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Microfluidic Manifolds by Polymer Hot Embossing for μ-Tas Applications
Abstract
In this paper we present a low-cost replication method for planar microstructures based on polymer substrates. Several microfluidic chips for capillary electrophoresis (CE) applications with a range of channel widths between 0.8 m and 100 m have been produced by this method, yielding a very good structural replication and short production times.
... Over the past couple of decades, microfluidics has revolutionized biological and biomedical research by enabling the precise analysis of samples in well controlled conditions while using minimal reagents, and has facilitated a paradigm shift in the way such research is conducted [1][2][3]. Techniques such as injection molding [4], hot embossing [5] and laser ablation [6] are often used as production methods for microfluidic devices. These processes may be suitable for the high-volume reproduction required for emerging commercial and clinical applications of microfluidics. ...
... Four different channels with 2 steps in each were made. These channels differed by changing the number of loops at each step (5,10,15,20). Fig. 3(A) shows the change in intensity measured by the fluorescence microscope, for a fluorescent dye pumped through the device, and compares it to the height of the channels (see Experimental Section). As the steps all have similar widths, the fluorescence intensity linearly correlates with the channel height. ...
Microfluidics has emerged as a powerful analytical tool for biology and biomedical research, with uses ranging from single-cell phenotyping to drug discovery and medical diagnostics, and only small sample volumes required for testing. The ability to rapidly prototype new designs is hugely beneficial in a research environment, but the high cost, slow turnaround, and wasteful nature of commonly used fabrication techniques, particularly for complex multi-layer geometries, severely impede the development process. In addition, microfluidic channels in most devices currently play a passive role and are typically used to direct flows. The ability to "functionalize" the channels with different materials in precise spatial locations would be a major advantage for a range of applications. This would involve incorporating functional materials directly within the channels that can partake in, guide or facilitate reactions in precisely controlled microenvironments. Here we demonstrate the use of Aerosol Jet Printing (AJP) to rapidly produce bespoke molds for microfluidic devices with a range of different geometries and precise "in-channel" functionalization. We show that such an advanced microscale additive manufacturing method can be used to rapidly design cost-efficient and customized microfluidic devices, with the ability to add functional coatings at specific locations within the microfluidic channels. We demonstrate the functionalization capabilities of our technique by specifically coating a section of a microfluidic channel with polyvinyl alcohol to render it hydrophilic. This versatile microfluidic device prototyping technique will be a powerful aid for biological and bio-medical research in both academic and industrial contexts.
... stoljeća opisalo nekoliko istraživačkih grupa. 29,[47][48][49] Mikroreaktori PS, PETG, PMMA, PVC i PC uspješno su izrađeni tim postupkom. 29,49,50 Najčešće se upotrebljava silikonsko utiskivalo kao alat za utiskivanje prilikom izrade mikroreaktora od polimernih materijala. ...
... 29,[47][48][49] Mikroreaktori PS, PETG, PMMA, PVC i PC uspješno su izrađeni tim postupkom. 29,49,50 Najčešće se upotrebljava silikonsko utiskivalo kao alat za utiskivanje prilikom izrade mikroreaktora od polimernih materijala. 29 Injekcijsko prešanje primjenjuje se za proizvodnju mikrokanala u polimernim materijalima kao što su PMMA i PC. 29,51 Utiskivanje i injekcijsko prešanje su dva postupka koja su uhodana za masovnu i serijsku proizvodnju mikroreaktorskih uređaja. ...
Mikroreaktori su reaktorski sustavi izvedeni u mikroskopskom mjerilu, a zbog svoje velike međufazne površine imaju prednosti u odnosu na klasične – makroreaktorske sustave. Odabir materijala za izradu mikroreaktora ovisi o vrsti reakcije koja se provodi u sustavu, kompatibilnosti otapala i materijala, mehaničkim zahtjevima te o cijeni i dostupnosti na tržištu. Materijali koji se najčešće upotrebljavaju za izradu su različite vrste stakla, keramike, metali te polimerni materijali. Ovisno o materijalu odabiru se postupci izrade, a najčešći postupci su jetkanje, litografija, pjeskarenje, strojna obrada, injekcijsko prešanje te aditivni postupci izrade.
Cilj ovog rada je predstaviti najčešće materijale i postupke izrade mikroreaktora.
... Advances in technology permitted the fabrication of much smaller diameters. Techniques such as hot embossing or imprinting [3,4], injection molding [5], soft lithography [6,7], laser photoablation [8,9], x-ray lithography [10], ion beam etching with Ar + ions [11] and plasma etching [12] allowed the creation of much smaller microfluidic channels, some of them with features down to 1.5 μm. Most of the aforementioned processes use costly equipment and require the use of a master, which introduce extra fabrication steps. ...
... The negative sidewall is attributed to the non-collimated nature of the deep-UV light, and will limit the aspect ratio of the features produced using this uncollimated light source. The fabrication procedure outlined above has a number of advantages over other microfluidics processes discussed in the literature [3][4][5][6][7][8][9][10][11][12]. First, it uses low-cost materials and an inexpensive exposure system. ...
Although PMMA can be exposed using a variety of exposure sources, deep-UV at 254 nm is of interest because it is relatively inexpensive. Additionally, deep-UV sources can be readily scaled to large area exposures. Moreover, this paper will show that depths of over 100µm can be created in commercial grade PMMA using an uncollimated source. These depths are sufficient for creating microfluidic channels. This paper will provide measurements of the dissolution depth of commercial grade PMMA as a function of the exposure dose and etch time, using an IPA:H2O developer. Additionally, experiments were run to characterize the dependence of the dissolution rate on temperature and agitation. The patterned substrates were thermally bonded to blank PMMA pieces to enclose the channels and ports were drilled into the reservoirs. The resulting fluidic systems were then tested for leakage. The work herein presents the patterning, development and system behaviour of a complete microfluidics system based on commercial grade PMMA.
... Many common plastics have been successfully imprinted or hot embossed with excellent device-to-device reproducibility. These include polystyrene (PS), polyethylenetetraphthalate glycol (PETG), polymethylmethacrylate (PMMA), polyvinylchloride (PVC), polystyrene, and poly- carbonate [10,21,31323334 . Instruments for automated hot embossing were developed and are sold commercially by Jenoptik Mikrotechnik GmbH in Germany. ...
... For many applications, however, other channel cross-sections are desirable including high aspect ratio square channels, channels with a defined but arbitrary wall angle, or channels with different heights. Polymer-based devices for application in capillary electrophoresis have been fabricated using all of the methods previously described including hot embossing [23,24,21,55,767778798081, injection molding [30,82], laser ablation [7,58,83] and direct X-ray exposure [84,85] in thermoplastic polymers as well as in elastomers, namely polydimethylsiloxane (PDMS) [38,14,86878889. The achievable separation speed and resolution is comparable with devices made out of glass. ...
