Polymeric Microfluidic Devices Research Articles

Enhanced capture system for mesenchymal‑type circulating tumor cells using a polymeric microfluidic device 'CTC‑Chip' incorporating cell‑surface vimentin.

CellSearch, the only approved epithelial cell adhesion molecule (EpCAM)‑dependent capture system approved for clinical use, overlooks circulating tumor cells (CTCs) undergoing epithelial‑mesenchymal transition (EMT‑CTCs), which is considered a crucial subtype responsible for metastasis. To address this limitation, a novel polymeric microfluidic device 'CTC‑chip' designed for the easy introduction of any antibody was developed, enabling EpCAM‑independent capture. In this study, antibodies against EpCAM and cell surface vimentin (CSV), identified as cancer‑specific EMT markers, were conjugated onto the chip (EpCAM‑chip and CSV‑chip, respectively), and the capture efficiency was examined using lung cancer (PC9, H441 and A549) and colon cancer (DLD1) cell lines, classified into three types based on EMT markers: Epithelial (PC9), intermediate (H441 and DLD1) and mesenchymal (A549). PC9, H441 and DLD1 cells were effectively captured using the EpCAM‑chip (average capture efficiencies: 99.4, 88.8 and 90.8%, respectively) when spiked into blood. However, A549 cells were scarcely captured (13.4%), indicating that EpCAM‑dependent capture is not suitable for mesenchymal‑type cells. The expression of CSV tended to be higher in cells exhibiting mesenchymal properties and A549 cells were effectively captured with the CSV‑chip (72.4 and 88.4% at concentrations of 10 and 100 µg/ml, respectively) when spiked into PBS. When spiked into blood, the average capture efficiencies were 27.7 and 46.8% at concentrations of 10 and 100 µg/ml, respectively. These results suggest that the CSV‑chip is useful for detecting mesenchymal‑type cells and has potential applications in capturing EMT‑CTCs.

Improving assay feasibility and biocompatibility of 3D cyclic olefin copolymer microwells by superhydrophilic modification via ultrasonic spray deposition of polyvinyl alcohol

Sample partitioning is a crucial step towards digitization of biological assays on polymer microfluidic platforms. However, effective liquid filling into microwells and long-term hydrophilicity remain a challenge in polymeric microfluidic devices, impeding the applicability in diagnostic and cell culture studies. To overcome this, a method to produce permanent superhydrophilic 3-dimensional microwells using cyclic olefin copolymer (COC) microfluidic chips is presented. The COC substrate is oxidized using UV treatment followed by ultrasonic spray coating of polyvinyl alcohol solution, offering uniform and long-term coating of high-aspect ratio microfeatures. The coated COC surfaces are UV-cured before bonding with a hydrophobic pressure-sensitive adhesive to drive selective filling into the wells. The surface hydrophilicity achieved using this method remains unchanged (water contact angle of 9°) for up to 6 months and the modified surface is characterized for physical (contact angle & surface energy, morphology, integrity of microfeatures and roughness), chemical composition (FTIR, Raman spectroscopy) and coating stability (pH, temperature, time). To establish the feasibility of the modified surface in biological applications, PVA-coated COC microfluidic chips are tested for DNA sensing (digital LAMP detection of CMV), and biocompatibility through protein adsorption and cell culture studies (cell adhesion, viability, and metabolic activity). Kidney and breast cells remained viable for the duration of testing (7 days) on this modified surface, and the coating did not affect the protein content, morphology or quality of the cultured cells. The ultrasonic spray coated system, coating with 0.25 % PVA for 15 cycles with 0.12 A current after UV oxidation, increased the surface energy of the COC (naturally hydrophobic) from 22.04 to 112.89 mJ/m2 and improved the filling efficiency from 40 % (native untreated COC) to 94 % in the microwells without interfering with the biocompatibility of the surface, proving to be an efficient, high-throughput and scalable method of microfluidic surface treatment for diagnostic and cell growth applications.

