Patent Grant
11779927
This invention is generally related to microfluidic devices, and, more specifically, to electrowetting on dielectric microfluidic devices.
Over the past decades, microscale chemical reaction technology has been attractive in diverse areas of chemistry. It allows the precise control of quantified reagents and highly efficient heat and mass transfer, because of a large interface-to-volume ratio, particularly in case of the exothermic reaction and mixing. Additionally, it allows for reduced consumption of toxic or expensive agents, improved reaction profiles, and enhanced selectivity compared to macro-scale reactions.
Conventional microscale reaction processes typically use continuous microchannel flow systems. For example, various chemical reaction have been performed, such as fluorination of toluene in microchannel reactors made of silicon, and formation of amides via carbonylative cross-coupling of aryl halides with benzyl amine using a reaction channel. Both cases achieved the higher yields than conventional batch reactions within the same time periods. Other examples include Suzuki cross-coupling, Wittig olefination reaction, nitration of benzene, and tripeptide synthesis. Despite successful demonstration of these proof of concept demonstrations, microchannel-based approaches suffer from several limitations. For example, clogging of the channels by products or byproducts often results in difficulty maintaining a constant hydrodynamic pressure and a stable flow. The requirement of a complex flow network and cross-contamination due to unwanted diffusion through channels also has been observed to be problematic. Moreover, solvent-swapping processes pose very challenging problems in microchannel reactors. Another in the context of combinatorial chemistry, microchannel reactors present additional challenges. For instance, since a combinatorial synthesis through either batch or flow reactors requires as many reactors as the number of all possible combinations of reactants, the reactor system tends to be excessively complex.
A digital microfluidic platform using electrowetting-on-dielectric (EWOD) principle can be an alternative and/or complement a microchannel reactor. An EWOD digital microfluidic platform eliminates the necessity of predetermined channel network and mechanical pumps and valves. Since the EWOD platform uses a droplet-based flow, it can prevent cross-mixing and cross-contamination. Each droplet acts as a batch reactor, which allows the feasibility of performing multi-step reactions that involve solvents swapping and combinatorial synthesis. Researchers have taken advantages of these unique features of EWOD microfluidic devices to conduct on-chip chemical reactions, e.g. reactions in ionic liquid droplets, synthesis of radiotracers, and synchronized synthesis of peptide-based macrocycles. However, all these reactions on EWOD chip utilized solvent fluids that are movable by EWOD actuation. However, contemporary organic synthesis generally requires non-polar or polar aprotic solvents, and their poor movability in an EWOD chip has been a long-standing problem.
Various studies have experimentally assessed the movability of organic solvents and solutions in the EWOD system, and it has been found that many organic solvents, such as cyclohexane, carbon tetrachloride, chloroform, and toluene, cannot be displaced by EWOD actuations. Recently, an electromechanical model has been reported that can predict the movability of a fluid by an EWOD device. This model showed that both the magnitude and the frequency of the operation voltage need to be tuned to obtain maximum force in an EWOD device. At the particular experimental parameters, the model predicted that many indispensable organic solvents for organic synthesis are not movable, which concurs with the reported experimental results.
Additional efforts to operate non-movable fluids in EWOD device resulted in a demonstration that oil, organic, and gaseous chemicals in the aqueous shell could be manipulated. However, such configuration fails to host fluids having a lower surface tension than aqueous solutions. For instance, most of organic solvents have much lower surface tensions (˜20 mN/m) than that of water, which does not allow them to be encapsulated in an aqueous shell. In addition, additional capillary tube settings were needed to create core-shell droplets, leading to unfavorable complexities of device design and fabrications. Another approach was to use dielectrophoretic (DEP) force to operate non-movable fluids; where a silicone oil droplet was observed to be manipulatable by DEP force in a typical EWOD device. However, exerting DEP force required extremely higher voltage than the voltage required in a typical EWOD operation. In addition, fluids must have some specific dielectric properties to be manipulated by DEP force. In fact, it has further been reported that most organic solvents commonly used in chemical reactions are not movable, even in the range of frequency at which DEP force is dominant. These hindrances limit the scope of possible chemical reactions in an EWOD device.
Consequently, there is a need for improved methods and EWOD devices that can move most organic solvents under typical EWOD conditions.