Since the introduction of lab-on-a-chip devices in the early 1990s, glass has been the dominant substrate material for their fabrication (J. Chromatogr. 593 (1992) 253; Science 261 (1993) 895). This is primarily driven by the fact that fabrication methods were well established by the semiconductor industry, and surface properties and derivatization methods were well characterized and developed by the chromatography industry among others. Several material properties of glass make it a very attractive material for use in microfluidic systems; however, the cost of producing systems in glass is driving commercial producers to seek other materials. Commercial manufacturers of microfluidic devices see many benefits in employing plastics that include reduced cost and simplified manufacturing procedures, particularly when compared to glass and silicon. An additional benefit that is extremely attractive is the wide range of available plastic materials which allows the manufacturer to choose materials' properties suitable for their specific application. In this article, we present a review of polymer-based microfluidic systems including their material properties, fabrication methods, device applications, and finally an analysis of the market that drives their development.
... Even if several technologies are available, most of the MFDs are manufactured by hot embossing the channel shape and then by bonding the two halves of the device. 6 To mitigate the warpage related to internal stresses that are induced by hot embossing, Yi et al. 7 adopted the Taguchi's optimisation method. With the same aim, Liang et al. 8 proposed an innovative bonding technique, which is capable of preventing distortions of the channel. ...
Lab-on-a-Chips integrate a variety of laboratory functions and embed microchannels for small fluid volume handling. These devices are used in medicine, chemistry, and biotechnology applications but a large diffusion is limited due to the manufacturing cost of traditional processes. Additive Manufacturing offers affordable alternatives for the production of microfluidic devices, because the fabrication of embedded micrometric channels is enabled. Stereolithography gained particular attention due to the low cost of both available machines and suitable polymeric materials to be processed. The main restriction to the adoption of this technique comes from the obtainable dimensional accuracy that depends not only on design, but also on process set-up. Firstly, the paper analyses theoretically the physics of stereolithographic processes and focuses on main phenomena related to microchannel manufacturing. Then, specific experimental activities are designed to investigate the combined effect of design and process parameters on the achievable dimensional accuracy of embedded microchannels manufactured through a commercial desktop stereolithography apparatus. In particular, the combined effect of channel nominal dimensions, build orientations and the layer thickness on the obtainable accuracy is examined by referring to a benchmark geometry. The collated experimental data showed that a number of combinations are successful. Besides, the experimental activity revealed that appropriate combinations of design, build orientation and manufacturing parameters can overcome the dimensional limitations reported in previous studies. Both binary logistic regression models to predict the manufacturability of microchannels and linear regression models to estimate the achievable accuracy for those geometries that can be produced successfully are developed.
... Even if perfect exposure allows the generation of sharp corners on the master mold, the replica elastomer (after release) will adopt an equilibrium shape (defined by material elasticity and interface tension) that is characterized by minute rounding (Gordan et al. 2008;Odom et al. 2002). Similarly, sharp corners are difficult to fabricate by hot embossing due to limitations in micromilled mold resolution (Griffiths et al. 2010;Becker et al. 1998), since the radius of curvature is restricted to the radius of the milling bit (Guber et al. 2004). It should be noted that near 90° features can be realized using UV-LIGA techniques to produce molds; however, slight rounding is almost unavoidable (Guber et al. 2004). ...
Herein we report microfluidic droplet formation in flow-focusing geometries possessing varying degrees of rounding. Rounding is incorporated in all four corners (symmetric) or only in the two exit corners (asymmetric). The ratios of the radius of curvature, R, to channel width, w, are varied where R/w = 0, 0.5 and 1. In all cases, monodisperse droplets are produced, with the largest droplets being produced at the junctions with the largest rounding. Junctions without rounding are shown to produce droplets at higher frequencies than those with rounding. Droplet pinch-off position is found to be dependent on both geometry and volumetric flow rates; the location shifts toward the interior of the rounded junctions with increasing oil-to-water flow rate ratios. Accordingly, we find that rounding within microfluidic flow-focusing junctions strongly influences droplet formation. Junction rounding may be deliberate due to the selected fabrication method or occur as an unintended result of microfabrication processes not held to strict tolerances. Indeed, understanding droplet characteristics for those formed in such structures is critical for microfluidic applications where droplet volume or reagent mass must be well controlled. Thus, rounding can be a valuable design parameter when tuning the size and production frequency for emulsion collection or ensuing downstream operations such as chemical reactions.
... The main reason to choose polymer over glass or silicon is the low material price and the production costs for mass fabrication. With dimensions of several cm 2 which appear here, structuring of silicon or glass is indeed less cost-efficient compared to polymer substrates this size, where structuring is realized with mass production technologies like injection molding, embossing, and casting processes [55,56,57]. One standard polymer material for lab-on-a-chip device for laboratory use is polydimethylsiloxane (PDMS [73]. ...
In this work a new pressure driven microfluidic platform (µFLATLab) is presented, consisting of a lab on a chip device and a processing instrument for functional control. The disposable lab on a chip device consists of a multilayer polymer stack made of structured polycarbonate (PC) bulk welded to a thermoplastic elastomer membrane (TPE). Fluid management is realized by integrated active membrane microvalves with a high sealing quality and short switching times in the range of 100 ms. The concept of a sealing membrane works reliable and independent from liquid viscosity or surface tension. Membrane micropumps with a broad controllable flow rate from 0.1 µl∙s-1 to 55.8 µl∙s-1 are realized for liquid transportation and circulation for mixing discrete liquid plugs. Compared to microfluidic platforms based on polydimethylsiloxane (PDMS) the working principle of this platform is characterized by a comparably low actuation pressure and a remarkable level of design flexibility. A full three dimensional fluidic network is created by lasercutting through the membrane layer. Basic operations for microfluidic applications such as valving, pumping and mixing can be realized using this lab on a chip device concept. In addition a liquid reagent storage method is implemented, where a liquid reagent is tightly sealed without any additional production process step. By applying pressure on the storage chamber the seal is broken and the liquid reagent is pushed into the fluidic network. The used materials PC and TPE can be manufactured and structured by mass production processes like injection molding and extrusion. A cost-efficient and production chain consistent way of manufacturing a disposable lab-on-a-chip device is achieved by using laserwelding as a joining technology.
A transportable processing instrument for the control and automation of the lab on a chip device forms the second part of the microfluidic platform. It includes a carrier for the lab-on-a-chip device, eight fluidic and twelve pneumatic interconnections to the macro world for fluid management, two resistive heaters, fan air coolers and temperature sensors for thermal management. Twelve pilot valves are independently controlled for the actuation of the integrated microvalves. Heating rates of 4 K∙s-1 and cooling rates of -1.3 K∙s-1 enable fast thermal cycling. This portable processing instrument with the size of a shoe box has a graphical user interface (GUI) for programming parameters as temperature, duration and pressure switch for each assay step.
