Anne-Marie Gué

Swimming behaviour and magnetotaxis function of the marine bacterium strain MO-1

Magnetotactic bacteria (MTB) have the unique capacity to align and swim along the geomagnetic field lines downward to the oxic-anoxic interface in chemically stratified water columns and sediments. They are most abundant within the first few centimetres of sediments below the water-sediment interface. It is unknown how MTB penetrate into the sediment layer and swim in the pocket water, while their movements are restricted by the alignment along the magnetic field lines. Here we characterized the swimming behaviour of the marine fast-swimming magnetotactic ovoid bacterium MO-1.We found that it rotates around and translates along its short body axis to the magnetic north (northward). MO-1 cells swim forward constantly for a minimum of 1770 μm without apparent stopping. When encountering obstacles, MO-1 cells squeeze through or swim southward to circumvent the obstacles. The distance of southward swimming is short and inversely proportional to the magnetic field strength. Using a magnetic shielding device, we provide direct evidence that magnetotaxis is beneficial to MO-1 growth and becomes essential at low cell density. Environmental implications of the fast-swimming magnetotactic behaviour of magnetococci are discussed.

An ejection microarray for in-situ oligonucleotide synthesis on DNA chips

A new microfluidic actuator for in situ oligonucleotides synthesis on DNA chips has been developed. It consists in a microarray of individually addressable ejectors able to deliver pl droplets. The working principle is based on thermal ink-jet printing. The design of the micro injector has been deduced from FEM simulation, in order to achieve 4000 ejectors/cm/sup 2/. The technological fabrication process includes the realisation of a thin dielectric and stress free membrane, of polysilicon heater resistors, and of SU8 photopolymerised nozzles. Ejections have been observed for 50 /spl mu/s pulses and 1.25 W power consumption without satellite droplets.

A Resazurin Based Bio Sensor for Detection of Organic Pollutants in Water

With the objective of water analysis, a microsystem was developed, by using Resazurin molecule as an indirect bio sensor. The detection principle consists to monitor optically the oxygen consumption of E. Coli bacteria towards their metabolism in presence of organic pollutants. Thus, aiming on Glucose detection, a concentration-dependent inhibition effect on oxygen consumption rate was evidenced in the [0–0.41 mM] range of organic pollutants.

Multilevel (3D) lab on chip for implementing reconfigurable magnetophoretic functionnalities

This study demonstrates the integration of a multilevel magnetophoretic lab on chip: combining 3D fluid engineering and localized magnetic actuation enables the full integration of a cell tagging and magnetic separation device. A system performing magnetic handling of beads at cell resolution was also devised based on the same technologies.

Atomic scale simulation of the growth of CdTe layers on GaAs

The initial stages of the growth of CdTe on (100) GaAs with 14. 7 lattice mismatch has been simulated. It is shown that growth in (111) direction with the presence of twins is always preferred on perfect substrate surfaces. In the case of growth in (100) direction misfit dislocations are formed. The critical thickness is evaluated by extrapolation to be 6 - 8 atomic monolayers .