A Microfluidic Approach for Screening Submicroliter Volumes against Multiple Reagents by Using Preformed Arrays of Nanoliter Plugs in a Three‐Phase Liquid/Liquid/Gas Flow

Abstract

Plugging a gap in screening-Arrays of nanoliter-sized plugs of different compositions can be preformed in a three-phase liquid/liquid/gas flow. The arrays can be transported into a microfluidic channel to test against a target (see schematic representation), as demonstrated in protein crystallization and an enzymatic assay.Keywords crystal growth; enzymatic arrays; microreactors; screening methods; three-phase system Herein, we describe a simple, economical microfluidic method of screening a small volume (down to submicroliter volumes) of a solution against a large number of reagents on the nanoliter scale. The use of microfluidics to miniaturize chemical and biological screening is an important and active area of research in such diverse areas as biochemical assays, protein crystallization, and combinatorial chemistry. [1][2][3][4][5][6][7] Nanoliter aqueous plugs (droplets) transported through microchannels in an immiscible liquid have been used in a liquid/liquid flow system and allow miniaturization while eliminating dispersion, [8,9] accelerating mixing, [10] and providing control over the surface chemistry. [11] Applications of such systems to protein crystallization, [3,12] kinetic measurements, [10] assays, [13,14] DNA analysis, [8] and chemical synthesis [15] have been demonstrated. Such plug-based microfluidic systems have been especially attractive for applications in which the concentrations of several reagents had to be varied. The concentrations were varied by rapidly changing the flow rates of the reagent streams as the droplets were formed. [3,12] Plugbased methods of that type require equipment for varying flow rates, and even though such equipment could be as simple as a few computer-controlled syringe pumps, this requirement presents a barrier to many potential users in chemical and biochemical laboratories. In addition, to increase the number of reagents that can be screened, both the number of the microfluidic channels in the device and the number of flow control devices have to be increased proportionally. Herein, we implement a complementary approach that uses pre-formed arrays of plugs to simplify the experiment for the user, relies on a liquid/liquid/gas three-phase flow system to ensure robustness, and allows a much larger number of reagents to be tested in a scalable fashion.

Reaction Rates as a Function of Scale within Ionic Liquids: Microscale in Droplet Microreactors versus Macroscale Reactions in the Case of the Grieco Three‐Component Condensation Reaction

“…However, in spite of many advantages, these microsystems suffer from several drawbacks, such as large dead volumes, frequent obstruction of the channels, difficulties to maintain a constant hydrodynamic pressure (especially for viscous liquids) or to control surface charges when electro-osmotic pumping is used. In an attempt to avoid these problems, Zheng and Ismagilov [25] have described a continuous-flow microfluidic system in which droplets are separated by liquid spacers involving complex protocols to work with these systems. This approach consists of an array of nanoliter plugs of many different reagents, separated and surrounded by a fluorinated carrier fluid and gas bubbles inside a hydrophobic glass or plastic capillary.…”

Droplet‐based microfluidics for microtoxicological studies

“…Each droplet represents a single test volume, which means a single test experiment. Droplets can be generated and processed easily in microfluidic systems [6]. The volumes of droplet can be adapted between the lower microliter and the femtoliter range, which can be formed with high reproducibility and homogeneity in size and composition [7][8][9][10].…”

Droplet‐Based DNA Purification in a Magnetic Lab‐on‐a‐Chip

“…[8][9][10][11] These devices are mainly based on microfluidic channels that have limited flexibility with respect to scale and reconfiguration. [11] Here, the manipulation of liquids in small discrete volumes (microdroplets) can provide an alternative, [12,13] especially when the droplets are not confined by microchannels, thus introducing additional degrees of freedom and reducing problems of adsorption on the channel walls. [14,15] Moreover, it has been…”