With this microfluidic platform, a lab-on-a-chip device was developed for the processing of a diagnostic example assay. The assay detects the resistance of Escherichia coli (E coli) against fluoroquinolone-based antibiotics. The required sub functions include the accumulation of E. coli bacteria directly from a 10 ml sample, their thermal lysis, a DNA amplification step using a polymerase chain reaction (PCR), before detection of the resistance information with a DNA microarray. An integrated silica filter is used for the accumulation of bacteria out of a 10 ml sample with a filter efficiency of over 90 %. The processable number of bacteria range from 104 to 107. The bacteria lysis is made as an initial thermal step at 95°C before the PCR. The 31 amplification cycles of the PCR are performed in less than 2 h with the processing instrument. The reaction time for the detection microarray could be accelerated from 60 min down to 30 min using an integrated micropump as an active circular mixer. At the same time the signal-to-noise-ratio could be increased. This fully automatable assay for the example application takes only 3 h from sample input to result. A diagnostic relevant bacteria concentration threshold of 104 bac/10 ml could be proven to be detected with the assay integrated on chip. The concept of this cost-efficient mass producible microfluidic platform promises a broad range of future applications with the benefit of a robust, fast and reproducible results.
... Effenhauser et al.[9] has demonstrated dsDNA separations in casted silicone structures. A number of other groups are investigating plastic technologies for microfluidic devices on polycarbonate[10], PMMA[11], teflon[12], and poly(ethylene terephtalate) (PET)[13]. Plastic substrates are a low-cost alternative to glass devices that hold potential for disposable analysis tools. ...
Electrophoresis devices have been microfabricated on polycarbonate substrates. A simple, 4 litho-graphic step, batch micromachining process was developed. Surface micromachined channels up to 2.7 cm in length have been fabricated and tested. The presence of access holes for the sacrificial release have been modeled using conformal transformations and predicted to contribute less than 10 of the total band variance. Experimental observations suggest this to be even lower. High-efficiency separations of dsDNA have been demonstrated in these devices. Separations on the order of 100,000 theoretical plates have been achieved. The use of polycarbonate reduces the substrate cost substantially and such devices have potential as disposable, single-use, electrophoresis chips for a variety of separation applications.
... This residue can be removed in an oxygen plasma at low wattage. The main advantage of MCC SU-8 is the provision of near vertical profiles in thick layers, a property that is favoured by designers of microfludic units and embossing masters [13]. Eagle ED2100 allows process engineers to perform lithographic tasks in demanding topographic cavities. ...
A growing interest in the development of high aspect ratio photoresists for micromachining microsystems (MST) products has resulted in the availability of a number of commercially available photoresist products. This paper describes in detail the applications of three such resists, namely EPON SU-8, Clariant AZ 4562 and the Shipley electroplated photoresist ED2100. Applications such as etch hard masks, micromoulds, severe topography coatings for metal interconnects and photoplastic mouldings are discussed, and novel examples are presented of where these resists are currently used in both telecomm and microfluidic markets. In particular, the versatility of the photoplastic negative resist EPON SU-8, which is used in a number of MST prototypes, is demonstrated. Future trends in resist technologies for MST are discussed.
... For these reasons, polymers are becoming an increasingly popular material for fabricating microfluidic devices. A number of techniques have been used for fabrication of plastic microfluidic devices including soft lithography [10, 11], laser ablation [12], hot embossing or imprinting [13][14][15], injection molding [16] and x-ray photolithography [17]. In this paper, for the first time, a novel method to fabricate microfluidic devices by proton beam writing (PBW) is reported. ...
The fabrication of microfluidic channels in poly(methylmethacrylate) (PMMA) by proton beam writing and the characterization of their electrokinetic behavior are reported. Microchannels down to 200 nm width have been fabricated in high-molecular-weight, thick PMMA sheets and a surface smoothness of 2.45 nm for the sidewalls of the channels was measured using atomic force microscopy. The polymeric channels were sealed using thermal bonding. The methods of digital video microscopy and current monitoring were used for characterization of the electrokinetic phenomena. The electrokinetic properties of the PMMA rectangular microchannels were measured in 20 mM buffered solutions of phosphate (pH 7.20), tris (pH 8.00) and borate (pH 9.05) at different voltages. In addition, particle image velocimetry was used to determine the electroosmotic flow profile and the electrophoretic mobility of 600 nm polystyrene microspheres. A theoretical model was developed to predict the bulk electroosmotic flow of phosphate buffer solution in the PMMA microchannels and this model showed good agreement with the measured electroosmotic mobilities.
... The isotropicity of the etching process hinders the fabrication of channels with de®ned but arbitrary wall angles or with different heights, so that the variety of the geometrical design is limited [3] . Besides that, some microchemical applications require modi®cations of the substrate surface because of the material properties of silicon or quartz (e.g. protein sticking to silicon surfaces) [7]. These modi®cations often necessitate an additional process step and therefore prolong the production [3]. ...
This report describes the design, fabrication and use of new microanalytical devices based on polymer substrates for electrophoretic methods, especially isotachophoresis. The devices are fabricated by hot embossing and are sealed with a thin plexiglas cover plate which contains platinum electrodes for contact conductivity detection and power supply. Poly(methylmethacrylat) (PMMA) shows good prospects for the development of low-cost disposable or semi-disposable microanalytical devices. Two different chip-designs are introduced to demonstrate the advantages of the manufacturing procedure and the use of poly(methylmethacrylat) as substrate material. The channel system on the chips is equipped with two sample loops with different volumes to take advantage of the high sample loadability and the enrichment qualities of isotachophoresis. In addition, two separation columns allow two-dimensional on-column ITP–ITP- and CZE–ITP-coupling. Separations of organic acids are used to demonstrate the principle of the isotachophoresis-chips.
In this study the replication accuracy of embossed micro-channel has been investigated through traditional hot embossing setup. For hot embossing, positive-feature micro-patterned mold was fabricated through fiber laser machine. The embossing temperature (Te), embossing pressure (Pe), and embossing time (te) has been taken in to account for this study. The replication accuracy data is collected as per the Taguchi L9 orthogonal array. After analysis of variance it is observed that embossing temperature has a crucial impact over the replication accuracy and it contributes 70.52% in the overall process. The operating parameters have been optimized through Taguchi method and genetic algorithm. The best replication accuracy was achieved at Te = 135 °C, Pe = 30 Kg/cm², te = 180 s. Confirmation test confirms that after setting the operating parameters at optimum level the replication accuracy was increased from 59.34% to 96.33%. It is observed that the output from Taguchi method better matches the experimental results as compared to genetic algorithm.
