Chemically resistant microfluidic valves from Viton® membranes bonded to COC and PMMA

Novel thermoplastic microvalves based on an elastomeric cyclic olefin copolymer

Microfluidic systems combine multiple processing steps and components to perform complex assays in an autonomous fashion. To enable the integration of several bio-analytical processing steps into a single system, valving is used as a component that directs fluids and controls introduction of sample and reagents. While elastomer polydimethylsiloxane has been the material of choice for valving, it does not scale well to accommodate disposable integrated systems where inexpensive and fast production is needed. As an alternative to polydimethylsiloxane, we introduce a membrane made of thermoplastic elastomeric cyclic olefin copolymer (eCOC), that displays unique attributes for the fabrication of reliable valving. The eCOC membrane can be extruded or injection molded to allow for high scale production of inexpensive valves. Normally hydrophobic, eCOC can be activated with UV/ozone to produce a stable hydrophilic monolayer. Valves are assembled following in situ UV/ozone activation of eCOC membrane and thermoplastic valve seat and bonded by lamination at room temperature. eCOC formed strong bonding with polycarbonate (PC) and polyethylene terephthalate glycol (PETG) able to hold high fluidic pressures of 75 kPa and 350 kPa, respectively. We characterized the eCOC valves with mechanical and pneumatic actuation and found the valves could be reproducibly actuated >50 times without failure. Finally, an integrated system with eCOC valves was employed to detect minimal residual disease (MRD) from a blood sample of a pediatric acute lymphoblastic leukemia (ALL) patient. The two module integrated system evaluated MRD by affinity-selecting CD19(+) cells and enumerating leukemia cells via immunophenotyping with ALL-specific markers.

Millifluidic valves and pumps made of tape and plastic

There is growing interest in producing micro- and milli-fluidic technologies made of thermoplastic with integrated fluidic control elements that are easy to assemble and suitable for mass production. Here, we developed millifluidic valves and pumps made of acrylic layers bonded with double-sided tape that are simple and fast to assemble. We demonstrate that a layer of pressure-sensitive adhesive (PSA) is flexible enough to be deformed at relatively low pressures. A chemical treatment deposited on specific regions of the PSA prevents it from sticking to the thermoplastic, which enabled us to create three different types of valves in normally open or closed configurations. We characterized different aspects of their performance, their operating pressures, the cut-off pressure values to open or close the valves (for different configurations and sizes), and the flow rate and volume pumped by seven different micropumps. As an application, we implemented a glucose assay with integrated pumps and valves, automatically generating glucose dilutions and reagent mixing. The ability to create polymeric microfluidic control units made with tape paves the way for their mass manufacturing.

Simultaneous Absorbance and Fluorescence Measurements Using an Inlaid Microfluidic Approach

A novel microfluidic optical cell is presented that enables simultaneous measurement of both light absorbance and fluorescence on microlitre volumes of fluid. The chip design is based on an inlaid fabrication technique using clear and opaque poly(methyl methacrylate) or PMMA to create a 20.2 mm long optical cell. The inlaid approach allows fluid interrogation with minimal interference from external light over centimeter long path lengths. The performance of the optical cell is evaluated using a stable fluorescent dye: rhodamine B. Excellent linear relationships (R² > 0.99) are found for both absorbance and fluorescence over a 0.1-10 µM concentration range. Furthermore, the molar attenuation spectrum is accurately measured over the range 460-550 nm. The approach presented here is applicable to numerous colorimetric- or fluorescence-based assays and presents an important step in the development of multipurpose lab-on-chip sensors.

Thermally-actuated microfluidic membrane valve for point-of-care applications

Microfluidics has enabled low volume biochemistry reactions to be carried out at the point-of-care. A key component in microfluidics is the microfluidic valve. Microfluidic valves are not only useful for directing flow at intersections but also allow mixtures/dilutions to be tuned real-time and even provide peristaltic pumping capabilities. In the transition from chip-in-a-lab to lab-on-a-chip, it is essential to ensure that microfluidic valves are designed to require less peripheral equipment and that they are transportable. In this paper, a thermally-actuated microfluidic valve is presented. The valve itself is fabricated with off-the-shelf components without the need for sophisticated cleanroom techniques. It is shown that multiple valves can be controlled and operated via a power supply and an Arduino microcontroller; an important step towards transportable microfluidic devices capable of carrying out analytical assays at the point-of-care. It is been calculated that a single actuator costs less than $1, this highlights the potential of the presented valve for scaling out. The valve operation is demonstrated by adjusting the ratio of a water/dye mixture in a continuous flow microfluidic chip with Y-junction channel geometry. The power required to operate one microfluidic valve has been characterised both theoretically and experimentally. Cyclical operation of the valve has been demonstrated for 65 h with 585 actuations. The presented valve is capable of actuating rectangular microfluidic channels of 500 μm × 50 μm with an expected temperature increase of up to 5 °C. The fastest actuation times achieved were 2 s for valve closing (heating) and 9 s for valve opening (cooling).

