Influence of Wettability and Geometry on Contact Electrification between Nonionic Insulators

Contact electrification is an interfacial process in which two surfaces exchange electrical charges when they are in contact with one another. Consequently, the surfaces may gain opposite polarity, inducing an electrostatic attraction. Therefore, this principle can be exploited to generate electricity, which has been precisely done in triboelectric nanogenerators (TENGs) over the last decades. The details of the underlying mechanisms are still ill-understood, especially the influence of relative humidity (RH). Using the colloidal probe technique, we convincingly show that water plays an important role in the charge exchange process when two distinct insulators with different wettability are contacted and separated in <1 s at ambient conditions. The charging process is faster, and more charge is acquired with increasing relative humidity, also beyond RH = 40% (at which TENGs have their maximum power generation), due to the geometrical asymmetry (curved colloid surface vs planar substrate) introduced in the system. In addition, the charging time constant is determined, which is found to decrease with increasing relative humidity. Altogether, the current study adds to our understanding of how humidity levels affect the charging process between two solid surfaces, which is even enhanced up to RH = 90% as long as the curved surface is hydrophilic, paving the way for designing novel and more efficient TENGs, eco-energy harvesting devices which utilize water and solid charge interaction mechanism, self-powered sensors, and tribotronics.

Stress-dependent macromolecular crowding in the mitochondrial matrix

Macromolecules of various sizes induce crowding of the cellular environment. This crowding impacts on biochemical reactions by increasing solvent viscosity, decreasing the water-accessible volume and altering protein shape, function, and interactions. Although mitochondria represent highly protein-rich organelles, most of these proteins are somehow immobilized. Therefore, whether the mitochondrial matrix solvent exhibits macromolecular crowding is still unclear. Here, we demonstrate that fluorescent protein fusion peptides (AcGFP1 concatemers) in the mitochondrial matrix of HeLa cells display an elongated molecular structure and that their diffusion constant decreases with increasing molecular weight in a manner typical of macromolecular crowding. Chloramphenicol (CAP) treatment impaired mitochondrial function and reduced the number of cristae without triggering mitochondrial orthodox-to-condensed transition or a mitochondrial unfolded protein response. CAP-treated cells displayed progressive concatemer immobilization with increasing molecular weight and an eightfold matrix viscosity increase, compatible with increased macromolecular crowding. These results establish that the matrix solvent exhibits macromolecular crowding in functional and dysfunctional mitochondria. Therefore, changes in matrix crowding likely affect matrix biochemical reactions in a manner depending on the molecular weight of the involved crowders and reactants.

Triboelectric Charging of Particles, an Ongoing Matter: From the Early Onset of Planet Formation to Assembling Crystals

Triboelectrification is the spontaneous charging of two bodies when released from contact. Even though its manifestation is commonplace, in for instance triboelectric nanogenerators, scientists find the tribocharging mechanism a mystery. The primary aim of this mini-review is to provide an overview of different tribocharging concepts that have been applied to study and realize the formation of ordered stable structures using different objects on various length scales. Relevance spans from materials to planet formations. Especially, dry assembly methods of particles of different shapes based on tribocharging to obtain crystal structures or monolayers are considered. In addition, the current technology employed to examine tribocharging in (semi)dry environments is discussed as well as the relevant forces playing a role in the assembly process. In brief, this mini-review is expected to provide a better understanding of tribocharging in assembling objects on the nano- and micrometer scales.

