Low-cost origami fabrication of 3D self-aligned hybrid microfluidic structures

3D microfluidic device fabrication methods are normally quite expensive and tedious. In this paper, we present an easy and cheap alternative wherein thin cyclic olefin polymer (COP) sheets and pressure sensitive adhesive (PSA) were used to fabricate hybrid 3D microfluidic structures, by the Origami technique, which enables the fabrication of microfluidic devices without the need of any alignment tool. The COP and PSA layers were both cut simultaneously using a portable, low-cost plotter allowing for rapid prototyping of a large variety of designs in a single production step. The devices were then manually assembled using the Origami technique by simply combining COP and PSA layers and mild pressure. This fast fabrication method was applied, as proof of concept, to the generation of a micromixer with a 3D-stepped serpentine design made of ten layers in less than 8 min. Moreover, the micromixer was characterized as a function of its pressure failure, achieving pressures of up to 1000 mbar. This fabrication method is readily accessible across a large range of potential end users, such as educational agencies (schools, universities), low-income/developing world research and industry or any laboratory without access to clean room facilities, enabling the fabrication of robust, reproducible microfluidic devices.     

Non-woven fabric-based microfluidic devices with hydrophobic wax barrier

This study proposed a novel method for the fabrication of non-woven based microfluidic devices with a wax hydrophobic barrier. Current microfluidic devices were fabricated with glass or polymer material, and paper is also widely used for the fabrication of low-cost microfluidic devices. The application of non-woven fabric based microfluidic devices provides a new option of bulk materials for microfluidics. Compared with the glass or polymer material used in microfluidics, non-woven fabric is low-cost, easy to process and disposable. Fluid can penetrate through the non-woven fabric material with capillary force without the requirement of external pumps. As fiber-based material, comparing with paper, non-woven fabric material is more durable with higher mechanical strength, and various types of non-woven fabric material also provide a board choice of surface chemical/physical properties for microfluidic applications. In this study, the hydrophilic non-woven fabric is chosen as the bulk material for microfluidic devices, a wax pattern transfer protocol is also proposed in this study for the deposition of hydrophobic barriers. For a demonstration of the proposed fabrication technique, a microfluidic mixer was also fabricated in this study.

     

Automating fluid delivery in a capillary microfluidic device using low-voltage electrowetting valves

A multilayer capillary polymeric microfluidic device integrated with three normally closed electrowetting valves for timed fluidic delivery was developed. The microfluidic channel consisted two flexible layers of poly (ethylene terephthalate) bonded by a pressure-sensitive adhesive spacer tape. Channels were patterned in the spacer tape using laser ablation. Each valve contained two inkjet-printed silver electrodes in series. Capillary flow within the microchannel was stopped at the second electrode which was modified with a hydrophobic monolayer (valve closed). When a potential was applied across the electrodes, the hydrophobic monolayer became hydrophilic and allowed flow to continue (valve opened). The relationship between the actuation voltage, the actuation time, and the distance between two electrodes was performed using a microfluidic chip containing a single microchannel design. The results showed that a low voltage (4.5 V) was able to open the valve within 1 s when the distance between two electrodes was 1 mm. Increased voltages were needed to open the valves when the distance between two electrodes was increased. Additionally, the actuation time required to open the valve increased when voltage was decreased. A multichannel device was fabricated to demonstrate timed fluid delivery between three solutions. Our electrowetting valve system was fabricated using low-cost materials and techniques, can be actuated by a battery, and can be integrated into portable microfluidic devices suitable for point-of-care analysis in resource-limited settings.     

