Rapid and Uniform NHS-Ester-Based Membrane Protein Labeling of Live Mammalian Cells

Rapid and uniform labeling of plasma membrane proteins is essential for high-resolution imaging of dynamic membrane topologies and intercellular communication in live mammalian cells. Existing strategies for labeling live cell membranes, such as fluorescent fusion proteins, enzyme-mediated tags, metabolic bioorthogonal labeling, and lipophilic dyes, face trade-offs in the requirement of genetic manipulation, the presence of non-uniform labeling, the need for extensive preparation times, and limited choices of fluorophores. Here, we present a streamlined protocol that leverages N-hydroxysuccinimide (NHS)-ester chemistry to achieve rapid (≤5 min), covalent conjugation of synthetic small-molecule dyes to surface-exposed primary amines, enabling pan-membrane-protein labeling. This workflow covers dye stock preparation, labeling for suspension and adherent cells, multiplex live-cell imaging, fusion protein co-staining (including insulin-triggered receptor endocytosis), 3D membrane visualization, and in vivo assays for visualizing membrane-derived material transfers between donor and recipient cells using a lymphoma T-cell mouse model. This high-density labeling approach is compatible with various cell types across diverse imaging platforms. Its speed, versatility, and stability make it a broadly applicable tool for studying plasma membrane dynamics and intercellular membrane trafficking. Key features • Rapid high-density membrane labeling with small-molecule fluorescent dyes. • Enables live-cell multiplexed imaging, amenable to primary cells and cells expressing fluorescent fusion proteins, and supports in vivo studies of membrane-associated cell-cell communications. • Compatible with various fluorescence imaging modalities.