PMMA Channel Research Articles

A novel microfluidics PMMA/paper hybrid bioimmunosensor for laser-induced fluorescence detection in the determination of alpha-fetoprotein from serum

Low loss and high capture efficiency of target samples are prerequisites for sensitive detection by fluorescence immunosensors. For quantitative and ultrasensitive detection of alpha-fetoprotein (AFP), we designed a novel microfluidics pump-free PMMA/paper hybrid immunosensor. Here, the 2D planar structure of the detection area of the plastic microfluidic chip is improved to a 3D spatial structure, which increases the number of capture antibodies immobilized and the cross-section area of the “intercept” target protein. PMMA channels efficiently transport target proteins. The paper-based, three-dimensional detection area not only increases the amount of immobilization of the captured antibody but also improves the contact probability between the captured antibody and the target protein. This greatly improves the efficiency of immune binding. A laser-induced fluorescence detector is applied to detect the target protein on the paper-based detecting unit. Under optimal conditions, the immunosensor ensures that the reaction time is 12 min and the residual liquid is only 6.1% of the original volume, achieving ultra-sensitive detection of AFP in the range of 0.01 ng/mL to 100 ng/mL with a limit of quantitation (LOQ) as low as 4.5 pg/mL. The recoveries for AFP ranged from 96.6% to 101.5%, which means the hybrid microfluidics chip is reliable and has great potential for early screening.

Polymeric micro gas preconcentrators based on graphene oxide and carbon nanopowder adsorbents for gas detection application

In this study, an application of novel polymer-based microfluidic channels for preconcentration and detection of methane gas is investigated. Poly (methyl methacrylate) (PMMA) microfluidic channel is filled by graphene oxide (GO) as a new adsorbent for thermal preconcentration and carbon nanopowder is loaded into a polydimethylsiloxane (PDMS) microfluidic channel. The effective microfluidic channels area is 14 mm × 10 mm. The laser cutting and etching followed by thermally-solvent bonding process are used for PMMA microfluidic channel fabrication. Also, PDMS microfluidic channel is fabricated by SU-8 molding technique, lithography process, and oxygen plasma bonding on glass. SEM, Raman spectroscopy, and FTIR characterizations are carried out for investigation of the synthesized GO. The amount of electrical power consumption of devices is also investigated by simulation and experiment. The performance of both micro preconcentrators (μPCs) are compared through the similar experimental tests which exhibit the suitable performance of fabricated μPCs with proper repeatability for preconcentration purposes. The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated for both microfluidic channels and their optimized values were obtained. According to the lower desorption temperature of GO, despite its slightly lower response (10.41) compared to carbon nanopowder μPCs (12.34), due to its almost half power consumption (0.375 W in comparison with 0.8 W), it can be an appropriate candidate for preconcentration applications. PMMA and PDMS-based microfluidic channels show promising choices in the preconcentration application for the adsorbents with low desorption temperatures. As a result, PMMA as a low-cost material with a simple fabrication process in microchannels and GO as the novel adsorbent material can be suitable candidates in low working temperature and rapid preconcentration devices. • Microfluidic channels are fabricated based on poly (methyl methacrylate) (PMMA), and polydimethylsiloxane (PDMS) • Graphene oxide (GO) and carbon nanopowder are used as the adsorbent materials for PMMA and PDMS microfluidic channels, respectively. • The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated to achieve the optimized values. • The power consumption and temperature distribution of heater are studied through the simulation.

Optical Reflection from Unforbidden Diffraction of Block Copolymer Templated Gyroid Films.

We present material substitutions and optical characterization of block copolymer (BCP)-templated gyroid structures that are obtained from a volume-asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). In addition to the structural analyses reported earlier, we elucidate the optical responses to the nonaffine gyroid planes, in which the PMMA channels are complexed with Al2O3 by sequential infiltration synthesis and the organic components are further eliminated to produce an inorganic air-Al2O3 gyroid film. Grazing-incidence small-angle X-ray scattering measurements show that three-dimensional gyroid lattices are retained in both in-plane and out-of-plane directions through these material substitution processes. Our BCP-templated gyroid films respond to the middle UV wavelength from 200 to 300 nm, and peculiar optical reflectance peaks correlate with the unforbidden {110} diffraction spots. Together with the red- and blue-shifts of the reflectance peaks by the component substitutions, the air-Al2O3 gyroid structure reveals the high-amplitude spectrum due to the large refractive-index difference between channel and matrix.

