Probing molecular diversity and ultrastructure of brain cells with fluorescent aptamers

Detergent-free immunolabeling has been proven feasible for volumetric correlated light and electron microscopy (vCLEM) with the application of small immunoprobes, providing a reliable method to superimpose essential molecular information of cells onto their high-resolution electron microscopic images. However, the application of this method is restricted by the availability of suitable affinity reagents. Here we introduce CAptVE, a method using slow off-rate modified aptamers for cell fluorescence labeling on ultrastructurally reconstructable electron micrographs. CAptVE provides labeling for a wide range of biomarkers, offering a pathway to integrate molecular analysis into volumetric electron microscopic studies of tissues, including neural circuit investigations via connectomics.