Self-Aligned Crystallographic Multiplication of Nanoscale Silicon Wedges for High-Density Fabrication of 3D Nanodevices

High-density arrays of silicon wedges bound by {111} planes on silicon (100) wafers have been created by combining convex corner lithography on a silicon dioxide hard mask with anisotropic, crystallographic etching in a repetitive, self-aligned multiplication procedure. A mean pitch of around 30 nm has been achieved, based on an initial pitch of ∼120 nm obtained through displacement Talbot lithography. The typical resolution of the convex corner lithography was reduced to the sub-10 nm range by employing an 8 nm silicon dioxide mask layer (measured on the {111} planes). Nanogaps of 6 nm and freestanding silicon dioxide flaps as thin as 1-2 nm can be obtained when etching the silicon at the exposed apices of the wedges. To enable the repetitive procedure, it was necessary to protect the concave corners between the wedges through "concave" corner lithography. The produced high-density arrays of wedges offer a promising template for the fabrication of large arrays of nanodevices in various domains with relevant details in the sub-10 nm range.

Large Dense Periodic Arrays of Vertically Aligned Sharp Silicon Nanocones

Convex cylindrical silicon nanostructures, also referred to as silicon nanocones, find their value in many applications ranging from photovoltaics to nanofluidics, nanophotonics, and nanoelectronic applications. To fabricate silicon nanocones, both bottom-up and top-down methods can be used. The top-down method presented in this work relies on pre-shaping of silicon nanowires by ion beam etching followed by self-limited thermal oxidation. The combination of pre-shaping and oxidation obtains high-density, high aspect ratio, periodic, and vertically aligned sharp single-crystalline silicon nanocones at the wafer-scale. The homogeneity of the presented nanocones is unprecedented and may give rise to applications where numerical modeling and experiments are combined without assumptions about morphology of the nanocone. The silicon nanocones are organized in a square periodic lattice, with 250 nm pitch giving arrays containing 1.6 billion structures per square centimeter. The nanocone arrays were several mm² in size and located centimeters apart across a 100-mm-diameter single-crystalline silicon (100) substrate. For single nanocones, tip radii of curvature < 3 nm were measured. The silicon nanocones were vertically aligned, baring a height variation of < 5 nm (< 1%) for seven adjacent nanocones, whereas the height inhomogeneity is < 80 nm (< 16%) across the full wafer scale. The height inhomogeneity can be explained by inhomogeneity present in the radii of the initial columnar polymer mask. The presented method might also be applicable to silicon micro- and nanowires derived through other top-down or bottom-up methods because of the combination of ion beam etching pre-shaping and thermal oxidation sharpening. A novel method is presented where argon ion beam etching and thermal oxidation sharpening are combined to tailor a high-density single-crystalline silicon nanowire array into a vertically aligned single-crystalline silicon nanocones array with < 3 nm apex radius of curvature tips, at the wafer scale.

Towards controlled bubble nucleation in microreactors for enhanced mass transport

The exact location of bubbles with respect to the catalytic layer impacts the microreactor performance. In this work, we propose to control bubble nucleation using micropits to maximize the microreactor efficiency.

Wafer-scale 3D shaping of high aspect ratio structures by multistep plasma etching and corner lithography

The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density. In this work, a wafer-scale out-of-plane 3D silicon (Si) shaping technology is reported, which combines a multistep plasma etching process with corner lithography. The multistep plasma etching procedure results in high aspect ratio structures with stacked semicircles etched deep into the sidewall and thereby introduces corners with a proper geometry for the subsequent corner lithography. Due to the geometrical contrast between the gaps and sidewall, residues are left only inside the gaps and form an inversion mask inside the semicircles. Using this mask, octahedra and donuts can be etched in a repeated manner into Si over the full wafer area, which demonstrates the potential of this technology for constructing high-density 3D structures with good dimensional control in the bulk of Si wafers.

Inline Reaction Monitoring of Amine-Catalyzed Acetylation of Benzyl Alcohol Using a Microfluidic Stripline Nuclear Magnetic Resonance Setup

We present an in-depth study of the acetylation of benzyl alcohol in the presence of N, N-diisopropylethylamine (DIPEA) by nuclear magnetic resonance (NMR) monitoring of the reaction from 1.5 s to several minutes. We have adapted the NMR setup to be compatible to microreactor technology, scaling down the typical sample volume of commercial NMR probes (500 μL) to a microfluidic stripline setup with 150 nL detection volume. Inline spectra are obtained to monitor the kinetics and unravel the reaction mechanism of this industrially relevant reaction. The experiments are combined with conventional 2D NMR measurements to identify the reaction products. In addition, we replace DIPEA with triethylamine and pyridine to validate the reaction mechanism for different amine catalysts. In all three acetylation reactions, we find that the acetyl ammonium ion is a key intermediate. The formation of ketene is observed during the first minutes of the reaction when tertiary amines were present. The pyridine-catalyzed reaction proceeds via a different mechanism.

