Chip-based biosensor arrays for label-free and high-throughput detection were fabricated and tested. The sensor array was composed of a 150-nm-thick, 50-nm-gap, and 600-nm-period gold nanoslits. Each array size was 100 µm×100 µm. A transverse-magnetic polarized wave in these metallic nanostructures generated resonant surface plasmons at a wavelength of about 800 nm in a water environment. Using the resonant wavelength shift in the nanoslit array, we achieved detection sensitivity up to 668 nm per refractive index unit, about 1.7 times larger than that reported on an array of nanoholes. An antigen–antibody interaction experiment in an aqueous environment verified the sensitivity in a surface binding event.
This study develops a coupled waveguide-surface plasmon resonance (CWSPR) biosensor with a sub-wavelength grating structure for the real-time analysis of biomolecular interactions. In the proposed optical metrology system, normally incident white light is coupled into the waveguide layer through the sub-wavelength grating structure thereby enhancing the wave vector which excites the surface plasmons on the metal sensing surface. The proposed CWSPR biosensor not only retains the same sensing sensitivity as that of a conventional surface plasmon resonance device, but also yields a sharper dip in the reflectivity spectrum and therefore provides an improved measurement precision. Moreover, the metrology setup overcomes the limitations of the conventional Kretschmann attenuated total reflection approach and is less sensitive to slight variations in the angle of the incident light. The experimental results confirm that the current CWSPR biosensor provides a straightforward yet powerful technique for real-time biomolecular interaction analysis.
In this paper, the reflection resonance spectrum of a sub-wavelength diffraction grating-coupled waveguide is used to analyze biomolecular interactions in real time. When the diffraction grating waveguide structure is destroyed by external factors such as slight refractive index changes of the buffer or molecule adsorption on the grating surface, the optical path of the light coupled through the grating into the waveguide is changed and a resonance wavelength shift is induced as a result. By detecting this resonance wavelength shift, the optical waveguide biosensor provides the ability to identify the kinetics of the biomolecular interaction on an on-line basis without the need for the extrinsic labeling of the biomolecules. A theoretical analysis of the sub-wavelength optical waveguide biosensor is performed. A biosensor with a narrow reflection resonance spectrum, and hence an enhanced detection resolution, is then designed and fabricated. Currently, the detection limit of the optical waveguide sensor is found to be approximately 10-5 refractive index units. The developed biosensor is successfully applied to study the kinetics of an antibody interaction with protein G adsorbed on the sensing surface.
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