J.M. Chovelon

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.

Sensitive detection of pesticide using ENFET with enzymes immobilized by cross-linking and entrapment method

Abstract Trichlorfon as a common pesticide is detected using a BuChE-FET sensor which is prepared either with cross-linked BSA–glutaraldehyde membrane or photocross-linkable PVA/SbQ (poly(vinyl alcohol) containing styrylpyridinium) membrane. On the basis of these BuChE-FET sensors, a biochemical test for trichlorfon in liquid was developed by enzyme inhibition. PVA/SbQ membrane shows better characteristics compared to BSA membrane: larger linear dynamic range in kinetic mode, better reproducibility, and above all, better stability in storage. Nevertheless, the both membranes present the same detection limit for trichlorfon: 10−6 M. The biosensor response after the enzyme inhibition can be partially recovered by using 2-methiodide pyridaldoxime, and the degree of enzymatic reactivation depends on the concentration of pesticides and on the time of incubation.

Development of a fiber-optic sensor based on surface plasmon resonance on silver film for monitoring aqueous media

Abstract A reliable fiber-optic SPR sensor based on silver is developed in this paper for chemical and biological applications. The range of measurable indices is shifted down by coating an overlay of zirconium acetate on the silver surface by sol–gel technique. The feasibility has been investigated in advance by theoretical analyses. The experimental fiber-optic sensor demonstrates its capability to operate in the aqueous media with the detectable range of refractive indices of 1.33–1.36. A self-assembled monolayer (SAM) of long chain thiol is introduced to cover the surface of silver in order to prevent silver from deterioration. Experimental studies demonstrate that in this way, the sensor lifetime increases from days to weeks. This work provides a base for developing an affinity biosensor.

Sensitive cyclodextrin–polysiloxane gel membrane on EIS structure and ISFET for heavy metal ion detection

Abstract Cylodextrin (CD)–polysiloxane gel matrices are used to functionalize EIS (Electrolyte Insulator Semiconductor structure) and ISFET (Ion-Sensitive Field Transistor) devices. Electrochemical measurements were made to study the sensitivity and the selectivity of this sensitive membrane towards heavy metal ions. For both structures, a Nernstian response and good detection limit of an αCD gel membrane towards Cd2+ ion and for a βCD towards Pb2+ ion were obtained. The selectivity with respect to other cations are given through the potentiometric selectivity coefficients (Kij).

ISFET microsensors for the detection of pollutants in liquid media

Abstract Different types of polymeric matrices were tested in order to optimize the characteristics of the specific ISFETs developed for the detection of an ionic pollutant, the ammonium ion and of a molecular pollutant, the trichlorfon which is a common organophosphorus pesticide. A miniaturized sensor for ammonium detection, based on the integration of both ammonium and reference FETs in a single chip, was fabricated. A differential measurement mode between both FETs was used, this mode of measurement allowed to reduce interferences of Na + and K + ions, the effect of ionic strength and of temperature. The sensitivity of the ammonium detection was around 30 mV/pNH 4 + and the detection limit 2×10 −6 M. Trichlorfon as a common pesticide is detected using a BuChE–FET sensor which is prepared either with cross-linked BSA–glutaraldehyde membrane or photocross-linkable PVA/SbQ (poly(vinyl alcohol) containing styrylpyridinium) membrane. PVA/SbQ membrane shows better characteristics compared to BSA membrane: larger linear dynamic range in kinetic mode, better reproducibility, and above all, better stability in storage. Nevertheless, both membranes present the same detection limit for trichlorfon: 10 −6 M.

Optical fibre sensors sensitized by phenyl-modified porous silica prepared by sol–gel

Abstract Porous silica and phenyl-modified porous silica were prepared by sol–gel method as cladding for optical fibres and tested for the chemical detection of aromatic and alkane vapours. The refractive indices and optical attenuation of the layers have been determined from the measured angular distributions of the output optical power. For this purpose, a model based on geometrical optics has been developed. The interaction of the porous layers with benzene, toluene, xylene and hexane has been investigated by measuring the changes of the output optical power induced by the effect of vapours of the hydrocarbons in air. On the basis of these measurements, the porosity of the layer, and the partition coefficients of the hydrocarbons have been estimated. The measured decrease of the optical power for the aromatic hydrocarbons and the increase of the output power for the aliphatic hydrocarbon have been explained on the basis of the developed model. Higher sensitivity for aromatic hydrocarbons has been found for the porous silica modified by phenyl moieties used as cladding for fiber-optic chemical sensor.

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.

Sensitive immunodetection through impedance measurements onto gold functionalized electrodes.

This article deals with a direct electrochemical method of detecting antigens using new methods of functionalization of gold electrodes. Based on the reacting ability of gold with sulfhydryl groups, three protocols for the fixation of antibodies have been explored. They are based on either the self-assembling properties of functional thiols bearing long alkyl chains or the possibility of a direct coupling of antibody moieties. Coverage rates as high as 97% can be reached. The analysis of the electrochemical impedance behavior of such layers can lead to a sensitive method for the direct detection of the antibody/antigen interaction. The addition of a redox couple in the tested solution, acting as an amplifier, allowed detection limits for the antigens as low as a few picograms/milliliter to be reached.

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.