Membrane integration into PDMS-free microfluidic platforms for organ-on-chip and analytical chemistry applications

Membranes play a crucial role in many microfluidic systems, enabling versatile applications in highly diverse research fields. However, the tight and robust integration of membranes into microfluidic systems requires complex fabrication processes. Most integration approaches, so far, rely on polydimethylsiloxane (PDMS) as base material for the microfluidic chips. Several limitations of PDMS have resulted in the transition of many microfluidic approaches to PDMS-free systems using alternative materials such as thermoplastics. To integrate membranes in those PDMS-free systems, novel alternative approaches are required. This review provides an introduction into microfluidic systems applying membrane technology for analytical systems and organ-on-chip as well as a comprehensive overview of methods for the integration of membranes into PDMS-free systems. The overview and examples will provide a valuable resource and starting point for any researcher that is aiming at implementing membranes in microfluidic systems without using PDMS.

Toward a disposable low-cost LOC device: heterogeneous polymer micro valve and pump fabricated by UV/ozone-assisted thermal fusion bonding

Herein, a heterogeneous polymer micro valve and pump with a polypropylene (PP) membrane was developed in a low-cost manner via UV/ozone-assisted thermal fusion bonding. The proposed fabrication technique allowed for a geometrically selective bonding; consequently, the membrane was prevented from bonding with the valve seat of the diaphragm micro-valve, without patterning a protection layer or introducing an additional structure. The developed device withstands 480 kPa of static pressure and up to 350 kPa of a vibration pressure, providing sufficient bonding strength for microfluidic actuations. The fabricated micro valve and pump are fully characterized and compared with a poly(dimethylsiloxane) (PDMS) membrane glass device, showing comparable valving and pumping performance. As a result, the robust PP membrane micro valve and pump are simply implemented in a facile manner, and demonstrated excellent performance, which is highly desirable for mass production of disposable lab-on-a-chip (LOC) devices.

Heat and pressure-resistant room temperature irreversible sealing of hybrid PDMS–thermoplastic microfluidic devices via carbon–nitrogen covalent bonding and its application in a continuous-flow polymerase chain reaction

In this study, we have introduced a facile room-temperature strategy for irreversibly sealing polydimethylsiloxane to various thermoplastics using (3-aminopropyl)triethoxysilane (APTES) and [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane (ECTMS).

Microfluidic device fabrication mediated by surface chemical bonding

This review discusses on various bonding techniques for fabricating microdevices with a special emphasis on the modification of surface assisted by the use of chemicals to assemble microfluidic devices at room temperature under atmospheric pressure.

A Fully Integrated In Vitro Diagnostic Microsystem for Pathogen Detection Developed Using a "3D Extensible" Microfluidic Design Paradigm

Microfluidics is facing critical challenges in the quest of miniaturizing, integrating, and automating in vitro diagnostics, including the increasing complexity of assays, the gap between the macroscale world and the microscale devices, and the diverse throughput demands in various clinical settings. Here, a "3D extensible" microfluidic design paradigm that consists of a set of basic structures and unit operations was developed for constructing any application-specific assay. Four basic structures-check valve (in), check valve (out), double-check valve (in and out), and on-off valve-were designed to mimic basic acts in biochemical assays. By combining these structures linearly, a series of unit operations can be readily formed. We then proposed a "3D extensible" architecture to fulfill the needs of the function integration, the adaptive "world-to-chip" interface, and the adjustable throughput in the X, Y, and Z directions, respectively. To verify this design paradigm, we developed a fully integrated loop-mediated isothermal amplification microsystem that can directly accept swab samples and detect Chlamydia trachomatis automatically with a sensitivity one order higher than that of the conventional kit. This demonstration validated the feasibility of using this paradigm to develop integrated and automated microsystems in a less risky and more consistent manner.

