PMMA Channel Research Articles

Sulphur dioxide plasma modification on poly(methyl methacrylate) for fluidic devices

Abstract We developed a sulphur dioxide plasma modification on a poly(methyl methacrylate) (PMMA) material for fluidic electrophoresis devices. The inner surface of the PMMA channel of a chip was modified by using sulphur dioxide plasma treatment. Contact angle measurements indicated that the buffer solutions were able to fill the capillary because of the hydrophilic property of the internal surface of the chip. XPS analysis indicated that the sulphur dioxide plasma treatment introduced a negative charge originating from the dissociation of the hydrogen atoms of sulphonic groups. Since this introduced a negative charge originating from strong acid sulphonic groups onto the surface of the channel, the electroosmotic flow (EOF) was observed to be large (∼7 × 10−4 m2 V−1 s−1) and stable over a wide range of pH (4–10). The chip was fabricated by using plastic injection moulding methods for enabling the mass fabrication and disposable use of chips. The separation method is based on the net electric charge of the material, which enables the separation of identical samples on the basis of both isoelectric points and molecular weight. Two synthetic peptides with similar isoelectric points and molecular weights but different net charges were selected as model protein samples for the separation. The sample peptides were detected under fluorescence microscopy. The resulting electropherograms obtained by using the sulphur dioxide plasma-treated PMMA chip demonstrated that the two peptides were separated and that the migration time of the peptides was correlated with the net charge.

Investigation of birefringence in PMMA channel waveguides inscribed with DUV radiation

We studied both experimentally and numerically the spectral behavior of modal birefringence in channel waveguides inscribed in PMMA by DUV illumination. The measurements of birefringence were carried out using a spectral interference method for different waveguide widths, respectively 2, 3, 4, 5, 6 µm, which were inscribed using 2 J cm−2 and 3 J cm−2 irradiation doses. We have also modeled the spectral dependence of birefringence related only to waveguide geometry using the finite element method. High discrepancy was observed between measured and calculated birefringence. This is related to the fact that numerical analysis accounts only for the so-called geometrical birefringence induced by an asymmetry of the waveguide, while in measurements the overall modal birefringence relates to both the geometrical and the material effect. Our measurement results indicate that the contribution of the material birefringence in the analyzed waveguides may reach up to 3 × 10−4 in a short wavelength range.

A Sol–Gel‐Modified Poly(methyl methacrylate) Electrophoresis Microchip with a Hydrophilic Channel Wall

A sol-gel method was employed to fabricate a poly(methyl methacrylate) (PMMA) electrophoresis microchip that contains a hydrophilic channel wall. To fabricate such a device, tetraethoxysilane (TEOS) was injected into the PMMA channel and was allowed to diffuse into the surface layer for 24 h. After removing the excess TEOS, the channel was filled with an acidic solution for 3 h. Subsequently, the channel was flushed with water and was pretreated in an oven to obtain a sol-gel-modified PMMA microchip. The water contact angle for the sol-gel-modified PMMA was approximately 27.4 degrees compared with approximately 66.3 degrees for the pure PMMA. In addition, the electro-osmotic flow increased from 2.13x10(-4) cm2 V(-1) s(-1) for the native-PMMA channel to 4.86x10(-4) cm2 V(-1) s(-1) for the modified one. The analytical performance of the sol-gel-modified PMMA microchip was demonstrated for the electrophoretic separation of several purines, coupled with amperometric detection. The separation efficiency of uric acid increased to 74,882.3 m(-1) compared with 14,730.5 m(-1) for native-PMMA microchips. The result of this simple modification is a significant improvement in the performance of PMMA for microchip electrophoresis and microfluidic applications.

CE chips fabricated by injection molding and polyethylene/thermoplastic elastomer film packaging methods

This study presents a new packaging method using a polyethylene/thermoplastic elastomer (PE/TPE) film to seal an injection-molded CE chip made of either poly(methyl methacrylate) (PMMA) or polycarbonate (PC) materials. The packaging is performed at atmospheric pressure and at room temperature, which is a fast, easy, and reliable bonding method to form a sealed CE chip for chemical analysis and biomedical applications. The fabrication of PMMA and PC microfluidic channels is accomplished by using an injection-molding process, which could be mass-produced for commercial applications. In addition to microfluidic CE channels, 3-D reservoirs for storing biosamples, and CE buffers are also formed during this injection-molding process. With this approach, a commercial CE chip can be of low cost and disposable. Finally, the functionality of the mass-produced CE chip is demonstrated through its successful separation of phiX174 DNA/HaeIII markers. Experimental data show that the S/N for the CE chips using the PE/TPE film has a value of 5.34, when utilizing DNA markers with a concentration of 2 ng/microL and a CE buffer of 2% hydroxypropyl-methylcellulose (HPMC) in Tris-borate-EDTA (TBE) with 1% YO-PRO-1 fluorescent dye. Thus, the detection limit of the developed chips is improved. Lastly, the developed CE chips are used for the separation and detection of PCR products. A mixture of an amplified antibiotic gene for Streptococcus pneumoniae and phiX174 DNA/HaeIII markers was successfully separated and detected by using the proposed CE chips. Experimental data show that these DNA samples were separated within 2 min. The study proposed a promising method for the development of mass-produced CE chips.

