New publication in Nano Letters: Visualizing single-cell secretion dynamics with single protein sensitivity

Cellular secretion of proteins into the extracellular environment is an essential mediator of critical biological mechanisms, including cell-to-cell communication, immunological response, targeted delivery, and differentiation. The field of secretomics has thus emerged in the past decades in an effort to quantify and identify all proteins released by a biological system. However, the secretome is generally analyzed via conventional proteomic techniques that are limited by their dependence on high analyte concentrations and long measurement times.

Here, we employ interferometric detection of scattered light (iSCAT) microscopy to probe a living cell's secretome with single-protein sensitivity and millisecond temporal resolution. iSCAT works by mixing the weak field scattered by a protein with a strong coherent reference beam. Importantly, the method is label-free and does not require immunosorbent reagents or fluorescent probes although either of these can be implemented to complement iSCAT detection. In this work we probe the secretome of single Laz388 cells derived from B lymphocytes and immortalized with Epstein-Barr virus (EBV). We find that single Laz388 cells actively secrete IgG antibodies at a rate of the order of 100 molecules per second. Intriguingly, we also find that other proteins and particles spanning ca. 100 kDa – 1 MDa are secreted from the Laz388 cells in tandem with IgG antibody release, likely arising from EBV-related viral proteins. The technique is general, and as we show, can also be applied to studying the lysate of a single cell. Our results establish label-free iSCAT imaging as a powerful tool for studying the real-time exchange between cells and their immediate environment with single protein sensitivity.

Visualizing single-cell secretion dynamics with single protein sensitivity

M. McDonald, A. Gemeinhardt, K. König, M. Piliarik, S. Schaffer, S. Völkl, M. Aigner, A. Mackensen and V. Sandoghdar

Nano Letters, Just Accepted Manuscript (11/2017)