Characterization of molecule and particle transport through nanoscale conduits
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Nanofluidic devices have been of great interest due to their applications in variety of fields, including energy conversion and storage, water desalination, biological and chemical separations, and lab-on-a-chip devices. Although these applications cross the boundaries of many different disciplines, they all share the demand for understanding transport in nanoscale conduits. In this thesis, different elusive aspects of molecule and particle transport through nanofluidic conduits are investigated, including liquid and ion transport in nanochannels, diffusion- and reaction-governed enzyme transport in nanofluidic channels, and finally translocation of nanobeads through nanopores. Liquid or solvent transport through nanoconfinements is an essential yet barely characterized component of any nanofluidic systems. In the first chapter, water transport through single hydrophilic nanochannels with heights down to 7 nm is experimentally investigated using a new measurement technique. This technique has been developed based on the capillary flow and a novel hybrid nanochannel design and is capable of characterizing flow in both single nanoconduits as well as nanoporous media. The presence of a 0.7 nm thick hydration layer on hydrophilic surfaces and its effect on increasing the hydraulic resistance of the nanochannels is verified. Next, ion transport in a new class of nanofluidic rectifiers is theoretically and experimentally investigated. These so called nanofluidic diodes are nanochannels with asymmetric geometries which preferentially allow ion transport in one direction. A nondimensional number as a function of electrolyte concentration, nanochannel dimensions, and surface charge is derived that summarizes the rectification behavior of this system. In the fourth chapter, diffusion- and reaction-governed enzyme transport in nanofluidic channels is studied and the theoretical background necessary for understanding enzymatic activity in nanofluidic channels is presented. A simple analytical expression that describes different reaction kinetics is derived and confirmed against available experimental data of reaction of Trypsin with Poly-L-lysine. Finally, in the last chapter translocation of nanobeads through synthetic nanopores is experimentally investigated using resistive pulse sensing. The emphasis is placed on elucidating the effect of nanobead size on the translocation current and time. The key goals pursued in this study are multiplex detection of different nanobead sizes in a mixture of nanobeads as well as determining the concentration of each component. This problem other than its fundamental significance paves the way for developing new biosensing mechanisms for detection of biomolecules. This thesis further explores the molecule and particle transport in nanoscale conduits and serves for better characterization and development of nanofluidic devices for various applications.