Prediction of Burr Formation in End Micro Milling Poly methyl Methacrylate (PMMA) and Polycarbonate (PC) Substrates Using Convolutional Neural Network (CNN)

Polymer microfluidic device is growing in the fields of disease detection, drug synthesis, and environmental monitoring because of the benefits of the miniaturized platforms that provides rapid high-throughput analysis at small sample volumes. A machining technique called micro milling is employed in the manufacture of micro components (micro fluidic devices) such as poly methyl methacrylate (PMMA) or polycarbonate (PC). Micro milling has the advantage of being a quicker, more affordable, and more effective method for fabricating more complex structures. PMMA has been used as the substrate in this study for micro milling followed by factor analysis. This aim of this study is to understand the influence of each micro milling parameter to the surface quality. This paper includes 450 microscopic images of the micro-milling substrate by different parameters like spindle speed, depth of cut and Surface quality. The microscopic images are divided to test, train and Val dataset, using three datasets and a Convolutional Neural Network (CNN) is designed.

Polymeric Microfluidic Devices Fabricated Using Epoxy Resin for Chemically Demanding and Day-Long Experiments.

Polydimethylsiloxane (PDMS) is a widely used material in laboratories for fabricating microfluidic devices with a rapid and reproducible prototypingability, owing to its inherent properties (e.g., flexibility, air permeability, and transparency). However, the PDMS channel is easily deformed under pressures applied to generate flows because of its elasticity, which can affect the robustness of experiments. In addition, air permeability of PDMS causes the pervaporation of water, and its porous structure absorbs oil and even small hydrophobic molecules, rendering it inappropriate for chemically demanding or day-long experiments. In this study, we develop a rapid and reproducible fabrication method for polymer-based rigid microfluidic devices, using epoxy resin that can overcome the limitations of PDMS channels, which are structurally and chemically robust. We first optimize a high-resolution fabrication protocol to achieve convenient and repeatable prototyping of polymeric devices via epoxy casting using PDMS soft molds. In addition, we compare the velocity changes in PDMS microchannels by tracking fluorescent particles in various flows (~133 μL/min) to demonstrate the structural robustness of the polymeric device. Furthermore, by comparing the adsorption of fluorescent hydrophobic chemicals and the pervaporation through channel walls, we demonstrate the excellent chemical resistance of the polymeric device and its suitability for day-long experiments. The rigid polymeric device can facilitate lab-on-chip research and enable various applications, such as high-performance liquid chromatography, anaerobic bacterial culture, and polymerase chain reaction, which require chemically or physically demanding experiments.

Manufacturability and surface characterisation of polymeric microfluidic devices for biomedical applications

Generally, machining of polymeric microfluidic devices is a one-step manufacturing process. It is economical compared to lithography and can be used for batch production and rapid prototyping. However, surface properties are modified during machining due to the viscoelasticity property of polymers and the mechanical nature of fractures. In this present work, the manufacturing capability of the mechanical micromachining process of polymers has been explored. Surface characteristics like surface roughness, surface energy, and burr formation are investigated. Surface quality is chosen as a contributing factor for defining the manufacturing capability as it is one of the significant factors influencing the physics of fluid flow in microchannels. In the present work, several manufacturing methods, such as 3D printing, hot embossing, photolithography, and mechanical micromachining, were considered. The surface energy of various surfaces machined using the abovementioned methods is evaluated and compared. It has been observed that mechanical micromachining is the most suitable methods as they have less wettability with lower surface energy. Further investigations are carried out by machining microfluidic devices using polymethylmethacrylate (PMMA) and polycarbonate (PC) materials, as they are extensively used in biomedical applications. Surface roughness was measured on the PMMA and PC surfaces after milling. The surface roughness values and surface energies are used for evaluating the suitability of the machining process to fabricate microfluidic devices. Microfluidic devices with serpentine channels were machined on PMMA with a depth of 50 µm and width of 200 µm for evaluating inertial focusing in the channels. These devices were further evaluated for blood cell separation at different dilution rates. It is observed that PMMA is the preferable choice for fabricating microfluidic devices using mechanical micro-milling.

