Glass-based Microfluidic Devices Research Articles

High-profile-quality microchannels fabricated by UV picosecond laser for microfluidic mixing

Ultrafast laser direct writing technology has been widely investigated in the fabrication of glass-based microfluidic devices. However, in the machining of microchannels, the importance of cross-sectional profile quality is overlooked. Therefore, we have investigated the influence of scanning strategies and process parameters on the cross-sectional profile characteristics of microchannels. A picosecond laser with a pulse duration of 10 ps and a wavelength of 355 nm was employed to engrave microchannels. To achieve symmetrical cross-sectional profiles and smooth channel bottoms, a combined strategy of the offset method combined with the double bidirectional method (OM + DBM) has been proposed. Compared to the traditional sequential method (SM) and the improved bidirectional method (BM) strategy, the new strategy eliminates the protrusions at the starting edge and in the middle of the channel bottom. The new strategy also demonstrates quality optimization of the microchannel edges. A microfluidic mixing channel with a width of 400 µm and a depth of 240 µm has been successfully manufactured without defects. A split and recombine structure, known for its high mixing efficiency, has been utilized to conduct microfluidic mixing experiments. The mixing results of liquid–liquid and liquid–gas demonstrate that microfluidic channels with high-quality profiles exhibit high efficiency and stability of flow. The input flux of the mixing liquids reached 20 mL/min.

Glass based micro total analysis systems: Materials, fabrication methods, and applications

Microfluidics has become recognized as a powerful platform technology with a wide range of applications in various fields, such as biology, biomedicine, chemistry and environment. To achieve higher performance, microfluidic devices are required to have superior optical transparency; mechanical, chemical and thermal stability; as well as easy design and fabrication. All of these requirements make glass as an attractive and ideal material for the fabrication of microfluidic devices due to its excellent characteristics in optical, mechanical, thermal, electrical and chemical aspects in comparison to other materials (e.g., silicon and polydimethylsiloxane). In order to give preliminary guidance for researchers from different backgrounds, we provide a comprehensive overview of the fabrication methods for glass-based microfluidic devices as well as various applications based on different types of glass. This review takes into account recent advances in the fabrication of microfluidics, such as, liquid glass and ultra-thin glass, so as to provide a full understanding of the latest research trend in this area. Finally, some remaining challenges facing the field are summarized, and potential prospects for future work with an emphasis on both emerging techniques are discussed.

Bench scale glass-to-glass bonding for microfluidic prototyping

Microfluidics, an increasingly ubiquitous technology platform, has been extensively utilized in assorted research areas. Commonly, microfluidic devices are fabricated using cheap and convenient elastomers such as poly(dimethylsiloxane) (PDMS). However, despite the popularity of these materials, their disadvantages such like deformation under moderate pressure, chemical incompatibility, and surface heterogeneity have been widely recognized as impediments to expanding the utility of microfluidics. Glass-based microfluidic devices, on the other hand, exhibit desirable properties including rigidity, chemically inertness, and surface chemistry homogeneity. That the universal adoption of glass-based microfluidics has not yet been achieved is largely attributable to the difficulties in device fabrication and bonding, which usually require large capital investment. Therefore, in this work, we have developed a bench-scale glass-to-glass bonding protocol that allows the automated bonding of glass microfluidic devices within 6 h via a commercially available furnace. The quality of the bonds was inspected comprehensively in terms of bonding strength, channel deformation and reliability. Additionally, femtosecond pulsed laser micromachining was employed to rapidly engrave channels on a glass substrate with arbitrary-triangular in this case-cross-section. Bonded glass microfluidic devices with machined channels have been used to verify calculated capillary entry pressures. This combination of fast laser micromachining that produces arbitrary cross-sectioned microstructures and convenient bench-scale glass bonding protocol will facilitate a broad range of micro-scale applications.

Low‐cost pyrophyllite‐based microfluidic device for the study of enhanced oil recovery

This work proposed a novel method for the fabrication of pyrophyllite-based microfluidic devices for enhanced oil recovery (EOR). Pyrophyllite has good heat resistance, corrosion resistance and similar molecular structure to quartz sandstone, and is suitable for EOR research. A rectangular matrix of the pore structure is designed, representing an idealised porous medium and then fabricated on the surface of pyrophyllite substrate by using the micro-milling method. Finally, a layer of sealing film was applied on the surface of substrate to finish the bonding process. A droplet generator was also fabricated for the demonstration of the proposed technology. A series of displacement experiments with water flooding and surfactant flooding were conducted and the result was carefully analysed and discussed. Compared with the previous study using polymer-based or glass-based microfluidic devices as micromodels for the displacement study in oil recovery process, the surface properties of pyrophyllite are more close to real reservoirs and have compelling advantages as bulk material for microfluidic devices for the EOR study. This work has wide potential applications as the micromodels in EOR research, the proposed fabrication protocols of the pyrophyllite-based microfluidic device are rapid and low-cost, the on-site field test could also be conducted with the proposed technology.

