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Investigation of the Effect of Particle Motion in Hydrophobic Nanopores: Effect of Hydrophobicity on Ionic Current, Electroosmotic Flow, and Resistive Pulse

Mousavi, Ali | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58570 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saeedi, Mohammad Hassan
  7. Abstract:
  8. In recent years, nanopores have emerged as powerful tools for detecting and separating nanoparticles, playing a prominent role in nanotechnology and the life sciences. The translocation of a nanoparticle through a nanopore induces transient perturbations in the ionic current, which appear as current pulses and serve as the basis for particle sensing. Since the resolution and accuracy of these signals play a crucial role in the sensitivity of nanopore-based measurements, various strategies have been investigated to enhance the output signal. Among the factors influencing nanopore behavior, the surface hydrophobicity is of particular significance. Hydrophobicity, in addition to its effect on electroosmotic flow and baseline current, can modify the local electric field and ion distribution inside the pore. Moreover, during particle translocation, hydrophobicity may alter the characteristics of the current pulse, thereby offering potential as a means of both signal enhancement and particle separation. In this thesis, a continuous numerical solution method including the coupling of Poisson, Nernst-Planck, and Navier-Stokes equations (PNP-NS model) was firstly used to investigate the influence of nanopore hydrophobicity on the baseline ionic current and electroosmotic flow profile. This effect was examined under varying pore radii, pore thicknesses, and applied voltages, and in all cases a substantial increase in electroosmotic velocity was observed. With increasing slip length from 0 to 50 nm, the baseline ionic current increased by approximately 1–2 nA. Subsequently, the velocity and flow field around nanoparticles translocating through nanopores with different slip lengths were analyzed. As expected, when both the nanopore and the nanoparticle possessed surface charges of the same sign, the particle velocity was altered even at small slip lengths and increased further with larger slip lengths. This feature was then used to demonstrate the possibility of separating particles based on slip length. We obtained suitable ranges of the slip length to separate different particles. Thereafter, by modeling nanoparticle translocation through nanopores of varying slip lengths, the effect of hydrophobicity on the characteristics of the resistive pulse was examined. The results revealed that a nanoparticle with a radius of 50 nm and a surface charge of -20 mC/m2 generates very different pulses while passing through nanopores with different slip lengths. In 0, 5, and 50 nm slip length cases, the pulse amplitudes were 2, 0.8, and 0.31 nanoamperes, and the pulse widths were 0.7, 0.4, and 0.03, respectively. These results were also extracted for the passage of a particle with a radius of 100 nm and a surface charge of -20 mC/m2, and the shape of pulses was similar, but the pulse amplitude for the nanopores with slip length of 0, 5, and 50 nm was 6, 3, and 2 times that of the particle with a radius of 50 nm, respectively. Finally, the possibility of using hydrophobicity as a method for amplifying the resistive pulse was investigated. The results showed that by appropriately adjusting the nanopore slip length, the signal resulting from the passage of a specific particle can be amplified. In these results, a particle with a radius of 50 nm and a surface charge of -100 mC/m2, while passing through a nanopore with a slip length of 10 nm, generated a signal 5 times stronger than a hydrophilic nanopore
  9. Keywords:
  10. Electroosmotic Flow ; Resistive Pulse Sensing ; Nanoparticles ; Slip Length ; Hydrophobic Nanopore

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