Scalable 3D Nanoparticle Trap for Electron Microscopy Analysis

Arrays of nanoscale pyramidal cages embedded in a silicon nitride membrane are fabricated with an order of magnitude miniaturization in the size of the cages compared to previous work. This becomes possible by combining the previously published wafer-scale corner lithography process with displacement Talbot lithography, including an additional resist etching step that allows the creation of masking dots with a size down to 50 nm, using a conventional 365 nm UV source. The resulting pyramidal cages have different entrance and exit openings, which allows trapping of nanoparticles within a predefined size range. The cages are arranged in a well-defined array, which guarantees traceability of individual particles during post-trapping analysis. Gold nanoparticles with a size of 25, 150, and 200 nm are used to demonstrate the trapping capability of the fabricated devices. The traceability of individual particles is demonstrated by transferring the transmission electron microscopy (TEM) transparent devices between scanning electron microscopy and TEM instruments and relocating a desired collection of particles.

An All-Glass Microfluidic Network with Integrated Amorphous Silicon Photosensors for on-Chip Monitoring of Enzymatic Biochemical Assay

A lab-on-chip system, integrating an all-glass microfluidics and on-chip optical detection, was developed and tested. The microfluidic network is etched in a glass substrate, which is then sealed with a glass cover by direct bonding. Thin film amorphous silicon photosensors have been fabricated on the sealed microfluidic substrate preventing the contamination of the micro-channels. The microfluidic network is then made accessible by opening inlets and outlets just prior to the use, ensuring the sterility of the device. The entire fabrication process relies on conventional photolithographic microfabrication techniques and is suitable for low-cost mass production of the device. The lab-on-chip system has been tested by implementing a chemiluminescent biochemical reaction. The inner channel walls of the microfluidic network are chemically functionalized with a layer of polymer brushes and horseradish peroxidase is immobilized into the coated channel. The results demonstrate the successful on-chip detection of hydrogen peroxide down to 18 μM by using luminol and 4-iodophenol as enhancer agent.

Continuous Flow 1H and 13C NMR Spectroscopy in Microfluidic Stripline NMR Chips

Microfluidic stripline NMR technology not only allows for NMR experiments to be performed on small sample volumes in the submicroliter range, but also experiments can easily be performed in continuous flow because of the stripline's favorable geometry. In this study we demonstrate the possibility of dual-channel operation of a microfluidic stripline NMR setup showing one- and two-dimensional 1H, 13C and heteronuclear NMR experiments under continuous flow. We performed experiments on ethyl crotonate and menthol, using three different types of NMR chips aiming for straightforward microfluidic connectivity. The detection volumes are approximately 150 and 250 nL, while flow rates ranging from 0.5 μL/min to 15 μL/min have been employed. We show that in continuous flow the pulse delay is determined by the replenishment time of the detector volume, if the sample trajectory in the magnet toward NMR detector is long enough to polarize the spin systems. This can considerably speed up quantitative measurement of samples needing signal averaging. So it can be beneficial to perform continuous flow measurements in this setup for analysis of, e.g., reactive, unstable, or mass-limited compounds.