CO₂ Laser-Based Rapid Prototyping of Micropumps

The fabrication of microdevices for fluidic control often requires the use of flexible diaphragms in a way that requires cleanroom equipment and compromises performance. We use a CO2 laser to perform the standard ablative techniques of cutting and engraving materials, but we also apply a method that we call laser placement. This allows us to fabricate precisely-positioned and precisely-sized, isolated diaphragms. This in turn enables the rapid prototyping of integrated multilayer microfluidic devices to form complex structures without the need for manual positioning or cleanroom equipment. The fabrication process is also remarkably rapid and capable of being scaled to manufacturing levels of production. We explore the use of these devices to construct a compact system of peristaltic pumps that can form water in oil droplets without the use of the non-pulsatile pumping systems typically required. Many devices can be fabricated at a time on a sheet by sheet basis with a fabrication process that, to our knowledge, is the fastest reported to date for devices of this type (requiring only 3 h). Moreover, this system is unusually compact and self-contained.

Highly Fluorinated Methacrylates for Optical 3D Printing of Microfluidic Devices

Highly fluorinated perfluoropolyether (PFPE) methacrylates are of great interest for transparent and chemically resistant microfluidic chips. However, so far only a few examples of material formulations for three-dimensional (3D) printing of these polymers have been demonstrated. In this paper we show that microfluidic chips can be printed using these highly fluorinated polymers by 3D stereolithography printing. We developed photocurable resin formulations that can be printed in commercial benchtop stereolithography printers. We demonstrate that the developed formulations can be printed with minimal cross-sectional area of 600 µm for monolithic embedded microfluidic channels and 200 µm for open structures. The printed and polymerized PFPE methacrylates show a good transmittance above 70% at wavelengths between 520–900 nm and a high chemical resistance when being exposed to organic solvents. Microfluidic mixers were printed to demonstrate the great variability of different designs that can be printed using stereolithography.

Pressure-actuated monolithic acrylic microfluidic valves and pumps

In this article, we describe a microfluidic device with embedded valves and pumps made exclusively of layers of acrylic glass. Flat acrylic sheets are carved out with a micromilling machine and bonded together by solvent bonding. The working principle of the valves is based on a thin flexible membrane (≈100 μm) machined on one acrylic sheet and actuated with pneumatic pressure. A completely closed valve resists a pressure difference of ≈17 kPa (≈2.5 psi), and when open, it can sustain flow rates of up to 100 μL s^-1. Pumping is achieved by combining two valves and a pumping chamber in series, which is also based on the bending of a thin acrylic membrane. The maximum flow rate obtained with this pumping mechanism is 20 μL min^-1. Acrylic is a popular rigid thermoplastic because it is inexpensive, making it ideal for mass production of disposable devices, and also because it has demonstrated compatibility with different biochemical assays. The physical and optical properties it shares with other thermoplastics could lead to this material being implemented for similar valves and pumps. As a proof-of-concept of our technology, we implemented a controlled cell-staining assay in two parallel incubation chambers integrating four valves and one pump into one device. Our monolithic acrylic valves can enable the mass production of disposable microfluidic devices that require fluid control with pressure-actuated valves and aid in the automation of biochemical assays.

The upcoming 3D-printing revolution in microfluidics

In the last two decades, the vast majority of microfluidic systems have been built in poly(dimethylsiloxane) (PDMS) by soft lithography, a technique based on PDMS micromolding. A long list of key PDMS properties have contributed to the success of soft lithography: PDMS is biocompatible, elastomeric, transparent, gas-permeable, water-impermeable, fairly inexpensive, copyright-free, and rapidly prototyped with high precision using simple procedures. However, the fabrication process typically involves substantial human labor, which tends to make PDMS devices difficult to disseminate outside of research labs, and the layered molding limits the 3D complexity of the devices that can be produced. 3D-printing has recently attracted attention as a way to fabricate microfluidic systems due to its automated, assembly-free 3D fabrication, rapidly decreasing costs, and fast-improving resolution and throughput. Resins with properties approaching those of PDMS are being developed. Here we review past and recent efforts in 3D-printing of microfluidic systems. We compare the salient features of PDMS molding with those of 3D-printing and we give an overview of the critical barriers that have prevented the adoption of 3D-printing by microfluidic developers, namely resolution, throughput, and resin biocompatibility. We also evaluate the various forces that are persuading researchers to abandon PDMS molding in favor of 3D-printing in growing numbers.

