Fluid handling operations in droplet microreactors: optical tweezing, sorting, particle segregation, and label free sensing in picoliter volumes

A.S. Basu
Wayne State University, US

Keywords: microreactors micro fluidics

Summary:

Multiphase microfluidics utilizes water-in-oil droplets as containers for biochemical reactions. With volumes of nL-pL, they provide a hundred to million-fold smaller reaction volumes than conventional microplates or single-phase microfluidic channels. As modern biology evolves from studies of single genes and proteins to systematic, high-throughput studies involving of thousands of biomolecules, drop-based fluidics can provide compelling benefits to the fields of ‘-omics’ and drug discovery, including: dramatic cost reductions by conserving expensive reagents, high throughput due to lower diffusion times, and novel ways to query single cells in small volumes. To be able to reap these benefits, however, one must be able to emulate typical benchtop fluid handling operations in the droplet format. Multiphase microfluidics is considerably more complex as it involves coupled flow interactions between two immiscible phases, interfacial tension, Laplace pressures, shape deformation, and other phenomena acting in cohort with laminar flow. Rather than work against these phenomena, we exploit them in novel ways in order to perform key fluid handling operations. Several examples will be discussed in this talk: 1) the formation of heterogeneous screening libraries using microfractionation-in-droplets (µFD); 2) Particle concentration using hydrodynamic microvortices and sedimentation in plug flow; 3) Light-based droplet manipulation using optofluidic tweezers (OFT), a novel technique which uses laser-induced thermocapillary microvortices to trap droplets with µN forces (100,000X larger than traditional optical tweezers); 4) Sorting droplets by size using tensiophoresis, the cross-stream migration of droplets in interfacial tension (IFT) gradients; and 5) Detecting femtomoles of proteins in droplets using interfacial adsorption phenomena together with tensiophoresis. Computational modeling and experimental image velocimetry methods will also be discussed.