Figure 5. Future directions and extensions for microfluidic devices.

a | Multiple cells can be deposited onto well-based profiling platforms, enabling the examination of multicellular and cooperative events, such as the killing of target cells by natural killer cells by Yamanaka et al.¹²³ (side view). b | The Fluidigm C1 valve-based integrated fluidic circuit (IFC; top view) was used to simultaneously detect several transcripts and proteins from the same single cell in a single series of reactions¹⁵. During lysis, targeted primers and complementary DNA-tagged antibodies were introduced, and reverse transcription and DNA extension reactions were carried out on both species to yield uniquely detectable, PCR-amplifiable DNAs for both cellular analytes. c | The directed evolution of enzymes in single cells can be probed with an activity assay in droplets¹³⁶. Here, horseradish peroxidase (HRP) surface proteins from mutated vectors were interrogated for substrate turnover with single-cell resolution (top view). Following capture of the most active cells, the interrogation was repeated to study their evolution over time. Part a is adapted from REF. ¹²³ with permission of The Royal Society of Chemistry. Part b is adapted with permission from REF. ¹⁵, Macmillan Publishers Limited. Part c is adapted with permission from REF. ¹³⁶ (Agresti, J. J. et al. Ultrahigh-throughput screening in drop-based microfluidics for directed evolution. Proc. Natl Acad. Sci. USA 107, 4004–4009; 2010).