T-junction Droplet Generator Research Articles

Parallel Congruent Electrode Sensor to Detect and Characterize Droplets in a T-Junction Droplet Generator

Parallel Congruent Electrode Sensor to Detect and Characterize Droplets in a T-Junction Droplet Generator

Low Cost, Ease-of-Access Fabrication of Microfluidic Devices Using Wet Paper Molds.

Rapid prototyping methods enable the widespread adoption of microfluidic technologies by empowering end-users from non-engineering disciplines to make devices using processes that are rapid, simple and inexpensive. In this work, we developed a liquid molding technique to create silicone/PDMS microfluidic devices by replica molding. To construct a liquid mold, we use inexpensive adhesive-backed paper, an acetate backing sheet, and an off-the-shelf digital cutter to create paper molds, which we then wet with predetermined amounts of water. Due to the immiscibility of water and PDMS, mold patterns can be effectively transferred onto PDMS similarly to solid molds. We demonstrate the feasibility of these wet paper molds for the fabrication of PDMS microfluidic devices and assess the influence of various process parameters on device yield and quality. This method possesses some distinct benefits compared to conventional techniques such as photolithography and 3D printing. First, we demonstrate that the shape of a channel’s cross-section may be altered from rectangular to semicircular by merely modifying the wetting parameters. Second, we illustrate how electrical impedance can be utilized as a marker for inspecting mold quality and identifying defects in a non-invasive manner without using visual tools such as microscopes or cameras. As a proof-of-concept device, we created a microfluidic T-junction droplet generator to produce water droplets in mineral oil ranging in size from 1.2 µL to 75 µL. We feel that this technology is an excellent addition to the microfluidic rapid prototyping toolbox and will find several applications in biological research.

Theoretical and experimental limits of monodisperse droplet generation

Droplet microfluidic systems are becoming routine in advanced biochemical studies such as single cell gene expression, immuno profiling, precise nucleic acid quantification (dPCR) and particle synthesis. For all these applications, ensuring droplet monodispersity is critical to minimize the uncertainty due to droplet volume variation. Despite the wide usage of droplet-based microfluidic systems, the limit of monodispersity for droplet generation systems is still unknown. Here, we present an analytical approach that takes into account all the system dynamics and internal/external factors that disturb monodispersity. Interestingly, we are able to model the dynamics of a segmented two-phase flow system using a single-phase flow analogy, electron flow, in electrical circuits. We offer a unique solution and design guidelines to ensure ultra-monodisperse droplet generation. Our analytical conclusions are experimentally verified using a T-junction droplet generator. Equally importantly, we show the limiting experimental factors for reaching the theoretical maximum of monodispersity.

Active sorting of droplets by using an ECF (Electro-conjugate Fluid) micropump

This paper proposes an on-demand method to sort water-in-oil (W/O) droplets by using an ECF (Electro-Conjugate Fluid) micropump on a chip. ECF is a kind of functional and dielectric oil, which can generate a strong and active flow (called ECF jet) when a high DC voltage is applied to its corresponding anode & cathode in ECF. Targeting at on-demand droplets sorting, we design a new sorter including several parts: a T-junction droplet generator made of SU-8, a sorting area, an ECF micropump, and I/O ports. The ECF combined with a suitable concentration of a surfactant (Span 80) and DI (deionized) water are utilized as the continuous and the dispersed fluids, respectively. The mixture of ECF and Span 80 can also be pumped by our ECF micropump and then forms the ECF jet. The fabrication of the sorter is based on the photolithographic patterning of thick resists (KMPR and SU-8) and the electroforming. We model the ECF micropump and also analyze the sorting performance of our sorter based on the FEM analysis. To validate the sorter, we investigate the influence of two vital parameters of the strength of ECF jets and the droplet sizes on the sorter. Then, we also research the working zones (areas), throughput and sorting efficiency in terms of flow rate ratios and the applied voltages of our device.

