Fabrication of Hybrid Nano/Microstructured Optic and Biosensor Components using Gas-Assisted Hot Embossing and AAO Mold
Date Issued
2010
Date
2010
Author(s)
Chang, Wei-Yi
Abstract
Nanostructured surfaces are widely used for anti-reflection and bio-sensing. But the production of nanostructured mold most relies on expensive high-end facilities. This study presents an easy and low-cost approach. Anodic aluminum oxide (AAO) mold and gas-assisted hot embossing process are employed to fabricate the nanostructures on the surface of polycarbonate (PC). They are further used for optical and bio-sensing applications.
The alumina oxide membranes with nanoholes of 100 nm, 160 nm and 450 nm in pitches were fabricated via two-step anodization, employing anodization voltage of 40 V, 80 V and 180 V respectively, and the pore size can be controlled by anodization time and concentration of electrolyte. The soften polymeric material can be filled into mold with periodic nanopores by gas-assisted hot embossing process, with the depth of filling determined by embossing temperature and pressure. Sub-wavelength structures (SWSs) can thus be produced.
Two applications are investigated in this study. The first is the anti-reflection film. PC film with nanorods of 150 nm in diameter, 160 nm in pitch and 1 μm in height was protruded in the AAO mold. The cone-shaped nanostructures with height of 260 nm were then obtained when the PC film was stripped off from the AAO mold. The PC film with nanocone structures reduces the reflectivity from 8.9 % of a bare film to 2 % of a film with tapered SWSs at the wavelength of 550 nm. This technology is further used to fabricate microlens array with anti-reflective SWSs on it. The nanostructures and microlens array are fabricated on the same PC substrate by hot embossing in sequence. First, AAO template is used as the template for fabricating nanostructures on the PC film by hot embossing. Stainless steel mold of micro-holes array, with 145 μm in diameter and 200 μm in pitch, is then used as the mold to form microlens array. By protrusion of the nanostructured PC film into the micro-holes of the mold, an array of convex microlenses with anti-reflective nanostructures is formed. This proposed technique has proven effective and efficient in fabricating nano/micro hybrid lens array on the polymeric substrate.
Another application is the biosensors. AAO molds with nanopores of 70 nm, 150 nm in diameter and 100 nm, 450 nm in pitch are coated with a layer of gold film, then a gas-assisted hot embossing process is used to imprint gold film nanostructure onto polymer (PC) substrates. Since localized surface plasmon resonance (LSPR) taking place in periodic-gold-film-nanostructured surface, the red shift can be detected, based on transmission spectra, when they are immersed in different solutions. In this study, the transmission spectrum in air and water are compared, showing the potential for biosensing applications. Another approach is to fabricate the nanocones on the surface of PC film by protruding the PC into nanopores of AAO and then tearing the PC film off the mold. The pitch of the nanocones is about 100 nm. The nanocones are subsequently coated with gold. When the gold-coated nanocones are immersed in monolayer-foring aqueous solutions of p-mercaptobenzoic acid (PMBA), the surface-enhanced Raman scattering (SERS) spectra is detected, showing that this surface has the function of enhancing the signal of the SERS. This reveals the potential of using this gold-coated periodic nanorod structures for sensing the molecular structure of different organisms based on SERS.
Subjects
AAO
anti-reflection
SWSs
biosensor
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