| Summary: | 博士 === 國立清華大學 === 化學系 === 92 === Abstract
Supercritical water (SCW) is used for the first time for the opening and thinning of multiwall carbon nanotubes (MWNTs). The influence of variation of pressure, temperature and time on the opening and thinning of MWNTs is examined. In SCW, opening and thinning of MWNTs is observed. The presence of oxygen (~2 mmol) shows improved thinning of MWNTs with the collapsed outer graphene layers tending towards the inner layers. The morphologies of MWNTs are critically analyzed using transmission electron microscopy (TEM). MWNTs with different morphology were prepared using SCW oxidation and investigated by TEM and electron energy-loss spectroscopy (EELS). TEM results indicate that the peeling and sharpening of MWNTs are influenced by the etching process in SCW oxidation, of which oxidation time and amount of oxygen used is crucial. A simplified etching model is proposed, which indicates that the difference of mean etching rate between two adjoining blocks causes the morphological variation of MWNTs. The EELS results show change in characteristic energy-loss peaks as a function of total shell numbers along longitudinal axis of individual peeled-tube.
SCW medium also served as a highly destructive environment, which broke the silver aggregates into nanoparticles (diameter 2~20 nm). Water was drawn into open-ended MWNTs by capillary suction which caused silver (Ag) nanoparticles being pulled into the ends of MWNTs. The Ag nanoparticles presumably transported in nanochannels of MWNTs by the fluidity of SCW, stacked and fused to form nanorods, suggesting SCW associated with MWNTs might be exploited as a nanoreactor. Furthermore, SCW used to be a medium alone for fragmenting Ag aggregates and organized the resulting Ag nanoparticles into chain-like nanowires and nanobanners. A variety of 1D and 2D nanostructured assemblies were formed from the nanoparticles by variations in pressure, temperature, and time. The size distribution of Ag nanoparticles is controllable in the range of 2–20 nm. Under appropriate conditions, the SCW medium allows the merging of Ag nanoparticles to form Ag nanowires with diameters of ~60 nm, and nanobanners of triangle-shaped morphology with lengths of several hundred �慆.
Rather than just preparation of silver nanoparticles, the bioapplication of these metal nanoparticles were also concerned. Since fluorescent probes for biomolecular recognition are of great importance in the fields of chemistry, biology, and medical sciences, as well as in biotechnology. These probes have been used for mechanism studies of biological functions and in ultra sensitive detection of biological species responsible for many diseases. In the post-genome era, quantitative studies of genomic information for disease diagnosis and prevention and drug discovery become fast growing areas of research and development. This has led to a continued demand for advanced biomolecular recognition probes with high sensitivity and high specificity. The molecular beacon (MB), a recently developed single-stranded DNA molecule, appears to be a very promising probe for quantitative genomic studies. MBs are hairpin-shaped oligonucleotides that contain both fluorophore and quencher moieties and act like switches that are normally closed to bring the fluorophore/quencher pair together to turn fluorescence “off”. When prompted to undergo conformational changes that open the hairpin structure, the fluorophore and the quencher are separated, and fluorescence is turned “on”. A hybrided system composed of a ssDNA molecule and a 20 nm diameter gold/silver alloy nanoparticles. The quenching efficiency was varied by the mole ratio of gold and silver. The pure silver nanoparticles as quencher shows the best quenching efficiency and the regain efficiency was increased by gold mole fraction.
Except metal nanoparticles used as the quencher of MBs for reorganizing target DNA, fluorescent silica nanoparticles and gold nanorods were also applied in the obesity-related protein assay and immunosensing, respectively. Fluorescent silica NPs were prepared using reverse microemussion method and can be functionalized with carboxylate, amine, and thiol group for conjugated with biomolecules. The phosphonate group plays an important role in the dispersion of fluorescent silica NPs with amine and thiol groups. Obesity is a common nutritional disorder associated with diabetes, hypertension, hyperlipidemia, cancer and the other health related problems. Fluorescent silica NPs with carboxylate group were further used as the probe in the obesity-related protein assay. The oriented assembly of gold nanorods as biorecognition system was useful for the immune sensing events. Self-assembled thioctic acid containing a terminal carboxylate group at the end of gold nanorod can facilitate conjugation with anti-mouse IgG, which provides an anchoring site. Driven by the biorecognition with mouse IgG, nanorods assemble to form extended nanorod chains.
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