Sample Preparation

It is beyond the scope of this document to provide guidance for preparation of all the possible samples that may be examined with the Dimension Icon. However, certain general guidelines are provided regarding:

• General Sample Mounting Procedures
• Notes on Sample Binding for Fluid Imaging

Typical Sample Substrates

Most scanning probe systems are able use the following substrates:

• Microscope slides
• Cover slips
• Mica discs and sheets
• Petri dishes

The Importance of Good Sample Adhesion

Good sample adhesion is critical for obtaining useful AFM images. Using the following basic ideas as guides to imaging your samples will increase you chances of success.

Specimen binding is usually accomplished using electrostatic attraction between charges on the specimen and charges on a mica surface. Proteins, for example, exhibit positive charges, especially when the buffer pH is lower than the isoelectric pH of the proteins. DNA, on the other hand, is negatively charged and can be bound either by creating positive charges at the surface (using a silanization process), or by adding a divalent metal counter ion (e.g. Mg²⁺, Ni²⁺) to the DNA buffer.

Sample preparation remains a challenging part of AFM studies in biology. It is still challenging to immobilize red blood cells or bacteria, for examples, to make them stick on a surface after immersion in a buffer solution. Tissues are also difficult to study for that reason, and also because of their softness. However, the steady progress in immobilization techniques explains the improved results being obtained daily. Keep in mind that it can take a while to find the right conditions to prepare and image a sample. Often, helpful ideas can be found in the scientific literature from previous work on similar samples.

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