Degree Type

Dissertation

Date of Award

2013

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Pranav Shrotriya

Abstract

Seamless integration of artificial components with biological systems to form an elegant biotic-abiotic interface or smart surface has promising application potential in biomedical engineering. The specific aim of this study is to implement the actuation and modulation of binding behavior between biomolecules under electrostatic stimuli, and investigate the corresponding force interaction between the complementary pairs. The nanofabrication technology was utilized to establish the patterned binding pair of thrombin and DNA aptamer on gold substrate, and different electrical fields were applied on the system to evaluate electrostatic influence. The atomic force microscopy (AFM) surface imaging was then used to explicate the surface height change after the removal of the electrical fields. The height change of the surface showed that positive electrical fields can successfully break the bonds between thrombin and aptamer, while moderate negative electrical fields kept the integral structure. The experimental studies implement the idea of electrostatic actuation and modulation of the complementary pair. The force interaction between the pair was then investigated through AFM based dynamic force spectroscopy (DFS). The open circuit DFS experiment was conducted first to clarify the magnitude of single molecule level force interaction between thrombin and aptamer, and the linear dependence of rupture force on logarithmic loading rate was observed. A single energy barrier model was used to understand the binding physics and kinetics. By fitting the model with experiment data, we could acquire important kinetic parameters toff and xβ. Then in-situ electrochemical atomic force microscopy (ECAFM) based DFS experiment was conducted to investigate the electrostatic influence upon molecular force interaction between thrombin and aptamer. The force interaction difference showed that positive electrical fields lowered the dissociation force between thrombin and aptamer, while negative electrical fields held similar force level with zero potential. The ECAFM experimental studies further support the conclusion of electrostatic actuation and modulation of the complementary pair. Besides, the root cause for the change of binding behavior and force interaction between the biomolecules under electrostatic fields is the conformational transition of the molecules, which might be illustrated by the molecular dynamics (MD) simulation. Therefore, a MD based computational study was performed on self-assembled monolayer (SAM) with polar end group under the application of electrical fields to clarify the conformational transition and associated friction change of the monomolecular thin films. The simulation results showed that positive electrical fields can generate larger conformational transition of the SAMs, which led to a greater frictional coefficient drop of the surface, while negative electrical fields kept similar conformational state and frictional response as the zero potential. The simulation result provides another explanation of the electrostatic actuation based modulation of polar molecule functionalized surface.

Copyright Owner

Xiao Ma

Language

en

File Format

application/pdf

File Size

189 pages

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