Fab-Paint enables nanoscale molecular survey in-situ

Consistent molecular quantification remains challenging for superresolution imaging due to labeling and detection artifacts associated with immunolabeling. Here, we propose a straightforward and versatile molecular survey technique termed quantitative Fab-PAINT (qFab-PAINT). The central strategy is two-pronged. First, we use transient antibody fragment (Fab)-epitope tag interactions to overcome the immunolabeling barrier and achieve superresolution. We discovered that the fragments of a high-affinity antibody against a standard hemagglutinin (HA) epitope tag (YPYDVPDYA) displayed highly dynamic and transient interactions with the epitope at nanomolar concentrations.