Engineering the surface properties of microfluidic stickers

Lab on a chip for a low-carbon future

Transitioning our society to a sustainable future, with low or net-zero carbon emissions to the atmosphere, will require a wide-spread transformation of energy and environmental technologies. In this perspective article, we describe how lab-on-a-chip (LoC) systems can help address this challenge by providing insight into the fundamental physical and geochemical processes underlying new technologies critical to this transition, and developing the new processes and materials required. We focus on six areas: (I) subsurface carbon sequestration, (II) subsurface hydrogen storage, (III) geothermal energy extraction, (IV) bioenergy, (V) recovering critical materials, and (VI) water filtration and remediation. We hope to engage the LoC community in the many opportunities within the transition ahead, and highlight the potential of LoC approaches to the broader community of researchers, industry experts, and policy makers working toward a low-carbon future.

Wettability Alteration of a Thiolene-Based Polymer (NOA81): Surface Characterization and Fabrication Techniques

Wettability plays a significant role in controlling multiphase flow in porous media for many industrial applications, including geologic carbon dioxide sequestration, enhanced oil recovery, and fuel cells. Microfluidics is a powerful tool to study the complexities of interfacial phenomena involved in multiphase flow in well-controlled geometries. Recently, the thiolene-based polymer called NOA81 emerged as an ideal material in the fabrication of microfluidic devices, since it combines the versatility of conventional soft photolithography with a wide range of achievable wettability conditions. Specifically, the wettability of NOA81 can be continuously tuned through exposure to UV-ozone. Despite its growing popularity, the exact physical and chemical mechanisms behind the wettability alteration have not been fully characterized. Here, we apply different characterization techniques, including contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) to investigate the impact of UV-ozone on the chemical and physical properties of NOA81 surfaces. We find that UV-ozone exposure increases the oxygen-containing polar functional groups, which enhances the surface energy and hydrophilicity of NOA81. Additionally, our AFM measurements show that spin-coated NOA81 surfaces have a roughness less than a nanometer, which is further reduced after UV-ozone exposure. Lastly, we extend NOA81 use cases by creating (i) 2D surface with controlled wettability gradient and (ii) a 3D column packed with monodisperse NOA81 beads of controlled size and wettability.

Universal pre-mixing dry-film stickers capable of retrofitting existing microfluidics

Integrating microfluidic mixers into lab-on-a-chip devices remains challenging yet important for numerous applications including dilutions, extractions, addition of reagents or drugs, and particle synthesis. High-efficiency mixers utilize large or intricate geometries that are difficult to manufacture and co-implement with lab-on-a-chip processes, leading to cumbersome two-chip solutions. We present a universal dry-film microfluidic mixing sticker that can retrofit pre-existing microfluidics and maintain high mixing performance over a range of Reynolds numbers and input mixing ratios. To attach our pre-mixing sticker module, remove the backing material and press the sticker onto an existing microfluidic/substrate. Our innovation centers around the multilayer use of laser-cut commercially available silicone-adhesive-coated polymer sheets as microfluidic layers to create geometrically complex, easy to assemble designs that can be adhered to a variety of surfaces, namely, existing microfluidic devices. Our approach enabled us to assemble the traditional yet difficult to manufacture "F-mixer" in minutes and conceptually extend this design to create a novel space-saving spiral F-mixer. Computational fluid dynamic simulations and experimental results confirmed that both designs maintained high performance for 0.1 < Re < 10 and disparate input mixing ratios of 1:10. We tested the integration of our system by using the pre-mixer to fluorescently tag proteins encapsulated in an existing microfluidic. When integrated with another microfluidic, our pre-mixing sticker successfully combined primary and secondary antibodies to fluorescently tag micropatterned proteins with high spatial uniformity, unlike a traditional pre-mixing "T-mixer" sticker. Given the ease of this technology, we anticipate numerous applications for point-of-care devices, microphysiological-systems-on-a-chip, and microfluidic-based biomedical research.

