Two-photon polarization microscopy is a powerful new microscopy technique suitable for observing membrane proteins and cytoskeletal proteins labeled with a fluorescent moiety (such as a fluorescent protein).  Two-photon polarization microscopy detects the angle at which the fluorescent moiety is oriented with respect to the cell membrane (or cytoskeleton).  If the mean tilt angle (or the distribution of the tilt angle) changes during a molecular process, you can observe this process by using two-photon polarization microscopy. 

For example, the technique has been shown to be exceptionally sensitive in direct detection of G-protein activation.  In a resting state, the G-protein subunits form a trimer, restricting the orientational freedom of the fluorescent label.  During activation, the orientational freedom of the label increases.  After activation ends, the orientational freedom decreases again, due to formation of the G-protein dimer.  The process is illustrated below.

Fluorescent protein orientation changes during G-protein activation:

This is what it looks like in two-photon polarization microscopy images:

Two-photon polarization microscopy can even detect changes in membrane protein conformation, such as in a genetically encoded calcium sensor:

Two-photon polarization can detect many other molecular processes.  Innovative Bioimaging, LLC, provides cutting edge hardware and software tools to take advantage two-photon polarization microscopy.  It also provides two-photon polarization microscopy as a service.  Learn more from our pages, or contact us for more information!