Enhancing acoustic cavitation using artificial crevice bubbles

We study the response of pre-defined cavitation nuclei driven continuously in the kHz regime (80, 100 and 200 kHz). The nuclei consist of stabilized gaspockets in cylindrical pits of 30 μm diameter etched in silicon or glass substrates. It is found that above an acoustic pressure threshold the dynamics of the liquid-gas meniscus switches from a stable drum-like vibration to expansion and deformation, frequently resulting in detachment of microbubbles. Just above this threshold small bubbles are continuously and intermittently ejected. At elevated input powers bubble detachment becomes more frequent and cavitation bubble clouds are formed and remain in the vicinity of the pit bubble. Surprisingly, the resulting loss of gas does not lead to deactivation of the pit which can be explained by a rectified gas diffusion process.

Fabrication of integrated porous glass for microfluidic applications

This paper presents a method for the fabrication of integrated porous silica layers in microfluidic channel networks by microfabrication techniques. Porous silica is obtained by anodization of silicon, followed by full conversion of the porous silicon network into porous silica by means of thermal oxidation. A series of experiments were performed with various channel layouts to determine the critical parameters, including the I-V characteristics and the optimal working potential for stable pore formation, during anodic etching. Typical test structures were anodized in 5% HF for 15 min at 1 V, yielding an average pore size of around 5.4 nm and porosity of 49%. Complete conversion of porous silicon into porous glass was accomplished with wet oxidation at 900 °C. The average pore size and porosity of porous glass network were around 3.8 nm and 34%, respectively. This decrease in both pore size and porosity is caused by the increase in molar volume when silicon oxidizes to silicon oxide. The transparency and the hydrophilicity of porous glass layers are evidenced by means of monitoring the diffusion of Rhodamine B fluorescent dye through the porous network. This fabrication method can be applied to (3-D) structured microfluidic channels and it is envisioned that the resulting porous silica layers can be employed for a wide range of application areas, such as membrane technology, catalyst supports, chromatography and electrokinetics.

Design and implementation of injector/distributor structures for microfabricated non-porous pillar columns for capillary electrochromatography

A previously proposed foil definition is applied in the design of injector/distributor structures for solid microfabricated column structures for capillary electrochromatography. In addition to a typical bifurcated distributor, an optimized design alternative with two different configurations is experimentally evaluated. Optimized designs yielded a flat profile for the injected sample with a maximum of 3% variation from the mean width, while it went up to 18% for the typical bifurcated distributor. The implemented electrokinetic injection approach enabled controlling the volume of the injected sample accurately without sacrificing the compactness of the device design. The width of the injected sample was directly proportional to the injection time, namely 165 and 218 μm base widths were obtained for 0.6 and 0.8s of feeding, respectively. Reducing the external porosity of the distributor by 85% compared to the typical design, optimized distributors caused a decrease in the mean flow velocity of up to 70%. However, having a flat initial plug shape enabled the separation of a mixture of Coumarin 440, 460, 480 and 540 at 1 mm downstream of the injection point in 80s, while it was even not possible to detect the C440 signal for a typical bifurcated design.

Ultrasound artificially nucleated bubbles and their sonochemical radical production

We describe the ejection of bubbles from air-filled pits micromachined on a silicon surface when exposed to ultrasound at a frequency of approximately 200 kHz. As the pressure amplitude is increased the bubbles ejected from the micropits tend to be larger and they interact in complex ways. With more than one pit, there is a threshold pressure beyond which the bubbles follow a trajectory parallel to the substrate surface and converge at the center point of the pit array. We have determined the size distribution of bubbles ejected from one, two and three pits, for three different pressure amplitudes and correlated them with sonochemical OH· radical production. Experimental evidence of shock wave emission from the bubble clusters, deformed bubble shapes and jetting events that might lead to surface erosion are presented. We describe numerical simulations of sonochemical conversion using the empirical bubble size distributions, and compare the calculated values with experimental results.