Two-dimensional micromodels for studying the convective dissolution of carbon dioxide in 2D water-saturated porous media

Convective dissolution is a perennial trapping mechanism of carbon dioxide in geological formations saturated with an aqueous phase. This process, which couples dissolution of supercritical CO₂, convection of the liquid containing the dissolved CO₂, and mixing of the latter within the liquid, has so far not been studied in two-dimensional porous media. In order to do so, two-dimensional (2D) porous micromodels (patterned Hele-Shaw cells) have been fabricated from UV-curable NOA63 glue. NOA63 is used instead of PDMS, which is permeable to CO₂ and does not allow for a controlled no flux boundary condition at the walls. The novel fabrication protocol proposed here, based on the bonding of a patterned photo-lithographed NOA63 layer on a flat NOA63 base, shows good reproducibility regardless of the patterns' typical size, and allows for easy filling of the cell despite the small value of the gap. A pressure chamber allows pressurizing the CO₂ and outside of the flow cell up to 10 bars. Experiments were performed in 11 different porous media geometries. As expected, a gravitational fingering instability is observed upon injection of gaseous carbon dioxide in the cell, resulting in the downwards migration of dissolved CO₂ plumes through the 2D porous structure. The initial wavelength of the fingers is larger in the presence of a hexagonal lattice of pillars. This effect can be correctly predicted from the theory for the gravitational instability in a Hele-Shaw cell devoid of pillars, provided that the permeability of the hexagonal porous medium is considered in the theory instead of that of the Hele-Shaw cell. Fluctuations around the theoretical prediction observed in the data are mostly attributed to a hitherto unknown weak locking of the wavelength on the distance between closest pillars.

Fabrication and Bonding of Refractive Index Matched Microfluidics for Precise Measurements of Cell Mass

The optical properties of polymer materials used for microfluidic device fabrication can impact device performance when used for optical measurements. In particular, conventional polymer materials used for microfluidic devices have a large difference in refractive index relative to aqueous media generally used for biomedical applications. This can create artifacts when used for microscopy-based assays. Fluorination can reduce polymer refractive index, but at the cost of reduced adhesion, creating issues with device bonding. Here, we present a novel fabrication technique for bonding microfluidic devices made of NOA1348, which is a fluorinated, UV-curable polymer with a refractive index similar to that of water, to a glass substrate. This technique is compatible with soft lithography techniques, making this approach readily integrated into existing microfabrication workflows. We also demonstrate that this material is compatible with quantitative phase imaging, which we used to validate the refractive index of the material post-fabrication. Finally, we demonstrate the use of this material with a novel image processing approach to precisely quantify the mass of cells in the microchannel without the use of cell segmentation or tracking. The novel image processing approach combined with this low refractive index material eliminates an important source of error, allowing for high-precision measurements of cell mass with a coefficient of variance of 1%.

Emergence of scale-free smectic rivers and critical depinning in emulsions driven through disorder

During the past 60 min, oil companies have extracted 6 trillion liters of oil from the ground, thereby giving a striking illustration of the impact of multiphase flows on the world economy. From a fundamental perspective, we largely understand the dynamics of interfaces separating immiscible fluids driven through heterogeneous environments. In stark contrast, the basic mechanisms ruling the transport of fragmented fluids, such as foams and emulsions, remain elusive with studies mostly limited to isolated droplets and bubbles. Here, we demonstrate that the mobilization of emulsion driven through model disordered media is a critical plastic depinning transition. To elucidate this collective dynamics, we track the trajectories of hundreds of thousands of microfluidic droplets advected through random lattices of pinning sites. Their dynamics reveals that macroscopic mobilization only requires the coordinated motion of small groups of particles and does not involve any large-scale avalanches. Criticality arises from the interplay between contact and hydrodynamic interaction, which channel seemingly erratic depinning events along smectic river networks correlated over system spanning scales. Beyond the specifics of emulsion transport, we close our article discussing the similarities and profound differences with the plastic depinning transitions of driven flux lines in high-T _c superconductors, charged colloids, and grain transport in eroded sand beds.

Functionalized multiscale visual models to unravel flow and transport physics in porous structures

The fluid flow, species transport, and chemical reactions in geological formations are the chief mechanisms in engineering the exploitation of fossil fuels and geothermal energy, the geological storage of carbon dioxide (CO₂), and the disposal of hazardous materials. Porous rock is characterized by a wide surface area, where the physicochemical fluid-solid interactions dominate the multiphase flow behavior. A variety of visual models with differences in dimensions, patterns, surface properties, and fabrication techniques have been widely utilized to simulate and directly visualize such interactions in porous media. This review discusses the six categories of visual models used in geological flow applications, including packed beds, Hele-Shaw cells, synthesized microchips (also known as microfluidic chips or micromodels), geomaterial-dominated microchips, three-dimensional (3D) microchips, and nanofluidics. For each category, critical technical points (such as surface chemistry and geometry) and practical applications are summarized. Finally, we discuss opportunities and provide a framework for the development of custom-built visual models.