Methods of conducting a microfluidic chemical reaction using an electro-wetting-on-dielectric (EWOD) digital microfluidic device are described herein. Despite of numbers of chemical/biological applications using EWOD digital microfluidic device, its application to organic reactions have been seriously limited because most of common solvents used for synthetic organic chemistry are not operable on EWOD device. In some embodiments, an “engine-and-cargo” system that enables use of non-movable fluids (e.g., organic solvents) on an EWOD device is described herein. With esterification as the model reaction, on-chip chemical reactions can be performed. Conversion data obtained from on-chip reactions were used in the demonstration of reaction characterization and optimization such as reaction kinetics, solvent screening, and catalyst loading. As the first step toward on-chip combinatorial synthesis, parallel esterification of three different alcohols are also demonstrated.
In an aspect, a method of moving a solvent without electrowetting properties on an electro-wetting-on-dielectric (EWOD) microfluidic device is described herein, the method comprising: disposing a first droplet of a first fluid having electrowetting properties on a surface of the EWOD microfluidic device; disposing a second droplet of a second fluid without electrowetting properties on the surface; applying a voltage to the surface to move the first droplet towards the second droplet; contacting the first droplet with the second droplet to form a encapsulated droplet, where the second droplet encapsulates the first droplet. In some embodiments, the method can further comprise transporting the encapsulated droplet across the surface by applying a voltage to the surface. The first fluid and the second fluid are immiscible.
In another aspect, a method of moving a solvent without electrowetting properties on an electro-wetting-on-dielectric (EWOD) microfluidic device comprises combining a first fluid with an immiscible second fluid in an EWOD reservoir puddle, the first fluid having electrowetting properties and the second fluid lacking electrowetting properties; moving a first droplet of the first fluid out of the reservoir puddle by applying a voltage to a surface of the EWOD device; encapsulating the first droplet with a second droplet of the second fluid as the first droplet is moved out of the reservoir puddle to form an encapsulated droplet.
In some embodiments, the first fluid comprises an ionic liquid. The ionic liquid can comprise an organic cation that is imidazolium-based, pyridinium-based, pyrrolidinium-based, phosphonium-based, ammonium based, sulfonium-based, or any combination thereof. The ionic liquid can comprise an anion that is an alkylsulfate, tosylate, methansulfonate, trifluoromethanesulfonate (triflate), bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, a halide, or an combination thereof. In a preferred embodiment, the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6).
In some embodiments, the second fluid has a lower surface tension than water. In some cases, the first fluid has a higher surface tension than the second fluid. In some instances, the second fluid is an organic solvent.
Methods described herein can further comprise forming a two or more encapsulated droplets on the surface. The methods can further comprise applying a voltage to the surface to move the two or more encapsulated droplets together. In some instances, the method can further comprise merging the two or more encapsulated droplets together. The merging the two or more encapsulated droplets can comprise mixing the second fluids from each encapsulated droplets together.
In some embodiments, the second fluid of each encapsulated droplet comprises one or more reactants. In this example, merging the two or more encapsulated droplets together can initiate a chemical reaction between the one or more reactants present in the encapsulated droplets.
The first fluid in each encapsulated droplet can be the same or different. Similarly, the second fluid in each encapsulated droplet can be the same or can be different.
Embodiments described herein can be understood more readily by reference to the following detailed description, examples, and figures. Elements, apparatus, and methods described herein, however, are not limited to the specific embodiments presented in the detailed description, examples, and figures. It should be recognized that the exemplary embodiments herein are merely illustrative of the principles of the invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.
In addition, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1.0 to 10.0” should be considered to include any and all subranges beginning with a minimum value of 1.0 or more and ending with a maximum value of 10.0 or less, e.g., 1.0 to 5.3, or 4.7 to 10.0, or 3.6 to 7.9.
All ranges disclosed herein are also to be considered to include the end points of the range, unless expressly stated otherwise. For example, a range of “between 5 and 10” or “5 to 10” or “5-10” should generally be considered to include the end points 5 and 10.
Further, when the phrase “up to” is used in connection with an amount or quantity; it is to be understood that the amount is at least a detectable amount or quantity. For example, a material present in an amount “up to” a specified amount can be present from a detectable amount and up to and including the specified amount.
Additionally, in any disclosed embodiment, the terms “substantially,” “approximately,” and “about” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.
