Fabrication of Photonic Crystal Biosensors using Micro-molding of Nanoporous Glass
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Fabrication of Photonic Crystal Biosensors Using Micro-molding of Nanoporous Glass Ian D. Block, Leo L. Chan, and Brian T. Cunningham Nano Sensors Group, University of Illinois at Urbana-Champaign Urbana, IL 61801, U.S.A. ABSTRACT We demonstrate a micro-molding method for submicron patterning of a low-index sol-gel nanoporous glass for the purpose of fabricating large-area (~3”x5”) label-free photonic crystal optical biosensors. SEM images show that the sol-gel exhibited minimal shrinkage and good substrate adhesion and depict precise and uniform pattern transfer over the fabricated area within the limits of measurement resolution. A unique characterization approach accurately and quickly revealed porous glass patterned over a large area with geometrical and material properties uniform within 1%. We suggest that this robust method is an excellent approach for photonic crystal sensor fabrication, and may also find applications in integrated optics and electronics.
INTRODUCTION Imprint lithography and nanoreplication methods are emerging as important techniques for imparting submicron features to a wide array of devices. In comparison to photolithography, and to a greater extent e-beam lithography, these methods provide higher throughput, lower cost, decreased processing complexity and equipment requirements, and the ability to directly pattern a large variety of materials [1]. This approach has been previously used to successfully mold sol-gel glass precursors into diffractive optical elements, lenses, and waveguides [2]. While porous low-k thin-films are important for interconnect dielectrics in IC manufacturing, their low refractive index also makes them attractive for optical device applications. In particular, we have found the low refractive index of porous dielectrics to be valuable for significantly increasing the sensitivity of a label-free photonic crystal optical biosensor [3]. In addition to the requirement of a low-index material, the biosensor application also mandates a subwavelength periodic surface structure, low-cost manufacturing for single-use disposable products, and a large surface area to enable incorporation within microplates and microarray slides. In this paper we present a novel micro-molding process for the purpose of fabricating enhanced sensitivity label-free optical biosensors. Using a unique characterization approach, we demonstrate the ability to uniformly pattern a sub-micron periodic surface structure into a low-index nanoporous sol-gel glass over a large area.
FABRICATION By adapting a sol-gel micro-molding process to a low-index porous glass precursor, we were able to design a low-cost, high-throughput process and avoid the use
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of photolithography. We chose to use polydimethylsiloxane (PDMS) as a molding tool because it has the beneficial properties of a low interfacial free energy, high flexibility and good chemical stability, enabling easy release from and accurate pattern transfer both from a rigid master mold and into the sol-gel material. Furt
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