Wire-guided droplet manipulation for molecular biology

Wire-guided droplet manipulation (WDM) is a simple method of manipulating liquid droplets in a hydrophobic environment to conduct experiments, reactions, and assays. In WDM, a wire (or needle tip) manipulates microlitersized liquid droplets within an immiscible liquid or on a hydrophobic surface. The attributes of this format for liquid handling address some of the challenges facing the use of conventional techniques. Specifically, WDM provides solutions for development of automated, sample-to-answer, point-of-care systems with potential applications in medicine, life science research, forensics, veterinary diagnostics, and disease control. The widespread applicability of this technique is due to its inherent simplicity stemming from the attractive force between the droplet and the wire. The physics of this interaction will be explained in this chapter. WDM can be applied to standard protocols and is easily reprogrammable for different liquid handling applications. Dilution, mixing, centrifugation, and thermocycling have all been automated by WDM (You and Yoon, J Biol Eng 6:15, 2012). If desired, the principles of droplet manipulation can be easily integrated into the common scientific automation strategy, using commercially available robotic pipetting systems. WDM is automatable, reprogrammable, easy to use, and robust. These are essential features of rapid, all-in-one, sample-to-answer systems to be used at the point-of-care. The applications of WDM within molecular biology that have been demonstrated include DNA extraction (lysing, precipitation, washing, and rehydration), nanoparticle surface deposition for fabrication of a protein nanoarray, immunoassay, PCR thermocycling, and real-time PCR.