We study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double... Show moreWe study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double-stranded DNA molecules to access micro-second dynamics of single molecules, and reveal the influences of dye-dye interaction at short interdye distances on the observed FRET values. We use neutron-scattering techniques to examine the origin of solid-like structures suggested in previous reports and the influence of the thermal history. We find that crystal nucleation takes place in glycerol at temperatures very close to the glass transition temperature. This observation suggests that the thermal history of the glycerol sample needs to be controlled for studying dynamical heterogeneity in supercooled liquids. For the first time, we demonstrate gold nanorods as local viscosity reporter to study heterogeneity in supercooled liquids. Following rotational dynamics of individual gold nanorods in glycerol upon cooling below 226K, we start to observe deviations of local viscosity from the bulk viscosity of glycerol. Our observation suggests heterogeneity on relatively large length scale exists at surprisingly high temperatures. In the end, we demonstrate gold nanorods for enhancing fluorescence from single molecules and for fluorescence correlation spectroscopy at micromolar concentrations with single-molecule sensitivity. Show less
This thesis presents two lines of research. On the one hand, we investigate heterogeneity in supercooled glycerol by means of rheometry, small-angle neutron scattering, and fluorescence imaging. We... Show moreThis thesis presents two lines of research. On the one hand, we investigate heterogeneity in supercooled glycerol by means of rheometry, small-angle neutron scattering, and fluorescence imaging. We find from the rheological experiments that supercooled glycerol can behave like weak solids at temperatures well above the glass transition. This is very surprising because glycerol is supposed to be purely liquid-like in this temperature range. However, the structural origin of this solid-like state of glycerol still remains unclear. The preliminary results from small-angle neutron scattering show that the solidified glycerol is structurally different from both the supercooled liquid and the crystal. In addition, fluorescence imaging of a thin film of glycerol doped with fluorescent probes reveals heterogeneous patterns of the fluorescence intensity, which is related to long-lived and micrometer scale density fluctuations in supercooled glycerol. All these results will contribute to understanding heterogeneity or even glass transition of supercooled liquids. On the other hand, we study the conformational dynamics of polyprolines by single-molecule FRET (F_rster resonance energy transfer) combined with temperature-cycle microscopy, a novel technique developed in our group, and demonstrate the potential of this new method to address complex molecular dynamics, for example the dynamics of protein-folding, at the single-molecule level. Show less
