Quantitative Imaging of Protein Secretions from Single Cells in Real Time

Abstract

Cell-to-cell signaling often involves the secretion of proteins, which creates spatial and temporal concentration profiles in the extra-cellular environment for the receiving cells to detect and interpret. Real-time measurements of secreted protein concentrations at the single cell level are thus fundamental to understanding these communications pathways but have proven difficult to realize in practice. Here we present a label-free technique based upon nanoplasmonic imaging and high-affinity binding which enabled the measurement of individual cell secretions in real time. When applied to the detection of antibody secretions from individual hybridoma cells, the enhanced time resolution revealed two modes of secretion: one in which the cell secreted continuously and another in which antibodies were released in concentrated bursts that coincided with minute-long morphological contractions of the cell. From the continuous secretion measurements we determined the local concentration of antibodies at the sensing array closest to the cell. The technique is incorporated on to a wide-field microscope which enables real-time transmitted light and fluorescence imaging of the cells as well. We anticipate this technique will be broadly applicable to the real-time characterization of both paracrine and autocrine signaling pathways.