Fabrication, modification and self-assembly of metallic nano-particles for localized surface plasmon resonance and surface enhanced vibrational spectroscopy applications
Date
2012-09-12
Authors
Fan, Meikun
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Abstract
Metallic nanoparticles (MNPs), especially those made of gold, silver, and copper, are of great importance in many scientific disciplines. The free electrons inside the MNPs can respond collectively to applied electromagnetic fields. This is called the excitation of localized surface plasmon resonance (LSPR).
One of tile most important aspects of surface plasmons (SPs) excitation is that it allows the localization of 'the electromagnetic field al certain regions of tile nanostructured surface (or, in other words, the local field is "enhanced"). Based on this. surface enhanced Ramlln scattering ( ERS) and localized surface plasmon resonance (LSPR) sensing can be realized.
The work in this thesis can be divided in two parts: These include the exploration of self-assembled MNPs as new substrates for surface enhanced vibrational spectroscopy: and the sensing applications of these assembled MNPs.
In the first part. the assembly ofMNPs on gold electrodes and glass slides were explored.
Firstly. "layer-by-layer"' self-assembly of Au NPs on gold electrode was used to construct n highly sensitive and reproducible SERS substrate that can work in an electrochemical environment. The SERS perfonlmnce. in terms of enhancement and reproducibility, with the the numbers Au NPs "Iayers", was examined. Meanwhile, the potential window. during which a reproducible in sit" SERS experiment can be performed, was investigated. The possibility of such kind of substrate to be used in surface enhanced polarization modulation infrared absorption spectroscopy (PM-IRRAS) was also discussed.
The "layer-by-layer" self-assembly idea was extended to Ag NPs supported on glass. The resulted substrate revealed that after multiple time self-assembly, the SERS enhancement performance of lhe substrate can be 3 to 4 orders of magnitude higher than just one Ag NPs deposition, depending on the wavelength used. Using this substrate, a near-single-molecule sensitivity has been achieved.
In the second pan, sensing applications of the assembled MNPs were examined. The multiple "layers" Au NPs on gold electrode was used to characterize a sample biofuel cell anode, which consists three molecular "layers": the linker 4-hydroxyphenol (HTP), the co-enzyme analog Cibacron blue (CB), and the formaldehyde dehydrogenase (FaIDH). (In situ) SERS spectra or the sample biofuel cell at different construction stages were recorded and compared.
The work about self-assembly ofAg NPs on glass was extended to fiber optics. The tip of a fiber optic was modified with multiple "layers" ofAg PSt and the analytical performance for remote sensing of this device was examined by the using of dyes with different structures and charges. It was found that this device was among one of the most sensitive SERS remote sensors when compared to the literature.
Finally, a LSPR biosensor based on self-assembly of Ag NPs on PET, a common type of plastic, has been developed. The advantage of this sensor is that the surface of the Ag Ps was able to be tailored into differenl functional groups, and therefore met different requirements. Sample analysis for biological relevant species was performed.
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Keywords
nanoparticles