A 3D printed screw-and-nut based droplet generator with facile and precise droplet size controllability

Herein, we present the fabrication of a novel vertical T-junction based droplet generator using a desktop 3D printer and the production of a variety of size of polymer particles by tuning the vertical T-junction gap height (hg) with ease. The droplet generator device consists of two main components: an internal thread nut with a vertical T-junction droplet generator unit, and a screw with an external thread for adjusting hg. The two components were fabricated by a 3D printer and assembled simply by a bolt-and-nut combination. The clockwise or counter-clockwise rotation of the screw is converted into the downward and upward linear motion of the screw, adjusting the hg value. The hg value can be tuned precisely from 0 to 750 μm by designing 75 control teeth on the top of the screw. The size of the produced droplets is proportional to the hg value. The size range of the droplets was 39–1404 μm, when hg changed from 20 to 200 μm. We synthesized poly(ethylene glycol) diacrylate (PEGDA) particles using the droplet as a reactor, and accordingly the PEGDA particle size could be controlled. Our proposed 3D printed droplet generator is rapid, simple and cost-effective to be fabricated without need of lithographic processes.

Fast packaging by a partially-crosslinked SU-8 adhesive tape for microfluidic sensors and actuators

This paper proposes a novel SU-8 adhesive tape by using the dose-controlled UV exposure method, which enables the fast packaging with fluidic interconnections for microfluidic sensors and actuators. The conventional packaging for microfluidic devices demands two complicated steps: (1) to drill the fluidic connections on the glass cover in the first process, which may make the glass cover broken due to poor machinability of glass; and then (2) to spread a thin adhesive on the cover in the second process, which may induce the clogging of the fluidic connections. To realize a fast and simple packaging for microfluidic devices, we propose a versatile method that employs a partially-crosslinked SU-8 adhesive tape composed of an adhesive layer (uncrosslinked SU-8) onto the backing material (crosslinked SU-8) with fluid connections, which can be fabricated in one simple step. We choose a suitable substrate from which we can release the SU-8 adhesive tape and build the mathematic model of the dose-controlled UV exposure method which can estimate the thickness of the crosslinked SU-8. Then, we investigate the influence of developing time on the formation of the SU-8 adhesive tape. We also examine the bonding quality by using the visual inspection method and measuring the bonding strength based on the pull-test experiments. Moreover, its applications to a T-junction droplet generator and a shallow channelprove the feasibility to be widely applied to microfluidic sensors and actuators.

Fast electric control of the droplet size in a microfluidic T-junction droplet generator

The effect of DC electric fields on the generation of droplets of water and xanthan gum solutions in sunflower oil at a microfluidic T-junction is experimentally studied. The electric field leads to a significant reduction of the droplet diameter, by about a factor of 2 in the case of water droplets. The droplet size can be tuned by varying the electric field strength, an effect that can be employed to produce a stream of droplets with a tailor-made size sequence. Compared to the case of purely hydrodynamic droplet production without electric fields, the electric control has about the same effect on the droplet size if the electric stress at the liquid/liquid interface is the same as the hydrodynamic stress.

Flow-Based Surface Decoration of Microparticles with Titania and Other Transition Metal Oxide Nanoparticles

We present a rapid approach for forming monodisperse silica microcapsules decorated with metal oxide nanoparticles; the silica–metal oxide composites have a hierarchical architecture and a range of compositions. The details of the method were defined using titania precursors. Silica capsules containing low concentrations of titania (<1 wt. %) were produced via an interfacial reaction using a simple mesofluidic T-junction droplet generator. Increasing the titania content of the capsules was achieved using two related, flow-based postsynthetic approaches. In the first approach, a precursor solution containing titanium alkoxides was flowed through a packed-bed of capsules. The second approach provided the highest concentration of titania (3.5 wt. %) and was achieved by evaporating titanium precursor solutions onto a capsule packed-bed using air flow to accelerate evaporation. Decorated capsules, regardless of the method, were annealed to improve the titania crystallinity and analyzed by optical microscopy, s...

Experimental validation of a simple, low-cost, T-junction droplet generator fabricated through 3D printing

Three-dimensional printing has been recently proposed and assessed for continuous flow microfluidic devices. In this paper the focus is on a new application of this rapid and low cost method for microfluidic device prototyping: droplets production through a T-junction generator. The feasibility of this new methodology is assessed by means of an experimental study in which the statistical parameters which characterize the production of droplets are analyzed. Furthermore, this study assesses the validity of previous theoretical and experimental results, obtained for a PDMS T-junction droplet generator, also in the case of a 3D printed Acrylonitrile microfluidic chip. Finally, the feasibility of producing monodisperse droplets by analyzing the polydispersity index of the prepared droplets is demonstrated.