A reusable PMMA/paper hybrid plug-and-play microfluidic device for an ultrasensitive immunoassay with a wide dynamic range

Conventional colorimetric enzyme-linked immunosorbent assay (ELISA) is a time-consuming laboratory assay that is not very sensitive and consumes a large amount of samples. Herein, the development of a reusable, cost-effective, and eco-friendly poly(methyl methacrylate) (PMMA)/paper hybrid plug-and-play (PnP) device for high-sensitivity immunoassay by analyte enrichment and efficient passing-through washing has been reported. The PMMA device has multiple slots where a pre-patterned paper substrate can be inserted. The sample flows back-and-forth through a low-cost, 3D paper substrate within the PMMA channels, thereby enhancing the amount of analyte adsorbed and dramatically increasing the sensitivity while decreasing the assay time. After the enrichment assay, the paper substrate can simply be pulled out of the device, and the results can be qualitatively viewed with the naked eye or scanned through a simple desktop scanner for quantitative analysis. The paper substrate can be replaced with a new substrate so that the device can be reused. The limits of detection (LODs) of 200 pg/mL for immunoglobulin G (IgG) and 270 pg/mL for hepatitis B surface antigen (HBsAg) were obtained. This IgG assay is at least 10 times more sensitive than commercial ELISA kits. In addition, the PnP ELISA exhibited a significant increase in the linear dynamic range from 3 orders of magnitude in a common paper-based device to a wide range of six orders of magnitude in the PnP hybrid device. This reusable PnP device has great potential for the low-cost yet high-sensitivity detection of infectious diseases, cancers, and other important biomolecules.

Monodisperse water-in-oil-in-water emulsions generation for synthesising alginate hydrogel microspheres via locally hydrophobic modification to PMMA microchannels

The inherent hydrophobic poly(methyl methacrylate) (PMMA) will show hydrophilic property due to the impurity or fabrication process in the practical use, which limits its application in water-in-oil (W/O) emulsions, e.g. hydrogel microparticles synthesised using water-in-oil-in-water (W/O/W) emulsions as precursors. In this paper, we propose an easy-to-use method for hydrophobic modification of PMMA channels by coating liquid poly(dimethylsiloxane) (PDMS) at arbitrarily chosen locations, thus making the hydrophilic PMMA channel wall hydrophobic and increasing the water contact angle from 67.1±1.3° to 108.7±1.1°. Monodisperse W/O/W emulsions can be easily produced using the modified PMMA devices, whereas, only water plug, which sticking to the channel walls, can be formed even with the aid of surfactant. As a verification, hydrogel microspheres were synthesised using W/O/W emulsions as precursors. Furthermore, fluorescent microparticles were encapsulated in alginate hydrogel microspheres to demonstrate the cells encapsulation process, which will be benefit to cells culture and analysis.

A simple, openable and electroosmotic flow-free PMMA chip for electrophoretic titration of moving reaction boundary

Poor control of electroosmotic flow (EOF) often occurs in chip electrophoretic titration (ET) of moving reaction boundary due to both absence of PMMA channel coating and coexistence of acid-base. Also, chip ET still suffers from low reproducibility, instability, disposability and high cost as well. To address these issues, a reusable ET chip (60mm×60mm×5.0mm) was designed via an upper PMMA sheet, a middle silicon membrane and a lower sheet. In the upper sheet, enlarged channel (500μm×200μm×12mm) was fabricated and linked to the anodic and cathodic wells. The upper sheet, middle membrane and lower sheet could be easily assembled together in 20s as an ET chip of supporting 1.4kg tension force, indicating good mechanical stability. Regeneration and reassembling of chip could be finished in 50s. EOF could be simply suppressed by mass chemical cross-linked polyacrylamide gel or physical agarose gel in the enlarged channel. The EOF-free chip could be well used for: (i) acid-base ET; (ii) EOF monitoring; (iii) pKa determination; (iv) protein content analysis. The EOF-free chip showed the following merits: (i) 98% success rate in contrast to less than 30% in normal channels (80μm×20μm×5.0mm); (ii) more than 30 times reuse, indicating reusability and low cost; (iii) less than 10% of relative standard deviation, suggesting fair stability; and (iv) good recovery and accuracy. The developed chip makes great advancement towards real use of chip in acid- base titration, EOF monitoring, pKa determination and protein content analysis.