This research work focuses on the development of plastic microfabrication techniques, specifically epoxy based casting for the fabrication of microfluidic platforms that can then be used for different chemical and biological applications. Over the past few years there have been various applications of miniaturization in life sciences for different areas like drug discovery in the pharmaceutical industry, molecular recognition in clinical diagnostics, cell culture and manipulation for cellular and tissue engineering, which have radically changed the way in which information is processed and experiments are performed. A casting technique using optical grade epoxies has been developed to fabricate these microfluidic systems. Miniaturization offers the possibility to integrate multiple functions onto a single platform. Two separate techniques for integration of control elements onto plastic based systems are discussed. The first one involves embedding active silicon micromachined devices in plastic microsystems using a Polymer Flip chip process and the other involves surface micromachining to build from the bottom up devices that can be integrated within the system. A polyethylene glycol (PEG) based actuator has been developed and used to fabricate nozzle-diffuser pumps that can be integrated easily within a microfluidic system. Flow rates of up to 80 nl/min and pressures of up to 1400 Pa can be generated. Work has been done in developing tools for molecular and cellular biology applications. Fabricated devices can be used for molecular assays of bio-molecules like nucleic acids and proteins. Demonstration devices were designed and fabricated to perform Polymerase Chain Reaction (PCR) and Capillary electrophoresis (CE). Also, application of microfluidics and microfabrication can be used to engineer cellular interactions with surfaces and surroundings. Cell attachment is critical to the normal functioning of the cell and requires Extra Cellular Matrix (ECM) proteins for proper attachment. An electrochemical deposition technique for patterning conductive biomolecules doped with proteins is explained. Laminar flows in channels are used to precisely control the flow of the electrolyte over the electrodes to define the area of deposition. Using this technique precisely controlled deposition of polypyyrole (PPY) doped with collagen is achieved on gold microelectrodes.
The minimization of the sample quantities required by analytical laboratories, as well as the increase of the fastness of the analytical operations are emerging axes for improved radiochemical analyses related to D&D issues. Two microsystem-based protocols were developed for the selective recovery of 55 Fe from radioactive samples by solvent extraction. Both protocols were tested on iron solutions in two different microchips. The yields of Fe extraction were compared with macroscale batch experiments. Better performances with more than 80% of iron extracted were obtained with the second protocol, which is based on a reactive transfer of the iron cation, and more suited to the use of microchannels and very low contact times. This study already demonstrate the high potential of microfluidic technology to improve analytical operations on D&D samples. This method will further be validated with radioactive samples.
Nowadays, the demand of micro-components is steadily on the rise so that it is becoming increasingly necessary to develop a process, which can manufacture the micro-component with less cost and time. In terms of cost and time Hot Embossing is the best replication technique for the manufacturing of micro-component on a mass scale. In the Hot Embossing, mostly polymers like PMMA, PC, etc. are mainly used as the work material. These replicated structures have a wide range of applications in MEMS. In single-stage hot embossing the parameters which are considered are: applied pressure, heating temperature, embossing time, and demolding temperature. The major important process parameters studied in case of Roller Hot Embossing are roller speed, roller temperature, and applied pressure. Most of the researchers tried to achieve good replication accuracy of embossed parts by varying the process parameters. The present paper aims at reviewing the work carried out in hot embossing process, different modified setups of the hot embossing process, hot embossing of different thermoplastic polymers, and simulation of hot embossing process. The papers discussed in the present review covers research work published in the past 20 years. This review papers aims at providing as consolidated source for all the research work carried out in Hot Embossing and is expected to be a help for any researcher who is new to the field. Through this paper the wiling researcher will be able to get an overview of the type of research work that has already been carried out in the field of Hot Embossing.
Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. Polymer hot embossing and injection molding are replication methods applicable to microreplication of a diversity of materials and microstructures.
Equipment with high precision control of pressure and temperature for hot embossing of polymer materials is now available commercially. These systems have made possible the replication of chips containing microchannels for capillary electrophoresis (CE) and microfluidics devices, microoptical components and microreactors. Stable and reproducible polymer microstructures have been demonstrated in several types of materials with structural and optical properties meeting other biocompatibility and detection requirements. The process involves few variable parameters and results in high structural accuracy suited for a wide range of microfabrication applications.
After demonstrating equivalent and, in cases, improved performance, the alternative use of plastic as the microdevice material addresses needs for rapid prototyping in product development and provides cost advantages in product commercialization. Thus an increasing number of devices have been reported recently in the literature, fabricated on a variety of polymer substrates and using different fabrication methods such as laser ablation, injection molding, silicone rubber casting or embossing for microfabrication.
Various microfluidic components and their characteristics, along with the demonstration of two recent achievements of lab-on-a-chip systems have been reviewed and discussed. Many microfluidic devices and components have been developed during the past few decades, as introduced earlier for various applications. The design and development of microfluidic devices still depend on the specific purposes of the devices (actuation or sensing) due to a wide variety of application areas, which encourages researchers to develop novel, purpose-specific microfluidic devices and systems. Microfluidics is the real multidisciplinary research field that requires basic knowledge in fluidics, micromachining, electromagnetics, materials, and chemistry for better applications.
Among the various application areas of microfluidics, one of the most important application areas is the lab-on-a-chip system. Lab-on-a-chip is becoming a revolutionary tool for many different applications in chemical and biological analyses due to its fascinating advantages (fast and low cost) over conventional chemical or biological laboratories. Furthermore, the simplicity of lab-on-a-chip systems will enable self-testing capability for patients or health consumers overcoming space limitation.
The fabrication of polymer based microfluidc systems requires a complex technology chain with process steps significantly different from systems based on silicon or glass. In this paper we present the fabrication technology based on polymer replication techniques, which offer the potential for low-cost high volume manufacturing of μ-TAS devices.
Resistive IC-based thin film microheating elements of polysilicon encapsulated in glass are coupled with polymeric microfluid channels. These microheating elements have several advantages over other resistive heating elements including high thermal isolation and good chemical compatibility due to the fact that they are encapsulated in glass. The microheating elements have been aligned and permanently bonded to plastic imprinted microfluid channels. The first demonstration of the utility of integrated microheating elements is their use as integrated microflow sensors.
The assembly of plastic microfluidic devices, MOEMS and microarrays requiring high positioning and welding accuracy in the micrometer range, has been successfully achieved using a new technology based on laser transmission welding combined with a photolithographic mask technique. This paper reviews a laser assembly platform for the joining of microfluidic plastic parts with its main related process characteristics and its potential for low-cost and high volume manufacturing. The system consists of a of diode laser with a mask and an automated alignment function to generate micro welding seams with freely definable geometries. A fully automated mask alignment system with a resolution of < 2 μm and a precise, non-contact energy input allows a fast welding of micro structured plastic parts with high reproducibility and excellent welding quality.
This chapter describes different techniques developed for the fabrication of polymer-based μ -TAS devices using replication methods. Polymer replication methods have gained high attention as alternative fabrication methods for microfluidic devices. They represent a pathway to a commercial fabrication of such devices as well as, in the case of casting and embossing, an attractive way of rapid prototyping. One basic property common for all replication techniques is the need for a replication master. The replication master can be fabricated by a large variety of techniques, covering the whole spectrum of microfabrication technologies developed over the years. The most widely used elastomer used for microfluidic applications is polydimethylsiloxane. Normally, at the end of any of replication processes, a polymer part is not in its final state of its use. To have a device usable for microfluidics, several back-end processes typically have to take place to finish the part. These include enclosing, metallization, and surface modification. The range of polymer materials examined for microfluidic applications is steadily increasing. So it is clear that there is not only the replication method, but for each application, a suitable method should be there to fulfill the user's needs.
