PDMS-based Microfluidic Channel Research Articles

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.

Conventional and emerging strategies for the fabrication and functionalization of PDMS-based microfluidic devices

Microfluidics is an emerging and multidisciplinary field that is of great interest to manufacturers in medicine, biotechnology, and chemistry, as it provides unique tools for the development of point-of-care diagnostics, organs-on-chip systems, and biosensors. Polymeric microfluidics, unlike glass and silicon, offer several advantages such as low-cost mass manufacturing and a wide range of beneficial material properties, which make them the material of choice for commercial applications and high-throughput systems. Among polymers used for the fabrication of microfluidic devices, polydimethylsiloxane (PDMS) still remains the most widely used material in academia due to its advantageous properties, such as excellent transparency and biocompatibility. However, commercialization of PDMS has been a challenge mostly due to the high cost of the current fabrication strategies. Moreover, specific surface modification and functionalization steps are required to tailor the surface chemistry of PDMS channels (e.g. biomolecule immobilization, surface hydrophobicity and antifouling properties) with respect to the desired application. While significant research has been reported in the field of PDMS microfluidics, functionalization of PDMS surfaces remains a critical step in the fabrication process that is difficult to navigate. This review first offers a thorough illustration of existing fabrication methods for PDMS-based microfluidic devices, providing several recent advancements in this field with the aim of reducing the cost and time for mass production of these devices. Next, various conventional and emerging approaches for engineering the surface chemistry of PDMS are discussed in detail. We provide a wide range of functionalization techniques rendering PDMS microchannels highly biocompatible for physical or covalent immobilization of various biological entities while preventing non-specific interactions.

A Microfluidic MEMS-Microbalance Platform With Minimized Acoustic Radiation in Liquid.

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( S ) and antisymmetric ( A ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( Q ) are observed for the S modes, among which Q values above 400 are recorded for a specific mode named S (4, 2) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the Q and resonance frequency of the disk resonators is experimentally validated.

Microfluidically Controlled Frequency-Tunable Monopole Antenna for High-Power Applications

A microfluidically controlled frequency-tunable monopole antenna with high RF power-handling capability is presented. Different than previous work, the frequency tunability of this monopole is achieved by using a movable metallized plate inside a microfluidic channel. The monopole is capacitively coupled to a feeding microstrip line through a 12- μm-thick benzo-cyclobutene (BCB) insulator that is used to seal and bond the polydimethylsiloxane (PDMS)-based microfluidic channel to the feed board substrate (RO4003C). It is shown that the presented reconfigurable monopole implemented with the metallized plate, low-loss BCB insulator, and RO4003C board exhibits 200% more power-handling capability as compared to prior implementation that relied on liquid metal, liquid crystal polymer, and RO5880 substrate. The presented monopole provides continuous tuning in the 1.7-3.5 GHz range with a tuning ratio of ~ 2:1. The RF power handling of the antenna is demonstrated through the agreement between multiphysics simulations and experiments conducted under high RF power excitation. The liquid metal free nature of the antenna and using BCB to bond the PDMS-based microfluidic channels with the printed circuit board substrates offer a new approach for realizing reconfigurable devices with higher efficiency and high power-handling capability.

Effect of shear stress on the formation of bacterial biofilm in a microfluidic channel

Biofilms form an irregular network matrix that is surrounded by extracellular polymeric substrate (EPS). The architecture of biofilm plays an important role in protecting bacteria under physical, chemical, and biological stress. The shear stress is one of the major factors to construct stable bioflim. The experimental observation of biofilm formation on large-scale water flow has been limited because most of fluid pipe are water and sewer lines. This study presents the biofilm formation in a PDMS-based microfluidic channel which is able to simulate fluid pipes at small scale. We could characterize the hydrodynamics of the growth of single-species bacteria between biofilm formation and the external environmental factors. Particularly, the dynamics of biofilm formation confirms that biofilm, under the optimum shear stress, efficiently form a stable EPS structure which provides a mechanical shield against high-pressure fluidic flow.