Ultra-monodisperse droplet formation using PMMA microchannels integrated with low-pulsation electrolysis micropumps

This paper presents a method for stable and reliable generation of ultra-monodisperse oil-in-water (O/W) droplets using poly(methyl methacrylate) (PMMA) microchannels integrated with three low-pulsation electrolysis micropumps (EMPs) on a chip. The EMPs are proposed to be driven by constant electric current with the optimized interdigital electrodes to achieve a smaller pulsations in the output flow. The flow pulsations are characterized via a fluidic comparator, and the results show that smaller pulsations in the flow rates can be achieved, thus polydispersity of the generated droplets is lowered. Both dripping and alternating droplets generation are demonstrated. In dripping scenario, highly uniform droplets ranging from 465μm to 360μm with a polydispersity index (σ) value between 1.3% and 2.6% are achieved. In alternating scenario, monodisperse droplets ranging from 441μm to 342μm with σ value between 1.8% and 2.8% are also achieved. Based on the proposed modular assembly process, the PMMA channels and/or the substrate can be easily replaced and re-assembled to realize other functions such as flow rate measurement or flow pulsations characterization. In all, the proposed microfluidics platform provides robust ultra-monodisperse droplet generation capability which could facilitate the development of high-performance droplet-based microsystems.

A high performance microfluidic analyser for phosphate measurements in marine waters using the vanadomolybdate method

We report a high performance autonomous analytical system based on the vanadomolybdate method for the determination of soluble reactive phosphorus in seawater. The system combines a microfluidic chip manufactured from tinted poly (methyl methacrylate) (PMMA), a custom made syringe pump, embedded control electronics and on-board calibration standards. This “lab-on-a-chip” analytical system was successfully deployed and cross-compared with reference analytical methods in coastal (south west England) and open ocean waters (tropical North Atlantic). The results of the miniaturized system compared well with a reference bench-operated phosphate auto-analyser and showed no significant differences in the analytical results (student’s t-test at 95% confidence level). The optical technology used, comprising of tinted PMMA and polished fluidic channels, has allowed an improvement of two orders of magnitude of the limit of detection (52nM) compared to currently available portable systems based on this method. The system has a wide linear dynamic range 0.1–60μM, and a good precision (13.6% at 0.4μM, n=4). The analytical results were corrected for silicate interferences at 0.7μM, and the measurement frequency was configurable with a sampling throughput of up to 20 samples per hour. This portable micro-analytical system has a low reagent requirement (340μL per sample) and power consumption (756J per sample), and has allowed accurate high resolution measurements of soluble reactive phosphorus in seawater.

Analytical study of a microfludic DNA amplification chip using water cooling effect

A novel continuous-flow polymerase chain reaction (PCR) chip has been analyzed in our work. Two temperature zones are controlled by two external controllers and the other temperature zone at the chip center is controlled by the flow rate of the fluid inside a channel under the glass chip. By employing a water cooling channel at the chip center, the sequence of denaturation, annealing, and extension can be created due to the forced convection effect. The required annealing temperature of PCR less than 313 K can also be demonstrated in this chip. The Poly(methyl methacrylate) (PMMA) cooling channel with the thin aluminum cover is utilized to enhance the temperature uniformity. The size of this chip is 76 mm × 26 mm × 3 mm. This device represents the first demonstration of water cooling thermocycling within continuous-flow PCR microfluidics. The commercial software CFD-ACE+(TM) is utilized to determine the distances between the heating assemblies within the chip. We investigate the influences of various chip materials, operational parameters of the cooling channel and geometric parameters of the chip on the temperature uniformity on the chip surface. Concerning the temperature uniformity of the working zones and the lowest temperature at the annealing zone, the air gap spacing of 1 mm and the cooling channel thicknesses of 1 mm of the PMMA channel with an aluminum cover are recommended in our design. The hydrophobic surface of the PDMS channel was modified by filling it with 20 % Tween 20 solution and then adding bovine serum albumin (BSA) solution to the PCR mixture. DNA fragments with different lengths (372 bp and 478 bp) are successfully amplified with the device.