Thiol-Ene Based Polymers as Versatile Materials for Microfluidic Devices for Life Sciences Applications

While there is a steady growth in the number of microfluidics applications, the search for an optimal material that delivers the diverse characteristics needed for the numerous tasks is still nowhere close to being settled. Often overlooked and still underrepresented, the thiol-ene family of polymer materials has an enormous potential for applications in organs-on-a-chip, droplet productions, microanalytics, and point of care testing. In this review, the main characteristics of the thiol-ene materials are given, and advantages and drawbacks with respect to their potential in microfluidic chip fabrication are critically assessed. Select applications, which exploit the versatility of the thiol-ene polymers, are presented and discussed. It is concluded that, in particular, the rapid prototyping possibility combined with the material's resulting mechanical strength, solvent resistance, and biocompatibility, as well as the inherently easy surface functionalization, are strong factors to make thiol-ene polymers strong contenders for promising future materials for many biological, clinical, and technical lab-on-a-chip applications.

Microfluidic Sensors with Impregnated Fluorophores for Simultaneous Imaging of Spatial Structure and Chemical Oxygen Gradients

Interior surfaces of polystyrene microfluidic structures were impregnated with the oxygen sensing dye Pt(II) tetra(pentafluorophenyl)porphyrin (PtTFPP) using a solvent-induced fluorophore impregnation (SIFI) method. Using this technique, microfluidic oxygen sensors are obtained that enable simultaneous imaging of both chemical oxygen gradients and the physical structure of the microfluidic interior. A gentle method of fluorophore impregnation using acetonitrile solutions of PtTFPP at 50 °C was developed leading to a 10-μm-deep region containing fluorophore. This region is localized at the surface to sense oxygen in the interior fluid during use. Regions of the device that do not contact the interior fluid pathways lack fluorophores and are dark in fluorescent imaging. The technique was demonstrated on straight microchannel and pore network devices, the latter having pillars of 300 μm diameter spaced center to center at 340 μm providing pore throats of 40 μm. Sensing within channels or pores and imaging across the pore network devices were performed using a Lambert LIFA-P frequency domain fluorescence lifetime imaging system on a Leica microscope platform. Calibrations of different devices prepared by the SIFI method were indistinguishable. Gradient imaging showed fluorescent regions corresponding to the fluid pore network, dark pillars, and fluorescent lifetime varying across the gradient, thus providing both physical and chemical imaging. More generally, the SIFI technique can impregnate the interior surfaces of other polystyrene containers, such as cuvettes or cell and tissue culture containers, to enable sensing of interior conditions.

Fabrication of composite microfluidic devices for local control of oxygen tension in cell cultures

Oxygen tension is a central component of the cellular microenvironment and can serve as a trigger for changes in cell phenotype and function. There is a strong need to precisely control and modulate oxygen tension in cell culture systems in order to more accurately model the physiology and pathophysiology observed in vivo. The objective of this paper was to develop a simple, yet effective strategy for local control of oxygen tension in microfluidic cell cultures. Our strategy relied on fabrication of microfluidic devices using oxygen-permeable and impermeable materials. This composite device was designed so as to incorporate regions of gas permeability into the roof of the cell culture chamber and was outfitted with a reservoir for the oxygen-consuming chemical pyrogallol. When assembled and filled with pyrogallol, this device allowed oxygen depletion to occur within a specific region of the microfluidic culture chamber. The geometry and dimensions of the hypoxic region inside a microfluidic chamber were controlled by features fabricated into the oxygen-impermeable layer. Oxygen tension as low as 0.5% could be achieved using this strategy. To prove the utility of this device, we demonstrated that hypoxia induced anaerobic metabolism in a group of liver cancer cells, and that neighboring cancer cells residing under normoxic conditions upregulated the expression of transporters for taking up lactate - a product of anaerobic respiration. The microfluidic devices described here may be broadly applicable for mimicking multiple physiological scenarios where oxygen tension varies on the length scale of tens of micrometers including the cancer microenvironment, liver zonation, and luminal microenvironment of the gut.