3D-Printed Microfluidics

The advent of soft lithography allowed for an unprecedented expansion in the field of microfluidics. However, the vast majority of PDMS microfluidic devices are still made with extensive manual labor, are tethered to bulky control systems, and have cumbersome user interfaces, which all render commercialization difficult. On the other hand, 3D printing has begun to embrace the range of sizes and materials that appeal to the developers of microfluidic devices. Prior to fabrication, a design is digitally built as a detailed 3D CAD file. The design can be assembled in modules by remotely collaborating teams, and its mechanical and fluidic behavior can be simulated using finite-element modeling. As structures are created by adding materials without the need for etching or dissolution, processing is environmentally friendly and economically efficient. We predict that in the next few years, 3D printing will replace most PDMS and plastic molding techniques in academia.

Customizable 3D Printed 'Plug and Play' Millifluidic Devices for Programmable Fluidics

Three dimensional (3D) printing is actively sought after in recent years as a promising novel technology to construct complex objects, which scope spans from nano- to over millimeter scale. Previously we utilized Fused deposition modeling (FDM)-based 3D printer to construct complex 3D chemical fluidic systems, and here we demonstrate the construction of 3D milli-fluidic structures for programmable liquid handling and control of biological samples. Basic fluidic operation devices, such as water-in-oil (W/O) droplet generators for producing compartmentalized mono-disperse droplets, sensor-integrated chamber for online monitoring of cellular growth, are presented. In addition, chemical surface treatment techniques are used to construct valve-based flow selector for liquid flow control and inter-connectable modular devices for networking fluidic parts. As such this work paves the way for complex operations, such as mixing, flow control, and monitoring of reaction / cell culture progress can be carried out by constructing both passive and active components in 3D printed structures, which designs can be shared online so that anyone with 3D printers can reproduce them by themselves.

Instantaneous room temperature bonding of a wide range of non-silicon substrates with poly(dimethylsiloxane) (PDMS) elastomer mediated by a mercaptosilane

This paper introduces an instantaneous and robust strategy for bonding a variety of non-silicon substrates such as thermoplastics, metals, an alloy, and ceramics to poly(dimethylsiloxane) (PDMS) irreversibly, mediated by one-step chemical modification using a mercaptosilane at room temperature followed by corona treatment to realize heterogeneous assembly also at room temperature. The mercapto functional group is one of the strongest nucleophiles, and it can instantaneously react with electrophiles of substrates, resulting in an alkoxysilane-terminated substrate at room temperature. In this way, prior oxidation of the substrate is dispensed with, and the alkoxysilane-terminated substrate can be readily oxidized and irreversibly bonded with oxidized PDMS at room temperature. A commercially available Tesla coil was used for surface oxidation, replacing a bulky and expensive plasma generator. Surface characterization was conducted by water contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis. A total of fifteen non-silicon substrates including polycarbonate (PC), two types of poly(vinylchloride) (PVC), poly(methylmethacrylate) (PMMA), polystyrene (PS), polyimide (PI), two types of poly(ethylene terephthalate) (PET), polypropylene (PP), iron (Fe), aluminum (Al), copper (Cu), brass, alumina (Al2O3), and zirconia (ZrO2) were bonded successfully with PDMS using this method, and the bond strengths of PDMS-PMMA, PDMS-PC, PDMS-PVC, PDMS-PET, PDMS-Al, and PDMS-Cu assemblies were measured to be approximately 335.9, 511.4, 467.3, 476.4, 282.2, and 236.7 kPa, respectively. The overall processes including surface modification followed by surface oxidation using corona treatment for bonding were realized within 12 to 17 min for most of the substrates tested except for ceramics which required 1 h for the bonding. In addition, large area (10 × 10 cm(2)) bonding was also successfully realized, ensuring the high reliability and stability of the introduced method.

