Electrocoalescence based serial dilution of microfluidic droplets

Abstract

Dilution of microfluidic droplets where the concentration of a reagent is incrementally varied is a key operation in drop-based biological analysis. Here, we present an electrocoalescence based dilution scheme for droplets based on merging between moving and parked drops. We study the effects of fluidic and electrical parameters on the dilution process. Highly consistent coalescence and fine resolution in dilution factor are achieved with an AC signal as low as 10 V even though the electrodes are separated from the fluidic channel by insulator. We find that the amount of material exchange between the droplets per coalescence event is high for low capillary number. We also observe different types of coalescence depending on the flow and electrical parameters and discuss their influence on the rate of dilution. Overall, we find the key parameter governing the rate of dilution is the duration of coalescence between the moving and parked drop. The proposed design is simple incorporating the channel electrodes in the same layer as that of the fluidic channels. Our approach allows on-demand and controlled dilution of droplets and is simple enough to be useful for assays that require serial dilutions. The approach can also be useful for applications where there is a need to replace or wash fluid from stored drops.

Volume-of-fluid simulations in microfluidic T-junction devices: Influence of viscosity ratio on droplet size

“…Droplet size is an extremely important parameter as it controls the efficiency of encapsulation of individual cells and biomolecules [6][7][8] and rates of reaction 1, 9,10 . From a fundamental point of view, droplet size dictates the mixing dynamics 1, [9][10][11][12][13] , flow resistance [14][15][16][17] , breakup [18][19][20] , coalescence [21][22][23] and collective 24,25 behavior. Since experimental conditions including flow rates, fluid properties and channel dimensions, may vary for different applications 26 it is important to understand drop formation and develop predictive models of how system parameters influence droplet size.…”

Microfluidic Chamber Design for Controlled Droplet Expansion and Coalescence

“…The so-called electrocoalescence is necessary to break the stabilizing surface energy of the droplets, especially if surfactants are used. Various examples of selective coalescence of droplets were reported earlier [29,30,[55][56][57][58][59][60][61][62].…”

“…However, the combination of both principles needs a fluidic interface which allows appropriate transfer operations on a droplet level. In droplet-based microfluidics, dilution of dissolved compounds means the expansion of an initial droplet volume to a larger volume [30,31]. The well-defined coalescence of groups of droplets with different ingredients or compositions allows on the one hand the procedural conversion of low-volume droplets into larger-volume droplets and on the other hand the stochastically confined combination of different droplet-based building blocks.…”

Concentration gradient generation methods based on microfluidic systems

“…Along the owing direction, concentrations of the blue dye within the resulting droplets increase while concentrations of the yellow dye reduce. 191 Based on earlier works, Bhattacharjee et al 194 recently presented an electro-coalescence based scheme for uids with surfactants, which could also realize on-demand dilution by alternatively switching the active control eld. It is noteworthy that the size of the trap chamber should be designed properly as volumes of the resulting droplets are predetermined by the chamber capacity.…”