Electrophoresis separation and electrochemical detection on a novel thread-based microfluidic device

This paper describes a thread-based microfluidic system for rapid and low-cost electrophoresis separation and electrochemical (EC) detection of ion samples. Instead of using liquid channel for sample separation, thin polyester threads of various diameters are used as the routes for separating the samples with electrophoresis. Hot-pressed PMMA chip with protruding sleeper structures are adopted to set up the polyester threads and for electrochemical detection of the ion samples on the thread. Plasma treatment greatly improves the wetability of thin threads and surface quality of the threads. The measured electrical currents on plasma treated threads are 10 times greater than the threads without treatment. Results indicate that nice redox signals can be obtained by measuring ferric cyanide salt on the polyester thread. The estimated detection limit for EC sensing of potassium ferricyanide (K₃Fe(CN)₆) is around 6.25 μM using the developed thread-based microfluidic device. Mixed ion samples (Cl^?, Br^? and I^?) and bio-sample are successfully separated and detected using the developed thread-based microfluidic device.     

Fast fabrication of microfluidic devices using a low-cost prototyping method

Conventional ways to produce microfluidic devices cost a lot due to the requirements for cleanroom environments and expensive equipment, which prevents the wider applications of microfluidics in academia and in industry. In this paper, a dry film photoresist was utilized in a simple way to reduce the fabrication cost of microfluidic masters. Thus, a fast prototyping and fabrication of microstructures in polydimethylsiloxane microchips through a replica molding technology was achieved in a low-cost setting within 2.5 h. Subsequently, major manufacturing conditions were optimized to acquire well-resolved microfluidic molds, and the replicated microchips were validated to be of good performance. A T-junction channel microchip was fabricated by using a dry film master to generate water droplets of uniform target size. Meanwhile, a gated injection of fluorescein sodium and a contactless conductivity detection of Na⁺ were both performed in a crosslink channel microchip via capillary electrophoresis, in other words, this fast prototyping and fabrication method would be an efficient, economical way to embody structural design into microfluidic chips for various applications.     

Modular membrane valves for universal integration within thermoplastic devices

While much research has been conducted on elastomeric valves within PDMS microfluidic devices, we rarely see scalable manufacturing processes for integrating such valves into rigid thermoplastic devices. Most thermoplastic materials do not share intrinsic bonding compatibility to flexible elastomer membranes, making it difficult to ensure leak-proof operation of such valves within thermoplastic devices. In order to overcome bonding compatibility issues, we propose decoupling the valve architecture from the fluidic routing device layers. This can be achieved by prefabricating modular valves via molding processes and subsequently inserting them into thermoplastic layers containing valve seats. Thermoplastic layers containing modular valves are then thermally bonded to thermoplastic layers containing the fluidic routing channels, resulting in leak-proof valve integration. At valve actuation pressures of approximately 60 kPa, the modular membrane valves seal fluidic channels operating at a flow rate of 100 µl min^?1. Modular valves that were incorporated into a concentration gradient generator demonstrated dynamically configurable fluid routing at a response frequency of 5 Hz. The integration of modular membrane valves is an effective solution to streamline and cost-down the manufacturing of hybrid elastomer–thermoplastic devices. As this solution does not rely on bonding compatibility between the elastomeric membranes and the thermoplastic device, it can be applied universally to solve integration issues for low-cost thermoplastic device fabrication.     

Deterministic lateral displacement (DLD) in the high Reynolds number regime: high-throughput and dynamic separation characteristics

Recent progress in the development of biosensors has created a demand for high-throughput sample preparation techniques that can be easily integrated into microfluidic or lab-on-a-chip platforms. One mechanism that may satisfy this demand is deterministic lateral displacement (DLD), which uses hydrodynamic forces to separate particles based on size. Numerous medically relevant cellular organisms, such as circulating tumor cells (10–15 µm) and red blood cells (6–8 µm), can be manipulated using microscale DLD devices. In general, these often-viscous samples require some form of dilution or other treatment prior to microfluidic transport, further increasing the need for high-throughput operation to compensate for the increased sample volume. However, high-throughput DLD devices will require a high flow rate, leading to an increase in Reynolds numbers (Re) much higher than those covered by existing studies for microscale (≤?100 µm) DLD devices. This study characterizes the separation performance for microscale DLD devices in the high-Re regime (10?<?Re?<?60) through numerical simulation and experimental validation. As Re increases, streamlines evolve and microvortices emerge in the wake of the pillars, resulting in a particle trajectory shift within the DLD array. This differs from previous DLD works, in that traditional models only account for streamlines that are characteristic of low-Re flow, with no consideration for the transformation of these streamlines with increasing Re. We have established a trend through numerical modeling, which agrees with our experimental findings, to serve as a guideline for microscale DLD performance in the high-Re regime. Finally, this new phenomenon could be exploited to design passive DLD devices with a dynamic separation range, controlled simply by adjusting the device flow rate.     

