Brandy Perkins
Southern University
Chemistry

Using the Tapping Mode of an Atomic Force Microscope to Study Biological Membranes

Introduction

Often times as humans we notice the larger things in life but seldom take the time to notice the smaller and/or microscopic pieces of our society. With the aide of an instrument such as an Atomic Force Microscope (AFM ) , one can observe the surface of materials such as metals, ceramics, and biological tissues down to a nanoscale level.

The AFM is a from of scanning probe microscope that uses a Si based cantilever to probe the surface of a sample. By probing the surface in tapping mode, one can obtain a topographic map of the sample surface. This map is based on a detection system involving the deflection of a laser beam off the back of an oscillating cantilever and the measurement of the change in amplitude due to the interaction of the cantilever and the sample.

In the laboratory of Professor R.P. Andres in the Chemical Engineering department of Purdue University, successful experiments dealing with attaching carbon nanotubes onto commercial cantilevers used in AFM research. The flexible nanotube makes for a perfect attachment for the enhancement of the ability of the instrument to obtain a more detailed topographical map of the sample surface. Unfortunately, this modification has not been successful on the surface of living cells. In past research, when the nanotube is scanned across the cell membrane, the carboxylic acid groups located at the tip of the nanotubes interact with the various groups located on the surface of the membrane. This interaction ruptures the cell membrane. A solution would be to chemically change or bond another molecule to the tips of the carbon nanotubes such as dodecylamine. The chemical change would perhaps allow one to probe the cell surface without rupturing it.

Presently, Professor Andres and his group are working on replicating the method used by Charles M. Lieber at Harvard University to derivatize the tips of carbon nanotubes attached to gold plated tapping and contact cantilevers. It is hoped that advances in nanotube derivatization will eventually lead to a map of the surface of living cells.

Project Objectives

  • Attach carbon nanotubes onto hydrophobic gold plated tapping mode and contact mode cantilevers
  • Obtain tapping mode images using stiff and soft cantilevers
  • Derivatize the tips of carbon nanotubes
  • Probe the surface of a bilayer membrane
  • Probe the surface of a living cell membrane

Experimental Approach

  • Using an optical microscope to attach carbon nanotubes onto the various cantilevers
  • Using the tapping mode of the Atomic Force Microscope to probe the surface of the samples
  • Developing an apparatus by which the tips of the carbon nanotubes can be derivatized
  • An apparatus where a nanotube is slowly introduced to a small stable drop of solution
  • Lowering a nanotube into a beaker filled with the derivatizing solution

Accomplishments

  • Able to operate an Atomic Fore Microscope
  • Able to attach carbon nanotubes to hydrophobic gold plated tapping and contact cantilevers
  • Obtained images from stiff cantilevers with and without nanotubes attached to prove that with a nanotube one can obtain clearer images of samples

Final Research Presentation

Links of Interest