This study develops a thread-based microfluidic device with variable volume injection capability and 3-dimensional (3D) detection electrodes for capillary electrophoresis electrochemical (CE–EC) detection of blood urea nitrogen (BUN) in whole blood. A poly methyl methacrylate (PMMA) substrate with concave 3D electrodes produced by the hot embossing method is used to enhance the sensing performance of the CE–EC system. Results show that the chip with 3D sensing electrodes exhibits a measured current response nine times higher and signal-to-noise ratio five times higher when compared to the peak responses obtained using a chip with conventional 2D sensing electrodes. In addition, the developed thread-based microfluidic system is capable of injecting variable sample volumes into the separation thread simply by wrapping the injection thread different numbers of times around the separation thread. The peak S/N ratio can be further enhanced with this simple approach. Results also indicate that the CE–EC system exhibits good linear dynamic range for detecting a urea sample in concentrations from 0.1 to 10.0 mM (R
2 = 0.9848), which is suitable for adoption in detecting the BUN concentration in human blood (1.78–7.12 mM). Separation and detection of the ammonia ions converted from BUN in whole blood is successfully demonstrated in the present study, with the developed thread-based microfluidic system providing a low-cost, high-performance method for detecting BUN in human blood.
A miniaturized monolithically integrated plastic thermal reactor has been realized using plastic casting method. The thermal reactor device consists of a reaction chamber, a resistive heater, a thermal electric device and a thermocouple. The temperature in the reaction chamber is controlled through a PC programmable processor. The typical heating and cooling rates were 2.4°C/s and 2°C/s respectively. The thermal characteristic of the device was also studied through modeling. On−chip lysis of Escherichia coli cells and subsequent amplification of the released genomic DNA segments were demonstrated.
In den Life Sciences erleben wir zur Zeit eine Revolution, die nur mit der Begründung der Informationsgesellschaft durch die Mikroelektronik zu vergleichen ist. Der Einsatz der Mikrosystemtechnik bei der Erforschung des menschlichen Genoms, der Wirkstofforschung in der pharmazeutischen Industrie, der klinischen Diagnostik oder der analytischen Chemie beschleunigt nicht nur die konventionellen Technologien und verändert unser Verständnis von chemischer Analytik, sondern ermöglicht auch völlig neue Zugänge zur Informationsgewinnung auf molekularer Ebene [1].
Capillary electrophoresis and related techniques on microchips have made great strides in recent years. This review concentrates on progress in capillary zone electrophoresis, but also covers other capillary techniques such as isoelectric focusing, isotachophoresis, free flow electrophoresis, and micellar electrokinetic chromatography. The material and technologies used to prepare microchips, microchip designs, channel geometries, sample manipulation and derivatization, detection, and applications of capillary electrophoresis to microchips are discussed. The progress in separation of nucleic acids and proteins is particularly emphasized.
Over the past two decades, the application of microengineered systems in the chemical and biological sciences has transformed the way in which high-throughput experimentation is performed. The ability to fabricate complex microfluidic architectures has allowed scientists to create new experimental formats for processing ultra-small analytical volumes in short periods and with high efficiency. The development of such microfluidic systems has been driven by a range of fundamental features that accompany miniaturization. These include the ability to handle small sample volumes, ultra-low fabrication costs, reduced analysis times, enhanced operational flexibility, facile automation, and the ability to integrate functional components within complex analytical schemes. Herein we discuss the impact of microfluidics in the area of high-throughput screening and drug discovery and highlight some of the most pertinent studies in the recent literature.
The use of SU-8 based optofluidic systems (OFS) is validated as an affordable and easy alternative to expensive glass device manufacturing for small molecule crystallization studies and, in comparison with other polymers, able to withstand most organic solvents. A comparison between two identical OFS (using SU-8 and polydimethylsiloxane, PDMS) against the 36 most commonly used organic solvents for small molecule crystallization studies have confirmed both the structural and optical stability of the SU-8, whereas PDMS suffered from unsealing or tearing in most cases. In order to test its compatibility, measurements before and after 24 hours of continued exposure against solvents have been pursued. Here, three aspects have been considered: in the macroscale, swelling has been determined by analyzing the variations in the optical path in the OFS. For determining compatibility at microscale, fabricated SU-8 micropatterns were solvent etched and subsequently characterized by SEM. Roughness of the polymer has also been studied through AFM measurements at nanoscale. Experimental measurements of PDMS swelling were in accordance with previously reported observations, whilst SU-8 displayed a great stability against all the tested solvents. Through this experimental procedure we also show that the OFS are suitable for real time, on-chip, UV-Vis spectroscopy. Micro and nano scale observations did not show apparent corrosion on SU-8 surface. Also two commonly used carrier fluids for microdroplet generation (FC-70 fluorinert oil and Silicone oil) were also tested against the different solvents with the aim of providing useful information for later microbatch experiments.
Biotechnology, in conjunction with semiconductor and microelectronics, would have a tremendous impact on new solutions in gene and drug discovery, point-of-care systems, pharmacogenomics, and environmental and food safety applications. A combination of microfabrica-tion techniques and molecular biology procedures have the potential to produce powerful, inexpensive, and miniature analytical devices (e.g., microfluidic lab chips), aiding further development of genetic analysis. Microfluidics for biotechnology applications require development of inexpensive, high-volume fabrication techniques and reduction of biochemical assays to the chip format. We discuss design, fabrication, and testing of plastic microfluidic devices for on-chip genetic sample preparation and DNA microarray detection. Plastic microfabrication methods are being used to produce components of a complete microsystem for genetic analysis. A detailed discussion on the development of micromixers, mi-crovalves, cell capture, micro-polymerase chain reaction (PCR) devices, and biochannel hybridization arrays is given. We also describe a path to further individual component integration.
The move to miniaturization of biomedical systems offers tremendous potential for the improvement of health care, both in terms of reduced analysis time, and in significantly lowering the volume requirements of patient blood, or other bodily fluid. In order to fabricate microchannels for microfluidics, we have investigated two approaches using high-density plasma etching to achieve channel depths of 20–50 microns. The first was plasma etching of tapered silicon masters for hot embossing of plastics to form a capillary electrophoresis device. The second approach was the direct plasma etching of plastic to form a microfluidics device for DNA analysis. In both cases, we report the development of optimized etch conditions using SAS Institute, Inc. design of experiment software. © 2001 American Vacuum Society.
Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. We present in this paper the technology of hot embossing as a flexible, low-cost microfabrication method for polymer microstructures, which uses the replication of a micromachined embossing master to generate microstructures on a polymer substrate. With this fabrication technology high aspect ratio structures can be fabricated over large surface areas, which allows a commercially successful manufacturing of polymer microcomponents.
Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. Polymer hot embossing and injection molding are replication methods applicable to microreplication of a diversity of materials and microstructures.Equipment with high precision control of pressure and temperature for hot embossing of polymer materials is now available commercially. These systems have made possible the replication of chips containing microchannels for capillary electrophoresis (CE) and microfluidics devices, microoptical components and microreactors. Stable and reproducible polymer microstructures have been demonstrated in several types of materials with structural and optical properties meeting other biocompatibility and detection requirements. The process involves few variable parameters and results in high structural accuracy suited for a wide range of microfabrication applications.After demonstrating equivalent and, in cases, improved performance, the alternative use of plastic as the microdevice material addresses needs for rapid prototyping in product development and provides cost advantages in product commercialization. Thus an increasing number of devices have been reported recently in the literature, fabricated on a variety of polymer substrates and using different fabrication methods such as laser ablation, injection molding, silicone rubber casting or embossing for microfabrication.
Abstract The separation of cells is an important technology,in medicine. Every day millions of separations are conducted in hospitals all over the world. The most,common separation might be the separation of whole blood into its di! erent parts. This is one of the most challenging problems,there is in separation science. The blood has a myriad of di!eren t constituents. Within each little drop there are more than hundreds, if not thousands, of di! erent cells, proteins, markers and other biological data that can hold the key to the diagnosis of a particular disease. But, as can be imagined, it is not all that easy to find what,you are looking for. Adequate separation techniques are essential for proper diagnostics.,In this project an attempt to separate cells di! ering in size has been made. Separation of cells, and especially of whole blood, is an old scientific practice that has been in use for more,than a century. Right now we are standing on the verge of a new,revolution. The use of micro- and nanotechnology,in separation shows great promise. This could make it possible to analyze minute samples of proteins and cells, and at the same time have a very high through-put, be cheap and easy to use. This project examines,a novel separation technique that has shown very promising results on polystyrene beads, and could possibly be used to separate cells discriminating solely on size. The technique is based on the use of a device called "the bumper array". The device has been developed by Robert Austin’s lab at Princeton University[7][23][24]. It relies on a simple,geometric,pattern that creates discrete flow lines in a microfluidic
A micro total analytical system (μTAS) is a system that enhances the performance of a complete chemical analysis by minimizing the scale on which it is performed. The main advantages are automated analyses, higher speed and better separation performance as well as the ability to analyze extremely small (picoliter) sample volumes and reactions involving minute amounts of reagents. A complete analysis may involve taking a sample, its pretreatment and separation into its different components and their detection. In order to perform this sequence of functions, the sample is transported through microchannels that connect the various system parts performing these tasks, while the various (feedback) signals are transported through a separate microelectronic network. Examples of system parts in silicon, glass and polymers that perform tasks such as hydrodynamic and electroosmotic pumping, laminar and turbulent reagent mixing and (di)electrophoretic separations of DNA fragments and particles and cells are presented. Currently, μTAS are mainly being developed and used for remote environmental and process monitoring, patient monitoring and the analysis of nucleic acids. An integrated system in each of these areas is discussed.
DNA microarray technology has become one of the most promising analytical tools in molecular biology. It has been widely used
for studying mRNA levels and examining gene expression in biological samples. It is becoming a powerful tool in the arena
of diagnostics and personalized medicine. In this chapter, we present a fully integrated and self-contained microfluidic biochip
device that has been developed to automate the fluidic handling steps required to carry out microarray-based gene expression
or genotyping analysis. The device consists of a semiconductor-based CustomArray™ chip with 12,000 features and a microfluidic
cartridge. The CustomArray™ was manufactured using a semiconductor-based in situ synthesis technology. The oligonucleotides
were synthesized on an array of electrodes on a semiconductor chip using phosphoramidite chemistry under electrochemical control.
The microfluidic cartridge consists of microfluidic pumps, mixers, valves, fluid channels and reagent storage chambers. Microarray
hybridization and subsequent fluidic handling and reactions (including a number of washing and labeling steps) were performed
in this fully automated and miniature device before fluorescent image scanning of the microarray chip. Electrochemical micropumps
were integrated in the cartridge to provide pumping of liquid solutions. A micromixing technique based on gas bubbling generated
by electrochemical micropumps was developed. Low-cost check valves were implemented in the cartridge to prevent cross talk
of the stored reagents. Gene expression study of the human leukemia cell line (K562) and genotyping detection and sequencing
of influenza A subtypes have been demonstrated using this integrated biochip platform. For gene expression assays, the microfluidic
CustomArray™ device detected sample RNAs with a concentration as low as 0.375 pM. Detection was quantitative over more than
three orders of magnitude. Experiment also showed that chip-to-chip variability was low indicating that the integrated microfluidic
devices eliminate manual fluidic handling steps that can be a significant source of variability in genomic analysis. The genotyping
results showed that the device identified influenza A hemagglutinin and neuraminidase subtypes and sequenced portions of both
genes, demonstrating the potential of integrated microfluidic and microarray technology for multiple virus detection. The
device provides a cost-effective solution to eliminate labor-intensive and time-consuming fluidic handling steps and allows
microarray-based DNA analysis in a rapid and automated fashion.
Rapid developments in back-end detection platforms (such as DNA microarrays, capillary electrophoresis, real-time polymerase
chain reaction and mass spectroscopy) for genetic analysis have shifted the bottleneck to front-end sample preparation where
the ‘real’ samples are used. In this chapter, we present a fully integrated biochip device that can perform on-chip sample
preparation (including magnetic bead-based cell capture, cell preconcentration and purification and cell lysis) of complex
biological sample solutions (such as whole blood), polymerase chain reaction, DNA hybridization and electrochemical detection.
This fully automated and miniature device consists of microfluidic mixers, valves, pumps, channels, chambers, heaters and
DNA microarray sensors. Cavitation microstreaming was implemented to enhance target cell capture from whole blood samples
using immunomagnetic beads and accelerate DNA hybridization reaction. Thermally actuated paraffin-based microvalves were developed
to regulate flows. Electrochemical pumps and thermopneumatic pumps were integrated on the chip to provide pumping of liquid
solutions. The device is completely self-contained: no external pressure sources, fluid storage, mechanical pumps, or valves
are necessary for fluid manipulation, thus eliminating possible sample contamination and simplifying device operation. Pathogenic
bacteria detection from ≈ mL whole blood samples and single-nucleotide polymorphism analysis directly from diluted blood were
demonstrated. The device provides a cost-effective solution to direct sample-to-answer genetic analysis and thus has a potential
impact in the fields of point-of-care genetic analysis, environmental testing and biological warfare agent detection.
