Fabrication and characterization of a plasmonic biosensor using non-spherical metal nanoparticles

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Title: Fabrication and characterization of a plasmonic biosensor using non-spherical metal nanoparticles
Author: Jung, Bong-Su, 1972-
Abstract: Label -free detection techniques have an important role in many applications , such as situations where few molecules - - rather than low molarity - - need to be detected , such as in single -cell screening . While surface plasmon resonance (SPR ) scattering from metal nanoparticles has been shown to achieve significantly higher sensitivity in gene arrays , such an approach has not been demonstrated for protein arrays . SPR -based sensors could either use simple absorption measurement in a UV -Vis spectrometer or possibly surfaceenhanced Raman spectroscopy as the detection mechanism for molecules of interest . However , non -spherical particles are needed to achieve high sensitivity and field enhancement that is a requirement in both techniques , but these shapes are not easy toproduce reproducibly and preserve for extended periods of time . Here I present a carbonbased template -stripping method combined with nanosphere lithography (NSL ) . This fabrication allows to preserve the sharp features in atomically flat surfaces which are a composite of a non -spherical metal nano -particle (gold or silver ) and a transparent embedding material such as glass . The stripping process is residue -free due to the introduction of a sacrificial carbon layer . The nanometer scale flat surface of our template stripping process is also precious for general protein absorption studies , because an inherent material contrast can resolve binding of layers on the 2 nm scale . These nanocomposite surfaces also allow us to tailor well -defined SPR extinction peaks with locations in the visible or infrared spectrum depending on the metal and the particle size and the degree of non -symmetry . As the particle thickness is reduced and the particle bisector length is increased , the peak position of the resonance shifts to the red . Not only the peak position shifts , but also the sensitivity to environmental changes increases . Therefore , the peak position of the resonance spectrum is dependent on the dielectric environmental changes of each particle , and the particle geometries . The resulting silver or gold nanoparticles in the surface of a glass slide are capable of detecting thiol surface modification , and biotin -streptavidin protein binding events . Since each gold or silver particle principally acts as an independent sensor , on the order of a few thousand molecules can be detected , and the sensor can be miniaturized without loss of sensitivity . UNSL -Au metal nanoparticle (MNP ) sensors achieve the sensitivity of close to 300 nm /RIU which is higher than any other report of localized surface plasmon resonance (LSPR ) sensors except gold nanocrescents . Finite -difference -time -domain (FDTD ) and finite -element -method (FEM ) numerical calculations display the influence of the sharp features on the resonance peak position . The maximum near -field intensity is dependent on the polarization direction , the sharpness of the feature , and the near -field confinement from the substrate . 3D FDTD simulation shows the local refractive index sensitivity of the gold truncated tetrahedron , which is in agreement with our experimental result . Both experimental and numerical calculations show that each particle can act as its own sensor .
URI: http : / /hdl .handle .net /2152 /3614
Date: 2008-08-28

Citation

Fabrication and characterization of a plasmonic biosensor using non-spherical metal nanoparticles. Doctoral dissertation, The University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /3614 .

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