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Gammoudi I.,University of Bordeaux 1 | Gammoudi I.,French National Center for Scientific Research | Gammoudi I.,National Institute for Research and Physicochemical Analysis | Blanc L.,University of Bordeaux 1 | And 7 more authors.
Biosensors and Bioelectronics | Year: 2014

This work deals with the design of a highly sensitive whole cell-based biosensor for heavy metal detection in liquid medium. The biosensor is constituted of a Love wave sensor coated with a polyelectrolyte multilayer (PEM). Escherichia coli bacteria are used as bioreceptors as their viscoelastic properties are influenced by toxic heavy metals. The acoustic sensor is constituted of a quartz substrate with interdigitated transducers and a SiO2 guiding layer. However, SiO2 shows some degradation when used in a saline medium. Mesoporous TiO2 presents good mechanical and chemical stability and offers a high active surface area. Then, the addition of a thin titania layer dip-coated onto the acoustic path of the sensor is proposed to overcome the silica degradation and to improve the mass effect sensitivity of the acoustic device.PEM and bacteria deposition, and heavy metal influence, are real time monitored through the resonance frequency variations of the acoustic device. The first polyelectrolyte layer is inserted through the titania mesoporosity, favouring rigid link of the PEM on the sensor and improving the device sensitivity. Also, the mesoporosity of surface increases the specific surface area which can be occupied and favors the formation of homogeneous PEM. It was found a frequency shift near -20±1. kHz for bacteria immobilization with titania film instead of -7±3. kHz with bare silica surface. The sensitivity is highlighted towards cadmium detection.Moreover, in this paper, particular attention is given to the immobilization of bacteria and to biosensor lifetime. Atomic Force Microscopy characterizations of the biosurface have been done for several weeks. They showed significant morphological differences depending on the bacterial life time. We noticed that the lifetime of the biosensor is longer in the case of using a mesoporous TiO2 layer. © 2013 Elsevier B.V.


Gammoudi I.,University of Bordeaux 1 | Gammoudi I.,French National Center for Scientific Research | Gammoudi I.,University of Monastir | Gammoudi I.,National Institute for Research and Physicochemical Analysis | And 11 more authors.
Sensors and Actuators, B: Chemical | Year: 2014

Environmental pollution by toxic heavy metals (HM) presents a real threat for aquatic medium and human health. Therefore aquatic ecosystem management requires early warning systems for on line monitoring. Microtechnologies can give rise to innovative bio-inspired hybrid microsensors, likely to meet this need and providing cost reductions by reducing reagents consumption and manufacturing cost. This work deals with a bacteria-based Love wave sensor, with enhanced properties provided by integration of a polydimethylsiloxane (PDMS) microfluidic network for a better control of the sample flow, and devoted to in situ monitoring of Cd(II) and Hg(II). Whole Escherichia coli (E. coli) bacteria are used as bioreceptor, mimicking in vivo enzymatic activity. They were immobilized on polyelectrolyte multilayer (PEM) films realized using layer by layer technique (LbL) with alternatively adsorption of positive and negative chains. The acoustic delay line was inserted into an electronic oscillation loop for real time monitoring. Compared to previous work, this paper deepens the results obtained with two types of microfluidic chips (measurements in static and dynamic modes), including analysis in terms of reproducibility. These results are analyzed and interpreted thoroughly leading to assumptions about the phenomena involved in the detection mechanisms. These hypotheses are validated through a pioneering study with atomic force microscopy (AFM), performed to characterize bacteria adhesion and to establish the relationship between bacteria morphological evolution and mechanical properties. AFM was chosen for its ability to maintain the bacteria alive during the experience without inducing irreversible damage. The resulting microsystem led to efficient HM detection, characterized by a reduced response-time (less than 60 s) and a detection limit inferior to 10-12 M. AFM measurements have demonstrated a high bacterial attachment and the stressing effect of toxic HM on bacterial morphological state. These results are consistent with those obtained from Love wave measurements. © 2014 Elsevier B.V.


PubMed | National Institute for Research and Physicochemical Analysis, University of Bordeaux 1, French National Center for Scientific Research and CNRS Laboratory of Condensed Matter Chemistry, Paris
Type: | Journal: Biosensors & bioelectronics | Year: 2014

This work deals with the design of a highly sensitive whole cell-based biosensor for heavy metal detection in liquid medium. The biosensor is constituted of a Love wave sensor coated with a polyelectrolyte multilayer (PEM). Escherichia coli bacteria are used as bioreceptors as their viscoelastic properties are influenced by toxic heavy metals. The acoustic sensor is constituted of a quartz substrate with interdigitated transducers and a SiO2 guiding layer. However, SiO2 shows some degradation when used in a saline medium. Mesoporous TiO2 presents good mechanical and chemical stability and offers a high active surface area. Then, the addition of a thin titania layer dip-coated onto the acoustic path of the sensor is proposed to overcome the silica degradation and to improve the mass effect sensitivity of the acoustic device. PEM and bacteria deposition, and heavy metal influence, are real time monitored through the resonance frequency variations of the acoustic device. The first polyelectrolyte layer is inserted through the titania mesoporosity, favouring rigid link of the PEM on the sensor and improving the device sensitivity. Also, the mesoporosity of surface increases the specific surface area which can be occupied and favors the formation of homogeneous PEM. It was found a frequency shift near -201 kHz for bacteria immobilization with titania film instead of -73 kHz with bare silica surface. The sensitivity is highlighted towards cadmium detection. Moreover, in this paper, particular attention is given to the immobilization of bacteria and to biosensor lifetime. Atomic Force Microscopy characterizations of the biosurface have been done for several weeks. They showed significant morphological differences depending on the bacterial life time. We noticed that the lifetime of the biosensor is longer in the case of using a mesoporous TiO2 layer.

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