Differential labelling of human sub-cellular compartments with fluorescent dye esters and expansion microscopy

Abstract

Amine-reactive esters of aromatic fluorescent dyes are emerging as imaging probes for nondescript staining of cellular and tissue architectures. We characterised the differential staining patterns of 14 fluorescent dye ester species with varying physical and spectral properties in the broadly studied human cell line - HeLa. When combined with expansion microscopy (ExM), these stains reveal nanoscale features such as the nuclear proteome, membrane-bound compartments and vesicles. Among N-Hydroxysuccinimide (NHS) esters, we observe differential compartment specificity and weighting of labelling density which correlates with the hydrophobicity of the dye ester. We also observe changes in both staining density and compartment specificity for a given dye ester depending on the presence of a second dye ester species and on the timepoint of application in the ExM protocol. Our findings confirm these dye esters as a useful addition to the repertoire of biomedical stains of the cellular proteome, either on their own, or as counterstains to immunofluorescence.