Fabrication of three-dimensional microfluidic channels in a single layer of cellulose paper

Three-dimensional microfluidic paper-based analytical devices (3D-μPADs) represent a promising platform technology that permits complex fluid manipulation, parallel sample distribution, high throughput, and multiplexed analytical tests. Conventional fabrication techniques of 3D-μPADs always involve stacking and assembling layers of patterned paper using adhesives, which are tedious and time-consuming. This paper reports a novel technique for fabricating 3D microfluidic channels in a single layer of cellulose paper, which greatly simplifies the fabrication process of 3D-μPADs. This technique, evolved from the popular wax-printing technique for paper channel patterning, is capable of controlling the penetration depth of melted wax, printed on both sides of a paper substrate, and thus forming multilayers of patterned channels in the substrate. We control two fabrication parameters, the density of printed wax (i.e., grayscale level of printing) and the heating time, to adjust the penetration depth of wax upon heating. Through double-sided printing of patterns at different grayscale levels and proper selection of the heating time, we construct up to four layers of channels in a 315.4-μm-thick sheet of paper. As a proof-of-concept demonstration, we fabricate a 3D-μPAD with three layers of channels from a paper substrate and demonstrate multiplexed enzymatic detection of three biomarkers (glucose, lactate, and uric acid). This technique is also compatible with the conventional fabrication techniques of 3D-μPADs, and can decrease the number of paper layers required for forming a 3D-μPAD and therefore make the device quality control easier. This technique holds a great potential to further popularize the use of 3D-μPADs and enhance the mass-production quality of these devices.     

Rapid,simple and low cost fabrication of a microfluidic direct methanol fuel cell based on polydimethylsiloxane

In this paper a simple and rapid fabrication method for a microfluidic direct methanol fuel cell using polydimethylsiloxane (PDMS) as substrate is demonstrated. A gold layer on PDMS substrate as seed layer was obtained by chemical plating instead of conventional metal evaporation or sputtering. The morphology of the gold layer can be controlled by adjusting the ratio of curing agent to the PDMS monomer. The chemical properties of the gold films were examined. Then catalyst nanoparticles were grown on the films either by cyclic voltammetry or electrophoretic deposition. The microfluidic fuel cell was assembled by simple oxygen plasma bonding between two PDMS substrates. The cell operated at room temperature with a maximum power density around 6.28 mW cm^?2. Such a fuel cell is low-cost and easy to construct, and is convenient to be integrated with other devices because of the viscosity of the PDMS. This work will facilitate the development of miniature on-chip power sources for portable electronic devices.     

An integrated microfluidic system using mannose-binding lectin for bacteria isolation and biofilm-related gene detection

Molecular diagnosis of biofilm-related genes (BRGs) in common bacteria that cause periprosthetic joint infections may provide crucial information for clinicians. In this study, several BRGs, including ica, fnbA, and fnbB, were rapidly detected (within 1 h) with a new integrated microfluidic system. Mannose-binding lectin (MBL)-coated magnetic beads were used to isolate these bacteria, and on-chip nucleic acid amplification (polymerase chain reaction, PCR) was then performed to detect BRGs. Both eukaryotic and prokaryotic MBLs were able to isolate common bacterial strains, regardless of their antibiotic resistance, and limits of detection were as low as 3 and 9 CFU for methicillin-resistant Staphylococcus aureus and Escherichia coli, respectively, when using a universal 16S rRNA PCR assay for bacterial identification. It is worth noting that the entire process including bacteria isolation by using MBL-coated beads for sample pre-treatment, on-chip PCR, and fluorescent signal detection could be completed on an integrated microfluidic system within 1 h. This is the first time that an integrated microfluidic system capable of detecting BRGs by using MBL as a universal capturing probe was reported. This integrated microfluidic system might therefore prove useful for monitoring profiles of BRGs and give clinicians more clues for their clinical judgments in the near future.     