A supramolecular approach to enzyme immobilization in micro-channels

A supramolecular assembly scheme is developed to enable the facile in-situ immobilization of enzymes in a microfluidic channel system. A combination of orthogonal supramolecular interactions of host (β-cyclodextrin)-guest (adamantane) and biotin-Streptavidin (SAv) interactions are employed to generate reusable homogeneous enzyme layers in microchannels. The structural integrity and catalytic activity of the immobilized enzyme calf-intestine alkaline phosphatase (AlkPh) is demonstrated. From the kinetic analysis of a dephosphorylation reaction, the specificity constant k(cat)/K(M) for immobilized alkaline phosphatase in the channels is on the order of 10(5) M(-1) s(-1) and comparable to known literature values in other environments. These observations are ascribed to the good access of the substrate to favorably oriented enzymes across the microchannel. Therefore, this study demonstrates the great potential for adopting a supramolecular assembly scheme to immobilize enzymes in microfluidic devices.

Mimicking insect communication: release and detection of pheromone, biosynthesized by an alcohol acetyl transferase immobilized in a microreactor

Infochemical production, release and detection of (Z,E)-9,11-tetradecadienyl acetate, the major component of the pheromone of the moth Spodoptera littoralis, is achieved in a novel microfluidic system designed to mimic the final step of the pheromone biosynthesis by immobilized recombinant alcohol acetyl transferase. The microfluidic system is part of an “artificial gland”, i.e., a chemoemitter that comprises a microreactor connected to a microevaporator and is able to produce and release a pre-defined amount of the major component of the pheromone from the corresponding (Z,E)-9,11-tetradecadienol. Performance of the entire chemoemitter has been assessed in electrophysiological and behavioral experiments. Electroantennographic depolarizations of the pheromone produced by the chemoemitter were ca. 40% relative to that evoked by the synthetic pheromone. In a wind tunnel, the pheromone released from the evaporator elicited on males a similar attraction behavior as 3 virgin females in most of the parameters considered.

Performance evaluation of different design alternatives for microfabricated nonporous fused silica pillar columns for capillary electrochromatography

An experimental study comparing the performance of different designs for microfabricated column structures for microchip capillary electrochromatography is presented. The work is a follow-up to our previously published modeling and simulation study on the same topic. Experiments were performed using fused silica microchips with and without octadecyltrimethoxysilane coating for nonretained and retained modes of operation, respectively. Showing the same trends as the modeling results, the foil shape produces a significant decrease in plate height with an increase of around 15% in mobile phase velocity in nonretained measurements of Coumarin 480 (C480). Measured plate heights at 1 kV/cm applied electric field were 0.77, 1.33, and 1.42 μm for foil, diamond, and hexagon, respectively. Chromatographic runs of C480 yielded minimal plate height values of 1.85 and 3.28 μm for foil and diamond, respectively. The optimization of the shape and placement of the structures appeared to have a considerable impact on the achievable performance.

Sonoluminescence and sonochemiluminescence from a microreactor

Micromachined pits on a substrate can be used to nucleate and stabilize microbubbles in a liquid exposed to an ultrasonic field. Under suitable conditions, the collapse of these bubbles can result in light emission (sonoluminescence, SL). Hydroxyl radicals (OH()) generated during bubble collapse can react with luminol to produce light (sonochemiluminescence, SCL). SL and SCL intensities were recorded for several regimes related to the pressure amplitude (low and high acoustic power levels) at a given ultrasonic frequency (200kHz) for pure water, and aqueous luminol and propanol solutions. Various arrangements of pits were studied, with the number of pits ranging from no pits (comparable to a classic ultrasound reactor), to three-pits. Where there was more than one pit present, in the high pressure regime the ejected microbubbles combined into linear (two-pits) or triangular (three-pits) bubble clouds (streamers). In all situations where a pit was present on the substrate, the SL was intensified and increased with the number of pits at both low and high power levels. For imaging SL emitting regions, Argon (Ar) saturated water was used under similar conditions. SL emission from aqueous propanol solution (50mM) provided evidence of transient bubble cavitation. Solutions containing 0.1mM luminol were also used to demonstrate the radical production by attaining the SCL emission regions.

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.