Microarray assays typically involve multistage sample processing and fluidic handling, which are generally labor-intensive
and time-consuming. Automation of these processes would improve robustness, reduce run-to-run and operator-to-operator variation,
and reduce costs. In this chapter, a fully integrated and self-contained microfluidic biochip device that has been developed
to automate the fluidic handling steps for microarray-based gene expression or genotyping analysis is presented. The device
consists of a semiconductor-based CustomArray® chip with 12,000 features and a microfluidic cartridge. The CustomArray was
manufactured using a semiconductor-based in situ synthesis technology. The micro-fluidic cartridge consists of microfluidic
pumps, mixers, valves, fluid channels, and reagent storage chambers. Microarray hybridization and subsequent fluidic handling
and reactions (including a number of washing and labeling steps) were performed in this fully automated and miniature device
before fluorescent image scanning of the microarray chip. Electrochemical micropumps were integrated in the cartridge to provide
pumping of liquid solutions. A micromixing technique based on gas bubbling generated by electrochemical micropumps was developed.
Low-cost check valves were implemented in the cartridge to prevent cross-talk of the stored reagents. Gene expression study
of the human leukemia cell line (K562) and genotyping detection and sequencing of influenza A subtypes have been demonstrated
using this integrated biochip platform. For gene expression assays, the microfluidic CustomArray device detected sample RNAs
with a concentration as low as 0.375 pM. Detection was quantitative over more than three orders of magnitude. Experiment also
showed that chip-to-chip variability was low indicating that the integrated microfluidic devices eliminate manual fluidic
handling steps that can be a significant source of variability in genomic analysis. The genotyping results showed that the
device identified influenza A hemagglutinin and neuraminidase subtypes and sequenced portions of both genes, demonstrating
the potential of integrated microfluidic and microarray technology for multiple virus detection. The device provides a cost-effective
solution to eliminate labor-intensive and time-consuming fluidic handling steps and allows microarray-based DNA analysis in
a rapid and automated fashion.
Various microfluidic components and their characteristics, along with the demonstration of two recent achievements of lab-on-chip
systems are reviewed and discussed. Many microfluidic devices and components have been developed during the past few decades,
as introduced earlier for various applications. The design and development of microfluidic devices still depend on the specific
purposes of the devices (actuation and sensing) due to awide variety of application areas, which encourages researchers to
develop novel, purpose-specific microfluidic devices and systems. Microfluidics is the multidisciplinary research field that
requires basic knowledge in fluidics, micromachining, electromagnetics, materials, and chemistry for various applications.
Among the various application areas of microfluidics, one of the most important is the lab-on-a-chip system. Lab-on-a-chip
is becoming arevolutionary tool for many different applications in chemical and biological analyses due to its fascinating
advantages (fast speed and low cost) over conventional chemical or biological laboratories. Furthermore, the simplicity of
lab-on-a-chip systems will enable self-testing capability for patients or health consumers by overcoming space limitations.
A new pathway for the generation of polymer‐based microfluidic devices with tailor‐made surface chemistry is described. A simple photochemical process is used to covalently bind polymer molecules to the surfaces of microchannels fabricated by hot embossing. The substrates for the embossing process have the format of a compact disk (CD). CDs from polymethylmethacrylate and polyethylene‐ co ‐norbornene were chosen due to their good optical properties. Thin films of polymers containing photoactive benzophenone units were deposited onto the surface of the thus generated devices. These films were subsequently irradiated with UV light leading to the surface‐attachment of ultrathin polymer networks. In contrast to their unmodified peers, the obtained, modified microfluidic channels coated with hydrophilic, photoattached layers can be filled in a straightforward manner with water by capillary forces. Channels coated by thin films of poly(ethyloxazoline) show complete resistance to non‐specific protein binding. Generation of hydrophobic patches inside the modified microfluidic channels using benzophenone‐containing fluoropolymers allows the generation of passive microfluidic valves to direct fluid motion in these CD‐based devices.
magnified image
The physical morphology and chemical functionality of fluid microchannels formed in poly(methyl methacrylate) (PMMA) substrates were studied to increase the fundamental understanding of polymer microchannel surface properties for ‘lab-on-a-chip’ devices. Microchannels were formed by a hot-imprint method using a silicon template or by a laser ablation process (248 nm KrF laser) operating at low to moderate fluence levels (up to 1180 mJ/cm2). The carboxylate groups, which are responsible for the surface charges, were fluorescently labeled by reaction with an ethyl-dimethylaminopropyl-carbodiimide hydrochloride/amino-fluorescein solution. Fluorescence microscopy was then used to locate and measure qualitatively the charge present on the microchannel walls. Results suggest that surface charges are localized on the corners of trapezoidal channels formed by the hot-imprint method and that the amount of charge present is significantly less compared to laser-ablated microchannels where charges appear to be distributed uniformly. For substrates irradiated at fluences above the laser ablation threshold, it was found that one pass of the laser produced a surface with greater charge than channels made with multiple passes, that ablation under nitrogen resulted in more charge than ablation under oxygen, and that non-sonicated substrates had more charge than samples that were sonicated after ablation. Trends in the data for sonicated samples are explained through scanning electron microscopy images showing etch depth and UV-laser penetration to depths below the surface of the formed microchannel. Finally, we have determined that the surface charge on the substrate can be modified by using the laser at fluence levels lower than those required to ablate the substrate.
Several commercially available plastic materials were used as substrates in the fabrication of microfluid channels for biochemical analysis. Protocols for fabrication using the wire-imprinting method are reported for polystyrene, polymethylmethacrylate and a copolyester material. Channel sealing was accomplished by low-temperature bonding of a substrate of similar material; therefore, each channel was composed of a single material on all sides. The electroosmotic flow in 25-microm imprinted channels was evaluated for each substrate material. The copolyester material exhibited the highest electroosmotic flow mobility of 4.3 x 10(-4) cm2 V(-1) s(-1) which is similar to that previously reported for fused-silica capillaries. Polystyrene exhibited the lowest electroosmotic flow mobility of 1.8 x 10(-4) cm2 V(-1) s(-1). Plots of linear velocity versus applied electric field strength were linear from 100 V cm(-1) to 500 V cm(-1) indicating that heat dissipation is effective for all substrates in this range. Electroosmotic flow was reevaluated in the plastic channels following incubation in antibody solution to access the non-specific binding characteristics of a common biochemical reagent onto the substrate materials. All materials tested showed a high degree of non-specific adsorption of IgG as indicated by a decrease in the electroosmotic flow mobility in post-incubation testing.
Protocols are described for control of the electroosmotic flow in microfabricated channels in Vivak copolyester. Alkaline hydrolysis of surface ionizable groups alone or such hydrolysis in combination with dynamic coating with cetyltrimethylammonium bromide (CTAB) is shown to provide reproducible electroosmotic flows. Dynamic coating with CTAB can be used to eliminate electroosmosis or to reverse its direction, depending on the concentration employed.
