Continuous Microfluidic System Research Articles

The kinetics study on sulfonation reaction of continuous microfluidic synthesis of 1-tetradecene

Sulfonation of 1-tetradecene with liquid-phase sulfur trioxide generates simultaneously the alkene sulfonic acid and alkene sulfonate. The kinetics study is contributed to a deeper understanding of the sulfonation reaction and better controlling the process. The continuous microfluidic system was established to determine the kinetic parameters of 1-tetradecene sulfonation. A comprehensive kinetic model was developed, and the kinetic parameters were obtained. The activation energy is 14.7 ± 0.8 kJ mol−1, with a pre-exponential factor of 118.4 ± 1.4. The reaction order for 1-tetradecene is second-order, and for sulfur trioxide, the reaction order is 0.3. By discretizing the reactor into microelements and conducting mass balance on each differential element method, integrating the obtained reaction kinetics model, calculating the required reaction time, and comparing it with experimental data within a reasonable range of error, the correctness of the derived reaction kinetics model has been verified.

Microfluidic In Situ Patterning of Silver Nanoparticles for Surface-Enhanced Raman Spectroscopic Sensing of Biomolecules.

This work integrates the advantages of microfluidic devices, nanoparticle synthesis, and on-chip sensing of biomolecules. The concept of microreactors brings new opportunities in chemical synthesis, especially for metallic nanoparticles favorable in surface-enhanced Raman spectroscopy (SERS) for high-resolution and low-limit detection of biomolecules. However, still missing is our understanding of reactions at the microscale and how microsystems can be exploited in biosensing applications via precise control of nanomaterial synthesis. We investigate how microfluidic geometry affects nanoparticle patterning for high-resolution SERS-based sensing and propose a spiral-shaped microchannel that can achieve enhanced mixing, rapid reaction at room temperature, and uniform in situ patterning. The roles of channel geometry as the key parameter on patterning have been studied systematically to provide insight into the rational design of continuous microfluidic systems for SERS applications. We also demonstrate potential applications of this integrated system in label-free on-chip detection of 1 pM rhodamine B (enhancement factor, ∼4.3 × 1011) and a 1 nM 41-base single-stranded deoxyribonucleic acid (DNA) sequence (enhancement factor, ∼1.5 × 108). Our ready-to-use multifunctional system provides an alternative strategy for the facile fabrication of SERS-active substrates and promotes system integration, miniaturization, and on-site biological applications.

Synthesis of PEDOT in a continuous microfluidic system

Polyethylenedioxytiophene (PEDOT) is synthesized successfully and for the first time from its monomer by chemical oxidation polymerization in a microchannel device inside micro-droplets. The oxidizing agent, ammonium persulfate, with different molar ratios to the monomer was used and compared with an out-of-channel synthesized PEDOT. Details of the procedure, droplet formation mechanism inside the channel in addition to the effect of various factors are described. The device can be used as a fast and continuous method for the synthesis of PEDOT. Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, photoluminescence spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy are the methods for evaluating and comparison of the products. The results showed that despite the same materials and conditions for in-channel polymerization, the microfluidic synthesis is much more sensitive method compared to common bulk methods.

In Situ Photophysical Characterization of π-Conjugated Oligopeptides Assembled via Continuous Flow Processing.

Bioinspired materials have been developed with the aim of harnessing natural self-assembly for precisely engineered functionality. Microfluidics is poised to play a key role in the directed assembly of advanced materials with ordered nano and mesoscale features. More importantly, there is a strong need for understanding the kinetics of continuous assembly processes. In this work, we describe a continuous microfluidic system for the assembly and alignment of synthetic oligopeptides with π-conjugated cores using a three-dimensional (3D) flow focusing of inlet reactant streams. This system facilitates in situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM), which can be used in unprecedented capacity to characterize the integrity of peptides during the assembly process. To achieve continuous assembly, we integrate chevron patterns in the ceiling and floor of the microdevice to generate a 3D-focused sheath flow of the reactant peptide. Consequently, the peptide stream is directed toward an acidic triggering stream in a cross-slot geometry which mediates assembly into higher-order fiber-like structures. Using this approach, the focused peptide stream is assembled using a planar extensional flow, which ensures high degrees of microstructural alignment within the assembled material. We demonstrate the efficacy of this approach using three different synthetic oligopeptides, and in all cases, we observe the efficient and continuous assembly of oligopeptides. In addition, finite element simulations are used to guide device design and to validate 3D focusing. Overall, this approach presents an efficient and effective method for the continuous assembly and alignment of ordered materials using microfluidics.

An anti-clogging method for improving the performance and lifespan of blood plasma separation devices in real-time and continuous microfluidic systems

On-chip blood plasma separators using microfluidic channels are typically developed as disposable devices for short-term use only because blood cells tend to clog the microchannels, limiting their application in real-time and continuous systems. In this study, we propose an anti-clogging method. We applied dielectrophoresis to prevent microchannel clogging in a plasma separator that can be used over long periods for real-time and continuous monitoring. Prior to applying the anti-clogging method, the blood plasma separator stopped working after 4 h. In contrast, by manipulating the separator with the new anti-clogging method at a voltage of 20 V, it continued working in a long-term experiment for 12 h without performance deterioration or an increase in cell loss. Two critical performance parameters of the manipulated separator, the purity efficiency and the plasma yield, were 97.23 ± 5.43% and 38.95 ± 9.34%, respectively, at 20 V after 15 min. Interestingly, the two performance parameters did not decrease during the long-term experiment. Hence, the blood plasma separator with the anti-clogging method is an interesting device for use in real-time and continuous blood plasma separation systems because of its consistent performance and improved lifespan.

