Using ac-Field-Induced Electro-osmosis to Accelerate Biomolecular Binding in Fiber-Optic Sensing Chips with Microstructures

摘要

This article reports the use of ac-field-induced charges atnthe corners of microstructures on fiber-optic sensing chipsnto generate electro-osmotic vortex flows in flow cellnchannels that can accelerate solute binding on the fiber.nThe sensing chip made of a cyclic olefin copolymer COCnsubstrate contained a flow cell channel of dimensions 15nmm ×1mm× 1 mm. A partially unclad optical fiber wasnplaced within the channel. Relief-like strip structures ofn25-μm thickness fabricated on the channel bottom werenproduced with an injection-molding process. The externalnelectric field lines penetrating through the corners of thenplastic microstructures induce charges on the cornernsurfaces to build up electrical double layers. When a highfrequencynac field (∼100 kHz) is used to flip the fieldnpolarities quickly, neutralization of the induced chargencannot be accomplished. The electrical double layer isntherefore sustained. When absorbed charges in the doublenlayer are driven by the external field, electro-osmotic flowsnare generated. The unclad portion of the fiber was coatednwith biotin-functionalized gold nanoparticles. The streptavidinnsolution was filled in the channel from the feedingntube, and the ac field (∼50 V/cm) was subsequentlynturned on for 30 s. The ac-field-induced electro-osmoticnflows can accelerate solute transport in the sensingnchannel to enhance the binding kinetics of streptavidinnmolecules with biotin probes implanted on the goldnnanoparticle surface. As a result, the fiber-optic localizednplasmon resonance (FO-LPR) sensing signal becomesnsteady as soon as the external field is turned off. Inncontrast, the signal cannot reach steady state untiln200-300 s in a typical static sensing cell. A significantnreduction in the sensing response time is demonstrated.nThe binding assay of streptavidin with immobilized biotinnon gold nanoparticle-coated sensing fibers was validatednusing this mixing device. The detection limit for streptavidinnof ∼10-11 M is close to the reported valuesnobtained using static cells. Similarly, the sensingnresponse time of an orchid Odontoglossum ringspotnvirus (ORSV) sample was reduced from 1000 to 330 snwhen an external field was applied to mix the fluid forn60 s, even though the detection limit was maintained.