Adnane Abdelghani

Optical fibre sensor coated with porous silica layers for gas and chemical vapour detection

Fibre optic sensors have been conceived in new technologies for detecting very small amounts of chemical, gaseous and biological species. Recently, new polymer-clad silica (PCS) fibres coated with thin porous silica layers have been developed. These porous layers have been prepared by the sol-gel method using the dip-coating technique. In this work, this new material has been investigated for detecting gases and vapours. By choosing a fixed incident angle, variation of light power transmitted through the fibre is detected as the vapour or gas to be detected is sorbed in the porous silica layer. Good sensitivity and reversibility have been obtained for this system. Moreover, both the response time and the desorption time have been found less than 2 min. Chlorinated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform, dichloromethane and alkanes such as propane, butane and hexane can be detected with detection limits of 0.6, 1.5, 1.7, 4, 25, 10 and 5% respectively.

Surface plasmon resonance fibre-optic sensor for gas detection

Surface plasmon resonance (SPR) is a powerful technique for direct sensitive (bio)chemical detection. In this work, a surface plasmon resonance fibre-optic sensor has been developed allowing sensitive remote detection. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect the silver from oxidation, self-assembled monolayers (SAMs) of long-chain alkanethiols are used. For detecting gas and vapours, the surrounding dielectric medium consists of polyfluoroalkylsiloxane, deposited on the modified metallic film. Halogenated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform and methylene chloride have been tested with detection limits of 0.3, 0.7%, 1 and 2%, respectively. Moreover, both the response time and the desorption time are less than 2 min.

Labeled magnetic nanoparticles assembly on polypyrrole film for biosensor applications.

In recent years, conducting polymers combined with metallic nanoparticles have been paid more attention due to their potential applications in microelectronics, microsystems, optical sensors and photoelectronic chemistry. The work presented in this paper describes the preparation and characterization of a nanocomposite composed by a thin polypyrrole (PPy) film covered with an assembly of magnetic nanoparticles (NPs). The magnetic particles were immobilized on PPy films under appropriate magnetic field in order to control their organization on the PPy film and finally to improve the sensitivity of the system in potential sensing applications. The electrical properties and morphology of the resulting PPy film and the PPy film/NPs composite were characterized with cyclic voltammetry, impedance spectroscopy (IS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and infra-red spectroscopy (IR). By using streptavidin labeled magnetic particles it was possible to functionalize the NPs assembly with biotin-Fab fragment K47 antibody. The designed biosensor had been successfully applied in rapid, simple, and accurate measurements of atrazine concentrations, with a significantly low detection limit of 5 ng/ml.

Porous silicon as functionalized material for immunosensor application

Recently, for sensor application, porous silicon has received a great deal of attention due to the high specific surface area and the easy fabrication using some established processes of the usual silicon technology. We herein, report the development of a novel immunosensors based on porous silicon for antigen detection. The multilayer immunosensor structure was fabricated following the successive steps: APTS self-assembled monolayer (SAM) layer, glutaaldehyde linker, anti-rabbit IgG binding. The insulating properties of the aminopropyl-triethoxysilane (APTS) monolayer were studied with cyclic voltammetry and the molecular structure was characterized with Fourier-transform infrared (FTIR) technique. The binding between antibody and different antigen concentration (rabbit IgG) was monitored by measuring the capacitance-voltage curve of the antibody functionalized EIS structure. A detection limit of 10ng/ml of antigen can be detected.

Chemical vapour sensing by surface plasmon resonance optical fibre sensor coated with fluoropolymer

Abstract A surface plasmon resonance fibre optic sensor has been developed allowing sensitive remote detection. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect silver from oxidation, self-assembled monolayers (SAM) of long-chain alkanethiols were used. For detecting gas and vapours, the surrounding dielectric medium consists of a polymeric material deposited on the modified metallic film. Chlorinated and aromatic compounds have been tested with detection limits of 0.3%, 0.7%, 1% and 2% for trichloroethylene, carbon tetrachloride, chloroform and methylene chloride, respectively, and 0.13%, 0.19% and 0.95% for xylene, toluene and benzene, respectively. For aromatic compounds, the response of the sensor depends on the boiling temperature, whereas for chlorinated compounds it depends on the difference between the refractive index of the analyte and specific polymeric cladding. Moreover, both the response time (about 2 min) and the desorption time (about 2.5 min) have been obtained with good reproducibility.

