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Optical Bio-sensing And Imaging Assisted With Gold Nanoparticles

Posted on:2011-07-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:X LiFull Text:PDF
GTID:1118330332484255Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Nano-biophotonics is an emerging frontier that involves a fusion of nanotechnology, bioscience and photonics. It provides novel tools and opportunities for lifescience and medicine. Gold nanoparticles (GNPs), with notable surface plasmon resonance (SPR) properties, are widely utilized in nano-biophotonics. In this thesis, methods of synthesis, coating and conjugation of the nanoparticles are presented. The favorable performances of SPR optical properties of GNPs are summarized. With these optical properties, GNPs are applied in biomolular recognition sensing, optical imaging and photo-thermal therapy.Gold nanospheres (GNSs) and gold nanorods (GNRs) are utilized in this thesis. Synthesis of various sizes of these two particles are introduced. Coating with multilayered polyelectrolyte and silica on the particles and conjugation with biomolecules and other particles are investigated. GNSs and GNRs have some unique optical properities, including localized surface plasmon resonance (LSPR) extinction spectrum, which is sensitive to the size, shape, inter-particle distance and entironment of the particles; fluorescence quenching effect; enhanced local fields and robust two-photon emission.Streptavidin, which specifically conjugates with four molecules of biotin, induces the self-assembly of biotin-capped GNPs in their solution. Aggregations of GNPs are detected by monitoring the redshift and broadening of LSPR spectral band, since that is sensitive to the inter-particle distance of the GNPs. Streptavidin, which conjugates with the biotin-capped GNPs, induces increases of local refractive index near the immobilized GNPs. This specific adsorption is detected by monitoring the redshift of LSPR band, since that is sensitive to the entironment of the GNPs. Polymer-coated GNSs and GNRs are utilized to realize such LSPR-based biotin-streptavidin recognition. These two sensing mechanisms are also compared.For DNA sensing, the hybridization of two oligonucleotide sequences, which conjugated with quantum dots (QDs) and GNPs separately, makes the two particles getting close, that results in the fluorescence quenching of QDs. Whether the two DNA sequences are complementary is detected via monitoring the quenching effect on fluorescence intensities of QDs. Methods of DNA sensing associated with GNS-based quenching are optimized. Principles of GNP-induced quenching effect associated with Forster-resonance/ surface-energy-transfer are explored utilizing GNRs with tunable LSPR spectra and various polymer-coating thichnesses. Micro-fluidic technologies are also designed for such DNA sensing combined with GNPs.Enhanced local electromagnetic fields near GNPs have two main applications: fluorescence enhancement and surface-enhanced Raman scattering. Fluorescence lifetime and quantum yield of QDs near GNRs are investigated to clarify what impacts on the enhancement efficiency. GNRs and GNR-composed nano-structures with "hot spots" are studied to enhance Raman signals of nearby molecules.Taking advantage of a property of high optical scattering, GNRs are utilized for targeting cancer cells and for applications in liquid crystals via the dark-field microscopy. Combined with QDs, GNR-composites are developed in fluorescence lifetime imaging of cancer cells under one-photon and two-photon excitations. Fluorescence enhancement of QDs and notable two-photo emission of GNRs are observed. Photo-thermal therapy of cancer cells is realized with GNR-tags under an excitation with on-SPR-resonance wavelength, taking advantage of a property of high optical absorption of the GNR.
Keywords/Search Tags:Gold Nanoparticle, Surface Plasmon Resonance, Biomolecular Recognition Sensing, Fluorescence Quenching, Fluorescence Enhancement, Surface-Enhanced Raman Scattering, Dark-Field Microscopy Imaging, Fluorescence Lifetime Imaing Microscopy
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