Objective Approaches to Single-Molecule Time Series Analysis

[摘要] Single-molecule spectroscopy has provided a means to uncover pathways and heterogeneities that were previously hidden beneath the ensemble average. Such heterogeneity, however, is often obscured by the artifacts of experimental noise andthe occurrence of undesired processes within the experimental medium. This hassubsequently caused in the need for new analytical methodologies. It is particularlyimportant that objectivity be maintained in the development of new analyticalmethodology so that bias is not introduced and the results improperly characterized.The research presented herein identifies two such sources of experimental uncertainty,and constructs objective approaches to reduce their effects in the experimental results.The first, photoblinking, arises from the occupation of dark electronic states within theprobe molecule, resulting in experimental data that is distorted by its contribution. Amethod based in Bayesian inference is developed, and is found to nearly eliminatephotoblinks from the experimental data while minimally affecting the remaining dataand maintaining objectivity. The second source of uncertainty is electronic shot-noise,which arises as a result of Poissonian photon collection. A method based in waveletdecomposition is constructed and applied to simulated and experimental data. It isiiifound that, while making only one assumption, that photon collection is indeed aPoisson process, up to 75% of the shot-noise contribution may be removed from theexperimental signal by the wavelet-based procedure. Lastly, in an effort to connectmodel-based approaches such as molecular dynamics simulation to model-freeapproaches that rely solely on the experimental data, a coarse-grained molecular modelof a molecular ionic fluorophore diffusing within an electrostatically charged polymerbrush is constructed and characterized. It is found that, while the characteristics of thecoarse-grained simulation compare well with atomistic simulations, the model is lackingin its representation of the electrostatically-driven behavior of the experimental system.

[发布机构] Rice University

[效力级别] molecule