Surface Activation of Poly(Methyl methacrylate) by Plasma Treatment: Stable Antibody Immobilization for Microfluidic Enzyme-Linked Immunosorbent Assay

With the aim of obtaining stable antibody immobilization on the poly(methyl methacrylate), PMMA channel surface, PMMA substrates were activated with O2 plasma treatment to introduce surface polar groups on it. The plasma-treated PMMA surfaces were characterized using water contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). It was observed that plasma treatment significantly improved the surface wettability with changing surface chemistry and topography. The strategy of immobilization of a model antibody, anti-goat IgG on plasma-treated PMMA involved two steps. First the plasma-treated PMMA was functionalized with (3-aminopropyl)thriethoxy silane, APTES off-chip which facilitated covalent capturing of antibody via a crosslinking agent in the inner surface of PMMA channel in the second step. The antibody immobilization on plasma-treated PMMA was also confirmed using AFM, XPS, and fluorescence microscopy. The anti-IgG covalently captured on channel surface was evaluated with sandwich ELISA protocol on-chip using fluorescence microscopy. The observed results demonstrate that this technique could be extended to integrate the current diagnostic techniques into the plastic chip for important biomarker diagnosis.

Electromagnetically-Actuated Reciprocating Pump for High-Flow-Rate Microfluidic Applications

This study presents an electromagnetically-actuated reciprocating pump for high-flow-rate microfluidic applications. The pump comprises four major components, namely a lower glass plate containing a copper microcoil, a middle PMMA plate incorporating a PDMS diaphragm with a surface-mounted magnet, upper PMMA channel plates, and a ball-type check valve located at the channel inlet. When an AC current is passed through the microcoil, an alternating electromagnetic force is established between the coil and the magnet. The resulting bi-directional deflection of the PDMS diaphragm causes the check-valve to open and close; thereby creating a pumping effect. The experimental results show that a coil input current of 0.4 A generates an electromagnetic force of 47 mN and a diaphragm deflection of 108 μm. Given an actuating voltage of 3 V and a driving frequency of 15 Hz, the flow rate is found to be 13.2 mL/min under zero head pressure conditions.

Aligned Growth of Gold Nanorods in PMMA Channels: Parallel Preparation of Nanogaps

We demonstrate alignment and positional control of gold nanorods grown in situ on substrates using a seed-mediated synthetic approach. Alignment control is obtained by directing the growth of spherical nanoparticle seeds into nanorods in well-defined poly(methyl methacrylate) nanochannels. Substrates with prepatterned metallic electrodes provide an additional handle for the position of the gold nanorods and yield nanometer-sized gaps between the electrode and nanorod. The presented approach is a novel demonstration of bottom-up device fabrication of multiple nanogap junctions on a single chip mediated viain situ growth of gold nanorods acting as nanoelectrodes.

Solvent bonding of poly(methyl methacrylate) microfluidic chip using phase‐changing agar hydrogel as a sacrificial layer

In this report, a solvent bonding method based on phase-changing agar hydrogel has been developed for the fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Prior to bonding, the channels and the reservoir ports on PMMA channel plates were filled with molten agar hydrogel that could gelate to form solid sacrificial layers at room temperature. Subsequently, PMMA cover sheets were covered on the channeled plates and 1,2-dichlororethane was applied to the interspaces between them. The agar hydrogel in the channels could prevent the bonding solvent and the softened surface of the PMMA cover sheets from filling in the channels. After solvent bonding, the agar hydrogel in the channels and the reservoir ports was melted and removed under pressure. The sealed channels in the complete microchips had been examined by an optical microscope and a scanning electron microscope. The results indicated that high-quality bonding was achieved at room temperature. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of three cations in combination with contactless conductivity detection.

