IN – Track B



Determining the Probability Distribution Function of Molecular Overlap Times in Single Molecule Microscopy: Random Collisions and Constructive Interactions

Project Heads

Paolo Annibale, Martin Lohse, Christof Schütte

Project Members

Horst-Holger Boltz (ZIB)

Project Duration

01.03.2020 – 31.12.2020

Located at



When imaged under a microscope, fluorescently labeled receptor molecules on the plasma membrane of the cell appear as diffraction limited spots. These molecules and the corresponding microscopic spots diffuse and can interact depending on their relative affinity. Collisions among them may result either in random overlaps or in constructive interaction and therefore overlap of varying duration. While it is experimentally possible to extract overlap times with relative ease, modeling of these processes based on the underlying reaction-diffusion laws has received considerably less attention and would represent an important tool to characterize and assess molecular interactions at the cell surface.

Project Webpages

Selected Publications

Annibale, P., Lohse, M.J. Spatial heterogeneity in molecular brightness. Nat Methods 17, 273–275 (2020).


Boltz, H-H., et al. Quantitative spectroscopy of single molecule interaction times. Optics Letters (2021). DOI: 10.1364/OL.413030

Selected Pictures

Graphical abstract for the Incubator Project IN-B1
Project IN-B1
Starting from sequences of images (top left), we seek to identify particles and track them through the sequence. This way, we can identify times at which pairs of particles cannot be resolved and are thus considered collocalized from an imaging perspective. If the particles interact constructively, i.e. they “like” being close together, they will (in distribution) stay longer together than if they just overlap by random chance.

Statistical analysis of the distribution of these times together with suitable modeling (including generation of artificial data as a point of comparison) and analytics (there is a related first-passage problem offering valuable insight) are then used to extract some key parameters of the interaction between the two particles.

Selected Pictures

Numerically inferred tracks of beta-2 in a cell, color-coded by the apparent diffusitivity along each track
Project IN-B1
Tracking data from a real experiment (by A. Sirbu at MDC) using beta-2 receptors. Tracking all the particles allows us to highlight their dynamical heterogeneity (the color coding relates to the local motility of particles) and, thus, infer a interaction with cellular structures.

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