Pheromone synthesis in a biomicroreactor coated with anti-adsorption polyelectrolyte multilayer

To prepare a biosynthetic module in an infochemical communication project, we designed a silicon/glass microreactor with anti-adsorption polyelectrolyte multilayer coating and immobilized alcohol acetyl transferase (atf), one of the key biosynthetic enzymes of the pheromone of Spodoptera littoralis, on agarose beads inside. The system reproduces the last step of the biosynthesis in which the precursor diene alcohol (Z,E)-9,11-tetradecadienol is transformed into the major component (Z,E)-9,11-tetradecadienyl acetate. The scope of this study was to analyze and implement a multilayer, anti-adsorption coating based on layer-by-layer deposition of polyethylenimine/dextransulfate sodium salt (PEI/DSS). The multilayers were composed of two PEI with molecular weights 750 and 1.2 kDa at pH 9.2 or 6.0. Growth, morphology, and stability of the layers were analyzed by ellipsometry and atomic force microscopy (AFM). The anti-adsorption functionality of the multilayer inside the microreactor was validated. The activity of His(6)-(atf) was measured by gas chromatography coupled to mass spectrometer (GC-MS).

Cryo DualBeam Focused Ion Beam-Scanning Electron Microscopy to Evaluate the Interface Between Cells and Nanopatterned Scaffolds

With the advance of nanotechnology in biomaterials science and tissue engineering, it is essential that new techniques become available to observe processes that take place at the direct interface between tissue and scaffold materials. Here, Cryo DualBeam focused ion beam-scanning electron microscopy (FIB-SEM) was used as a novel approach to observe the interactions between frozen hydrated cells and nanometric structures in high detail. Through a comparison of images acquired with transmission electron microscopy (TEM), conventional FIB-SEM operated at ambient temperature, and Cryo DualBeam FIB-SEM, the advantages and disadvantages of each technique were evaluated. Ultrastructural details of both (extra)cellular components and cell organelles were best observe with TEM. However, processing artifacts such as shrinkage of cells at the substrate interface were introduced in both TEM and conventional FIB-SEM. In addition, the cellular contrast in conventional FIB-SEM was low; consequently, cells were difficult to distinguish from the adjoining substrate. Cryo DualBeam FIB-SEM did preserve (extra)cellular details like the contour, cell membrane, and mineralized matrix. The three described techniques have proven to be complementary for the evaluation of processes that take place at the interface between tissue and substrate.

Synchronized, continuous-flow zone electrophoresis

A new method for performing continuous electrophoretic separation of complex mixtures in microscale devices is proposed. Unlike in free-flow electrophoresis devices, no mechanical pumping is required--both fluid transport and separation are driven electrokinetically. This gives the method great potential for on-a-chip integration in multistep analytical systems. The method enables us to collect fractionated sample and tenfold purification is possible. The model of the operation is presented and a detailed description of the optimal conditions for performing purification is given. The chip devices with 10-microm-deep separation chamber of 1.5 mm x 4 mm in size were fabricated in glass. A standard microchip electrophoresis setup was used. Continuous separation of rhodamine B, rhodamine 6G, and fluorescein was accomplished. Purification was demonstrated on a mixture containing rhodamine B and fluorescein, and the recovery of both fractions was achieved. The results show the feasibility of the method.

Electrokinetic sorting and collection of fractions for preparative capillary electrophoresis on a chip

A microfabricated device capable of selecting and collecting multiple components from a mixture separated by capillary electrophoresis (CE) is described. This collection is automated and can be easily controlled by a set of rules defined by an operator, enabling fast and consistent operation. The device consists of an electrokinetically steered fluidic network that can be divided into three sections: a CE part, a fractions distribution region and a set of storage channels. Sample fractions leave the CE channel and are detected in the interfacial region by fluorescence intensity measurements. If an upcoming peak is detected, separation is withheld and the potentials are reconfigured to force the fraction into one of the collection channels, where they become available for further processing or analysis. The sequence of separation and collection is repeated until all the bands of interest are captured. A mixture of three fluorescent dyes (Rhodamine 6G, Rhodamine B and Fluorescein) was used to demonstrate the principle. The components were repeatedly separated by means of CE and pooled in their respective storage channels. In comparison to previous developments, the system presented in this paper offers automatic collection of all fractions in a single run. Furthermore, it is possible to run the system in a repetitive mode for accumulative pooling if more fractionated sample is required.