Open-channel chip-based solid-phase extraction combined with inductively coupled plasma-mass spectrometry for online determination of trace elements in volume-limited saline samples

In this study, we used an automated online chip-based solid-phase extraction (SPE)–inductively coupled plasma-mass spectrometry (ICP-MS) system for analyzing trace elements in small-volume saline samples (∼15 μL). The proposed method involved the adsorption of trace metal ions in the interior of a functionalized poly(methyl methacrylate) (PMMA) channel in order to separate these ions from saline matrices. The adsorption of transition metal ions was presumably dominated by the surface complexation between the carboxylate moieties in the interior of the PMMA channel and the metal ions, which facilitated the formation of metal–carboxylate complexes. The components of the proposed online analytical system used for the simultaneous detection of multiple trace metals in saline samples involved microdialysis (MD) sampling, an established chip-based SPE procedure, and ICP-MS. The SPE–ICP-MS hyphenated system was optimized, and then, the analytical reliability of this system was further confirmed by using it to analyze the certified reference materials—SRM 2670 (human urine) and SRM 1643e (artificial saline water). The satisfactory analytical results indicated that the proposed on-chip SPE device could be readily used as an interface for coupling the MD probe with the ICP-MS system. The dramatically reduced consumption of chemicals and “hands-on” manipulations enabled the realization of a simplified and relatively clean procedure with extremely low detection limits in the range of 5.86–76.91 ng L −1 for detecting Mn, Co, Ni, Cu, and Pb in 15-μL samples by ICP-MS. The effectiveness of an online MD–chip-based SPE–ICP-MS technique for continuous monitoring of trace elements in a simulated biological system was also demonstrated. To the best of our knowledge, this is the first paper to report the direct exploitation of a PMMA chip as an SPE adsorbent for online sample pretreatment and trace metal preconcentration prior to ICP-MS measurement.

A spring‐driven press device for hot embossing and thermal bonding of PMMA microfluidic chips

A novel spring-driven press device was designed and manufactured for hot embossing and thermal bonding of PMMA microfluidic chips in this work. This simple device consisted of two semi-cylinder silicone rubber press heads, three steel clamping plates, and three compression springs that were assembled together using two screw bolts and two butterfly nuts. The three springs were clamped between the upper and the middle clamping plates, whereas the two press heads were assembled between the middle and the lower clamping plates. After an epoxy template covered by a PMMA plate or a PMMA channel plate together with a cover were sandwiched between two microscopic glass slides for embossing or bonding, respectively, they were clamped between the two elastic press heads of the press device by fastening the screw nuts on the upper clamping plate. Because the convex press heads applied pressure along the middle line of the glass slides, they would deform resulting in a negative pressure gradient from the middle to the sides so that air bubbles between the sandwiched parts could be squeezed out during embossing and bonding processes. High-quality PMMA microfluidic chips were prepared by using this unique device and were successfully applied in the electrophoretic separation of several cations.

Low-cost fabrication of poly(methyl methacrylate) microchips using disposable gelatin gel templates

A simple method based on disposable gelatin gel templates has been developed for the low-cost fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Gelatin was dissolved in glycerol aqueous solution under heat to prepare a thermally reversible impression material. The molten gel was then sandwiched between a glass plate and a SU-8 template bearing negative relief of microstructure. After cooling, the negative SU-8 template could be easily separated from the solidified gelatin gel and a layer of gelatin template bearing positive relief of the microstructure was left on the glass plate. Subsequently, prepolymerized methyl methacrylate molding solution containing a UV-initiator was sandwiched between the gel template and a PMMA plate and was allowed to polymerize under UV light to fabricate PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers using plasticizer-assisted thermal bonding at 90 degrees C. Gelatin gel template can be mass-produced and will find application in the mass production of PMMA microchips at low cost. The prepared microfluidic microchips have been successfully employed in the capillary electrophoresis analysis of several ions in connection with contactless conductivity detection.

