Research highlights: Microfluidic single-cell analysis from nucleic acids to proteins to functions

We highlight recent reports using microfluidic systems to perform single-cell analysis. It has been demonstrated on numerous occasions that population averages are often not representative of single-cell behavior. These differences in behavior can be caused by stochastic fluctuations in temporal response, changes in the surrounding instructive environment, or hard-coded genetic changes. Because of the similar length scales, microfluidic approaches have been well-suited to isolating, analyzing, and culturing single-cells to better understand this heterogeneity. Here, we discuss recent works in which microfluidic researchers have extended single-cell characterization approaches, in order to improve analysis from nucleic acids to proteins to final functional behavior. Nucleic acid detection can be amplified beyond what is possible with fluorescence in situ hybridization using droplet-enabled PCR-activated cell sorting. Multiplexed protein detection that overcomes the problems with off-target antibody binding which are associated with traditional immunofluorescence is achieved with single-cell western blotting. Proliferation, migration, and secretion are analyzed in rare circulating tumor cells isolated in microwells. The next steps will be getting these new tools into the hands of a growing number of biologists and developing new tools to report on single-cell epigenetic modifications.