Transmembrane protein ion channels can regulate intercellular transport in response to external stimulus, playing a vital role in diverse physiological functions. Replicating such stimulus-responsive behaviors in the artificial counterparts, e.g. solid-state nanopores, is of great interest in a variety of cross-disciplinary studies and applications, yet has remained challenging due to complicated structures of naturally occurring protein channels and anomalous transport phenomena of the nanoscale fluid. Current stimulus-responsive solid-state nanopores are achieved by employing functional materials and/or geometrical/surface charge asymmetry but suffer from low sensitivity, slow response, and limited reversibility. To tackle the existing challenges, this thesis investigates electromechanical coupled transport phenomena in a new type of stimulus-responsive nanopores, i.e., nanoparticle-blocked nanopores, and their potential applications in gating and sensing. The first part of this thesis describes a bio-inspired liposome-enabled nanopore gating strategy inspired by the ''ball-and-chain'' inactivation mechanism in voltage-gated protein ion channels. By manipulating the position of the liposome nanoparticles around the nanopore, we demonstrate an electromechanically gated nanopore with rapid, reversible, and complete gating response, which allows unprecedented spatial and temporal control of ion/chemical transport across the nanopore. In the second part of the thesis, we report an ultra-mechanosensitive ion transport across the single nanopore blocked by the rigid nanoparticles. The observed pressure-suppressed ion conduction partially mimics the behavior of stretch-inactivated ion channels and is rationalized with mechanical-induced particle motion. Finally, in the third part of the thesis, we further utilize the mechanosensitive ion conduction in nanoparticle-blocked nanopores to develop a nanopore-based platform for mechanical characterization of single nanoparticles. This new platform overcomes the limitations of current characterization techniques and provides an alternative nano-mechanical characterization approach in an efficient and cost-effective manner. We expect this work to provide a convenient platform to achieve natural stimulus-responsive functionalities as well as to develop emerging applications in drug delivery, biosensing, single-molecule manipulation, and ionic-based computation and storage. / 2024-01-25T00:00:00Z

Transport phenomena at the nanoscale can differ from that at the continuum because the large surface area to volume ratio significantly influences material properties. While the modeling of many such transport processes have been reported in the literature, a few examples exist that integrate molecular approaches into the more typical macroscale perspective. This thesis extends the understanding of nanoscale transport governed by charge, mass and energy transfer, comparing these phenomena with the corresponding continuum behavior where applicable. For instance, molecular simulations enable us to predict the solvation structure around ions and describe the diffusion of water in salt solutions. In another case, we find that in the absence of interfacial effects, the stagnation flow produced by two opposing nanojets can be suitably described using continuum relations. We also examine heat conduction within solids of nanometer dimensions due to both the ballistic propagation of lattice vibrations in small confined dimensions and a diffusive behavior that is observed at larger length scales. Our simulations determine the length dependence of thermal conductivity for these cases as well as effects of isotope substitution in a material. We find that a temperature discontinuity at interfaces between dissimilar materials arises due to interfacial thermal resistance. We successfully incorporate these interfacial nanoscale effects into a continuum model through a modified heat conduction approach and also by a multiscale computational scheme. Finally, our efforts at integrating research with education are described through our initiative for developing and implementing a nanotechnology module for freshmen, which forms the first step of a spiral curriculum. / Ph. D.