Use of directly molded poly(methyl methacrylate) channels for microfluidic applications

A direct molding method for creating a homogeneous, polymer microfluidic channel is presented. By utilizing capillary rise and subsequent absorption of poly(methyl methacrylate) (PMMA) solution into a solvent-permeable poly(dimethyl siloxane) (PDMS) mold, various circular or elliptic polymer microchannels were fabricated without channel bonding and additional surface modification processes. In addition, the channel diameter was tunable from several micrometres to several hundreds of micrometres by controlling concentration and initial amount of polymer solution for a given PDMS mold geometry. The molded PMMA channels were used for two applications: blocking absorption of Rhodamine B dye and constructing artificial endothelial cell-cultured capillaries. It was observed that the molded PMMA channels effectively prevented absorption and diffusion of Rhodamine molecules over 5 h time span, demonstrating approximately 40 times higher blocking efficiency as compared to porous PDMS channels. Also, calf pulmonary artery endothelial cells (CPAEs) adhered, spread, and proliferated uniformly within the molded microchannels to form near confluency within 3 days and remained viable at day 6 without notable cell death, suggesting high biocompatibility and possibility for emulating in vivo-like three-dimensional architecture of blood vessels.

Fabrication of PMMA microfluidic chips using disposable agar hydrogel templates

A novel method based on disposable agar hydrogel temples have been developed for the fabrication of PMMA microfluidic chips. Molten agar hydrogel was sandwiched between a glass plate and a PMMA template bearing negative relief of microstructure. After cooling, the negative PMMA template could be easily separated from the solidified agar hydrogel and a layer of agar hydrogel temple bearing high-fidelity positive relief of the microstructure was left on the glass plate. Prepolymerized methyl methacrylate molding solution containing ultraviolet-initiator was subsequently sandwiched between the agar hydrogel template and a PMMA plate and was allowed to polymerize under ultraviolet light to fabricate the PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of several ions in connection with contactless conductivity detection.

Plasticizer-assisted bonding of poly(methyl methacrylate) microfluidic chips at low temperature

As an important phthalate plasticizer, dibutyl phthalate (DBP) was employed to decrease the bonding temperature of poly(methyl methacrylate) (PMMA) microfluidic chips in this work based on the fact that it can lower the glass transition temperature of PMMA. The channel plates of the PMMA microchips were fabricated by the UV-initiated polymerization of prepolymerized methyl methacrylate between a silicon template and a PMMA plate. Prior to bonding, DBP solution in isopropanol was coated on PMMA covers. When isopropanol in the coating was allowed to evaporate in air, DBP was left on the PMMA covers. Subsequently, the DBP-coated covers were bonded to the PMMA channel plates at 90 degrees C for 10min under pressure. The channels in the complete microchips had been examined by optical microscope and scanning electron microscope. The results indicated that high quality bonding was achieved below the glass transition temperature of PMMA ( approximately 105 degrees C). The performance of the PMMA microfluidic chips sealed by plasticizer-assisted bonding has been demonstrated by separating and detecting ionic species by capillary electrophoresis in connection with contactless conductivity detection.

Carbohydrate−Protein Interactions Investigated on Plastic Chips Statically Coated with Hydrophobically Modified Hydroxyethylcellulose

We developed a novel method for rapid screening of carbohydrate-protein interactions using poly(methyl methacrylate) (PMMA) channels statically coated with hydrophobically modified hydroxyethylcellulose (HM-HEC). We found that a self-assembled monolayer (SAM) of HM-HEC on a PMMA surface intact by water allows rapid and reproducible separations of glycan samples using a 20 mM phosphate without HM-HEC. The underlying mechanism for dynamic and static coatings on the PMMA surface is discussed. Simultaneous analysis of the molecular interaction between a complex mixture of carbohydrates from alpha1-acid glycoprotein and proteins has been successfully achieved in PMMA channels statically coated with a SAM of HM-HEC.