Intense pH Sensitivity Modulation in Carbon Nanotube-Based Field-Effect Transistor by Non-Covalent Polyfluorene Functionalization

We compare the pH sensing performance of non-functionalized carbon nanotubes (CNT) field-effect transistors (p-CNTFET) and CNTFET functionalized with a conjugated polyfluorene polymer (labeled FF-UR) bearing urea-based moieties (f-CNTFET). The devices are electrolyte-gated, PMMA-passivated, 5 µm-channel FETs with unsorted, inkjet-printed single-walled CNT. In phosphate (PBS) and borate (BBS) buffer solutions, the p-CNTFETs exhibit a p-type operation while f-CNTFETs exhibit p-type behavior in BBS and ambipolarity in PBS. The sensitivity to pH is evaluated by measuring the drain current at a gate and drain voltage of −0.8 V. In PBS, p-CNTFETs show a linear, reversible pH response between pH 3 and pH 9 with a sensitivity of 26 ± 2.2%/pH unit; while f-CNTFETs have a much stronger, reversible pH response (373%/pH unit), but only over the range of pH 7 to pH 9. In BBS, both p-CNTFET and f-CNTFET show a linear pH response between pH 5 and 9, with sensitivities of 56%/pH and 96%/pH, respectively. Analysis of the I–V curves as a function of pH suggests that the increased pH sensitivity of f-CNTFET is consistent with interactions of FF-UR with phosphate ions in PBS and boric acid in BBS, with the ratio and charge of the complexed species depending on pH. The complexation affects the efficiency of electrolyte gating and the surface charge around the CNT, both of which modify the I–V response of the CNTFET, leading to the observed current sensitivity as a function of pH. The performances of p-CNTFET in PBS are comparable to the best results in the literature, while the performances of the f-CNTFET far exceed the current state-of-the-art by a factor of four in BBS and more than 10 over a limited range of pH in BBS. This is the first time that a functionalization other than carboxylate moieties has significantly improved the state-of-the-art of pH sensing with CNTFET or CNT chemistors. On the other hand, this study also highlights the challenge of transferring this performance to a real water matrix, where many different species may compete for interactions with FF-UR

Controlled Interactions between Anhydrous Keggin-Type Heteropolyacids and Silica Support: Preparation and Characterization of Well-Defined Silica-Supported Polyoxometalate Species

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Capteurs à nanotubes de carbone couplés à un filtre pré- concentrateur pour la détection du benzène

International audienceLa détection d'hydrocarbures aromatiques monocycliques à basse température et dans la gamme sub-ppm requiert le développement de capteurs compacts et peu cQuteux. Parmi les différentes recherches menées dans le domaine des capteurs chimiques, l'utilisation de nanotubes de carbone (NTC) comme matériau sensible présentant une surface spécifique élevée a largement été étudiée. Plusieurs groupes ont démontré la potentialité des NTC à détecter des gaz, surtout lorsqu'ils sontdécorés de métal et-ou fonctionnalisés chimiquement, ce qui augmente la sensibilité des capteurs Dans ce contexte, notre objectif est de concevoir et d'optimiser un capteur chimique a base de nanotubes de carbone multl-parois (MWCNT) en le couplant à une couche de pré-concentration à base de silice nanoporeuse Le mécanisme de détection de la couche sensible à base de NTC est basé sur le changement de résistance d'un réseau de NTC lors de l'exposition au gaz. Notre choix de silicenanoporeuse en tant que préconcentrateur pour le capteur repose sur des travaux antérieurs qui ont montré la capacité de diverses matrices de silice nanoporeuses à piéger le benzéne et le toluène sur une plage allant de quelques ppb au ppm.Nous montrerons ici qu'il est possible d'utiliser une fine couche de silice fonctionnalisée comme préconcentrateur pour piéger et concentrer le benzéne et le toluène au voisinage des NTC Pour cela, les MWCNT ont été recouverts d'une couche de Si0$_2$ nanoporeuse dont la fonction est de concentrer le polluant afin d'améliorer les performances du capteur Dans cette contribution, nous décrirons la préparation du capteur et nous mettrons en évidence les effets bénéfiques de la couche de préconcentration et de la température de fonctionnement. Les capteurs MWCNT/SI0$_2$ fonctionnant à 125°C permettent de détecter jusqu'à la dizaine de ppb de benzéne dans l'air. Ces résultats soulignent le potentiel de ce matériau hybride MWCNT/Si0$_2$ pour la détection des polluants atmosphériques de l'air Intérieur et extérieur. D'autres développements sont en cours afin d'améliorer la limite de détection en utilisant ce nouveau concept de couplage de matériaux nanotubes de carbone multi-parois/couche de pré-concentration de S10$_2$

Polyoxometalate Grafting onto Silica: Stability Diagrams of H3PMo12O40 on {001}, {101}, and {111)-Cristobalite Surfaces Analyzed by DFT

International audienceThe process of grafting H3PMo12O40 onto silica surfaces is studied using periodic density functional theory methods. For surfaces with a high hydroxyl coverage, the hydroxyl groups are consumed by the polyoxometalate protons, resulting in water formation and the creation of a covalent bond between the polyoxometalate and the surface, and mostly no remaining acidic proton on the polyoxometalate. When the surfaces are partially dehydroxylated and more hydrophobic, after temperature pretreatment, less covalent and hydrogen bonds are formed and the polyoxometalate tends to retain surface hydroxyl groups, while at least one acidic proton remains. Hence the hydroxylation of the surface has a great impact on the chemical properties of the grafted polyoxometalate. In return, the polyoxometalate species affects the compared stability of the partially hydroxylated silica surfaces in comparison with the bare silica case

Large area CMOS bio-pixel array for compact high sensitive multiplex biosensing

International audienc

Chemical sensor based on carbon nanotube combined to a pre-concentrator nanoporous layer for the detection of benzene

International audienceOver the years, great effort has been made to use carbon nanotubes (CNT) as gas sensing materials with high specific surface area for detection of gases. Our objective is to design and optimize a chemical sensor based on CNT whose sensitivity arises via coupling with a pre-concentration nanoporous silica layer. The detection mechanism is based on the resistance change of CNT upon gas exposure which is due to the p-type semiconducting behavior of the CNTs. Our choice of nanoporous silica as pre-concentrator for the sensor is based on previous work that has shown the ability of various thick nanoporous silica matrices to trap benzene and toluene over the ppb to ppm range . Here we will show that it is possible to use a thin layer of functionalized silica as pre-concentrator to trap and concentrate benzene and toluene at the vicinity of CNT. The MWCNTs were covered with a nanoporous SiO$_2$ layer whose function is to concentrate the pollutant in order to enhance the sensor performances. We will describe the preparation of the sensor and highlight the beneficial effects of both the pre-concentration layer and the operating temperature. Thus, the mechanism involved with the functionalized silica layer will be discussed. MWCNT/SiO$_2$-based sensors operated at 125°C are able to detect 10 ppb of benzene in air. These results underline the potential of this MWCNTs/SiO$_2$ hybrid material for the detection of indoor and outdoor air pollutants. Recent developments have also demonstrated that this technology can be integrated into a prototype device