A very-long-chain (C22) organosilicon self-assembled monolayer (SAM) with terminal glycidyl groups was used to immobilize antibodies on the silica waveguide of a Love mode surface acoustic wave (SAW) immunosensor. This route enabled us to specifically detect, in real time, living Escherichia coli bacteria by using monoclonal anti-E. coli antibodies, leading to a marked sensor response in liquid aqueous medium. Conversely, no bacteria detection could be observed by this direct method upon functionalization of the waveguide surface by a (3-glycidoxypropyl) trimethoxysilane (GPTS) monolayer. This improvement was attributed to a surface smoothing effect resulting from the very-long-chain SAM and a better accessibility of the surface epoxide groups.

Novel glycidyl-terminated organosilicon coupling agents possessing a trialkoxysilyl head group and a very long hydrocarbon chain (C22) were synthesized. Their ability to afford densely packed self-assembled monolayers (SAMs) grafted on silica-based surfaces was investigated. Transmission FT-IR spectra showed that the most regular films were obtained by using trichloracetic acid as the catalyst (10 M%). Atomic force microscopy (AFM) and optical ellipsometry were consistent with well ordered monolayers exhibiting a marked decrease of the surface roughness. Epifluorescence microscopy revealed that these SAMs possessed a better surface reactivity than monolayers obtained with the commercially available (3-glycidoxypropyl) trimethoxysilane (GPTS) upon grafting of a fluorescent probe (dansylcadaverin). Moreover, direct attachment of fluorescent antibodies (RAG-TRITC) through covalent binding led to higher mean fluorescence intensities, showing that these new SAMs possess high potential for the immobilization of biological molecules.

The efficiency of a monomolecular film of (3-glycidoxypropyl) trimethoxysilane (GPTS) on a shear horizontal guided (Love) acoustic wave immunosensor to detect whole Escherichia coli (E. coli) bacteria is demonstrated. Direct anti-E. coli antibodies grafting onto the sensor surface did not lead to a significant bacteria immobilisation, partially attributed to the SiO2 sensor surface roughness. An innovative method has been set up to get around this difficulty and to detect whole bacteria. It consists in grafting goat anti-mouse antibodies (GAM) onto the sensor surface in a first step and introducing E. coli bacteria mixed with anti-E. coli antibodies onto the sensor in a second step. We describe the characteristics of such a technique like sample preparation time (lower than 30 min) and temperature improvements. A 37 degrees C experimental temperature led to the fastest bacteria binding kinetic, reducing the total analysis time. This method enables to keep the specificity of the antibody/antigen interaction and provides significant results in less than 1h. This leads to a detection threshold of 10(6) bacteria/ml in a 500 microl chamber.

Nous presentons une plateforme de detection rapide d'organismes biologiques a ondes acoustiques de Love, sensible de masse. Apres une revue des differentes technologies de biocapteurs, l'immunocapteur a ondes de Love, base sur une reaction antigene/anticorps, est presente en detail. Les etudes theoriques et experimentle sur la ligne a retard a ondes de Love, l'electronique de conditionnement, avec des voies d'ameliorations utilisant des materiaux polymeres en particulier, sont exposees. La couche bioreceptrice d'anticorps immobilisee sur la surface du capteur par liaison covalente grâce au (3-Glycidoxypropyl)trimethoxysilane (GPTS), offre une bonne densite et uniformite, validee par immunofluorescence. Les detections montrent une bonne reproductibilite et selectivite du capteur pour les differentes especes testees (bacteries, bacteriphages, proteines). Un seuil de detection des bacteries vivantes de typeEscherichia coli de l'ordre 10puissance 6 bacteries/ml en moins d'une heure est obtenu, grâce a la mise au point d'une nouvelle strategie immunologique d'immobilisation des bacteries utilisant un couple d'anticorps.