In an aspect, new methods of “engine-and-cargo” are described herein which enable an EWOD device to handle electrically non-responsive fluids such as organic solvents. This approach can allow a wide range of organic syntheses in EWOD devices. It has long been suggested that the true product from microfluidic reaction systems would be information, rather than a more tangible substances or intermediates. As like other types of microfluidic reactors, on-chip syntheses in EWOD devices would transform to parallel reactor systems (i.e., numbering up) rather than to scale up to production systems. Vast information obtained from fast and automated on-chip chemical reactions could be utilized for reaction optimization and chemical discovery. EWOD devices are capable of integrating on-chip chemical synthesis capacity with biological/biomedical functions such as cell culture, bio-separations, and biosensors, this permits a complete drug discovery platform to be performed on a single EWOD device.
In an aspect, a method of moving a solvent without electrowetting properties on an electro-wetting-on-dielectric (EWOD) microfluidic device is described herein comprising: disposing a first droplet of a first fluid having electrowetting properties on a surface of the EWOD microfluidic device, such as a fluid that is polar or electrically responsive; disposing a second droplet of a second fluid without electrowetting properties on the surface, such as a fluid that is non-polar or electrically non-responsive; applying a voltage to the surface to move the first droplet towards the second droplet; contacting the first droplet with the second droplet to form a encapsulated droplet, where the second droplet encapsulates the first droplet.
In some embodiments, the first fluid comprises an ionic liquid. An ionic liquid described herein can be any ionic liquid not inconsistent with the objectives of this disclosure. Generally, an ionic liquid is a salt that is in a liquid state. Often ionic liquids are a combination of an organic cation and a variety of organic and inorganic anions. In some embodiments, ionic liquids described herein have an organic cation that is imidazolium-based, pyridinium-based, pyrrolidinium-based, phosphonium-based, ammonium based, sulfonium-based, or any combination thereof. Ionic liquids described herein can have an anion that is an alkylsulfate, tosylate, methansulfonate, trifluoromethanesulfonate (triflate), bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, a halide, or an combination thereof.
In some embodiments, the ionic liquid is an imidazolium-based ionic liquid. For example, in some cases, the imidazolium-based ionic liquid comprises 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), ethyl-3 methylimidazoliuim triflate, ethyl-3 methylimidazoliuim tetrafluroboroate, ethyl-3 methylimidazoliuim bis(trifluromethylsulfonyl)imide, or any combination thereof. In a preferred embodiment, the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6).
In some embodiments, the second fluid has a lower surface tension than water, as described in more detail below in the Examples. However, the method is not limited to this, and in some cases, the first fluid can have a higher surface tension than the second fluid.
In some instances, the second fluid is an organic solvent that lacks electrowetting properties, such as toluene, acetone, dichloromethane, an ether, or any other commonly used organic solvent known to the skilled artisan.
Methods described herein can further comprise forming a two or more encapsulated droplets on the surface, such as a plurality of encapsulated droplets. The methods can further comprise applying a voltage to the surface to move the two or more encapsulated droplets together. In some instances, the method can further comprise merging the two or more encapsulated droplets together. The merging the two or more encapsulated droplets can comprise mixing the second fluids from each encapsulated droplets together. Merging can also comprise mixing the first fluids from each encapsulated droplet together in some instances.
In some embodiments, the second fluid of each encapsulated droplet comprises one or more reactants. In this example, merging the two or more encapsulated droplets together can initiate a chemical reaction between the one or more reactants present in the encapsulated droplets. Using a substitution reaction as a non-limiting example, one encapsulated droplet can comprise a nucleophile dissolved in a second fluid, and the other encapsulated droplet can comprise an electrophile dissolved in a second fluid, and upon merging of the encapsulated droplets, the nucleophile can react with the electrophile to form a reaction product. The first fluid in each encapsulated droplet can be the same or different, based on the solubility requirements of the reactant present in the droplet, and/or the requirements of the intended chemical reaction to be conducted. Similarly, the second fluid in each encapsulated droplet can be the same or can be different for at least the same reasons.
Some embodiments described herein are further illustrated in the following non-limiting examples.
An engine-and-cargo system described herein harnesses a compound droplet of two immiscible fluids. An engine can be referred to as a fluid that has the electrowetting properties such as a first fluid. A cargo can be referred to as a fluid without electrowetting properties such as a second fluid, and is thusly non-movable in an EWOD device.
Esters are an important class of organic molecules that are widely used in synthesis of fine chemicals, drugs, food preservatives, perfumes, plasticizers, and pharmaceuticals. In a biological aspect, acetylation is one of important protein modification methods in cell biology that has an impact on gene expression and metabolism. There are high demands of rapid, simple, and environmentally friendly protocols for the microscale esterification of alcohols for facile production of a wide variety of esters for medicinal and biological applications. Hence, the esterification in microchannel reactors has been studied comprehensively.