Stabilization of a surface plasmon resonance (SPR) optical fibre sensor with an ultra-thin organic film : application to the detection of chloro-fluoro-carbon (CFC)

Abstract Surface plasmon resonance (SPR) is a powerful technique for direct sensitive (bio) chemical detection. This phenomenon can be used to measure the refractive index of either bulk chemical samples or chemically sensing thin layers. In this work, a SPR fibre optic sensor has been developed. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect silver from oxidation, the evaporated silver film was covered with self-assembled monolayers (SAMs) of long-chain alkanethiols (1-octadecanethiol). To characterize these SAMs, silver films evaporated onto macroscopic glass surfaces as test samples and several techniques such as contact angle measurements (sessile drop method), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used. In the subsequent step, a chemically sensing thin layer (polyfluorosiloxane) was deposited onto the thiol surface. In such a configuration the SPR fibre optic sensor was able to detect a few percent of chloro-fluoro-carbon (CFC) vapours.

Detection of aromatic hydrocarbons in air and water by using xerogel layers coated on PCS fibers excited by an inclined collimated beam

This paper deals with experimental results on the sensitivity of silica optical fibers coated with detection xerogel membranes to benzene and toluene both in gaseous mixtures and in aqueous solutions. For this purpose thin polysiloxane and methyl-group-doped polysiloxane xerogel membranes are applied on straight segments of PCS fibers. The interaction of these membranes with hydrocarbons is investigated on the basis of changes of the output optical power from the fibers excited by an inclined collimated beam. The results obtained show that the hydrophobic methyl-group-doped xerogel layers exhibit higher sensitivity to hydrocarbons both in the gaseous phase and in solutions. The detection limits are about 230 ppm vol. for toluene in air and about 9 mg/l for toluene in water. Both the membranes show lower sensitivity to benzene than to toluene.

Sensitivity Improvement of an Impedimetric Immunosensor Using Functionalized Iron Oxide Nanoparticles

This work has explored the development of impedimetric immunosensors based on magnetic iron nanoparticles (IrNP) functionalized with streptavidin to which a biotinylated FAB part of the antibody has been bound using a biotin-streptavidin interaction. SPR analysis shows a deviation on the measured (angle) during antigen-antibody recognition whereas label free detection using by EIS allows us to monitor variation of polarization resistance. Before detection, layers were analyzed by FTIR and AFM. Compared to immobilization of antibody on bare gold surface using aminodecanethiol SAM, antibody immobilization on nanoparticles permitted to reach lower detection limit: 500 pg/ml instead of 1 ng/ml to in the case of EIS and 300 ng/ml instead of 4.5 g/ml in the case of SPR. Thus, it permitted to improve the sensitivity: from 257.3 to 1871 in the case of EIS and from to in the case of SPR.

Contact angle measurement on xerogel sensitive layer for optical fibre sensor

This paper deals with approach for the detection of chemical vapours based on refractive-index changes of a silica xerogel layer deposited as an optical cladding on the fibre core. The fibre is multimode fibre excited with an inclined collimated beam. The refractive-index changes are evaluated by means of changes of the output power at the end put of the fibre. The optical properties of the sensitive cladding (refractive index and absorption coefficient) can be obtained with modelisation program. The sensitivities of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS)-based xerogel layers to toluene and water are presented in the paper. The hydrophobicity of the two-xerogel layers and their surface-free energy has been determined with contact angle measurements. A correlation between optical detection results and contact angle measurements can be done.

Electrochemical Characterization of Streptavidin-HRP Immobilized on Multiwall Carbon Nanotubes for Biosensor Applications

In this work, we used gold labeled multiwall carbons nanotubes for peroxidase biosensor. The gold labeling on multiwall carbon nanotubes can be achieved with Pressure vapor Deposition (PVD) technique. The obtained carbon nanotubes can be immobilized on gold electrode with the airbrushing technique. The stability and the molecular structure of the labeled multiwall carbon nanotubes were characterized with cyclic voltammetry, impedance spectroscopy and Fourrier Transform Infra-Red spectroscopy (FTIR). It shows a higher conductivity and a good stability in water interface. For streptavidin-HRP immobilization, the labeled gold nanotubes were activated over night with thiol-acid (16 carbons). An activation procedure was achieved with EDC/NHS for HRP-streptavidin immobilization. The development of biosensor for H2O2 detection was observed with the impedance spectroscopy and cyclic voltammetry techniques. This method could be used to determine total H2O2 concentration in the range 4 μM - 160 μM. The results show that the biosensor response depends on the conductivity and the large surface-to-volume ratio attained with multiwall carbon nanotubes. The response of the developed biosensors was reproducible with higher stability.