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Surface plasmon resonance imaging enhanced by dielectrophoresis and AC-electroosmosis

Surface Plasmon Resonance (SPR) biosensors are standard tools for chemical and biological sensing. They provide sensitive, real-time and label-free detection of biological species in fluids. However, their performance (time and detection threshold) is now close to the theoretical limit. In particular, at low target concentrations, sensitivity is limited by the diffusion of the target analyte to the sensor surface. To overcome the diffusion limit, non-uniform electric fields can be used to induce electrokinetic effects (dielectrophoresis and alternative-current electroosmosis) which attract analytes toward the surface sensing zone. This work proposes to pattern the gold film used for SPR detection and use it as electrodes for the electric field generation. The magnitude of the electrokinetic effects and resulting analyte trapping efficiency of different electrodes designs were studied numerically with COMSOL by modeling the dielectrophoretic and drag forces induced by the AC-electroosmotic flow. A biochip, which consists of a structured gold film on a glass substrate, was mounted in the SPR Kretschmann configuration in contact with a fluidic cell to enable the injection of analyte and rinsing solutions. SPR imaging allowed us to compare the spatial distribution of the SPR response both a planar metal zone similar to a conventional SPR sensor as well as on the electrodes. After microbeads injection into the fluidic cell and application an AC voltage (V=1Vpp, f=1kHz), a strong SPR signal jump was observed due to the analyte’s arrival on the sensing zone. As a result of the electrokinetic effects, the detection threshold of mass transport assisted SPR chips was improved by several orders of magnitude.