Probe for Detecting Membrane Contact Sites

The invention describes a method for detecting and measuring the distances of contacts between biological membranes, such as contacts between intercellular organelles. The probe is composed of two parts inserted into adjacent membranes or organelles. A low-affinity interaction, which does not alter the physiological dynamics of the membranes, labeles one of the parts with a fluorogenic substrate. The signal can be detected via sub-cellular level microscopy or at the population level through Western blot.