Multivalent binding of small guest molecules and proteins to molecular printboards inside microchannels

Beta-Cyclodextrin (beta-CD) monolayers have been immobilized in microchannels. The host-guest interactions on the beta-CD monolayers inside the channels were comparable to the interactions on beta-CD monolayers on planar surfaces, and a divalent fluorescent guest attached with a comparable binding strength. Proteins were attached to these monolayers inside microchannels in a selective manner by employing a strategy that uses streptavidin and orthogonal linker molecules. The design of the chip, which involved a large channel that splits into four smaller channels, allowed the channels to be addressed separately and led to the selective immobilization of antibodies. Experiments with labeled antibodies showed the selective immobilization of these antibodies in the separate channels.

Nanochannels in SU-8 with floor and ceiling metal electrodes and integrated microchannels

Sacrificially etched 2-D nanofluidic channels and nanospaces with integrated floor and ceiling electrodes and arbitrary channel geometries have been demonstrated with channel heights from 20 nm to 400 nm, widths from 800 nm to 40 microm, and lengths up to 3 mm, using SU-8 as the channel structural material.

Multichannel quench-flow microreactor chip for parallel reaction monitoring

This paper describes a multichannel silicon-glass microreactor which has been utilized to investigate the kinetics of a Knoevenagel condensation reaction under different reaction conditions. The reaction is performed on the chip in four parallel channels under identical conditions but with different residence times. A special topology of the reaction coils overcomes the common problem arising from the difference in pressure drop of parallel channels having different length. The parallelization of reaction coils combined with chemical quenching at specific locations results in a considerable reduction in experimental effort and cost. The system was tested and showed good reproducibility in flow properties and reaction kinetic data generation.

Fluorescent sensor array in a microfluidic chip

Miniaturization and automation are highly important issues for the development of high-throughput processes. The area of micro total analysis systems (muTAS) is growing rapidly and the design of new schemes which are suitable for miniaturized analytical devices is of great importance. In this paper we report the immobilization of self-assembled monolayers (SAMs) with metal ion sensing properties, on the walls of glass microchannels. The parallel combinatorial synthesis of sensing SAMs in individually addressable microchannels towards the generation of optical sensor arrays and sensing chips has been developed. [figure: see text] The advantages of microfluidic devices, surface chemistry, parallel synthesis, and combinatorial approaches have been merged to integrate a fluorescent chemical sensor array in a microfluidic chip. Specifically, five different fluorescent self-assembled monolayers have been created on the internal walls of glass microchannels confined in a microfluidic chip.

Substantial rate enhancements of the esterification reaction of phthalic anhydride with methanol at high pressure and using supercritical CO2 as a co-solvent in a glass microreactor

The esterification reaction of phthalic anhydride with methanol was performed at different temperatures in a continuous flow glass microreactor at pressures up to 110 bar and using supercritical CO(2) as a co-solvent. The design is such that supercritical CO(2) can be generated inside the microreactor. Substantial rate enhancements were obtained, viz. a 53-fold increase was obtained at 110 bar and 60 degrees C. Supercritical CO(2) as a co-solvent gave rise to a 5400-fold increase (both with respect to batch experiments at 1 bar at the same temperature).

A MALDI-chip integrated system with a monitoring window

The integration of a monitoring port along the microfluidic path of a MALDI-chip integrated device is described. Optimization of the microreactor design allows longer reaction and measuring times. The Schiff base reaction between 4-tert-butylaniline (1) and 4-tert-butylbenzaldehyde (2) in ethanol was carried out on-chip in the MALDI ionization chamber and the formed imine 3 was detected in real time, demonstrating the feasibility of the "monitoring window" approach. This preliminary result opens the way to on-chip kinetic studies by MALDI-MS, by opening multiple monitoring windows along the microchannel.

