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This article reports the use of ac-field-induced charges at the comers of microstructures on fiber-optic sensing chips to generate electro-osmotic vortex flows in flow cell channels that can accelerate solute binding on the fiber. The sensing chip made of a cyclic olefin copolymer COC substrate contained a flow cell channel of dimensions 15 mm x 1 mm x 1 mm. A partially unclad optical fiber was placed within the channel. Relief-like strip sWuctures of 25-[micro]m thickness fabricated on the channel bottom were produced with an injection-molding process. The external electric field lines penetrating through the comers of the plastic microstructures induce charges on the comer surfaces to build up electrical double layers. When a high0-frequency ac field (~100 kHz) is used to flip the field polarities quickly, neutralization of the induced charge cannot be accomplished. The electrical double layer is therefore sustained. When absorbed charges in the double layer are driven by the external field, electro-osmotic flows are generated. The unclad portion of the fiber was coated with biotin-functionalized gold nanopartcles. The streptavidin solution was filled in the channel from the feeding tube, and the ac field (~50 V/cm) was subsequently turned on for 30 s. The ac-field-induced electro-osmotic flows can accelerate solute transport in the sensing channel to enhance the binding kinetics of streptavidin molecules with biotin probes implanted on the gold nanoparticle surface. As a result, the fiber-optic localized plasmon resonance (FO-LPR) sensing signal becomes steady as soon as the external field is turned off. In contrast, the signal cannot reach steady state until 200-300 s in a typical static sensing cell. A significant reduction in the sensing response time is demonstrated. The binding assay of streptavidin with immobilized biotin on gold nanoparticle-coated sensing fibers was validated using this mixing device. The detection limit for streptavidin of [~10.sup.-11] M is close to the reported values obtained using static cells. Similarly, the sensing response time of an orchid Odontoglossum ringspot virus (ORSV) sample was reduced from 1000 to 330 s 10.1021/ac902682k

A novel organically modified silica material has been prepared by covalent linking of the carboxylic acid group of lactate dehydrogenase to the amino group of an organoalkoxysilane precursor via a carbodiimide coupling reaction during the sol-gel process. The material was used to fabricate a leak-free biosensor. The experimental variables and characteristics of the biosensors were studied by electrochemical methods. Results showed that the coenzyme concentration, mediator concentration, and electrode rotation speed will influence the sensitivity of the biosensor. The biosensors exhibited high sensitivity (1.47 [micro]A/mM), low detection limit (1.5 [micro]M), reasonable apparent activity (1.31 [min.sup.-1]), good fabrication reproducibility, and good long-term operational stability (~1 week).

A novel class of fiber-optic evanescent-wave sensor was constructed on the basis of modification of the unclad portion of an optical fiber with serf-assembled gold colloids. The optical properties and, hence, the attenuated total reflection spectrum of serf-assembled gold colloids on the optical fiber changes with different refractive index of the environment near the colloidal gold surface. With sucrose solutions of increasing refractive index, the sensor response decreases linearly. The colloidal gold surface was also functionalized with glycine, succinic acid, or biotin to enhance the selectivity of the sensor. Results show that the sensor response decreases linearly with increasing concentration of each analyte. When the colloidal gold surface was functionalized with biotin, the detection limit of the sensor for streptavidin was 9.8 x [10.sup.-11] M. Using this approach, we demonstrate proof-of-concept of a class of refractive index sensor that is sensitive to the refractive index of the environment near the colloidal gold surface and, hence, is suitable for label-free detection of molecular or biomolecular binding at the surface of gold colloids.