Integrated hybrid polystyrene-polydimethylsiloxane device for monitoring cellular release with microchip electrophoresis and electrochemical detection

In this work, a polystyrene (PS)-polydimethylsiloxane (PDMS) hybrid device was developed to enable the integration of cell culture with analysis by microchip electrophoresis and electrochemical detection. It is shown that this approach combines the fundamental advantages of PDMS devices (the ability to integrate pumps and valves) and PS devices (the ability to permanently embed fluidic tubing and electrodes). The embedded fused-silica capillary enables high temporal resolution measurements from off-chip cell culture dishes and the embedded electrodes provide close to real-time analysis of small molecule neurotransmitters. A novel surface treatment for improved (reversible) adhesion between PS and PDMS is described using a chlorotrimethylsilane stamping method. It is demonstrated that a Pd decoupler is efficient at handling the high current (and cathodic hydrogen production) resulting from use of high ionic strength buffers needed for cellular analysis; thus allowing an electrophoretic separation and in-channel detection. The separation of norepinephrine (NE) and dopamine (DA) in highly conductive biological buffers was optimized using a mixed surfactant system. This PS-PDMS hybrid device integrates multiple processes including continuous sampling from a cell culture dish, on-chip pump and valving technologies, microchip electrophoresis, and electrochemical detection to monitor neurotransmitter release from PC 12 cells.

The reaction kinetics and mechanism of crude fluoroelastomer vulcanized by direct fluorination with fluorine/nitrogen gas

The novel vulcanization of fluoroelastomer by fluorination is studied; moreover, the simultaneously accompanied fluorine content increases and tribological property is improved.

A filter paper-based microdevice for low-cost, rapid, and automated DNA extraction and amplification from diverse sample types

A plastic microfluidic device that integrates a filter disc as a DNA capture phase was successfully developed for low-cost, rapid and automated DNA extraction and PCR amplification from various raw samples. The microdevice was constructed by sandwiching a piece of Fusion 5 filter, as well as a PDMS (polydimethylsiloxane) membrane, between two PMMA (poly(methyl methacrylate)) layers. An automated DNA extraction from 1 μL of human whole blood can be finished on the chip in 7 minutes by sequentially aspirating NaOH, HCl, and water through the filter. The filter disc containing extracted DNA was then taken out directly for PCR. On-chip DNA purification from 0.25-1 μL of human whole blood yielded 8.1-21.8 ng of DNA, higher than those obtained using QIAamp® DNA Micro kits. To realize DNA extraction from raw samples, an additional sample loading chamber containing a filter net with an 80 μm mesh size was designed in front of the extraction chamber to accommodate sample materials. Real-world samples, including whole blood, dried blood stains on Whatman® 903 paper, dried blood stains on FTA™ cards, buccal swabs, saliva, and cigarette butts, can all be processed in the system in 8 minutes. In addition, multiplex amplification of 15 STR (short tandem repeat) loci and Sanger-based DNA sequencing of the 520 bp GJB2 gene were accomplished from the filters that contained extracted DNA from blood. To further prove the feasibility of integrating this extraction method with downstream analyses, "in situ" PCR amplifications were successfully performed in the DNA extraction chamber following DNA purification from blood and blood stains without DNA elution. Using a modified protocol to bond the PDMS and PMMA, our plastic PDMS devices withstood the PCR process without any leakage. This study represents a significant step towards the practical application of on-chip DNA extraction methods, as well as the development of fully integrated genetic analytical systems.

A solvent resistant lab-on-chip platform for radiochemistry applications

The application of microfluidics to the synthesis of Positron Emission Tomography (PET) tracers has been explored for more than a decade. Microfluidic benefits such as superior temperature control have been successfully applied to PET tracer synthesis. However, the design of a compact microfluidic platform capable of executing a complete PET tracer synthesis workflow while maintaining prospects for commercialization remains a significant challenge. This study uses an integral system design approach to tackle commercialization challenges such as the material to process compatibility with a path towards cost effective lab-on-chip mass manufacturing from the start. It integrates all functional elements required for a simple PET tracer synthesis into one compact radiochemistry platform. For the lab-on-chip this includes the integration of on-chip valves, on-chip solid phase extraction (SPE), on-chip reactors and a reversible fluid interface while maintaining compatibility with all process chemicals, temperatures and chip mass manufacturing techniques. For the radiochemistry device it includes an automated chip-machine interface enabling one-move connection of all valve actuators and fluid connectors. A vial-based reagent supply as well as methods to transfer reagents efficiently from the vials to the chip has been integrated. After validation of all those functional elements, the microfluidic platform was exemplarily employed for the automated synthesis of a Gastrin-releasing peptide receptor (GRP-R) binding the PEGylated Bombesin BN(7-14)-derivative ([(18)F]PESIN) based PET tracer.

