This review article describes recent developments in microfluidics, with special emphasis on disposable plastic devices. Included is an overview of the common methods used in the fabrication of polymer microfluidic systems, including replica and injection molding, embossing, and laser ablation. Also described are the different methods by which on-chip operations--such as the pumping and valving of fluid flow, the mixing of different reagents, and the separation and detection of different chemical species--have been implemented in a microfluidic format. Finally, a few select biotechnological applications of microfluidics are presented to illustrate both the utility of this technology and its potential for development in the future.
This paper presents a simple procedure for the fabrication of thermoset polyester (TPE) microfluidic systems and discusses the properties of the final devices. TPE chips are fabricated in less than 3 h by casting TPE resin directly on a lithographically patterned (SU-8) silicon master. Thorough curing of the devices is obtained through the combined use of ultraviolet light and heat, as both an ultraviolet and a thermal initiator are employed in the resin mixture. Features on the order of micrometers and greater are routinely reproduced using the presented procedure, including complex designs and multilayer features. The surface of TPE was characterized using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Following oxygen plasma treatment, the hydrophilicity of the surface of TPE increases (determined by contact angle measurements) and the proportion of oxygen-containing functional groups also increases (determined by XPS), which indicates a correlated increase in the charge density on the surface. Native TPE microchannels support electroosmotic flow (EOF) toward the cathode, with an average electroosmotic mobility of 1.3 x 10(-4) cm(2) V(-1) s(-1) for a 50-microm square channel (20 mM borate at pH 9); following plasma treatment (5 min at 30 W and 0.3 mbar), EOF is enhanced by a factor of 2. This enhancement of the EOF from plasma treatment is stable for days, with no significant decrease noted during the 5-day period that we monitored. Using plasma-treated TPE microchannels, we demonstrate the separation of a mixture of fluorescein-tagged amino acids (glycine, glutamic acid, aspartic acid). TPE devices are up to 90% transparent (for approximately 2-mm-thick sample) to visible light (400-800 nm). The compatibility of TPE with a wide range of solvents was tested over a 24-h period, and the material performed well with acids, bases, alcohols, cyclohexane, n-heptane, and toluene but not with chlorinated solvents (dichloromethane, chloroform).
This paper demonstrates the ability to use capillary electrophoresis (CE) separation coupled with laser-induced fluorescence for analyzing the contents of single femtoliter-volume aqueous droplets. A single droplet was formed using a T-channel (3 microm wide by 3 microm tall) connected to microinjectors, and then the droplet was fluidically moved to an immiscible boundary that isolates the CE channel (50 microm wide by 50 microm tall) from the droplet generation region. Fusion of the aqueous droplet with the immiscible boundary effectively injects the droplet content into the separation channel. In addition to injecting the contents of droplets, we found aqueous samples can be introduced directly into the separation channel by reversibly penetrating and resealing the immiscible partition. Because droplet generation in channels requires hydrophobic surfaces, we have also investigated the advantages to using all hydrophobic channels versus channel systems with patterned hydrophobic and hydrophilic regions. To fabricate devices with patterned surface chemistry, we have developed a simple strategy based on differential wetting to deposit selectively a hydrophilic polymer (poly(styrenesulfonate)) onto desired regions of the microfluidic chip. Finally, we applied our device to the separation of a simple mixture of fluorescein-labeled amino acids contained within a approximately 10-fL droplet.
Plastics are increasingly being used for the fabrication of Lab-on-a-Chip devices due to the variety of beneficial material properties, affordable cost, and straightforward fabrication methods available from a range of different types of plastics. Rapid prototyping of polydimethylsiloxane (PDMS) devices has become a well-known process for the quick and easy fabrication of microfluidic devices in the research laboratory; however, PDMS is not always an appropriate material for every application. This paper describes the fabrication of thermoset polyester microfluidic devices and masters for hot embossing using replica molding techniques. Rapid prototyped PDMS molds are convienently used for the production of non-PDMS polymeric devices. The recessed features in the cast polyester can be bonded to a second polyester piece to form an enclosed microchannel. Thermoset polyester can withstand moderate amounts of pressure and elevated temperature; therefore, the cast polyester piece also can be used as a master for embossing polymethylmethacrylate (PMMA) microfluidic systems. Examples of enclosed polyester and PMMA microchannels are presented, and we discuss the electroosmotic properties of both types of channels, which are important for analytical applications such as capillary electrophoresis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.