employing single and two-photon absorption processes have afforded advanced opportunities to fabricate both planar and three-dimensional microstructures. The fabrication of such structures is dependent on the local polymerization of the organic moieties using photoinitiating molecules, and a key parameter to consider is the dependency of the photoreactivity of these initiators on the matrices in which they are dispersed. To our knowledge, there has been no comprehensive investigation reported on the photoreactivity dependency of commercially available photoinitiators inserted within hybrid sol–gel materials. The aim of this paper is to highlight and explain the influence of the composition of hybrid organic–inorganic sol–gel materials on the photoreactivity of UV-sensitive initiators. Of particular interest is the understanding of the interactions between photoinitiating molecules and the sol–gel matrix. It is shown that both the nature of the chelating agent as well as the degree of chelation of the inorganic part of the hybrid sol–gel material significantly influence the spectral absorption of the photoinitiator. It is demonstrated that metal–ligand charge transfer processes are the main phenomena responsible for the red shift of the absorption of the amino-functionalized photoinitiators, which is strongly dependent on the condensation of the materials.

This paper proposes the development and structural characterisation of an Er 3 + / Yb 3 + doped hybrid organic-inorganic material synthesised by a nonhydrolytic sol-gel process. By using a pumping laser diode at 980 nm, a typical Er 3 + luminescence has been recorded in the near infrared region (1.53–1.55  μ m). However, the detected fluorescence was particularly weak compared to that generally observed in pure mineral materials, suggesting the occurrence of strong quenching due to multiphonon relaxation processes. To understand this behaviour, structural characterisation of both of the matrix and the local environment of Er 3 + ions were conducted employing infrared spectroscopy, nuclear magnetic resonance, electron paramagnetic resonance, and neutron scattering. These studies showed that the major phenomenon competing with the Er 3 + fluorescence is intimately associated to the strong vibrational modes of the organic species that involve multiphonon relaxation processes, resulting in energy dissipation within the host matrix.

We present a novel study of the interaction of SF6-based plasmas with sol–gel materials in a parallel plate reactive ion etching (RIE) system. The purpose of these experiments was to obtain quantitative measures and optimisation of the RIE parameters, which can be used in the microfabrication of planar lightwave circuit (PLC) devices. The sulfur hexafluoride chemistry is chosen due to its excellent etching properties of SiO2, which is one of the components of the photopatternable sol–gel materials and is not present in typical photoresist materials. Fast process etching rate and good selectivity is achieved by varying SF6 flow and power delivered to the electrodes. The study also reveals a marginal influence of oxygen and argon flow on the character of the sol–gel etching. The experimental data obtained can be used as a reference for any sol–gel devices fabricated using widely available RIE reactors.

This work focuses on the role of photoinitiators and chelating agents in waveguide fabrication based on UV sensitive sol–gel materials. The key role that a photoinitiator plays in waveguide formation has been shown through examination of waveguide width and cross-sectional shape. Waveguides fabricated using Irgacure-907 were found to be on average 2.5 times wider at the top surface than those fabricated using Irgacure-819 or -1800. UV–Vis measurements on the photoinitiators confirmed that Irgacure-907 is approximately 35 times more absorbing than the other photoinitiators at the UV exposure wavelength of 325nm. This has been found to give rise to a highly trapezoidal waveguide shape which, also affects waveguide adhesion. The influence of the chelating agent within the hybrid sol has also been studied with reference to waveguide width. These experiments clearly showed that the Zr(OPr)4 molecule plays an active role in the photopolymerization process, and its activity is controlled by its degree of chelation. Two different chelating agents, methacrylic acid (MAAH) and isobutyric acid (IBA) were compared. The trend for both chelating agents was the same, but IBA chelated sols resulted in narrower waveguides. This has been attributed to the higher steric hindrance of IBA compared to MAAH, which would inhibit the propagation of polymerization in the coating.

In this paper we identify and explain the different chemical interactions involved between a sol–gel matrix and photoinitiators used in the fabrication of optical waveguides. A well-established sol–gel matrix composed of 3-methacryloxypropyltrimethoxysilane, zirconium n-propoxide and methacrylic acid was developed, and two different photoinitiators (Irgacure® 819 and 1800) were added to the host matrix. Optical microscopy was used to characterise the structure of the waveguides as a function of the photoinitiator nature and concentration, and aging of the hybrid sol–gel material. It is clearly demonstrated that the width of the waveguides is strongly influenced by the sol aging. Furthermore, it is shown that degradation of photoinitiators occurs during the sol–gel process. Oxidation of the phosphonyl groups by the zirconium complex accounts for this results.