Measuring reaction kinetics in a lab-on-a-chip by microcoil NMR

A microfluidic chip with an integrated planar microcoil was developed for Nuclear Magnetic Resonance (NMR) spectroscopy on samples with volumes of less than a microliter. Real-time monitoring of imine formation from benzaldehyde and aniline in the microreactor chip by NMR was demonstrated. The reaction times in the chip can be set from 30 min down to ca. 2 s, the latter being the mixing time in the microfluidic chip. Design rules will be described to optimize the microreactor and detection coil in order to deal with the inherent sensitivity of NMR and to minimize magnetic field inhomogeneities and obtain sufficient spectral resolution.

Comparison of capillary zone electrophoresis performance of powder-blasted and hydrogen fluoride-etched microchannels in glass

The applicability of glass chips with powder-blasted microchannels for electrophoretic separations was examined, and the performance was compared to microchannels etched with hydrogen fluoride (HF), using bicarbonate buffer and rhodamine B and fluorescein as model compounds. The measured electroosmotic mobilities in all chips were comparable, with values of ca. 7 x 10(-4) cm(2) V(-1)s(-1). The effect of electrical field strength and detection length on the separation efficiency was monitored. It was found that the main source of dispersion is of the Taylor-Aris type, which was discussed in relation to channel roughness differences. Although in powder-blasted channels with a separation length of 8.20 cm, 7-9 times lower plate numbers were obtained than in a HF-etched channel with similar dimensions, successful separation of five fluorescein isothiocyanate (FITC)-labeled amino acids was obtained on a powder-blasted chip within 80 s. Efficiencies of up to 360 000 plates/m were demonstrated on this chip, when a higher buffer concentration was used at a field strength of 664 V/cm. It can be concluded that powder-blasted microchannel chips, although they have a lower separation efficiency compared to HF-etched chips, perform well enough for many applications. Powder blasting can therefore be considered a low-cost and efficient alternative to HF etching, in particular because of the possibility to fabricate access holes through the glass with the same process.

A pressure driven injection system for an ultra-flat chromatographic microchannel

A pressure-actuated on-chip injection system has been developed that is compatible with shallow microchannels with a very large aspect ratio, i.e. 1 microm deep and up to 1000 microm wide. Such channels offer potential advantages in the miniaturisation of liquid chromatography and other separation methods as they allow high loadability and low sample dispersion at the same time. Computational fluid dynamics simulations were performed to predict the flow profiles and the transport of a sample in the system and to justify the injection principle. Based on these simulations, a prototype integrated into a chip for hydrodynamic chromatography has been realised and tested experimentally. The performance of the device is satisfactory and the results are in qualitative agreement with the numerical models.

A chip system for size separation of macromolecules and particles by hydrodynamic chromatography

For the first time, a miniaturized hydrodynamic chromatography chip system has been developed and tested on separation of fluorescent nanospheres and macromolecules. The device can be applied to size characterization of synthetic polymers, biopolymers, and particles, as an attractive alternative to the classical separation methods such as size exclusion chromatography or field-flow fractionation. The main advantages are fast analysis, high separation efficiency, negligible solvent consumption, and easy temperature control. The prototype chip contains a rectangular flat separation channel with dimensions of 1 microm deep and 1000 microm wide, integrated with a 300-pL injector on a silicon substrate. The silicon microtechnology provides precisely defined geometry, high rigidity, and compatibility with organic solvents or high temperature. All flows are pressure driven, and a specific injection system is employed to avoid excessive sample loading times, demonstrating an alternative way of lab-on-a-chip design. Separations obtained in 3 min show the high performance of the device and are also the first demonstration of flat channel hydrodynamic chromatography in practice.