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Microfluidic capacitive sensors have been used for detection of droplets, however they have been lacking the sensitivity required for detecting the content of droplets. In this study, we developed a scalable, portable, robust and high sensitivity capacitive microdroplet content detection system using coplanar electrodes with nanometer thick silicon dioxide (SiO2) passivation layer and off-the-shelf capacitive sensors. The microfluidic chip we have designed provides easy and rapid modification of droplet content by mixing two aqueous liquids at any given ratio. The change in dielectric constant of the droplet content leads to the change in capacitive signal. The dielectric content of droplets was modified continuously while corresponding capacitance signal was measured. The resolution of the system was measured as 3 dielectric permittivity units. The results were verified using a semiconductor parameter analyzer. The application specific integrated circuit used in this work enables a portable, low-cost detection system and matches the performance of bench-top analyzers. Automated and precise measurement of dielectric content in droplets for biochemical assay monitoring is a major application of the presented system. © 2015 Elsevier B.V. All rights reserved.

A novel procedure was developed to determine the direction of silica growth during the formation of a silica shell around aqueous microdroplets in water-in-oil Pickering emulsions. Two fluorescently labeled silica precursors were added consecutively and the resulting microcapsules were visualized via confocal fluorescence microscopy, allowing the conclusion that the locus of reaction moves in the positive radial direction, i.e. from the inside to the outside. A consequence of the growth direction is that water has to diffuse through the shell to participate in the reaction on the outer surface of the shell. This journal is cop. The Royal Society of Chemistry.

GULER, MUSTAFA TAHSIN/0000-0002-0478-3183; Elbuken, Caglar/0000-0001-8359-6871 WOS: 000375230700008 The conventional fabrication methods for microfluidic devices require cleanroom processes that are costly and time-consuming We present a novel, facile, and low-cost method for rapid fabrication of polydimethylsiloxane (PDMS) molds and devices. The method consists of three main fabrication steps: female mold (FM), male mold (MM), and chip fabrication. We use a CO, laser cutter to pattern a thin, spin -coated PDMS layer for FM fabrication. We then obtain reusable PDMS MM from the FM using PDMS/PDMS casting. Finally, a second casting step is used to replicate PDMS devices from the MM. Demolding of one PDMS layer from another is carried out without any potentially hazardous chemical surface treatment. We have successfully demonstrated that this novel method allows fabrication of microfluidic molds and devices with precise dimensions (thickness, width, length) using a single material, PDMS, which is very common across microfluidic laboratories. The whole process, from idea to device testing, can be completed in 1.5 h in a standard laboratory. European UnionEuropean Union (EU) [322019] This project was partially supported by European Union FP7 Marie Curie Career Integration Grant (no. 322019).

Recent advances in nanotechnology offer nano sized or nanostructured pharmaceutical particles, being as small as the size of cells such as receptors or nucleic acids, which can be engineered to provide enhanced efficacy, solubility, or biocompatibility, and to administer at much lower dosages. However, industrial production of these particles is still challenging. Among different techniques, aerosol based ones might be favorable since they are considered as contamination free processes and do not interfere with complex molecules of drugs. We, in this review, consider liquid atomization, where droplet formation is followed by conversion into solid particles. The best candidate is a method, which not only produces mono sized droplets with a diameter smaller than the inside nozzle diameter but also generates small enough start up sizes. Such a method is found in: Electro-Hydrodynamic Atomization (EHDA) or Electrospraying. Electrospraying is now a well practiced technique for producing very fine monodisperse droplets from a liquid under the influence of electrical forces. By controlling the liquid flow rate and the electrostatic potential between the liquid and the counter electrode, droplets within a narrow size range can be generated, while the mean diameter ranges from nanometers up to several micrometers. Besides generating monodisperse droplets, electrosprays are also distinguished by their self dispersing nature due to Coulomb repulsion, the possibility of trajectory control of the produced charged droplets, and the reduced risk of nozzle clogging due to the large size of the orifice compared to the size of the droplets. We will discuss different spraying modes depending on the strength of the electric stresses relative to the surface tension stress on the liquid surface and on the inertia of the liquid leaving the nozzle. However, for the production of monodisperse nanoparticles the so called cone-jet mode will be explained in depth. Scaling laws can be used to estimate the operational conditions for producing nanodroplets of a certain size. Hartman and coworkers refined the scaling laws for EHDA in the Cone-Jet mode using theoretically derived models for the cone, jet, and droplet size. By means of several examples, a generic way to produce nanoparticles, via scaling laws, from a multitude of different precursors will be discussed. Several examples of medicine particles with different properties made by EHDA will be given. Processes based on bipolar coagulation, where oppositely charged carrier particles and nano sized active agents are brought together to form composite drugs, will be discussed. Finally some attention will be given to challenges on out-scaling of EHDA methods for industrial production.

