Synthetic nanopores are a powerful tool to control the transport of ions, molecules, and water at the molecular level, mimicking biological systems. In this research, polymer pores are prepared of different geometries, sizes, and surface chemistry to utilize features seen in naturally occurring systems. Specifically, it was one of the goals of this research to prepare and characterize single polymer pores that rectify the current due to a combination of electrostatic and hydrophobic interactions, similar to naturally occurring ion channels. Prior to modification, aqueous electrolytic solutions are able to conduct readily through the single polymer pores, but after the chemisorption of hydrophobic chemical groups, the pore demonstrates open and closed states. This behavior is also observed to be voltage dependent. Increasing voltage increases the probability of the pore to be in the open states. There is also a voltage range where the pore does not conduct at all. The hydrophobic gating was studied as a function of pore diameter and charge of the residual groups and could be used for an on demand drug delivery system.
Another technique that was utilized in this research is the resistive-pulse technique, which is a powerful approach to detect single molecules and particles. A single particle passing through a pore can be observed as a transient drop of the transmembrane current. This research focuses on resistive-pulse sensing experiments performed with track-etched polymer pores characterized by an undulating diameter along the pore length. The resistive pulses generated by spherical beads passing through these pores have a repeatable pattern of large variations corresponding to these diameter changes. We show that this pattern of variations enables the unambiguous resolution of multiple particles simultaneously in the pore, the detection of transient sticking of particles within the pore, and confirmation whether any individual particle completely translocates the pore. This pattern of variations was also found to be independent of the particle size. Pores with undulating diameter can also differentiate between particles of different shape but similar volume as demonstrated by our experiments with rod-shaped particles. This is due to particle interaction with the internal structure of the pore in a way that is specific to their size and shape. It is important to mention that distinguishing between various shapes is not possible with the classical resistive-pulse technique which is based exclusively on the detection of particle volume. We have also performed resistive-pulse experiments with hydrogel particles which revealed their ability to squish and expel solvent during translocation. Pores with undulating pore diameter can therefore be also applied to probe mechanical properties of translocating particles.
|Commitee:||Krivorotov, Ilya, Ritz, Thorsten|
|School:||University of California, Irvine|
|Department:||Physics - Ph.D.|
|School Location:||United States -- California|
|Source:||DAI-B 74/05(E), Dissertation Abstracts International|
|Subjects:||Physics, Biophysics, Materials science|
|Keywords:||Coulter counter, Electrophoresis, Hydrophobicity, Ions transport, Microgel, Nanopore, Particles transport, Resistive pulse|
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