Microgram-Scale Testing of Reaction Conditions in Solution Using Nanoliter Plugs in Microfluidics with Detection by MALDI-MS

Abstract

This paper describes a microfluidic system to screen and optimize organic reaction conditions on a submicrogram scale. Optimization of reaction conditions is required to achieve high efficiency and selectivity in organic reactions. Combinatorial methods 1 and high-throughput screening 2 are powerful tools for optimization. To perform solution-phase synthesis, typical microtiter plates or reaction blocks for parallel synthesis run reactions on the scale of mL/ reaction 1 and are less applicable to precious substrates (e.g., products of long synthetic sequences and natural products that can be isolated only in small quantities). To address this problem, one approach used arrayed micro-wells in combination with a robotic liquid sampler on the scale of ~125 nL per reaction. 3 To reduce the use of robotics and to minimize evaporation, others used microchannels 4-6 to perform reactions, including synthesis of pyrazoles with UV detection (5 μL per reaction) 6 and optimization of glycosylation conditions 5 (~2 mg reagent per reaction).Here, we report a screening method that consumes substrates on the scale of less than 1 μg per reaction. The system uses discrete droplets (plugs) 7 as microreactors 8 separated and transported by a continuous phase of a fluorinated carrier fluid. Such approach is not limited to microfluidics-fluorinated fluids were used previously to segment samples in NMR 9 and PCR 10 in tubes to prevent dispersion of sample solutions. Previously, we demonstrated the use of a microfabricated PDMS plug-based microfluidic system to perform assays and crystallization experiments in aqueous solutions with optical detection. 11 Here, we developed an approach that does not require microfabrication of microfluidic devices, 12 is applicable to synthetic reactions in organic solvents, and uses detection by MALDI-MS.The system consisted of three components: preformed cartridge 11,13 of reagent plugs, a PEEK Tee, and a receiving tubing (Figure 1). A cartridge is an array of discrete plugs surrounded by fluorinated carrier fluid; each plug is composed of a solution of a different reagent. The cartridge was prepared by serially aspirating the reagents into a piece of Teflon tubing prefilled with carrier fluid. A commercially available PEEK Tee connected the cartridge and the inlet tubing, containing as little as a submicroliter volume of a solution of the substrate. Fluorinated carrier fluid (FC-70) was used to fill the two syringes ( Figure 1) and the connecting tubing, enabling no-loss manipulation of submicroliter volumes of solutions. FC-70 has low miscibility with organic reagents and reasonably low viscosity (Supporting Information). To perform the reactions, the flow was induced with the two syringes, and the reagent plugs were sequentially merged with the substrate solution. After all resulting plugs flowed out of the Tee into the receiving tubing, the flow was stopped, and the receiving tubing was sealed. After incubation, E-mail: r-ismagilov@uchicago.edu. Supporting Information Available: Materials and meth...

Nanoliter microfluidic hybrid method for simultaneous screening and optimization validated with crystallization of membrane proteins

“…To perform simultaneous hybrid screening and optimization, we used plugs [droplets surrounded by fluorinated carrier fluid and transported through microfluidic channels (24)]. Plugs have been used to perform the initial screening in a number of applications, including biochemical assays (25), chemical reactions (26), and crystallization of soluble proteins (22). In separate experiments, plugs have been used for optimization of protein crystallization conditions (23).…”

“…We used optical detection in all of the experiments, by using a microscope scanning stage or by pulling the capillary with plugs through the microscope's field of view. This method would benefit from simple automated systems for detection in plugs, either optical or based on mass spectrometry (26). Beyond crystallization, we believe this method would find applications in a number of areas (5,(42)(43)(44)(45)(46) of chemistry, biochemistry, molecular biology, and material science that require simultaneous screening and optimization economically and in small volumes.…”

Light-Driven Droplet Manipulation Technologies for Lab-on-a-Chip Applications

“…Recently, particular attention has been paid to droplet-based (digital) microfluidic devices since droplets isolated in immiscible oil or air can be free from cross-contamination and dispersion [4]. Numerous droplet-based applications including protein crystallization [5,6], polymerase chain reaction (PCR) [7,8], enzyme kinetic assays [3,9], and synthesis of organic molecules or nanoparticles [10,11] have been demonstrated.…”

The chemistrode: A droplet-based microfluidic device for stimulation and recording with high temporal, spatial, and chemical resolution

“…Because the carrier fluid completely encapsulates the aqueous plug and eliminates its contact with the walls, two-phase flow of the chemistrode reliably transported even molecules that tended to adsorb to PDMS and Teflon. We do not anticipate partitioning of hydrophobic or amphiphilic molecules from the aqueous plugs into the fluorocarbon carrier fluid, as shown in previous studies (33,34).…”