T-junction droplet generator realised in lithium niobate crystals by laser ablation

AbstractA femtosecond laser at 800 nm was used to create micro-fluidic circuits on lithium niobate (LiNbO3) substrates by means of laser ablation, using different scanning velocities (100-500 μm/s) and laser pulse energies (1-20 μJ). The T-junction geometry was exploited to create on y-cut LiNbO3 crystals a droplet generator, whose microfluidic performance was characterized in a wide range of droplet generation frequencies, from few Hz to about 1 kHz.

A Microfluidic Device for Continuous Sensing of Systemic Acute Toxicants in Drinking Water

A bioluminescent-cell-based microfluidic device for sensing toxicants in drinking water was designed and fabricated. The system employed Vibrio fischeri cells as broad-spectrum sensors to monitor potential systemic cell toxicants in water, such as heavy metal ions and phenol. Specifically, the chip was designed for continuous detection. The chip design included two counter-flow micromixers, a T-junction droplet generator and six spiral microchannels. The cell suspension and water sample were introduced into the micromixers and dispersed into droplets in the air flow. This guaranteed sufficient oxygen supply for the cell sensors. Copper (Cu2+), zinc (Zn2+), potassium dichromate and 3,5-dichlorophenol were selected as typical toxicants to validate the sensing system. Preliminary tests verified that the system was an effective screening tool for acute toxicants although it could not recognize or quantify specific toxicants. A distinct non-linear relationship was observed between the zinc ion concentration and the Relative Luminescence Units (RLU) obtained during testing. Thus, the concentration of simple toxic chemicals in water can be roughly estimated by this system. The proposed device shows great promise for an early warning system for water safety.

Simulation and Design of a Cell-Based Digital Microfluidic Chip for Continuous Monitoring of Acute Toxic Chemicals

In this study, a lab-on-chip (LOC) system is designed for the cell sensors to provide a high-efficient continuous analysis platform of acute toxicants in water environment. The chip is composed of three domains, including counter-flow micromixers, a T-junction droplet generator and time delay channels (TD-Cs). Water sample and bioluminescent bacterium Vibrio Fischeri (VF) are imported into the micromixers before that the droplet generator encapsulates them inside aqueous droplets separated by air. Air flow is the disperse medium, which can guarantee sufficient oxygen supply for the cells in droplets. The system shows high reliability and stability through numerical and experimental investigations.

Microfluidic droplet encapsulation of highly motile single zoospores for phenotypic screening of an antioomycete chemical.

Highly motile Phytophthora sojae (P. sojae) zoospores of an oomycete plant pathogen and antioomycete candidate chemicals were encapsulated into microdroplets. Random fast self-motion of P. sojae zoospores was overcome by choosing an appropriate flow rate for a zoospore suspension. To influence stochastic loading of zoospores into a microfluidic channel, a zoospore suspension was directly preloaded into a microtubing with a largely reduced inner diameter. A relatively high single zoospore encapsulation rate of 60.5% was achieved on a most trivial T-junction droplet generator platform, without involving any specially designed channel geometry. We speculated that spatial reduction in the diameter direction of microtubing added a degree of zoospore ordering in the longitudinal direction of microtubing and thus influenced positively to change the inherent limitation of stochastic encapsulation of zoospores. Comparative phenotypic study of a plant oomycete pathogen at a single zoospore level had not been achieved earlier. Phenotypic changes of zoospores responding to various chemical concentration conditions were measured in multiple droplets in parallel, providing a reliable data set and thus an improved statistic at a low chemical consumption. Since each droplet compartment contained a single zoospore, we were able to track the germinating history of individual zoospores without being interfered by other germinating zoospores, achieving a high spatial resolution. By adapting some existing droplet immobilization and concentration gradient generation techniques, the droplet approach could potentially lead to a medium-to-high throughput, reliable screening assay for chemicals against many other highly motile zoospores of pathogens.