Fig. 2.6.

Fusion and intermediate steps can be tracked by a dual-labeling approach. Virions first bind their receptor within the supported lipid bilayer (gray) in the evanescent wave (not shown here) of TIRF. After a trigger (such as a pH drop shown here at t = 0) membrane fusion occurs between the virion membrane, labeled with a green fluorophore, and the unlabeled supported bilayer. Fluorescence dequenching during fusion indicates hemifusion. Finally, a fusion pore is formed and the internal capsid fluorophores (red) are expelled across the supported bilayer. The plot to the far right shows the intensity change for the virion highlighted by the arrows in the images to the left