Microchannel Fabrication on Glass Materials for Microfluidic Devices

Microchannels are the main features that characterize microfluidic devices. Also, glass is given priority in selecting a substrate material in the development of microfluidic devices due to its high degree of transparency, high chemical resistance, inertness to most substances, ability to sustain higher temperature, biological compatibility, and relatively low non-specific adsorption. However, the high cost and time-consuming labor for fabricating microchannels on glass limit the development of glass-based microfluidic devices, especially for point-of-care test devices. Therefore, it is important to have a capability for fabricating microchannels on glass more efficiently. In this context, the present paper reviews the processes applicable for fabricating microchannels on glass, which include chemical, mechanical, laser-based, and other processes. The state of the art for these processes, and their advantages and limits are also addressed, which will guide in selecting the processes suitable for constructing glass-based microfluidic devices.

Fabrication of Glass Microfluidic Devices.

This chapter provides step-by-step procedures for the fabrication of glass-based microfluidic devices. These procedures include device design, photomask generation, photolithography, channel etching, and high-temperature bonding.

Geometrical effect characterization of femtosecond-laser manufactured glass microfluidic chips based on optical manipulation of submicroparticles

Microfluidic devices provide a platform with wide ranging applications from environmental monitoring to disease diagnosis. They offer substantive advantages but are often not optimized or designed to be used by nonexpert researchers. Microchannels of a microanalysis platform and their geometrical characterization are of eminent importance when designing such devices. We present a method that is used to optimize each microchannel within a device using high-throughput particle manipulation. For this purpose, glass-based microfluidic devices, with three-dimensional channel networks of several geometrical sizes, were fabricated by employing laser fabrication techniques. The effect of channel geometry was investigated by employing an optical tweezer. The optical trapping force depends on the flow velocity that is associated with the dimensions of the microchannel. We observe a linear dependence of the trapping efficiency and of the fluid flow velocity, with the channel dimensions. We determined that the highest trapping efficiency was achieved for microchannels with aspect ratio equal to one. Numerical simulation validated the impact of the device design dimensions on the trapping efficiency. This investigation indicates that the geometrical characteristics, the flow velocity, and trapping efficiency are crucial and should be considered when fabricating microfluidic devices for cell studies.

Direct bonding of polymer/glass-based microfluidic chips with dry film photoresist

Dry film has been widely used as a low-cost photoresist in the print circuit board industry which consists of a thin layer of photoresist sandwiched between two protective polymer layers. In this research, a simple, cleanroom-free, low-cost and highly adaptable bonding method for various polymer and glass-based microfluidic systems was proposed using the cross-linked dry film photoresist. In this proposed approach, the uncross-linked dry film photoresist was sandwiched between substrates and cover plate, then using UV exposure for the crosslinking of the photoresist to reach a secured bonding, after bonding, a cleaning process for the removal of photoresist residuals trapped inside the microchannels was also applied. The proposed bonding method is highly adaptable for different kinds of polymer or glass-based microfluidic devices, even the hybrid bonding between polymer and glass substrates could be achieved, which is usually very challenging using the conventional bonding technologies. Comparing with the traditional adhesive bonding method, the proposed method is simple, low-cost and without the requirement for toxic organic solvents, in addition, the cleaning procedure proposed in this study could effectively remove the residual of the adhesives trapped in the microchannels.

Quick and simple integration of optical oxygen sensors into glass-based microfluidic devices

A novel simple and inexpensive technique for integration of optical oxygen sensors into microfluidic channels made of glass. The channels are coated with conjugated polymeric nanoparticles containing a covalently grafted oxygen indicator.

Fabrication of glass-based microfluidic devices with dry film photoresists as pattern transfer masks for wet etching

A simple, cheap and rapid method is developed to fabricate glass microfluidic devices with dry film photoresist as pattern transfer masks for wet etching, which provides an efficient approach for mass-production of glass microchips.