The PDMS-based microfluidic channel fabricated by synchrotron radiation stimulated etching

Micro pattern on PDMS surface has been achieved by using synchrotron radiation (SR) stimulated etching. The experimental results indicated that SR stimulated etching has many advantages, such as extremely high etching rate (as large as 40-50 mum per 10 min), area-selectivity and anisotropy at room temperature, high spatial resolution. Combining the SR stimulated etching with photolithography, a PDMS-based microfluidic channel was obtained. The aim of this work is to develop a three-dimensional microfluidic channel with a special through hole, which is beneficial for cell differentiation, functionality and longevity and cannot be fabricated by conventional direct tooling techniques.

A simple PDMS-based microfluidic channel design that removes bubbles for long-term on-chip culture of mammalian cells

This report shows methods to fabricate polydimethylsiloxane (PDMS) microfluidic systems for long-term (up to 10 day) cell culture. Undesired bubble accumulation in microfluidic channels abruptly changes the microenvironment of adherent cells and leads to the damage and death of cells. Existing bubble trapping approaches have drawbacks such as the need to pause fluid flow, requirement for external vacuum or pressure source, and possible cytotoxicity. This study reports two kinds of integrated bubble trap (IBT) which have excellent properties, including simplicity in structure, ease in fabrication, no interference with the flow, and long-term stability. IBT-A provides the simplest solution to prevent bubbles from entering microfluidic channels. In situ time-lapse imaging experiments indicate that IBT-B is an excellent device both for bubble trapping and debubbling in cell-loaded microfluidics. MC 3T3 E1 cells, cultured in a long and curved microfluidic channel equipped with IBT-B, showed high viability and active proliferation after 10 days of continuous fluid flow. The comprehensive measures taken in our experiments have led to successful long-term, bubble-free, on-chip culture of cells.

Optofluidic Waveguides in Teflon AF-Coated PDMS Microfluidic Channels

We report a new method for fabricating an optofluidic waveguide that is compatible with polydimethylsiloxane (PDMS). The light path follows the microfluidic channels, an architecture that can maximize detection efficiency and make the most economic use of chip area in many lab-on-chip applications. The PDMS-based microfluidic channels are coated with Teflon amorphous fluoropolymers (Teflon AF) which has a lower refractive index (n = 1.31) than water (n = 1.33) to form a water/Teflon AF optical waveguide. Driven by a vacuum pump, the Teflon AF solution was flowed through the channels, leaving a thin (5-15 µm) layer of coating on the channel wall as the cladding layer of optical waveguides. This coating process resolves the limitations of spin-coating processes by reducing the elasticity mismatch between the Teflon AF cladding layer and the PDMS device body. We demonstrate that the resulting optofluidic waveguide confines and guides the laser light through the liquid core channel. Furthermore, the light in such a waveguide can be split when the fluid flow is split. This new method enables highly integrated biosensors such as lab-on-chip flow cytometers and micro-fabricated fluorescence-activated cell sorter with on-chip excitation.

On-chip colorimetric biosensor based on polydiacetylene (PDA) embedded in photopolymerized poly(ethylene glycol) diacrylate (PEG-DA) hydrogel

We have developed a new strategy to construct a colorimetric biosensor on a miniaturized platform. Polydiacetylene (PDA), which is widely known to change color by external stimuli, was employed as a sensing material. To construct a gel-based portable colorimetric biosensor using PDA, PDA was incorporated into poly(ethylene glycol) (PEG)-based hydrogel upon photopolymerization and PDA-embedded PEG hydrogel matrix was patterned within PDMS-based microfluidic channels. The resulting intrachannel hydrogel matrix containing PDA was reacted with α-cyclodextrin as a model target sample, which causes a color change of PDA from blue to red. Parallel analyses were performed inside microchannels for multiple solutions containing different amounts of α-cyclodextrin and color change gradients were successfully demonstrated depending on the contacting time and amount of α-cyclodextrin.