The noise is the signal: exploring physico-chemical fluctuations with multiscale experimental models

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Noise is a universal aspect of experimental science, usually considered detrimental. Yet fluctuations contain significant information, as famously proposed by Onsager. Such links between microscopic fluctuations and macroscopic transport are heavily exploited by simulation studies, but their relevance to physico-chemical experiments is only now emerging as data at the single-particle level becomes available. While many important transport phenomena are amenable to fluctuation analysis, interpreting data from molecular experiments is extremely challenging, due to the short time and length scales and inherent complexity of these systems. This project aims to uncover the origins of physico-chemical noise, and thereby develop the tools required to extract and interpret microscopic information from molecular data, by exploring fluctuations in a unique combination of highly controlled mesoscale and nanoscale experimental models that can be driven out of equilibrium. I will first consider how confinement and interactions modify fluctuations in currents of colloidal particles driven through microfluidic channels. Quantifying fluctuations via direct observation of trajectories and calculation of the power spectral density will allow me to address long-standing questions surrounding 'coloured' noise signatures. Secondly, I will use flexible, model polymers to probe the complex interplay between conformational fluctuations, entropy and hydrodynamic interactions that modulate confined polymer transport. Finally, I will build on these findings to study, analyse and interpret fluctuations in the ionic currents associated with transport through flexible DNA nanostructures. My combined results will provide unprecedented insights into physico-chemical noise at a fundamental level, while the analysis tools developed will facilitate research into diverse phenomena; from transport through biological membranes, to flow in lab-on-a-chip devices and sensing with functionalised nanopores.