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The plasmonic properties of metallic nanoparticles and macroscopic Au film have been thoroughly investigated for
the development of biosensors based on surface plasmon resonance (SPR). Nanoparticle based localized surface
plasmon resonance (LSPR) is a technique extremely sensitive to molecular adsorbate, whilst conventional SPR
based on the Kretschmann configuration (macroscopic smooth Au film) is especially sensitive to bulk refractive
index. SPR currently provides the best RI resolution, a measure typically used for comparison of the potential of
plasmonic sensor. A technique that could combine high bulk refractive index resolution and high sensitivity to
molecular adsorbate would increase the scope of SPR-based technique by providing lower detection limits. A
potential solution may exploit micro-structured Au films. However, the plasmonic properties of micropatterned
metallic films are still relatively unknown. We have undertaken the study of the plasmonic properties from Au film
with features on the order of 1 to 3 μm. Microtriangle and microhole arrays were fabricated by modified nanosphere
lithography, consisting of a polymer microsphere mask deposited in a close-packed hexagonal monolayer, etched by
oxygen plasma. Etch time controls the diameter of the microhole and the initial microsphere diameter sets the
periodicity. Investigation of the SPR properties in the Kretschmann configuration was undertaken using a SPR with
a dove prism and a multi-wavelength scanning angle SPR. The sensitivity of SPR with microhole arrays exhibits an
improvement by a factor of 3 in comparison to SPR using a smooth Au film. This is accomplished by tuning the
angle to near 73 degrees (with a BK7 glass prism). Moreover, the sensitivity to the immobilization of an antibody
was improved by at least a factor of 4 as demonstrated with the kinetics of immobilization for IgY, without
employing secondary amplification techniques. No modification to the instrumentation is required and microhole
arrays improve resolution of the SPR response.
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