Microfluidic Valves Made From Polymerized Polyethylene Glycol Diacrylate

Pneumatically actuated, non-elastomeric membrane valves fabricated from polymerized polyethylene glycol diacrylate (poly-PEGDA) have been characterized for temporal response, valve closure, and long-term durability. A ~100 ms valve opening time and a ~20 ms closure time offer valve operation as fast as 8 Hz with potential for further improvement. Comparison of circular and rectangular valve geometries indicates that the surface area for membrane interaction in the valve region is important for valve performance. After initial fabrication, the fluid pressure required to open a closed circular valve is ~50 kPa higher than the control pressure holding the valve closed. However, after ~1000 actuations to reconfigure polymer chains and increase elasticity in the membrane, the fluid pressure required to open a valve becomes the same as the control pressure holding the valve closed. After these initial conditioning actuations, poly-PEGDA valves show considerable robustness with no change in effective operation after 115,000 actuations. Such valves constructed from non-adsorptive poly-PEGDA could also find use as pumps, for application in small volume assays interfaced with biosensors or impedance detection, for example.

Recent developments in microfluidic large scale integration

In 2002, Thorsen et al. integrated thousands of micromechanical valves on a single microfluidic chip and demonstrated that the control of the fluidic networks can be simplified through multiplexors [1]. This enabled realization of highly parallel and automated fluidic processes with substantial sample economy advantage. Moreover, the fabrication of these devices by multilayer soft lithography was easy and reliable hence contributed to the power of the technology; microfluidic large scale integration (mLSI). Since then, mLSI has found use in wide variety of applications in biology and chemistry. In the meantime, efforts to improve the technology have been ongoing. These efforts mostly focus on; novel materials, components, micromechanical valve actuation methods, and chip architectures for mLSI. In this review, these technological advances are discussed and, recent examples of the mLSI applications are summarized.

The use of polyurethane as an elastomer in thermoplastic microfluidic devices and the study of its creep properties

We report using polyurethane (PU) as an elastomer in microvalves integrated with thermoplastic microfluidic devices. Elastomer-based microvalves have been used in a number of applications and the elastomer often used is PDMS. Although it is a convenient material for prototyping, PDMS has been recognized to possess shortcomings such as solvent incompatibility and unfavorable manufacturability. We investigated the use of PU as an elastomer to address the challenges. A reliable method was developed to bond hybrid materials such as PU and cyclic olefin copolymer. The film thickness from 3.5 to 24.5 μm was studied to identify an appropriate thickness of PU films for desirable elasticity in microvalves. We integrated PU with thermally actuated, elastomer-based microvalves in thermoplastic devices. Valve actuations were demonstrated, and the relationship between the valve actuation time and heater power was studied. We compared PU with PDMS in terms of their microvalve performance. Valves with PDMS failed to function after two weeks since the thermal-sensitive solution evaporated through porous PDMS membrane, whereas the same valve with PU functioned properly after eight months. In addition, we evaluated the creep and creep recovery of PU, which is a common phenomenon of viscoelastic materials and is related to the long-term elastic property of PU after prolonged use.

Superhydrophilic multilayer silica nanoparticle networks on a polymer microchannel using a spray layer-by-layer nanoassembly method

Nanoporous and superhydrophilic multilayer silica nanoparticle networks have been developed on a hydrophobic cyclic olefin copolymer (COC) microchannel using a spray layer-by-layer (LbL) electrostatic nanoassembly method. This powerful and promising LbL method provides a simple, cost-effective, and high-throughput nanoporous silica multilayer selectively onto the hydrophobic polymer surfaces. These newly developed multilayer networks have also been successfully characterized by contact angle measurement, environmental scanning electron microscopy (ESEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The superhydrophilic effect, which was confirmed by the contact angle measurements, of the silica networks ensured the hydrophilic nature of the selectively constructed nanoporous silica nanoparticles onto the patterned hydrophobic COC microchannel. The capillary effect of the developed surface was characterized by measuring the length of a test liquid driven by the induced capillary forces in an on-chip capillary pumping platform with horizontal microchannels. The pumping capability achieved from the sprayed nanoporous surface for the on-chip micropump was mainly due to the strong capillary imbibition driven by the multicoated bilayers of hydrophilic silica nanoparticles. The developed networks with spray-assembled nanoparticles were also applied for an on-chip blood plasma separation platform with closed microchannels. The spray LbL method developed in this work can be a highly practical approach for the modification of various polymer microchannels because of several advantages such as an extremely simple process for the multilayer formation and flexibly controlled surface functionality at room temperature.

