Various Ag and Au nanostructured films such as Ag nanoparticle (NP) films, Au NP films, and Au NP/TiO2/Au NP
sandwich structures are fabricated by oblique angle deposition (OAD) and glancing angle deposition (GLAD) methods.
Their optical absorbance properties and localized surface plasmon resonance (LSPR) have been studied systematically
for samples prepared at different deposition conditions. Under the same deposition conditions, the Ag or Au NP
substrates produced by GLAD method are more uniform and reproducible. The LSPR wavelength of Ag or Au NP
substrates can be easily tuned by changing the film thickness, the deposition angle, and the coating of dielectric layer.
The ability of the nanoparticle films as a chemical and biological biosensor has been explored by sensing the
biomolecule NeutrAvidin and the bacterium Salmonella. Those NP films are very sensitive to chemical detection but are
insensitive for bacteria detection. Based on Mie theory and effective medium theory, this is due to the small contact area
between the nanoparticle and the bacteria, and the short range interaction of the local electric field. Our results
demonstrate that shadowing based growth is a very versatile fabrication technique to produce reproducible and finetuned
LSPR substrates.
Metallic nanoparticles usually exhibit localized surface plasmon resonance (LSPR) due to the collective oscillation of
electrons upon light excitation. Different applications require specific LSPR wavelengths and absorbance spectra. The
ability to engineer the nanostructure and to tune the location of the LSPR wavelength is very important for the sensing
applications. We present a simple but versatile fabrication technique, the oblique angle deposition, to tune the LSPR
wavelength of Ag thin films. Oblique angle deposition was used to produce silver nanoparticle films with nominal
thickness from 5 nm to 100nm and two deposition angles, 0° and 85°. With increasing thickness, the LSPR wavelength is
blue shifted. At the large deposition angle, the LSPR wavelength is blue shifted by 3nm on average with every 5nm
thickness increment. The stability of the Ag LSPR substrate under liquid environment has been studied, and a surface
passivation method is proposed. Those substrates are capable of detection 10-10 M NeutrAvidin.
Nanotechnology applications for food safety and biosecurity, especially development of nanoscale sensors for foodborne
pathogen measurement are emerging. A novel bio-functional nanosensor for Salmonella detection was developed using
hetero-nanorods. The silica nanorods were fabricated by glancing angle deposition method and the gold was sputtered
onto the silica nanorods. Alexa488-succinimide dye was immobilized onto the annealed Si nanorods via the attachment
between dye ester and primary amine group supplied by the
3-Aminopropyltriethoxysilane. The anti-Salmonella was
conjugated to gold via Dithiobis[succinimidylpropionate]
self-assembly monolayer. Due to the high aspect ratio nature
of the Si nanorods, hundreds or thousands of dye molecules attached to the Si nanorods produced enhanced fluorescence
signal. These biologically functionalized nanorods can be used to detect Salmonella with fluorescent microscopic
imaging. This new nanoscale biosensor will be able to detect other foodborne pathogenic bacteria for food safety and
security applications.
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