Getting A Handle On Carbon Nanotubes
A single wall carbon nanotube is a linear polymer with exceptional mechanical properties. In particular with nanometer diameter and micron length scale a CNT has a high aspect ratio combined with unsurpassed mechanical strength. A CNT provides the ideal geometry for a truly molecular scale bio-mechanical probe. The work in this thesis was motivated by the concept of "getting a handle" on CNTs. We sought to be able to use the NT as a probe that could both exert forces and measure forces acting on it. The questions this thesis seeks to answer are twofold. (i) Can a carbon nanotube be used to probe biological systems at the molecular scale? And conversely: (ii) Can the techniques of single molecule biology be used to probe an individual carbon nanotube? In the process of answering these questions we have derived several different functional platforms for cell investigations, single molecule experiments, and exploration of CNT mechanics, as we will see. Chapters 1 through 3 introduce the unique properties of CNTs, mechanical theory, and growth methods. Chapter 4 shows motivating experiments where living cell-CNT interactions are studied. In Chapter 5 we demonstrate the ability to be able to fabricate highly aligned and parallel cantilevered CNTs-a necessary step toward realizing a probe for application. In Chapters 6-9 we will describe a platform we have developed borrowing the technique of magnetic-tweezers from the biophysics community. This technique has been used in singlemolecule studies to elucidate the properties of long biopolymers such as DNA using magnetic tags to optically resolve the molecules as well as exert forces upon them. In our work we show a similar scheme where the CNT is the molecule of interest. In our design the CNT devices are made by lithographically patterned magnetic iron pads at their ends. With this pad we can both optically resolve to position of the NT as well as exert forces on it. We will show how analysis of thermal fluctuations gives us measurement methods that are sensitive enough to elucidate the mechanical properties of the NTs. Additionally we can now exert well calibrated forces on the NT on the scale of fN-pN. We conclude by showing how this platform provides a new way to further study the physical properties of CNTs and simultaneously provides the framework to study the forces acting in CNT-biomolecule interactions.
Carbon Nanotubes; Magnetic Tweezers; NEMS
McEuen, Paul L.
Sethna, James Patarasp; Franck, Carl Peter
Ph. D., Physics
Doctor of Philosophy
dissertation or thesis