Figure 4.

Digitization advances included new means of droplet (a) generation and (b, c, d) manipulation as well as (e) high-density digital PCR. (a) A dual-coaxial microfluidic device produced gas/liquid/liquid double emulsions with a high degree of emulsion/droplet control. From ref 115. Reproduced with permission of The Royal Society of Chemistry. (b) A grid of electrodes allowed reagent actuation to the site of a dried blood spot for the quantification of amino acids in blood via in-line mass spectrometry. From ref 116. Reproduced with permission of The Royal Society of Chemistry. (c) Utilizing a silane-patterned open-surface microfluidics device, droplets containing an insoluble surfactant (green) were self-propelled along a sub-phase liquid (blue). From ref 122. Reproduced with permission of The Royal Society of Chemistry. (d) Electrowetting forces laterally spread droplets. Upon removal of electrowetting forces, the droplets converted stored energy to kinetic energy, causing them to “jump” off the surface. Reprinted with permission from Lee, S., Lee, S. & Kang, K. Droplet jumping by electrowetting and its application to the three-dimensional digital microfluidics. Appl. Phys. Lett.100, 081604. Copyright 2012, American Institute of Physics (ref 123). (e) High-density digitization of PCR samples into microscale compartments. This “megapixel” digital PCR device had reaction vessel densities exceeding 440,000 cm⁻² and a dynamic range of 10⁷. Reproduced from ref 127 with permission of the Nature Publishing Group.