What Does a Cell Secrete? On-Chip Analysis of Compounds and Vesicles Released From Single Cells

Single-cell analysis is an important research field, relevant for fundamental studies such as cell differentiation and evolution as well as for applications in the medical and diagnostic fields. In particular, compounds secreted from cells are mirroring the cell`s state and vitality and may be important for intercellular communication. However, single-cell analysis is facing numerous challenges due to limitations in the available analytical methods. The emergence of microfluidics has provided novel strategies for positioning, treatment and observation of individual cells. A great potential of microfluidics for analytical applications lays in the possibility to create small liquid environments of defined and reproducible volumes. We use two approaches to confine liquids in volumes of picoliters to a few nanoliters; (i) valve systems in multilayer microdevices made of silicone elastomer (PDMS) and (ii) droplet microfluidics. These approaches facilitate the isolation of individual cells and the analysis of secreted compounds, at unprecedented high sensitivity and will be discussed in this contribution.