Volumetric single-molecule tracking inside subcellular structures

The non-covalent interactions that underpin major cellular functions depend on molecular motion within three-dimensional environments. Large depth-of-field single-molecule localization microscopy (3D-SMLM) methods facilitate these measurements, but their increased optical complexity and bespoke post-processing pipelines often sacrifice important cellular context. Here we combine single-molecule light-field microscopy (SMLFM) with widefield Fourier light-field microscopy for correlative volumetric organelle imaging. The instantaneous acquisition of subcellular volumes improves the sensitivity of molecular organization, chemical environment, and diffusion measurements through the use of volumetric sub-cellular segmentation. We first demonstrate our approach by measuring the molecular organization of a nuclear-localized HaloTag protein relative to cell nuclei. Next, we characterize the molecular diffusion of the soluble protein, calreticulin, in the context of α₁-antitrypsin deficiency, which revealed an increase in heterogeneous motion within endoplasmic reticulum inclusions.