A novel procedure was developed to determine the direction of silica growth during the formation of a silica shell around aqueous microdroplets in water-in-oil Pickering emulsions. Two fluorescently labeled silica precursors were added consecutively and the resulting microcapsules were visualized via confocal fluorescence microscopy, allowing the conclusion that the locus of reaction moves in the positive radial direction, i.e. from the inside to the outside. A consequence of the growth direction is that water has to diffuse through the shell to participate in the reaction on the outer surface of the shell. This journal is cop. The Royal Society of Chemistry.

We present an integrated optofluidic sensor system for in-line characterization of micro-droplets. The device provides information about the droplet generation frequency, the droplet volume, and the content of the droplet. Due to its simplicity this principle can easily be implemented with other microfluidic components on one and the same device. The sensor is based on total internal reflection phenomena. Droplets are pushed through a microfluidic channel which is hit by slightly diverging monochromatic light. At the solid-liquid interface parts of the rays experience total internal reflection while another part is transmitted. The ratio of reflected to transmitted light depends on the refractive index of the solution. Both signals are recorded simultaneously and provide a very stable output signal for the droplet characterization. With the proposed system passing droplets were counted up to 320 droplets per second and droplets with different volumes could be discriminated. In a final experiment droplets with different amounts of dissolved CaCl2 were distinguished based on their reflected and transmitted light pattern. This principle can be applied for the detection of any molecules in microdroplets which significantly influence the refractive index of the buffer solution.

Diese Arbeit beschäftigt sich mit dem Benetzungsverhalten von Flüssigkeiten auf Oberflächen, die durch Mikrokontakt-Stempeln chemisch strukturiert sind. Dabei werden Experimente zur Morphologie und zur Kondensation und Verdampfung von Flüssigkeiten auf solchen Oberflächen vorgestellt. Im Gegensatz zu homogenen Oberflächen, auf denen ein benetzender Film oder ein kugelkappenförmiger Tropfen die einzigen mechanisch stabilen Zustände einer adsorbierten Flüssigkeit sind, hängt ihre Gestalt auf strukturierten Oberflächen neben den Grenzflächenenergien auch vom adsorbierten Volumen ab. Diese Form der Flüssigkeitsoberfläche wird bei unterschiedlichen zugrundeliegenden Geometrien untersucht: hydrophile Kreise in hydrophober Umgebung, dazu komplementär hydrophobe Kreise in hydrophiler Umgebung, sowie hydrophile Ringe. Dabei treten neuartige morphologische Phasen auf. Bei der Verdampfung von Tropfen von einer Oberfläche wird festgestellt, daß diese Reifungsprozessen unterliegen. Kleine Tropfen verdampfen in der Umgebung von großen Tropfen schneller als in der Nachbarschaft kleiner. Bei geeigneter Wahl der Geometrie des Tropfenmusters können sich Überstrukturen ausbilden bei denen jeder zweite Tropfen schneller verdampft. Es wird außerdem gezeigt, daß Tropfen mit gepinnter Kontaktlinie ein anderes Phasenverhalten haben als Tropfen mit frei beweglicher Kontaktlinie. Freie Tropfen sind thermodynamisch instabil. Sie wachsen oder schrumpfen in Abhängigkeit des lokalen Übersättigungsgrads. Dagegen gibt es für gepinnte Tropfen ein Regime, in dem sie stabil sind. Kondensieren Tropfen auf einer benetzungsstrukturierten Oberfläche, dann adsorbiert die Flüssigkeit bevorzugt an den periodisch angeordneten hydrophilen Stellen. Zusätzlich entstehen Tropfen an wohldefinierten Zwischengitterplätzen der hydrophoben Umgebung, d.h. im unstrukturierten Bereich. Die sich bildende Substruktur wird durch Verarmungszonen erklärt, die um die Tropfen herum entstehen.

Polymer micro- and nano-particles are fundamental to a number of modern technological applications, including polymer blends or alloys, biomaterials for drug delivery systems, electro-optic and luminescent devices, coatings, polymer powder impregnation of inorganic fibers in composites, and are also critical in polymer-supported heterogeneous catalysis. In this article, we review some of our recent progress in experimental and simulation methods for generating, characterizing, and modeling polymer micro- and nano-particles in a number of polymer and polymer blend systems. By using instrumentation developed for probing single fluorescent molecules in micron-sized liquid droplets, we have shown that polymer particles of nearly arbitrary size and composition can be made with a size dispersion that is ultimately limited by the chain length and number distribution within the droplets. Depending on the time scale for solvent evaporation—a tunable parameter in our experiments—phase separation of otherwise immiscible polymers can be avoided by confinement effects, producing homogeneous polymer blend micro- or nano-particles. These particles have tunable properties that can be controlled simply by adjusting the size of the particle, or the relative mass fractions of the polymer components in solution. Physical, optical, and mechanical properties of a variety of micro and nano-particles, differing in size and composition, have been examined using extensive classical molecular dynamics calculations in conjunction with experiments to gain deeper insights into fundamental nature of their structure, dynamics, and properties.