Parallel Sampling of Nanoliter Droplet Arrays for Noninvasive Protein Analysis in Discrete Yeast Cultivations by MALDI-MS.

Miniaturization of cell-based assays enables the analysis of secreted compounds from low cell numbers down to a single cell. Droplet microfluidics is a well-established tool for high-throughput single-cell analysis. Nevertheless, the integration of label-free bioanalytical techniques like mass spectrometry is still ongoing. For example, without additional separation steps, droplet-enclosed cells do not survive the analysis. Cell separation techniques for droplets have been reported, but could not yet be coupled to mass spectrometric analysis. Here, we present a simple approach for high-throughput cell separation in parallel in nanoliter droplets and demonstrate that it can be used for qualitative analysis of protein secretion by the yeast