Adhesion promotion between PDMS and glass by oxygen plasma pre-treatment

Polydimethylsiloxane (PDMS) and glass are among the most widely used materials in biomedical and microfluidic applications. In this paper, oxygen plasma exposure was used to improve the adhesion properties of PDMS and glass. The effect of bonding quality parameters such as RF power, time of activation and oxygen flow was investigated. Bonding area and strength, two main indicators of bonding quality, were detected using manual peel and mechanical shear tests, respectively, to optimize the bonding parameters. It was observed that increase in activation time and RF power increased the bonding strength considerably. The oxygen flow had a slight influence in increasing the bonding strength. The application of this bond has also been demonstrated in PDMS–glass micropump, so this technique can be potentially applied for fabrication of PDMS–glass-based microfluidic and biomedical devices.

Fabrication of Glass-based Microfluidic Devices with Photoresist as Mask

Pateiktas nebrangus mikrohidrodinaminių įtaisų stiklo pagrindu ėsdinimo metodas. 150 μm gylio mikrokanalai buvo gauti implementuojant fotorezistą ir drėgną ėsdinimo procesą. Fotorezistas naudojamas kaip kaukė stiklui ėsdinti. Jis gali būti atsparus ėsdiklui daugiau nei 2 val. ir islaiko geras adhezijos savybes gaminant mikrohidrodinaminius kanalus. Kanalų plotis priklauso nuo fotokaukės linijų plocio ir stiklo izotropinio ėsdinimo santykio. Gautas kanalo plotis – nuo 30 μm iki 350 μm. Lygus ir svarus pavirsius po drėgno ėsdinimo yra svarbus veiksnys užtikrinant sklandų skyscių tekėjimą mikrokanalais. Tai pasiekta naudojant specialų ėsdiklį ir pridedant HCL į atskiestą BOE tirpalą. Buvo naudojami įvairių sudėcių tirpalai. Il. 4, bibl. 14 (anglų kalba; santraukos anglų ir lietuvių k.). http://dx.doi.org/10.5755/j01.eee.116.10.878

Thermal assisted direct bonding between structured glasses for lab-on-chip technology

A thermal assisted direct bonding (TADB) technique between structured glasses is proposed for micro-fluidic device fabrication. The bonded glass pairs were characterized by optical microscopy, scanning electron microscopy (SEM), apparent shear strength tests and Vickers hardness measurements across the bonded interface. The optimisation of TADB parameters on flat glasses and on structured glasses was analysed. This technique is user-friendly and low cost, and can be considered for mass production of glass-based micro-fluidic devices.

Fabrication and testing of high-performance detection sensor for capillary electrophoresis microchips

This study presents a new approach for high-performance detection sensors for MEMS-based capillary electrophoresis chips to substitute laser induced fluorescence (LIF) detection systems. The developed sensors easily integrate with well-known microfabrication techniques for glass-based microfluidic devices. Three-dimensional gold electrodes are structured in enveloping side channels by sputtering and patterned using a standard "lift-off" process. The variations in the capacitance between the electrodes in the side channels are measured as different samples and ions pass through the detection region of the capillary electrophoresis separation channel. Samples of beer, white wine and milk are each mixed in different buffer solutions, then successfully separated and detected using the developed device. The proposed high-performance detection sensors have microscale dimensions and provide a critical step towards the realization of the lab-on-a-chip concept.

A microchip electrophoresis system with integrated in-plane electrodes for contactless conductivity detection.

We present a new approach for contactless conductivity detection for microchip-based capillary electrophoresis (CE). The detector integrates easily with well-known microfabrication techniques for glass-based microfluidic devices. Platinum electrodes are structured in recesses in-plane with the microchannel network after glass etching, which allows precise positioning and batch fabrication of the electrodes. A thin glass wall of 10-15 microm separates the electrodes and the buffer electrolyte in the separation channel to achieve the electrical insulation necessary for contactless operation. The effective separation length is 34 mm, with a channel width of 50 microm and depth of 12 microm. Microchip CE devices with conductivity detection were characterized in terms of sensitivity and linearity of response, and were tested using samples containing up to three small cations. The limit of detection for K+ (18 microM) is good, though an order of magnitude higher than for comparable capillary-based systems and one recently reported example of contactless conductivity on chip. However, an integrated field-amplified stacking step could be employed prior to CE to preconcentrate the sample ions by a factor of four.