Analysis and measurements of mixing in pressure-driven microchannel flow

The mixing phenomena for two fluid streams in pressure-driven rectangular microchannels are analyzed and directly compared with the measurements of mixing intensity for a wide range of aspect ratio (width/depth = 1–20). In the analysis, the three-dimensional transport equation for species mixing was solved using the spectral method in a dimensionless fashion covering a large regime of the normalized downstream distance. The analysis reveals the details of non-uniform mixing process, which originates from the top and bottom walls of the channel and stretches out toward the center of the channel, and its transition to uniformity. Employing different length scales for the non-uniform and uniform mixing regimes, the growth of mixing intensity can be expressed in a simple relationship for various aspect ratios in the large range. The mixing experiments were carried out on silicon- and poly(methyl methacrylate) (PMMA)-based T-type micromixers utilizing fluids of pH indicator (in silicon channel) and fluorescent dye (in PMMA channel) to evaluate the mixing intensity based on flow visualization images. Using conventional microscopes, the experiments demonstrate the mixing intensity as a power law of the stream velocity for all the microfluidic channels tested. The variations of measured mixing intensity with the normalized downstream distance are found in favorable agreement with the numerical simulations. The comparison between the experiments and simulations tells the capabilities and limitations on the use of conventional microscopes to measure the mixing performance.

Hybrid Dynamic Coating with n-Dodecyl β-d-Maltoside and Methyl Cellulose for High-Performance Carbohydrate Analysis on Poly(methyl methacrylate) Chips

Hybrid dynamic coating using n-dodecyl beta-d-maltoside (DDM) and methyl cellulose (MC) has been developed for suppression of analyte adsorption and electroosmotic flow (EOF) in a poly(methyl methacrylate) (PMMA) channel. The adsorption of APTS-labeled sugars in a PMMA channel was obviously suppressed with DDM dynamic coating; however, EOF was reduced only by a factor of approximately 25%, resulting in irreproducible separations. In contrast, both analyte adsorption and EOF in a PMMA channel were efficiently minimized with MC coating; however, concentrated MC above 0.3% was required to achieve high-performance separations, which greatly increased viscosity of the solution and caused difficulties during buffer loading and rinsing. In addition, n-dodecyltrimethylammonium chloride did not show observable effects on reducing analyte adsorption, although it has the same hydrophobic alkyl chain as DDM. These results strongly indicated that the polysaccharide moiety of surface modifiers has a specific affinity to surface charges and is crucial to achieving efficient and stable dynamic coating on the PMMA surface. Hybrid dynamic coating with 0.25% DDM and 0.03% MC was found to minimize both analyte adsorption and EOF in a PMMA channel to a negligible level, while still keeping a low viscosity of the solution. High-speed and high-throughput profiling of the N-linked glycans derived from alpha1-acid glycoprotein, fetuin, and ribonuclease B was demonstrated in both single-channel and 10-channel PMMA chips using DDM-MC hybrid coating. We propose that DDM-MC hybrid coating might be a general method for suppressing analyte adsorption and EOF in polymer MCE devices. The current MCE-based method might be a promising alternative for high-throughput screening of carbohydrate alterations in glycoproteins.

Rapid fabrication of polymer microfluidic systems for the production of artificial lipid bilayers

A polymer microfluidic device has been fabricated using rapid prototyping techniques. The device was built to allow the formation and subsequent investigation of artificial bilayer lipid membranes (BLMs). A simple dry film photoresist stamp was used to hot emboss microfluidic channels into PMMA films. Laser micromachining was employed to form an aperture through the PMMA channels, across which the BLM was later formed. The dry film photoresist was also used as a simple etch mask for the deep etching of glass substrates in buffered HF solutions, which was used in this work for the production of glass embossing stamps. We show that bilayer films can be successfully produced across laser micromachined apertures in PMMA films.

Synthesis, Characterization, and Direct Observation of Star Microgels

The molecular sizes of four star microgels, synthesized by atom transfer radical polymerization of poly(methyl methacrylate) (PMMA) with ethylene glycol dimethacrylate as the cross-linker, have been investigated by light scattering methods and transmission electron microscopy (TEM). Gel permeation chromatography right-angle laser light scattering performed with a triple detector system and dynamic light scattering together confirm that individual particles of one star microgel in tetrahydrofuran and styrene solutions possess mean diameters of 31 and 18 nm, respectively. Complementary TEM reveals that another star microgel appears as discrete particles measuring 18-30 nm in diameter when added to styrene monomer subsequently polymerized to form a solid matrix. These particles likewise undergo macrophase separation to form microgel-rich domains consisting of nanoscale PMMA channels. Additional TEM examination of a star microgel deposited by dilute solution casting provides direct evidence for the existence of individual microgel molecules with a mean (dry) diameter of ∼15 nm.