ИНТЕРПРЕТАЦИЯ РЕЗУЛЬТАТОВ КОЛИЧЕСТВЕННОГО ГЕНЕТИЧЕСКОГО АНАЛИЗА НА ОСНОВЕ АППРОКСИМАЦИИ КИНЕТИЧЕСКОЙ КРИВОЙ ПОЛИМЕРАЗНОЙ ЦЕПНОЙ РЕАКЦИИ В РЕАЛЬНОМ ВРЕМЕНИ

A quantitative polymerase chain reaction in real time (real time PCR) has been implemented on polymer microfluidic devices made of polycarbonate and polypropylene. The threshold cycle is determined based on the inflection point of the first-order logistic growth function, which reliably approximates the PCR curve in the absence of interfering factors, for example, the presence of bubbles in the reaction chamber. Use of statistical criteria (generalized Student's criterion, one-way analysis of variance) revealed the insignificance of the influence of the polymer type on the estimation of the position of the threshold cycle in terms of the previously selected algorithm for its search. When using an alternative algorithm for finding the threshold cycle based on the plotting of a tangent to the kinetic curve, in some cases there is a significant influence of the polymer type on the estimation of the position of the threshold cycle and, as a consequence, on the result of quantitative analysis. Proposed and discussed are algorithms for detecting bubbles in the reaction chamber based on the detection of a discrepancy in the measurement sequence associated with both estimates of the approximating dependence's parameters and the characteristics of the time series formed by approximation errors.

Fabrication of Polymer Microfluidics: An Overview.

Microfluidic platform technology has presented a new strategy to detect and analyze analytes and biological entities thanks to its reduced dimensions, which results in lower reagent consumption, fast reaction, multiplex, simplified procedure, and high portability. In addition, various forces, such as hydrodynamic force, electrokinetic force, and acoustic force, become available to manipulate particles to be focused and aligned, sorted, trapped, patterned, etc. To fabricate microfluidic chips, silicon was the first to be used as a substrate material because its processing is highly correlated to semiconductor fabrication techniques. Nevertheless, other materials, such as glass, polymers, ceramics, and metals, were also adopted during the emergence of microfluidics. Among numerous applications of microfluidics, where repeated short-time monitoring and one-time usage at an affordable price is required, polymer microfluidics has stood out to fulfill demand by making good use of its variety in material properties and processing techniques. In this paper, the primary fabrication techniques for polymer microfluidics were reviewed and classified into two categories, e.g., mold-based and non-mold-based approaches. For the mold-based approaches, micro-embossing, micro-injection molding, and casting were discussed. As for the non-mold-based approaches, CNC micromachining, laser micromachining, and 3D printing were discussed. This review provides researchers and the general audience with an overview of the fabrication techniques of polymer microfluidic devices, which could serve as a reference when one embarks on studies in this field and deals with polymer microfluidics.

Passive mold alignment for the fabrication of polymer through-holes using punching and double-sided hot embossing

