Hafedh Ben Ouada

Assessing bacterial adhesion using DLVO and XDLVO theories and the jet impingement technique

In this study, the adhesion of two bacterial strains (Pseudomonas stutzeri PS, and Staphylococcus epidermidis, SE) to the glass and the indium tin oxide (ITO)-coated glass surfaces was examined qualitatively and quantitatively using the theoretical approaches and the jet impingement technique. A comparison between the DLVO and the extended DLVO (XDLVO) theories showed that the XDLVO predictions of bacterial adhesion and its reversibility are more accurate than DLVO predictions. The adhesion tests revealed that PS bacteria has much better adhesion rate than SE bacteria to both material surfaces, as predicted by XDLVO approach. Also both bacterial strains adhered better to the hydrophobic ITO-coated glass than to the hydrophilic glass surface, as predicted theoretically. Moreover, the microjet impingement technique was used not only to assess the bacterial adhesion strength on both materials, but also to verify the adhesion reversibility. The detachment stress values demonstrated that PS bacterial cells adhered strongly and irreversibly in the primary energy minimum, while SE bacterial cells adhered weakly and reversibly in the secondary energy minimum on both substrata surfaces. Also, the adhesion of both bacterial strains was found better and stronger on the hydrophobic ITO-coated glass surface than on the hydrophilic glass surface.

Ultra-sensitive conductometric detection of heavy metals based on inhibition of alkaline phosphatase activity from Arthrospira platensis

This study is based on the conductometric measurement of alkaline phosphatase activity (APA) from the cyanobacterium, Arthrospira platensis, called Spirulina. Cyanobacterium cells were directly immobilized, by physical adsorption, on the ceramic part of gold interdigitated transducers. This activity was inhibited in the presence of heavy metals and a variation of the local conductivity was measured after addition of the substrate. The Michaelis-Menten constant (Km) was evaluated to be 0.75 mM through a calibration curve of the substrate, disodium 4-nitrophenylphosphate p-nitrophenyl phosphate (pNPP). Inhibition of APA was observed with cadmium and mercury with a detection limit of 10(-20) M. The half maximal inhibitory concentration (IC50) was determined at 10(-19) M for Cd(2+) and 10(-17) M for Hg(2+), and the binding affinity of heavy metal (Ki) was equal to the IC50. On the sensor surface, scanning electron microscopy (SEM) images revealed a remarkable evolution of the cyanobacteriums external surface that was attributable to the first defense mechanism against toxic heavy metals in trace. This effect was also confirmed through the important increase of response time τ(90%) recorded for APA response towards the substrate pNPP after cell exposure to metallic cations. Lifetime of the Spirulina-based biosensor was estimated to be more than 25 days.

Optical and electrical properties of semi-conducting calix[5,9]arene thin films with potential applications in organic electronics

Indium tin oxide (ITO) substrates have been functionalized by several substituted calix[n]arene (n = 5 or 9) derivatives using spin coating to fabricate organic diode devices. The effect of rim size and side substituents has been investigated by UV–visible absorption spectrophotometry. The energy band gaps of these calixarene derivative thin films have been found in the 1.166–1.450 eV range. The electrical properties of ITO/calix[n]arene/Al diodes have been studied by current–voltage measurement showing an ohmic behaviour at low voltage. The I(V) characteristics could be modelled by a space-charge-limited current (SCLC) mechanism at high applied bias voltage. The ac electrical transport of calix[5,9]arene derivatives has been studied over a wide range of bias voltage and frequency by impedance spectroscopy. The device had been accurately modelled, for a frequency between 100 Hz and 10 MHz, by a single parallel resistor and capacitor network in series with a resistance. A dielectric relaxation time in the ms range and a transport mechanism controlled by an exponential trap distribution were deduced from the fit of the experimental data. The evolution of electrical parameters with chemical structure (rim size and substituent) has been discussed. The conductivity σ(ω) evolution with frequency and bias voltage was studied for ITO/calix[n]arene/Al devices. The dc conductivity σdc for these devices has been determined. The ac conductivity σac showed a variation in angular frequency as A.ωs with a critical exponent s < 1 suggesting a hopping conduction mechanism at high frequency and a microscopic picture of the relaxation and hopping processes has been proposed.

Electrodeposited biotinylated polypyrrole as an immobilization method for impedimetric immunosensors

The potentialities of an electrodeposited biotinylated polypyrrole film as an immobilization matrix for the fabrication of impedimetric immunosensors are described. Biotinylated antibody (anti-human IgG), used as a model system, was attached to free biotin groups on the electrogenerated polypyrrole film using avidin as a coupling reagent. The resulting recognition interface consisted of a highly oriented monolayer immobilized onto the polymer surface. Cyclic voltammetry was used to characterize the polymer film. Additionally, scanning electron microscopy and atomic force microscopy were used to investigate the morphology of the immobilized material. This immobilization method allows the obtention of a highly reproducible and stable device. The resulting immunosensor has a linear dynamic range of 10-80 ng.ml/sup -1/ of antigen and a detection limit of 10 pg.ml/sup -1/. Furthermore, this immunosensor exhibited minor loss in response after two regeneration steps.

Optical and electrochemical studies of thiacalix[4]arene film supported on Si/SiO2 for ion-sensitive sensor

The present work is motivated by the development of ion-sensitive sensors (suited for aqueous medium) based on functional supported thin film as sensitive membrane. Thin thiacalix[4]arene films was deposited using the technique of thermal evaporation under vacuum to fabricate chemical ion-sensitive field effect transistor (ISFET) microsensors. The aim is to characterize thiacalix[4]arene thin film (morphology, chemical composition) and its optical and electrical properties before and after detection of copper(II) ions.

Reuse of Textile Wastewater after Treatment with Isolated Bacteria from Oued Hamdoun River

ABSTRACT Industrialization is a boon for developing countries such as Tunisia. However, textile effluents that are being discharged are environmental pollutants, extremely toxic to plants and other living organisms, including humans. The current study was conducted to determine the phytotoxic effect of textile effluents, collected near an industrial zone in the center of Tunisia (Ksar Helal), on the germination and various growth indices of durum wheat (Triticumaestivum L.). Results showed that textile effluent treatments reduced significantly the percentage of seed germination and slowed its kinetic as compared with control. Roots and leaves were also significantly reduced. The phytotoxicity was highly reduced from textile effluents after aerobic biotreatment with bacteria. It can be concluded that the biological treatment process of textile wastewater might serve as a fertilizer production that is able to improve the growth of plants. These results are encouraging in the context of developing a low-budget technology for the effective management of these effluents.