Continuous Synthesis of Ag/AgCl/ZnO Composites Using Flow Chemistry and Photocatalytic Application

Ag/AgCl/ZnO composites were successfully synthesized in a continuous microfluidic system under visible light irradiation, which was employed in situ to reduce a portion of AgCl to metallic Ag. The formation of Ag/AgCl/ZnO composites was confined in small aqueous plugs, which were dispersed by octane as the continuous phase. In this way, enhanced mixing, low risk of channel clogging, and uniform light distribution were achieved. The characterization results revealed that the as-prepared Ag/AgCl/ZnO composites were composed of flowerlike ZnO with Ag/AgCl nanospheres anchored to them. It was found that the synthesis parameters such as water/oil volume flow ratio, total volume flow rate, temperature, and the molar ratio of Zn2+ to Ag+ had effects on the synthesis of Ag/AgCl/ZnO composites. Furthermore, the as-prepared Ag/AgCl/ZnO composites outperformed Ag/ZnO composites and AgCl/ZnO composites in the visible-light-driven degradation of methyl orange.

Aragonite crystallization in a Christmas-tree model microfluidic device with the addition of magnesium ions

Aragonite is an important dimorph of calcium carbonate, industrially and biologically. However, aragonite is so thermodynamically unstable that it is difficult to understand its formation mechanism. A continuous microfluidic system was employed, in which crystallization was induced only by diffusion in a micron-scale channel. Calcium carbonate (CaCO3) formed by liquid-liquid reaction and magnesium ions (Mg2+) were used as additives. To assess the influence of Mg2+ concentration, the Mg2+/Ca2+ molar ratio was set to 1, 3, and 5. Laminar streams flowed in the detection channel with different concentration gradients. The initial crystallization time (tI.C) increased exponentially and the density of crystals decreased as the Mg2+ ion concentration increased. Following transformation of all particles into snowman or sphere shapes, they became spinose sphere-shaped crystals, which was the final form in this study.

Continuous synthesis of hedgehog-like Ag–ZnO nanoparticles in a two-stage microfluidic system

Hedgehog-like Ag–ZnO nanoparticles were successfully prepared in a continuous microfluidic system and showed a superior photocatalytic activity in the degradation of methyl orange.

Inside Back Cover: Odorless Isocyanide Chemistry: An Integrated Microfluidic System for a Multistep Reaction Sequence (Angew. Chem. Int. Ed. 29/2013)

Despite the long history of isocyanide chemistry, the full utilization of these compounds has been hindered by their distressing odor. In their Communication on page 7564 ff., D.-P. Kim et al. report the development of an automated continuous microfluidic system that produces products through the serial synthesis, purification, and in situ consumption of isocyanides, with little exposure of these compounds to the surroundings.

Microfluidic Continuous Seeded Crystallization: Extraction of Growth Kinetics and Impact of Impurity on Morphology

We describe a continuous microfluidic system for seeded crystallization of small organic molecules, such as active pharmaceuticals, and demonstrate integration with in situ detection tools for determining the size and polymorphic form of the crystals. This integrated device is used to extract growth kinetics, as a screening platform for process parameter effects and optimization, and to gain insight into the fundamentals of the crystallization process. In addition, the microfluidic system also allows studies of additive effects on the crystal habit. The method is demonstrated with growth kinetics for α-, β-, and γ-forms of glycine along with the effects upon the morphology of adding glutamic acid and methionine.

Meniscus-Assisted High-Efficiency Magnetic Collection and Separation for EWOD Droplet Microfluidics

This paper describes a technique to increase the efficiency of magnetic concentration on an electrowetting-on-dielectric (EWOD)-based droplet (digital) microfluidic platform operated in air, i.e., on dry surface. Key differences in the force scenario for droplet microfluidics vis-a-vis the conventional continuous microfluidic systems are identified to explain the rationale behind the proposed idea. In particular, the weakness of the magnetic force relative to the bead-substrate adhesion and the liquid-air interfacial tension is highlighted, and a new technique to achieve high-efficiency magnetic collection with the assistance of the interfacial force is proposed. An improvement in collection efficiency (e.g., from ~ 73% to ~ 99%) is observed with the new technique of ldquomeniscus-assisted magnetic bead collectionrdquo. In addition, isolation of the magnetic species from a mixed sample of magnetic and nonmagnetic beads is demonstrated. Comparison with other related reports is also presented.

Integrated microreaction system for optical resolution of racemic amino acids

We developed a novel microreaction system for optical resolution of racemic amino acids. This device, which is based on a continuous microfluidic system, consists of an enzyme-immobilized microreactor and a microextractor. Use of the enzyme-microreactor, which was prepared by membrane formation on the microchannel surface, enabled a highly enantioselective reaction for a racemic amino acid derivative. The microextractor provided a laminar flow of two immiscible solutions, which enabled selective extraction of the product. Using this integrated device, we could perform efficient continuous production of optically pure unnatural amino acids.