Aligning two mold inserts is one of the most important steps in the punching of through-holes for polymer microfluidic devices. Significant misalignment of the mold inserts could reduce device functionality or allow for interference between mold inserts. Active and iterative methods require repetitive experiments, characterization, and mold adjustments making the process tedious. Passive set-up alignment using a temporary kinematic coupling can be an alternative to the active and iterative methods. To do this, the three v-grooves on the primary mold insert mate with the three spheres set in dimples on the complementary mold insert. Once the mold inserts are aligned and secured, the spheres are removed, and face-to-face contact between the mold inserts can be achieved for the molding operation. This aligns the primary and complementary mold inserts without any repeated measurements or adjustments. To validate the proposed design, primary and complementary mold inserts were fabricated with alignment joints and features to conduct a punching process. Prior to assembling the mold inserts to the thermal press for punching, they were pre-assembled to inspect the innate misalignment due to the machining of the mold inserts. Along the X-Axis, the X-magnitude (∆Xi) of the mean misalignment ranged from 2 to 7 µm and the Y-magnitude (∆Yi,) of the mean misalignment were from 7 to 13 µm. The X- and Y-magnitude (∆Xj and ∆Yj) of mean misalignment along the Y-Axis ranged from 1 to 4 µm, and 5–12 µm, respectively. The mold inserts were aligned and subsequently mounted to the thermal press. Punching was conducted on a polymer substrate Misalignment was the displacement of the center-point of a die hole impression from the center point of a through-hole. The X- and Y-magnitudes of the mean misalignment (∆Xk and ∆Yk) along the X-Axis ranged from 12 to 82 µm and 32–72 µm, respectively. The X- and Y-magnitudes of the misalignment (∆Xl and ∆Yl) along Y-Axis were 11–71 µm and 32–70 µm, respectively. The results of experiments showed that the proposed passive alignment method is applicable to the punching of through-holes for polymer microfluidic devices.

Prognostic impact of circulating tumor cells detected with the microfluidic "universal CTC-chip" for primary lung cancer.

Detecting rare circulating tumor cells (CTCs) in the bloodstream is extremely challenging. We had previously developed a novel polymeric microfluidic device, “CTC‐chip,” for capturing CTCs and have shown high capture efficiency in lung cancer cell lines by conjugating Abs against epithelial cell adhesion molecules (EpCAM). This study aimed to optimize the EpCAM‐chip and clarify the prognostic impact of CTCs in lung cancer patients. Of 123 patients with pathologically proven lung cancer, both progression‐free survival (P = .037) and cancer‐specific survival (P = .0041) were predominantly poor when CTCs were detected before treatment. After classification into surgical and chemotherapy groups, progression‐free survival was worse in CTC‐positive patients in both groups (surgery, P = .115; chemotherapy, P = .012), indicating that the detection of baseline CTCs is a risk factor for recurrence and progression. Furthermore, we recovered captured CTCs using micromanipulators and undertook mutation analysis using PCR. Thus, the EpCAM‐chip is a highly sensitive system for detecting CTCs that contributes to the prediction of recurrence and progression and enables genetic analysis of captured CTCs, which could open new diagnostic, therapeutic, and prognostic options for lung cancer patients.

Dielectric heating of highly corrosive and oxidizing reagents on a hybrid glass microfiber-polymer centrifugal microfluidic device.

Many assays necessitate the use of highly concentrated acids, powerful oxidizing agents, or a combination of the two. Although microfluidic devices offer vast potential for rapid analytical interrogation at the point-of-need (PON), they cannot escape the fundamental requirement for reagent compatibility. Worse, many innovative protocols have been developed that would represent a significant improvement to current field-forward practices within their respective disciplines, but adoption falters due to chemical incompatibility with challenging reagents. Polymeric centrifugal microfluidic devices meet many of the needs for accommodating complex chemical or biochemical protocols in a multiplexed and automatable format. Yet, they also struggle to accommodate highly reactive chemical components long term. In this work, we report on a simple and inexpensive reagent storage strategy that bypasses the typical complexity involved with integration of liquid reagents on microfluidic devices. Moreover, we demonstrate microdevice compatibility and operation after six months of corrosive reagent storage as well as post dielectric heating. This new strategy allows for storage of multiple highly corrosive and oxidative reagents simultaneously, enhancing the possibilities for multistep assay integration at the PON for a diverse array of applications. Successful detection after one week of corrosive reagent storage of an illicit drug and neurotransmitter metabolite, for forensic and clinical applications, is demonstrated. Furthermore, environmental sample preparation via microwave-assisted wet acid digestion is performed on-disc and integrated with downstream detection. Quantitative detection of a heavy metal in soil is achieved by way of on-disc calibration and found to be accurate within 2.4% compared to a gold standard reference (ICP-OES).

