Single-Molecule Fluorescence Trajectories for Investigating Molecular Transport in Thin Silica Sol−Gel Films

Abstract

Single-molecule fluorescence tracking has been used to examine diffusion of small molecules in sol-gel films in order to identify spatial heterogeneity in the structure and molecular diffusivities for different regions of the film. Fluorescence intensity profiles from single molecules are fit to a two-dimensional Gaussian function to determine their x,y positions with subpixel resolution. Scatter plots and histograms of molecular step sizes indicate that the trajectories conform to the predictions of a two-dimensional random walk. The mean-square step size is shown to be an unbiased estimate of the variance of the step-size probability distribution and a valid statistic for determining the diffusion coefficient from a molecular trajectory. The diffusion coefficients measured for different molecules are subjected to an F test, which showed that the sol-gel film exhibits spatial variation in the diffusion coefficient on a micrometer-length scale. The spatial variation in diffusivities is a measure of structural heterogeneity of these films.

Molecule motion at polymer brush interfaces from single‐molecule experimental perspectives

“…Subsequently, the trajectories derived from time‐dependent images can be analyzed to determine the modes of motion and the associated dynamic characteristic parameters. SMT has already been applied to study various complex material systems such as membrane‐incorporated molecule diffusion in cells, molecular transport in sol‐gel films, and intracellular delivery of nanomedicines . The example in Figure (b) exhibits the trajectories of individual fluorescence probes inside a polymer brush layer obtained by combining SMT with TIRF …”

Single-Molecule Investigations of Morphology and Mass Transport Dynamics in Nanostructured Materials

“…These same measurements have since been employed in studies of nanoporous alumina (64), mesoporous silica particles (55,65,66), monoliths (67,68), films (43,(69)(70)(71)(72)(73), and thermotropic (74)(75)(76)(77)(78)(79)(80) and lyotropic (67,81,82) LCs. As a representative example, Zhong et al (65) studied the diffusion and adsorption of rhodamine 6G (R6G) molecules within C18-modifed silica particles incorporating 10-nm pores, under conditions that mimic reversed-phase liquid-chromatographic separations.…”

Single‐Molecule Detection and Manipulation in Nanotechnology and Biology

“…To achieve even, wide-area illumination with lasers, however, some additional optics are required. For instance, a spinning holographic diffuser or ground glass plate is placed in the beam line prior to the objective to disrupt the coherence of the laser light and to eliminate specular patterns at the image plane [13,53]. Unfortunately, these designs can suffer unnecessary loss of incoming laser light to reflection and scattering.…”

“…For single molecules, point-source fluorescence is below the diffraction limit (~200-350 nm) and can be highly magnified to result in an imaged spot that is spread over several micron-sized pixels (~7-25 mm diameter) with each pixel corresponding to sample distances of tens of nanometers. Remarkably, diffusional information from imaging single-molecule movements over time can be recorded in sol-gel films, porous materials, and in lipid bilayer membranes [53,[69][70][71]. Because of low SNR, single-molecule trajectories are typically accurate only to within 100-200 nm.…”