Enhanced sample concentration on a three-dimensional origami paper-based analytical device with non-uniform assay channel

Traditional microfluidic paper-based analytical devices (μPADs) consist of a flat straight channel printed on a paper substrate. Such devices provide a promising low-cost solution for a variety of biomedical assays. However, they have a relatively high sample consumption due to their use of external reservoirs. Moreover, in μPADs based on the ion concentration polarization (ICP) effect, controlling the cross-sectional area of the Nafion membrane relative to that of the hydrophilic channel is difficult. Accordingly, the present study utilizes an origami technique to create a μPAD with a three-dimensional (3D) structure. The μPAD features short channels and embedded reservoirs, and therefore reduces both the driving voltage requirement and the sample consumption. Moreover, the preconcentration effect is enhanced through the use of an additional hydrophilic area adjacent to the Nafion membrane. The existence of electroosmotic flow (EOF) within the proposed device is confirmed using a current-monitoring method. In addition, the occurrence of ICP is evaluated by measuring the current–voltage response of the device at external voltages ranging from 0 to 50 V. The experimental results obtained for a fluorescein sample with an initial concentration of 10^?5 M show that a 100-fold enhancement factor can be achieved given the use of a non-uniform-geometry design for the assay channel and an additional hydrophilic region with an area equal to approximately 10% of the channel cross-sectional area. Finally, a 100-fold factor can also be achieved for a fluorescein isothiocyanate sample with an initial concentration of 10^?6 M given an external driving voltage of 40 V.     

High fidelity prototyping of PDMS electrophoresis microchips using laser-printed masters

Microsystem Technologies - Toner-based fabrication technology has appeared as one of the simplest and fastest techniques to produce low-cost microfluidic devices. The instrumental simplicity and...     

On-chip PMA labeling of foodborne pathogenic bacteria for viable qPCR and qLAMP detection

Propidium monoazide (PMA) is a membrane impermeable molecule that covalently bonds to double stranded DNA when exposed to light and inhibits the polymerase activity, thus enabling DNA amplification detection protocols that discriminate between viable and non-viable entities. Here, we present a microfluidic device for inexpensive, fast, and simple PMA labeling for viable qPCR and qLAMP assays. The three labeling stages of mixing, incubation, and cross-linking are completed within a microfluidic device that is designed with Tesla structures for passive microfluidic mixing, bubble trappers to improve flow uniformity, and a blue LED to cross-link the molecules. Our results show that the on-chip PMA labeling is equivalent to the standard manual protocols and prevents the replication of DNA from non-viable cells in amplification assays. However, the on-chip process is faster and simpler (30 min of hands-off work), has a reduced likelihood of false negatives, and it is less expensive because it only uses 1/20th of the reagents normally consumed in standard bench protocols. We used our microfluidic device to perform viable qPCR and qLAMP for the detection of S. typhi and E. coli O157. With this device, we are able to specifically detect viable bacteria, with a limit of detection of 7.6 × 10³ and 1.1 × 10³ CFU/mL for S. typhi and E. coli O157, respectively, while eliminating amplification from non-viable cells. Furthermore, we studied the effects of greater flow rates to expedite the labeling process and identified a maximum flow rate of 0.7 μL/min for complete labeling with the current design.     