In this Example, esterification of alcohols with acetic anhydride is used as a model reaction to demonstrate the on-chip organic synthesis capabilities of an EWOD digital microfluidic device using methods described herein. A total of 60 tests with 20 different conditions of esterification reactions of secondary alcohols with acetic anhydride were carried out on-chip. The esterification of menthol, one of 60 reactions is shown in
All EWOD microfluidic devices used in this study were fabricated in the Shimadzu Institute Nanotechnology Research Center of the University of Texas at Arlington. Actuation electrodes in the bottom plate of an EWOD device were fabricated by photolithography followed by wet etching of an indium tin oxide (ITO) layer (100 nm) coated on a glass wafer. The dielectric layer (SU-8, 5 μm) and the hydrophobic layer (Teflon, 300 nm) were spin-coated and oven baked. The details of the fabrication steps can be found elsewhere and in ESI.
The EWOD operation voltages (100 Vrms at 1 kHz) were provided by Agilent arbitrary waveform generator and the TEGAM high voltage amplifier (model 23400). Desired sequence of turning on/off electrodes were applied through Lab VIEW program. Droplet motions were recorded using Hirox KH-1300 digital microscope system.
(−)-Menthol (99%), phenol, ≥99.5% (GC), benzyl alcohol anhydrous, 99.8%, trimethylamine, acetic anhydride, 4-(dimethylamino) pyridine (DMAP) (≥90%) were purchased from SIGMA-ALDRICH (USA). Toluene (Certified ACS), 1,4-dioxane, N,N-dimethylformamide, 1,1-dichloroethane (DCE), dichloromethane, (>99.8%) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) (98+%) obtained from Fisher Scientific. Assorted food and egg dye purchased from Walmart (USA). All chemicals were analytical grade and used as received.
Before each test, reagents were placed in designated reservoirs as illustrated in
Each test began with forming an engine-and-cargo compound droplet.
The volume of dispensed cargo solution was estimated by multiplying the footprint area (i.e., the area observed from the top view of the droplet) of cargo with the gap between top and bottom plates of the device. Note that the gap (=100 μm) was well controlled and kept invariant throughout the entire device, so the variation in the footprint are was directly proportion to the variation in the droplet volume. The footprint area of cargo was measured using ImageJ software. The details of the volume measurement and calibration is described in ESI.
While demonstrating capability of an EWOD device to carry out organic reactions, three reaction parameters-reaction time, type of solvents, and catalyst concentration—of on-chip esterification reactions of secondary alcohols with acetic anhydride were independently evaluated and summarized in
For the kinetic study, other reaction parameters (e.g., catalyst concentration and solvent) were fixed and the reaction were monitored from 10 s to 90 s. For the solvent screening, catalyst concentration and reaction time were fixed and 4 different solvents (i.e., toluene, dioxane, N,N-dimethylformamide, and DCE) were tested. For the optimization of catalyst loading, solvent and reaction time were fixed and the concentration of catalyst was varied from 0.1 to 1.5 mol %.
As simulating parallel synthesis esterification of three substrates was performed under basic conditions, the substrates including menthol, benzyl alcohol, and phenol with acid anhydride (
It is generally observed that most of chemical and biological applications of lab-on-chip devices require the volume inconsistency below ±5%. To assess the cargo volume inconsistency, 26 engine-and-cargo droplets were generated consecutively and characterized cargo volumes. During the tests, the cargo reservoir was kept refilled as it depleted. As it is evident from
In some instances, the engine fluid is not meant to be a reagent for esterification while it is present in the reacting droplet during the course of the reaction. The inertness of the engine fluid was tested to establish that the presence of engine fluid would not interfere the reaction. Moreover, the addition of a color dye to the engine fluid is desirable for clear visualization of experiments, but, like the engine fluid, is often not meant to participate in the esterification reaction. To identify reaction compatibility of the engine and color dye, three off-chip reactions were investigated: (1) the model esterification, (2) the esterification in the presence the ionic liquid, and (3) the esterification in the presence of ionic liquid and the green food dye. As shown in
Reaction conditions often need to be optimized to achieve efficient reactions. Typically, optimized reaction conditions can be determined by conversion data from a number of reactions with varying reaction parameters. Such reaction optimization is a tedious process that requires substantial resources including time and efforts, and it generates chemical wastes. An EWOD digital microfluidic technology is particularly useful to address this issue; as an EWOD device can readily provide arrays of droplets and each droplet can carry unique reaction conditions while they are individually controlled. These features make an EWOD device suitable for the high-throughput (in numbers, rather than in volume) screening platform. In this study, 60 on-chip reactions were performed, and the conversion data from these reactions were used to optimize the esterification reaction as followed.