Forced Imbibition in Porous Media: A Fourfold Scenario

We establish a comprehensive description of the patterns formed when a wetting liquid displaces a viscous fluid confined in a porous medium. Building on model microfluidic experiments, we evidence four imbibition scenarios all yielding different large-scale morphologies. Combining high-resolution imaging and confocal microscopy, we show that they originate from two liquid-entrainment transitions and a Rayleigh-Plateau instability at the pore scale. Finally, we demonstrate and explain the long-time coarsening of the resulting patterns.

Toward Reservoir-on-a-Chip: Fabricating Reservoir Micromodels by in Situ Growing Calcium Carbonate Nanocrystals in Microfluidic Channels

We introduce a novel and simple method to fabricate calcium carbonate (CaCO₃) micromodels by in situ growing a thin layer of CaCO₃ nanocrystals with a thickness of 1-2 μm in microfluidic channels. This approach enables us to fabricate synthetic CaCO₃ reservoir micromodels having surfaces fully covered with calcite, while the dimensions and geometries of the micromodels are controllable on the basis of the original microfluidic channels. We have tuned the wettability of the CaCO₃-coated microchannels at simulated oil reservoir conditions without introducing any chemical additives to the system; thus the resulting oil-wet surface makes the micromodel more faithfully resemble a natural carbonate reservoir rock. With the advantage of its excellent optical transparency, the micromodel allows us to directly visualize the complex multiphase flows and geochemical fluid-calcite interactions by spectroscopic and microscopic imaging techniques. The CaCO₃-coated microfluidic channels provide new capabilities as a micromodel system to mimic real carbonate reservoir properties, which would allow us to perform a water-oil displacement experiment in small-volume samples for the rapid screening of candidate fluids for enhanced oil recovery (EOR). The immiscible fluid displacement process within carbonate micromodels has been demonstrated showing the water-oil-carbonate interactions at pore-scale in real time by fluorescence microscopic imaging.

Thiol-ene Monolithic Pepsin Microreactor with a 3D-Printed Interface for Efficient UPLC-MS Peptide Mapping Analyses

To improve the sample handling, and reduce cost and preparation time, of peptide mapping LC-MS workflows in protein analytical research, we here investigate the possibility of replacing conventional enzymatic digestion methods with a polymer microfluidic chip based enzyme reactor. Off-stoichiometric thiol-ene is utilized as both bulk material and as a monolithic stationary phase for immobilization of the proteolytic enzyme pepsin. The digestion efficiency of the, thiol-ene based, immobilized enzyme reactor (IMER) is compared to that of a conventional, agarose packed bed, pepsin IMER column commonly used in LC-MS based protein analyses. The chip IMER is found to rival the conventional column in terms of digestion efficiency at comparable residence time and, using a 3D-printed interface, be directly interfaceable with LC-MS.

Wettability control on multiphase flow in patterned microfluidics

Multiphase flow in porous media is important in many natural and industrial processes, including geologic CO2 sequestration, enhanced oil recovery, and water infiltration into soil. Although it is well known that the wetting properties of porous media can vary drastically depending on the type of media and pore fluids, the effect of wettability on multiphase flow continues to challenge our microscopic and macroscopic descriptions. Here, we study the impact of wettability on viscously unfavorable fluid-fluid displacement in disordered media by means of high-resolution imaging in microfluidic flow cells patterned with vertical posts. By systematically varying the wettability of the flow cell over a wide range of contact angles, we find that increasing the substrate's affinity to the invading fluid results in more efficient displacement of the defending fluid up to a critical wetting transition, beyond which the trend is reversed. We identify the pore-scale mechanisms-cooperative pore filling (increasing displacement efficiency) and corner flow (decreasing displacement efficiency)-responsible for this macroscale behavior, and show that they rely on the inherent 3D nature of interfacial flows, even in quasi-2D media. Our results demonstrate the powerful control of wettability on multiphase flow in porous media, and show that the markedly different invasion protocols that emerge-from pore filling to postbridging-are determined by physical mechanisms that are missing from current pore-scale and continuum-scale descriptions.