High-performance PCB-based capillary pumps for affordable point-of-care diagnostics

Capillary pumps are integral components of passive microfluidic devices. They can displace precise volumes of liquid, avoiding the need for external active components, providing a solution for sample preparation modules in Point-of-Care (PoC) diagnostic platforms. In this work, we describe a variety of high-performance capillary pump designs, suitable for the Lab-on-Printed-Circuit-Board technology (LoPCB). Pumps are fabricated entirely on Printed Circuit Board (PCB) substrates via commercially available manufacturing processes. We demonstrate the concept of LoPCB technology and detail the fabrication method of different architectures of PCB-based capillary pumps. The capillary pumps are combined with microfluidic channels of various hydraulic resistances and characterised experimentally for different micropillar shapes and minimum feature size. Their performance in terms of flow rate is reported. Due to the superhydrophilic properties of oxygen plasma treated FR-4 PCB substrate, the capillary pump flow rates are much higher (138 μL/min, for devices comprising micropillar arrays without preceding microchannel) than comparable devices based on glass, silicon or polymers. Finally, we comment on the technology’s prospects, such as incorporating more complicated microfluidic networks that can be tailored for assays.     

Effects of geometry factors on microvortices evolution in confined square microcavities

Recently, microcavities have become a central feature of diverse microfluidic devices for many biological applications. Thus, the flow and transport phenomena in microcavities characterized by microvortices have received increasing research attention. It is important to understand thoroughly the geometry factors on the flow behaviors in microcavities. In an effort to provide a design guideline for optimizing the microcavity configuration and better utilizing microvortices for different applications, we investigated quantitatively the liquid flow characteristics in different square microcavities located on one side of a main straight microchannel by using both microparticle image velocimetry (micro-PIV) and numerical simulation. The influences of the inlet Reynolds numbers (with relatively wider values Re?=?1–400) and the hydraulic diameter of the main microchannel (D_H?=?100, 133 μm) on the evolution of microvortices in different square microcavities (100, 200, 400 and 800 μm) were studied. The evolution and characteristic of the microvortices were investigated in detail. Moreover, the critical Reynolds numbers for the emergence of microvortices and the transformation of flow patterns in different microcavities were determined. The results will provide a useful guideline for the design of microcavity-featured microfluidic devices and their applications.     

3D-printed peristaltic microfluidic systems fabricated from thermoplastic elastomer

Recent advancements in 3D printing technology have provided a potential low-cost and time-saving alternative to conventional PDMS (polydimethylsiloxane)-based microfabrication for microfluidic systems. In addition to reducing the complexity of the fabrication procedure by eliminating such intermediate steps as molding and bonding, 3D printing also offers more flexibility in terms of structural design than the PDMS micromolding process. At present, 3D-printed microfluidic systems typically utilize a relatively ‘stiff’ printing material such as ABS (acrylonitrile butadiene styrene copolymers), which limits the implementation of large mechanical actuation for active pumping and mixing as routinely carried out in a PDMS system. In this paper, we report the development of an active 3D-printed microfluidic system with moving parts fabricated from a flexible thermoplastic elastomer (TPE). The 3D-printed microfluidic system consists of two pneumatically actuated micropumps and one micromixer. The completed system was successfully applied to the detection of low-level insulin concentration using a chemiluminescence immunoassay, and the test result compares favorably with a similarly designed PDMS microfluidic system. Prior to system fabrication and testing, the material properties of TPE were extensively evaluated. The result indicated that TPE is compatible with biological materials and its 3D-printed surface is hydrophilic as opposed to hydrophobic for a molded PDMS surface. The Young’s modulus of TPE is measured to be 16 MPa, which is approximately eight times higher than that of PDMS, but over one hundred times lower than that of ABS.     