Study of reaction kinetics is an essential part of the reaction optimization because it provides insights into the reaction mechanism. Kinetics study typically associates with a quenching process in which a quenching agent is added to the reaction mixture to stop the reaction at a desired time and conversion measurement is followed. However, quenching a reaction in a macroscale is not a well-controlled process because of the time for applying a quenching agent and its homogeneous diffusion throughout an entire reactor. These factors are, indeed, negligible in microscale reactions due to possible automated fluid handling and the short diffusion length. Consequentially, large numbers of precise conversions data can be obtained quickly and easily in a microscale reaction.
To this end, reactions were quenched at 9 different time intervals, such as at 10-90 seconds (s) at 10 s intervals.
As seen from
Different solvents were tested to study their impact on esterification reaction. For all tests, catalyst concentration and reaction time were fixed at 0.5 mol % and 30 s, respectively. A conversion rate of esterification of menthol with Ac2O in four different solvents are shown in
DMAP has been an efficient catalyst for traditional flask-based acylation reactions. In this study, DMAP is demonstrated to be a useful catalyst for esterification of the less reactive alcohols (i.e., secondary alcohols) on EWOD microfluidics platform. To investigate the optimal loading of DMAP, four different concentrations (0.1, 0.5, 1.0, and 1.5 mol %) were examined.
As seen from
Over the past decades, microscale combinational synthesis has been actively sought. For example, it has been demonstrated using 2×2 combinatorial synthesis of amides through a parallel micro-flow reactor system in a single glass microchip. This approach is mainly based on micro unit operations (MUOs) in pressure driven multi-phase laminar flow networks. A droplet-based microfluidic platform for combinatorial library synthesis of potential drug candidates has also been explored, where a 7×3 library of potential enzyme inhibitors was used. In both cases the design and architecture of the devices are quite complicated. For example, the 2×2 combinatorial synthesis of amides utilized three parallel plates to prevent the cross-contamination that caused the complexity in the fabrication process.
In contrast, an EWOD digital microfluidic device intrinsically has multiplexing capability so that achieving M×N combinations of reactants can be easily done without any complicate modification of a device. Moreover, each droplet can form an independent microreactor; therefore, cross-contamination and crosstalk can be minimized or eliminated, and reaction conditions constituting each combination of reactants can be individually controlled or altered. As a demonstration of the use of an EWOD device for combinatorial syntheses, esterification reactions were performed using three different substrates in a single device. Each droplet was independently generated and manipulated; all other reaction conditions, e.g., solvent, catalyst concentration, and reaction time, were predetermined (
As shown in
Methods described herein demonstrate that an EWOD digital microfluidic platform is an alternative or a complementary tool to microreactors based on continuous channel flow for organic synthesis. A “engine-and-cargo” strategy is described that addresses the shortcoming of an EWOD device; the novel method makes an EWOD device capable of handling electrically non-responsive fluids, particularly organic solvents, where organic fluids are not generally electrically movable. With the engine-and-cargo approach, esterification involving alcohols and phenols with acetic anhydride in the presence of base and DMAP were successfully carried out on EWOD devices. The study on reaction kinetics established benefits from an EWOD device on account of rapid and precise quenching of reactions. Furthermore, rapid reaction optimization was realized on a EWOD device, examining two parameters including solvents and catalyst loading. Finally, 3×1 combinatorial synthesis of esters with three substrates was completed in a rapid fashion.
While esterification was used as an exemplary reaction, methods described herein are not limited to this reaction. Instead, the skilled artisan would appreciate that nearly any organic reaction not inconsistent with the objectives of this disclosure can be performed using the methods described herein. For instances, any organic reaction requiring the use of a solvent without electrowetting properties could be performed on an EWOD device, such as substitution reaction, elimination reactions, addition reactions, oxidation-reduction reactions, or radical reactions.
This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/878,431 filed Jul. 25, 2019, the entirety of which is incorporated by reference herein.
This invention was made with government support under grant no. ECCS-1254602 awarded by the National Science Foundation. The government has certain rights in the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20210023563 A1 | Jan 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62878431 | Jul 2019 | US |