Photopatterned oil-reservoir micromodels with tailored wetting properties

Micromodels with a simplified porous network that represents geological porous media have been used as experimental test beds for multiphase flow studies in the petroleum industry. We present a new method to fabricate reservoir micromodels with heterogeneous wetting properties. Photopatterned, copolymerized microstructures were fabricated in a bottom-up manner. The use of rationally designed copolymers allowed us to tailor the wetting behavior (oleophilic/phobic) of the structures without requiring additional surface modifications. Using this approach, two separate techniques of constructing microstructures and tailoring their wetting behavior are combined in a simple, single-step ultraviolet lithography process. This microstructuring method is fast, economical, and versatile compared with previous fabrication methods used for multi-phase micromodel experiments. The wetting behaviors of the copolymerized microstructures were quantified and demonstrative oil/water immiscible displacement experiments were conducted.

Robust liquid-infused surfaces through patterned wettability

Liquid-infused surfaces display advantageous properties that are normally associated with conventional gas-cushioned superhydrophobic surfaces. However, the surfaces can lose their novel properties if the infused liquid drains from the surface. We explore how drainage due to gravity or due to an external flow can be prevented through the use of chemical patterning. A small area of the overall surface is chemically treated to be preferentially wetted by the external fluid rather than the infused liquid. These sacrificial regions disrupt the continuity of the infused liquid, thereby preventing the liquid from draining from the texture. If the regions are patterned with the correct periodicity, drainage can be prevented entirely. The chemical patterns are created using spray-coating or deep-UV exposure, two facile techniques that are scalable to generate large-scale failure-resistant surfaces.

Rapid and simple preparation of thiol-ene emulsion-templated monoliths and their application as enzymatic microreactors

A novel, rapid and simple method for the preparation of emulsion-templated monoliths in microfluidic channels based on thiol-ene chemistry is presented. The method allows monolith synthesis and anchoring inside thiol-ene microchannels in a single photoinitiated step. Characterization by scanning electron microscopy showed that the methanol-based emulsion templating process resulted in a network of highly interconnected and regular thiol-ene beads anchored solidly inside thiol-ene microchannels. Surface area measurements indicate that the monoliths are macroporous, with no or little micro- or mesopores. As a demonstration, galactose oxidase and peptide-N-glycosidase F (PNGase F) were immobilized at the surface of the synthesized thiol-ene monoliths via two different mechanisms. First, cysteine groups on the protein surface were used for reversible covalent linkage to free thiol functional groups on the monoliths. Second, covalent linkage was achieved via free primary amino groups on the protein surface by means of thiol-ene click chemistry and l-ascorbic acid linkage. Thus prepared galactose oxidase and PNGase F microreactors demonstrated good enzymatic activity in a galactose assay and the deglycosilation of ribonuclease B, respectively.

Fabrication of rigid microstructures with thiol-ene-based soft lithography for continuous-flow cell lysis

In this work, we introduce a method for the soft-lithography-based fabrication of rigid microstructures and a new, simple bonding technique for use as a continuous-flow cell lysis device. While on-chip cell lysis techniques have been reported previously, these techniques generally require a long on-chip residence time, and thus cannot be performed in a rapid, continuous-flow manner. Microstructured microfluidic devices can perform mechanical lysis of cells, enabling continuous-flow lysis; however, rigid silicon-based devices require complex and expensive fabrication of each device, while polydimethylsiloxane (PMDS), the most common material used for soft lithography fabrication, is not rigid and expands under the pressures required, resulting in poor lysis performance. Here, we demonstrate the fabrication of microfluidic microstructures from off-stoichiometry thiol-ene (OSTE) polymer using soft-lithography replica molding combined with a post-assembly cure for easy bonding. With finite element simulations, we show that the rigid microstructures generate an energy dissipation rate of nearly 10(7), which is sufficient for continuous-flow cell lysis. Correspondingly, with the OSTE device we achieve lysis of highly deformable MDA-MB-231 breast cancer cells at a rate of 85%, while a comparable PDMS device leads to a lysis rate of only 40%.

Revisiting the Saffman-Taylor experiment: imbibition patterns and liquid-entrainment transitions

We revisit the Saffman-Taylor experiment focusing on the forced-imbibition regime where the displacing fluid wets the confining walls. We demonstrate a new class of invasion patterns that do not display the canonical fingering shapes. We evidence that these unanticipated patterns stem from the entrainment of thin liquid films from the moving meniscus. We then theoretically explain how the interplay between the fluid flow at the contact line and the interface deformations results in the destabilization of liquid interfaces. In addition, this minimal model conveys a unified framework which consistently accounts for all the liquid-entrainment scenarios that have been hitherto reported.