Laser-induced graphene ablated polymeric microfluidic device with interdigital electrodes for taste sensing application

On-site taste monitoring is important for human health, and widespread adoption requires low-cost, easy-to-fabricate technology and very precise portable equipment. The portability and high sensitivity of the device are regulated by the electrode configuration and, in turn, the fabrication techniques employed. In this context, herein, sensitive and specific electrical detection of five human gustative sensory tastes leveraging unique properties of graphene to realize optimized electrodes is presented. Herein, first, a Microfluidic device with integrated microchannel and Interdigitated electrodes (IDEs), based on a capacitive sensing mechanism, was prepared by the laser-induced graphene (LIG) technique. Electrochemical Impedance Spectroscopy (EIS) characterized the performance of the LIG-IDE microfluidic device. Under microfluidic conditions, the impedance change was linearly varying for the concentration of different chemicals in the range of 1–1000 ppm, and a minimum detection limit of 1 ppm was obtained. A comparison of the differences in capacitive response by LIG-IDE sensor for the five chemicals related to various tastes was also performed at different concentrations with respective real samples. This microfluidic taste sensor has the potential to provide low-cost, simple-to-integrate multi-functional point-of-care sensors for human sensory tastes, clinical, and environmental applications.

Wash-free operation of smartphone-integrated optical immunosensor using retroreflective microparticles

Herein, we introduce a smartphone-integrated immunosensor based on non-spectroscopic optical detection. Sedimentation of the retroreflector and gentle inversion of the microfluidic chip was chosen as biosensing principles to ensure minimal human involvement. To realize this, wash-free immunosensing was implemented on a polymeric microfluidic chip device fabricated for light signal penetration in retroreflection signal acquisition. Applying a transparent chip and passive modulation of retroreflectors enabled the minimization of human error during sensing. In addition, a retroreflection-detectable optical gadget was constructed for integration with the commercial smartphone. The gadget had an optical chamber that induced retroreflection by integration with a smartphone. When the micro-sized reflector, named the retroreflective Janus microparticle, reacted on the sensing surface, the incident light was retroreflected towards the image sensor and quantified by a smartphone-installed Android application package. The developed application package features include time-lapse image capture performed by manipulating LED flash and camera modules, and quantification of retroreflected signal counts by image processing of time-lapse images. With this platform, the user could independently commence optical signal processing without a complicated optical setup and running software on a PC, and sensitive and reproducible immunosensing results could be obtained. The applicability test for creatine kinase-myocardial band detection from the buffer to serum was conducted and presented a calibration curve of 0–1000 ng/mL within 1 h. With the developed system, we believe that the applicability of the platform in bioanalytical detection can be expanded.

Modular micropumps fabricated by 3D printed technologies for polymeric microfluidic device applications

In order to facilitate the implementation of microfluidic technology for rapid point-of-care analysis, there is a demand for self-powered microfluidics. The modular architecture of degas driven plug-and-play polymeric micropumps and microfluidic cartridges arose during last decade as a powerful strategy for autonomous flow control. So far, reported polymeric micropumps were made of poly-dimethyl siloxane and were fabricated by casting. In this work, we showed that the advantages of three-dimensional printing can greatly benefit the development of modular micropumps. In addition, micropumps were created with a geometry that cannot be manufactured with conventional techniques, making it easily assemblable to microfluidic devices. Four types of polymeric resins and three printing methods were used to create a set of functional micropumps. It was shown that the material and the design of the printed micropumps were related to their power, making them tuneable and programmable. Finally, as proof of concept, a self-powered colorimetric test for the detection of starch was demonstrated. Three-dimensional printed micropumps emerge as an innovative element in the field of self-powered microfluidics, which may be the key to develop integrated microsystems for several applications such as in rapid point-of-care analysis.

Fabrication Methods for Microfluidic Devices: An Overview.

