Atomic Force Microscopy to Visualize Phage–Antigen Interactions

Take a cleaved mica surface, a flat substrate for nanoscale imaging.
Add a target antigen to the mica. Incubate to enable non-covalent binding of antigen to the mica surface.
Wash with water to remove unbound antigen.
Add a phage mixture containing clones that display different antibody fragments and incubate.
Antigen-specific phages bind to the immobilized antigen through displayed antibody fragments.
Wash to retain only high-affinity phage interactions. Air-dry to stabilize the complexes.
Place the sample under a tapping-mode atomic force microscope, or AFM.
Align the laser beam onto the cantilever with a nanometer-scale tip and initiate scanning.
The tip oscillates and taps the mica surface. Bound phage particles cause height changes that deflect the cantilever, shifting the reflected laser beam.
This shift is detected by a photodetector, generating high-resolution topographic images.
In these images, phages appear as long bright structures, indicating phage–antigen interactions.
To visualize phage binding using AFM, add 10 to 20 microliters of the target antigen to cleaved mica and incubate for 5 to 10 minutes. Wash the mica five times with water. Then, add 10 to 20 microliters of the pha