Dynamical role of slip heterogeneities in confined flows

We demonstrate that flows in confined systems are controlled by slip heterogeneities below a certain size. To show this we image the motion of soft glassy suspensions in microchannels whose inner walls impose different slip velocities. As the channel height decreases, the flow ceases to have the symmetric shape expected for yield-stress fluids. A theoretical model accounts for the role of slip heterogeneities and captures the velocity profiles. We generalize these results by introducing a length scale, valid for all fluids, below which slip heterogeneities dominate the flow in confined systems. General implications of this notion, concerning the interplay between slip and confinement, are presented.

Surface functionalized thiol-ene waveguides for fluorescence biosensing in microfluidic devices

Thiol-ene polymers possess physical, optical, and chemical characteristics that make them ideal substrates for the fabrication of optofluidic devices. In this work, thiol-ene polymers are used to simultaneously create microfluidic channels and optical waveguides in one simple moulding step. The reactive functional groups present at the surface of the thiol-ene polymer are subsequently used for the rapid, one step, site-specific functionalization of the waveguide with biological recognition molecules. It was found that while the bulk properties and chemical surface properties of thiol-ene materials vary considerably with variations in stoichiometric composition, their optical properties remain mostly unchanged with an average refractive index value of 1.566 ± 0.008 for thiol-ene substrates encompassing a range from 150% excess ene to 90% excess thiol. Microfluidic chips featuring thiol-ene waveguides were fabricated from 40% excess thiol thiol-ene to ensure the presence of thiol functional groups at the surface of the waveguide. Biotin alkyne was photografted at specific locations using a photomask, directly at the interface between the microfluidic channel and the thiol-ene waveguide prior to conjugation with fluorescently labeled streptavidin. Fluorescence excitation was achieved by launching light through the thiol-ene waveguide, revealing bright fluorescent patterns along the channel/waveguide interface.

Rapid photochemical surface patterning of proteins in thiol-ene based microfluidic devices

The suitable optical properties of thiol-ene polymers combined with the ease of modifying their surface for the attachment of recognition molecules make them ideal candidates in many biochip applications. This paper reports the rapid one-step photochemical surface patterning of biomolecules in microfluidic thiol-ene chips. This work focuses on thiol-ene substrates featuring an excess of thiol groups at their surface. The thiol-ene stoichiometric composition can be varied to precisely control the number of surface thiol groups available for surface modification up to an average surface density of 136 ± 17 SH nm(-2). Biotin alkyne was patterned directly inside thiol-ene microchannels prior to conjugation with fluorescently labelled streptavidin. The surface bound conjugates were detected by evanescent wave-induced fluorescence (EWIF), demonstrating the success of the grafting procedure and its potential for biochip applications.

Silicon-on-glass pore network micromodels with oxygen-sensing fluorophore films for chemical imaging and defined spatial structure

Pore network microfluidic models were fabricated by a silicon-on-glass technique that provides the precision advantage of dry etched silicon while creating a structure that is transparent across all microfluidic channels and pores, and can be imaged from either side. A silicon layer is bonded to an underlying borosilicate glass substrate and thinned to the desired height of the microfluidic channels and pores. The silicon is then patterned and through-etched by deep reactive ion etching (DRIE), with the underlying glass serving as an etch stop. After bonding on a transparent glass cover plate, one obtains a micromodel in oxygen impermeable materials with water-wet surfaces where the microfluidic channels are transparent and structural elements such as the pillars creating the pore network are opaque. The advantageous features of this approach in a chemical imaging application are demonstrated by incorporating a Pt porphyrin fluorophore in a PDMS film serving as the oxygen-sensing layer and a bonding surface, or in a polystyrene film coated with a PDMS layer for bonding. The sensing of a dissolved oxygen gradient was demonstrated using fluorescence lifetime imaging, and it is shown that different matrix polymers lead to optimal use in different ranges of oxygen concentration. Imaging with the opaque pillars in between the observation direction and the continuous fluorophore film yields images that retain defined spatial structure in the sensor image.

Tailoring the wetting properties of thiolene microfluidic materials

A post functionalization method for the control of the wettability of thiolene resins of the NOA family is presented. Treatment of open model surfaces or closed microchannels with chlorosilane derivatives resulted in dramatic changes in the behaviour of droplets and streams contacting the surfaces. The experimental findings are confirmed by the fabrication of a Y-junction device that works as a passive valve for water streams.