Microfluidic devices offer the potential to automate a wide variety of chemical and biological operations that are applicable for diagnostic and therapeutic operations with higher efficiency as well as higher repeatability and reproducibility. Polymer based microfluidic devices offer particular advantages including those of cost and biocompatibility. Here, we describe direct and replication approaches for manufacturing of polymer microfluidic devices. Replications approaches require fabrication of mould or master and we describe different methods of mould manufacture, including mechanical (micro-cutting; ultrasonic machining), energy-assisted methods (electrodischarge machining, micro-electrochemical machining, laser ablation, electron beam machining, focused ion beam (FIB) machining), traditional micro-electromechanical systems (MEMS) processes, as well as mould fabrication approaches for curved surfaces. The approaches for microfluidic device fabrications are described in terms of low volume production (casting, lamination, laser ablation, 3D printing) and high-volume production (hot embossing, injection moulding, and film or sheet operations).

Recent innovations in cost-effective polymer and paper hybrid microfluidic devices.

Hybrid microfluidic systems that are composed of multiple different types of substrates have been recognized as a versatile and superior platform, which can draw benefits from different substrates while avoiding their limitations. This review article introduces the recent innovations of different types of low-cost hybrid microfluidic devices, particularly focusing on cost-effective polymer- and paper-based hybrid microfluidic devices. In this article, the fabrication of these hybrid microfluidic devices is briefly described and summarized. We then highlight various hybrid microfluidic systems, including polydimethylsiloxane (PDMS)-based, thermoplastic-based, paper/polymer hybrid systems, as well as other emerging hybrid systems (such as thread-based). The special benefits of using these hybrid systems have been summarized accordingly. A broad range of biological and biomedical applications using these hybrid microfluidic devices are discussed in detail, including nucleic acid analysis, protein analysis, cellular analysis, 3D cell culture, organ-on-a-chip, and tissue engineering. The perspective trends of hybrid microfluidic systems involving the improvement of fabrication techniques and broader applications are also discussed at the end of the review.

A simple and reversible glass-glass bonding method to construct a microfluidic device and its application for cell recovery.

Compared with polymer microfluidic devices, glass microfluidic devices have advantages for diverse lab-on-a-chip applications due to their rigidity, optical transparency, thermal stability, and chemical/biological inertness. However, the bonding process to construct glass microfluidic devices usually involves treatment(s) like high temperature over 400 °C, oxygen plasma or piranha solution. Such processes require special skill, apparatus or harsh chemicals, and destroy molecules or cells in microchannels. Here, we present a simple method for glass-glass bonding to easily form microchannels. This method consists of two steps: placing water droplets on a glass substrate cleaned by neutral detergent, followed by fixing a cover glass plate on the glass substrate by binding clips for a few hours at room temperature. Surface analyses showed that the glass surface cleaned by neutral detergent had a higher ratio of SiOH over SiO than glass surfaces prepared by other cleaning steps. Thus, the suggested method could achieve stronger glass-glass bonding via dehydration condensation due to the higher density of SiOH. The pressure endurance reached over 600 kPa within 6 h of bonding, which is sufficient for practical microfluidic applications. Moreover, by exploiting the reversibility of this bonding method, cell recoveries after cultivating cells in a microchannel were demonstrated. This new bonding method can significantly improve both the productivity and the usability of glass microfluidic devices and extend the possibility of glass microfluidic applications in future.

Ultrahigh throughput beehive-like device for blood plasma separation.

