High Sensitivity Photonic Crystal Biosensor Incorporating Nanorod Structures for Enhanced Surface Area
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1010-V06-10
High Sensitivity Photonic Crystal Biosensor Incorporating Nanorod Structures for Enhanced Surface Area Wei Zhang, Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham Nano Sensors Group, University of Illinois at Urbana - Champaign, 208 North Wright Street, Urbana, IL, 61801
ABSTRACT We report efforts at enhancement of the surface area of a photonic crystal biosensor through incorporation of a porous titanium dioxide film into the device. The film possessing the structure of nanorods is deposited by the glancing angle deposition technique. Results for detection of polymer films, large proteins and small molecules indicate up to a four-fold enhancement of detected adsorbed mass density for high surface area sensors, compared with sensors without the high surface area coating. INTRODUCTION Label-free optical biosensors based on photonic crystals have emerged as important tools for pharmaceutical research, diagnostic testing, and environmental monitoring [1, 2]. Development of sensor designs that enhance sensitivity is especially important because it allows detection of lower concentrations of analytes and detection of small molecules with a higher signal-to-noise ratio. Previously, enhancement of the surface area for ligand attachment on an optical biosensor has been achieved through the use of polymer hydrogels such as dextran [3, 4]. Although hydrogel films offer a high surface area for covalent attachment of biomolecules, disadvantages of this method include (1) the hydrogel film is not an integral part of the device (2) it involves a complex procedure for deposition and functionalization using liquid-based processes (3) as a polymer based on a sugar monomer, the dextran layer is subject to swelling and/or dissociation by extremes in pH. Therefore, enhancement of biosensor surface area using a more chemically and mechanically robust system would be advantageous. Glancing angle deposition (GLAD) [5] has been shown to be a method able to create thin films with very high porosities and surface-area-to-volume ratios. By orientating the incoming flux at an oblique angle, the self-shadowing effect during the deposition results in a porous film with a structure composed of isolated vertical nanorods. This technique has been used in applications such as dielectric reflectors [6], optical filters [7] and liquid crystal displays [8]. In this work, we show the enhancement of photonic crystal optical biosensor sensitivity through application of a thin GLAD dielectric coating to the sensor surface. We demonstrate up to 4x sensitivity improvement compared to sensors without the GLAD film. Sensitivity is compared for detecting polymer film adsorption, large protein adsorption and detection of a small molecule. This method may be broadly applied to any type of biosensor ñ optical, acoustic, or otherwise to enhance sensitivity.
EXPERIMENTAL Sensor Fabrication and Reflection Spectrum Fabrication of the photonic crystal biosensor has been described in previous publications [9]. Figure 1 (a) shows the cross section of
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