From sample to PCR product in under 45 minutes: a polymeric integrated microdevice for clinical and forensic DNA analysis

The extraction and amplification of DNA from biological samples is laborious and time-consuming, requiring numerous instruments and sample handling steps. An integrated, single-use, poly(methyl methacrylate) (PMMA) microdevice for DNA extraction and amplification would benefit clinical and forensic communities, providing a completely closed system with rapid sample-in-PCR-product-out capability. Here, we show the design and simple flow control required for enzyme-based DNA preparation and PCR from buccal swabs or liquid whole blood samples with an ~5-fold reduction in time. A swab containing cells or DNA could be loaded into a novel receptacle together with the DNA liberation reagents, heated using an infrared heating system, mixed with PCR reagents for one of three different target sets under syringe-driven flow, and thermally-cycled in less than 45 min, an ~6-fold reduction in analysis time as compared to conventional methods. The 4 : 1 PCR reagents : DNA ratio required to provide the correct final concentration of all PCR components for effective amplification was verified using image analysis of colored dyes in the PCR chamber. Novel single-actuation, 'normally-open' adhesive valves were shown to effectively seal the PCR chamber during thermal cycling, preventing air bubble expansion. The effectiveness of the device was demonstrated using three target sets: the sex-typing gene Amelogenin, co-amplification of the β-globin and gelsolin genes, and the amplification of 15 short tandem repeat (STR) loci plus Amelogenin. The use of the integrated microdevice was expanded to the analysis of liquid blood samples which, when incubated with the DNA liberation reagents, form a brown precipitate that inhibits PCR. A simple centrifugation of the integrated microchips (on a custom centrifuge), mobilized the precipitate away from the microchannel entrance, improving amplification of the β-globin and gelsolin gene fragments by ~6-fold. This plastic integrated microdevice represents a microfluidic platform with potential for evolution into point-of-care prototypes for application to both clinical and forensic analyses, providing a 5-fold reduction from conventional analysis time.

One step high quality poly(dimethylsiloxane)-hydrocarbon plastics bonding

In this paper, one-step air plasma treatment is successfully used for poly(dimethylsiloxane)(PDMS)-plastic chip bonding. The technique is green, cheap, and requires no other reagent other than air. Hydrocarbon plastics: polystyrene (PS), cyclic olefin copolymer (COC), and polypropylene (PP) have all been successfully bonded to PDMS irreversibly. The corresponding compressed air resistances are measured to be around 500 kPa for PDMS-PS, PDMS-COC, and PDMS-PP hybrid chips. The bondings are also of good quality even after storage under different temperatures and subject to solutions from acid to base.

Rapid prototyping polymers for microfluidic devices and high pressure injections

Multiple methods of fabrication exist for microfluidic devices, with different advantages depending on the end goal of industrial mass production or rapid prototyping for the research laboratory. Polydimethylsiloxane (PDMS) has been the mainstay for rapid prototyping in the academic microfluidics community, because of its low cost, robustness and straightforward fabrication, which are particularly advantageous in the exploratory stages of research. However, despite its many advantages and its broad use in academic laboratories, its low elastic modulus becomes a significant issue for high pressure operation as it leads to a large alteration of channel geometry. Among other consequences, such deformation makes it difficult to accurately predict the flow rates in complex microfluidic networks, change flow speed quickly for applications in stop-flow lithography, or to have predictable inertial focusing positions for cytometry applications where an accurate alignment of the optical system is critical. Recently, other polymers have been identified as complementary to PDMS, with similar fabrication procedures being characteristic of rapid prototyping but with higher rigidity and better resistance to solvents; Thermoset Polyester (TPE), Polyurethane Methacrylate (PUMA) and Norland Adhesive 81 (NOA81). In this review, we assess these different polymer alternatives to PDMS for rapid prototyping, especially in view of high pressure injections with the specific example of inertial flow conditions. These materials are compared to PDMS, for which magnitudes of deformation and dynamic characteristics are also characterized. We provide a complete and systematic analysis of these materials with side-by-side experiments conducted in our lab that also evaluate other properties, such as biocompatibility, solvent compatibility, and ease of fabrication. We emphasize that these polymer alternatives, TPE, PUMA and NOA, have some considerable strengths for rapid prototyping when bond strength, predictable operation at high pressure, or transitioning to commercialization are considered important for the application.