We report here a low-cost, rapid-prototyping, and beehive-like multilayer polymer microfluidic device for ultrahigh-throughput blood plasma separation. To understand the device physics and optimize the device structure, the effect of cross-sectional dimension and operational parameter on particle focusing behavior was explored using a single spiral microchannel device. Then, the blood plasma separation performance of the determined channel structure was validated using the blood samples with different hematocrits (HCTs). It was found that a high separation efficiency of 99% could be achieved using the blood sample with an HCT of 0.5% at a high throughput of 1mL/min. Finally, a multilayer microfluidic device with a novel beehive-like multiplexing channel arrangement was developed for ultrahigh-throughput blood plasma separation. The prototype device could be fabricated within ∼1 hour utilizing the laser cutting and thermal lamination methods. The total processing throughput could reach up to 72mL/min for 0.5% HCT sample with a plasma separation ratio close to 90%. Our device may hold potentials for the ultrahigh-throughput separation of blood plasma from large volume blood samples for downstream disease diagnosis.

Towards Highly Efficient Polymer Fiber Laser Sources for Integrated Photonic Sensors

Lab-on-a-Chip (LoC) devices combining microfluidic analyte provision with integrated optical analysis are highly desirable for several applications in biological or medical sciences. While the microfluidic approach is already broadly addressed, some work needs to be done regarding the integrated optics, especially provision of highly integrable laser sources. Polymer optical fiber (POF) lasers represent an alignment-free, rugged, and flexible technology platform. Additionally, POFs are intrinsically compatible to polymer microfluidic devices. Home-made Rhodamine B (RB)-doped POFs were characterized with experimental and numerical parameter studies on their lasing potential. High output energies of 1.65 mJ, high slope efficiencies of , and -lifetimes of ≥900 k shots were extracted from RB:POFs. Furthermore, RB:POFs show broad spectral tunability over several tens of nanometers. A route to optimize polymer fiber lasers is revealed, providing functionality for a broad range of LoC devices. Spectral tunability, high efficiencies, and output energies enable a broad field of LoC applications.

Closable Valves and Channels for Polymeric Microfluidic Devices.

This study explores three unique approaches for closing valves and channels within microfluidic systems, specifically multilayer, centrifugally driven polymeric devices. Precise control over the cessation of liquid movement is achieved through either the introduction of expanding polyurethane foam, the application of direct contact heating, or the redeposition of xerographic toner via chloroform solvation and evaporation. Each of these techniques modifies the substrate of the microdevice in a different way. All three are effective at closing a previously open fluidic pathway after a desired unit operation has taken place, i.e., sample metering, chemical reaction, or analytical measurement. Closing previously open valves and channels imparts stringent fluidic control—preventing backflow, maintaining pressurized chambers within the microdevice, and facilitating sample fractionation without cross-contamination. As such, a variety of microfluidic bioanalytical systems would benefit from the integration of these valving approaches.

Poly-L-histidine coated microfluidic devices for bacterial DNA purification without chaotropic solutions.

We present a disposable polymeric microfluidic device capable of reversibly binding and purifying Salmonella DNA through solid phase extraction (SPE). The microfluidic channels are first oxygen plasma treated and simultaneously micro-nanotextured, and then functionalized with amine groups via modification with L-histidine or poly-L-histidine. L-Histidine and poly-L-histidine bind on the plasma treated chip surface, and are not detached when rinsing with DNA purification protocol buffers. A pH-dependent protocol is applied on-chip to purify Salmonella DNA, which is first bound on the protonated amines at a pH (5.0) lower than their pKa of surface amine-groups which is 6.0 and then released at a pH higher than the pKa value (10.5). It was found that modification with poly-L-histidine resulted in higher surface density of amine groups onto microfluidic channel. Using the chip modified with poly-L-histidine, high recovery efficiency of at least 550ng of isolated Salmonella DNA as well as DNA purification from Salmonella cell lysates corresponding to less than 5000 cells or 0.026ng of Salmonella DNA was achieved. The protocol developed does not require ethanol or chaotropic solutions typically used in DNA purification, which are known inhibitors for downstream operations such as polymerase chain reactions (PCR) and which can also attack some polymeric microfluidic materials. Therefore, the microfluidic device and the related protocol hold promise for facile incorporation in microfluidics and Lab-on-a-chip (LOC) platforms for pathogen detection or in general for DNA purification.