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Surface plasmon resonance imaging (SPRI) biosensors allow sensitive, real-time and label-free detection of biological species in fluids when they bound to the sensing surface. However, their sensitivity is now close to the theoretical limit. In particular, at ultra-low target concentration, the main limit is the diffusion of the biological target (protein, DNA, bacteria…) to the gold film surface. To locally increase the target concentration on the sensitive surface and overcome such diffusion limit, active mass transport of analytes can be induced by non-uniform electric fields using dielectrophoresis (DEP) and alternative-current electroosmosis (ACEO) flow. Depending on the frequency of the electric field applied and the conductivity of the suspension medium, DEP and ACEO can concentrate biological objects on electrodes. This work focuses on the trapping and the detection of bacteria. The gold film used for SPR imaging is also used as electrode for particle collection, after photolithography and wet etching. To obtain the most efficient electrode design, numerical simulations were performed to estimate the trapping force applied on bacteria in the fluidic chamber volume depending on the geometry of the electrodes. SPR biochips obtained were mounted in the Kretschmann configuration. Then, a DI water solution containing E.coli bacteria was injected in the fluidic chamber of the chip. AC voltage (10Vpp, 1 kHz) was applied. The arrival of bacteria on the sensing zone is monitored by a strong jump of the SPR signal when no signal was observed without mass transport. The easy integration of such DEP/ACEO-assisted SPR chips on commercial SPR benches makes them suitable fur ultralow detection of a wide range of biological species, from biomolecules to pathogens.
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