Miniaturized DNA amplification platform with soft-lithographically fabricated continuous-flow PCR microfluidic device on a portable temperature controller

Fabrication of 3D microfluidic devices is normally quite expensive and tedious. A strategy was established to rapidly and effectively produce multilayer 3D microfluidic chips which are made of two layers of poly(methyl methacrylate) (PMMA) sheets and three layers of double-sided pressure sensitive adhesive (PSA) tapes. The channel structures were cut in each layer by cutting plotter before assembly. The structured channels were covered by a PMMA sheet on top and a PMMA carrier which contained threads to connect with tubing. A large variety of PMMA slides and PSA tapes can easily be designed and cut with the help of a cutting plotter. The microfluidic chip was manually assembled by a simple lamination process.The complete fabrication process from device design concept to working device can be completed in minutes without the need of expensive equipment such as laser, thermal lamination, and cleanroom. This rapid frabrication method was applied for design of a 3D hydrodynamic focusing device for synthesis of gold nanoparticles (AuNPs) as proof-of-concept. The fouling of AuNPs was prevented by means of a sheath flow. Different parameters such as flow rate and concentration of reagents were controlled to achieve AuNPs of various sizes. The sheet-based fabrication method offers a possibility to create complex microfluidic devices in a rapid, cheap and easy way.

     

Microfabrication of single-use plastic microfluidic devices for high-throughput screening and DNA analysis

 Modern drug discovery and genomic analysis depend on rapid analysis of large numbers of samples in parallel. The applicability of microfluidic devices in this field needs low cost devices, which can be fabricated in mass production. In close collaboration, Greiner Bio-One and Forschungszentrum Karlsruhe have developed a single-use plastic microfluidic capillary electrophoresis (CE) array in the standardized microplate footprint. Feasibility studies have shown that hot embossing with a mechanical micromachined molding tool is the appropriate technology for low cost mass fabrication. A subsequent sealing of the microchannels allows sub-microliter sample volumes in 96-channel multiplexed microstructures. Received: 16 May 2001 / Accepted: 3 July 2001     

Laminated paper-based analytical devices (LPAD): fabrication, characterization, and assays

Paper-based microfluidic devices have recently garnered an increasing interest in the literature. The majority of these devices were produced by patterning hydrophobic zones in hydrophilic paper via photoresist or wax. Others were created by cutting paper using a laser. Here, we present a fabrication method for producing devices by simple craft-cutting and lamination, in a way similar to making an identification (ID) card. The method employs a digital craft cutter and roll laminator to produce laminated paper-based analytical devices (LPAD). Lamination with a plastic backing provides the mechanical strength for a paper device. The approach of using a craft cutter and laminator makes it possible to rapid-prototype LPAD with no more difficulty than producing a typical ID card, at very low cost. Devices constructed using this method have been exploited for simultaneous detection of bovine serum albumin (BSA) and glucose in synthetic urine with colorimetric assays. Both BSA and glucose are detectable at clinically relevant concentrations, with the detection limit at 2.5 μM for BSA and 0.5 mM for glucose.     

Soft lithography fabrication of index-matched microfluidic devices for reducing artifacts in fluorescence and quantitative phase imaging

Microfluidic devices are widely used for biomedical applications based on microscopy or other optical detection methods. However, the materials commonly used for microfabrication typically have a high refractive index relative to water, which can create artifacts at device edges and limit applicability to applications requiring high-precision imaging or morphological feature detection. Here we present a soft lithography method to fabricate microfluidic devices out of MY133-V2000, a UV-curable, fluorinated polymer with low refractive index that is close to that of water (n = 1.33). The primary challenge in the use of this material (and fluorinated materials in general) is the low adhesion of the fluorinated material; we present several alternative fabrication methods we have tested to improve inter-layer adhesion. The close match between the refractive index of this material and aqueous solutions commonly used in biomedical applications enables fluorescence imaging at microchannel or other microfabricated edges without distortion. The close match in refractive index also enables quantitative phase microscopy imaging across the full width of microchannels without error-inducing artifacts for measurement of cell biomass. Overall, our results demonstrate the utility of low-refractive index microfluidics for biological applications requiring high-precision optical imaging.