Electrokinetic forces are emerging as a powerful means to drive microfluidic systems with flow channel cross-sectional dimensions in the tens of micrometers and flow rates in the nanoliter per second range. These systems provide many advantages such as improved analysis speed, improved reproducibility, greatly reduced reagent consumption, and the ability to perform multiple operations in an integrated fashion. Planar microfabrication methods are used to make these analysis chips in materials such as glass or polymers. Many applications of this technology have been demonstrated, such as DNA separations, enzyme assays, immunoassays, and PCR amplification integrated with microfluidic assays. Further development of this technology is expected to yield higher levels of functionality of sample throughput on a single microfluidic analysis chip.
Microfabrication uses integrated-circuit manufacturing technology supplemented by its own processes to create objects with dimensions in the range of micrometers to millimeters. These objects can have miniature moving parts, stationary structures, or both. Microfabrication has been used for many applications in biology and medicine. These applications fall into four domains: tools for molecular biology and biochemistry, tools for cell biology, medical devices, and biosensors. Microfabricated device structures may provide significantly enhanced function with respect to a conventional device. Sometimes microfabrication can enable devices with novel capabilities. These enhancing and enabling qualities are conferred when microfabrication is used appropriately to address the right types of problems. Herein, we describe microfabrication technology and its application to biology and medicine. We detail several classes of advantages conferred by microfabrication and how these advantages have been used to date.
In this paper, we describe the fabrication technologies necessary for the production of polymer-based micro-fluidic devices. These technologies include hot embossing as a micro-structuring method as well as so-called back-end processes to complete the micro-devices. Applications such as capillary electrophoresis, micro-mixers and nanowell plates are presented.
DNA probe immobilization on plastic surfaces and device assembly are both critical to the fabrication of microfluidic hybridization array channel (MHAC) devices. Three oligonucleotide (oligo) probe immobilization procedures were investigated for attaching oligo probes on four different types of plastic surfaces (polystyrene, polycarbonate, poly(methylmethacrylate), and polypropylene). These procedures are the Surmodics procedure, the cetyltrimethylammonium bromide (CTAB) procedure, and the Reacti-Bind procedure. To determine the optimal plastic substrate and attachment chemistry for array fabrication, we investigated plastic hydrophobicity, intrinsic fluorescence, and oligo attachment efficiency. The Reacti-Bind procedure is least effective for attaching oligo probes in the microarray format. The CTAB procedure performs well enough to use in array fabrication, and the concentration of CTAB has a significant effect on oligo immobilization efficiency. We also found that use of amine-modified oligo probes resulted in better immobilization efficiency than use of unmodified oligos with the CTAB procedure. The oligo probe immobilization on plastic surfaces by the Surmodics procedure is the most effective with regard to probe spot quality and hybridization sensitivity. A DNA hybridization assay on such a device results in a limit of detection of 12pM. Utilizing a CO(2) IR laser machining and adhesive layer approach, we have developed an improved procedure for realizing a DNA microarray inside a microfluidic channel. This device fabrication procedure allows for more feasible spot placement in the channel and reduced sample adsorption by adhesive tapes used in the fabrication procedure. We also demonstrated improved hybridization kinetics and increased detection sensitivity in MHAC devices by implementing sample oscillation inside the channel. A limit of detection of 5pM has been achieved in MHAC devices with sample oscillation.
Technological advances in miniaturization have found a niche in biology and signal the beginning of a new revolution. Most of the attention and advances have been made with DNA chips yet a lot of progress is being made in the use of other biomolecules and cells. A variety of reviews have covered only different aspects and technologies but leading to the shared terminology of "biochips." This review provides a basic introduction and an in-depth survey of the different technologies and applications involving the use of non-DNA molecules such as proteins and cells. The review focuses on microarrays and microfluidics, but also describes some cellular systems (studies involving patterning and sensor chips) and nanotechnology. The principles of each technology including parameters involved in biochip design and operation are outlined. A discussion of the different biological and biomedical applications illustrates the significance of biochips in biotechnology.
A fully integrated and self-contained microfluidic biochip device has been developed to automate the fluidic handling steps required to perform a gene expression study of the human leukemia cell line (K-562). The device consists of a DNA microarray semiconductor chip with 12,000 features and a microfluidic cartridge that consists of microfluidic pumps, mixers, valves, fluid channels and reagent storage chambers. Microarray hybridization and subsequent fluidic handling and reactions (including a number of washing and labeling steps) were performed in this fully automated and miniature device before fluorescent image scanning of the microarray chip. Electrochemical micropumps were integrated in the cartridge to provide pumping of liquid solutions. A micromixing technique based on gas bubbling generated by electrochemical micropumps was developed. Low-cost check valves were implemented in the cartridge to prevent cross-talk of the stored reagents. A single-color transcriptional analysis of K-562 cells with a series of calibration controls (spiked-in controls) was performed to characterize this new platform with regard to sensitivity, specificity and dynamic range. The device detected sample RNAs with a concentration as low as 0.375 pM. Detection was quantitative over more than 3 orders of magnitude. Experiments also demonstrated that chip-to-chip variability was low, indicating that the integrated microfluidic devices eliminate manual fluidic handling steps that can be a significant source of variability in genomic analysis.
D.Quin, Y. Xia , J.A. Rogers, R.J. Jackman, X.-M. Zhao, G.M. Whitesides: Microfabrication, Microstructures and Microsystems .- A. van den Berg, T.S.J. Lammerink: Micro Total Analysis Systems: Microfluidic Aspects, Integration Concept and Applications .- C.S. Effenhauser: Integrated Chip-Based Microcolumn Separation Systems .- G. Fuhr, S.G. Shirley: Biological Application of Microstructures .- R.C. Anderson, G. McGall, R.J. Lipshutz: Polynucleotide Arrays for Genetic Sequence Analysis .- T. Stieglitz, J.W. Meyer: Microtechnical Interfaces to Neurons .- S. Shoji: Fluids for Sensor Systems .- G.A. Urban, G.Jobst: Sensor Systems .- J. Cheng, L.J. Kricka, E.L. Sheldon, P. Wilding: Sample Preparation in Microstructures Devices .- W. Ehrfeld, V. Hessel, H. Lehr: Microreactors for Chemical Synthesis and Biotechnology - Current Developments and Future Applications.
We have fabricated a planar chip on a fused quartz substrate with a two-dimensional channel array for capillary electrophoresis applications. The first separation dimension consists of a single channel 16 mm long, 80 m wide and 3-7 m deep; the second separation dimension of an array of 500 channels, 5 mm long, 900 nm wide and 3-6 m deep. The channels were fabricated using reactive ion etching under maximum anisotropic etching conditions, yielding an aspect ratio of up to 5 for the narrow channels. The microchannels were closed using a novel NaOH assisted bonding technique.
For fabricating microstructures with extreme structural heights a technology has been developed which is based on deep-etch lithography and subsequent replication processes. A particularly high precision is achieved when the lithographic process is carried out by means of synchrotron radiation. Electroforming and molding processes are used for the replication of microstructures from a large variety of materials. The field of application comprises sensors, electrical and optical microconnectors, components for fluid technology, micromechanical components, microfiltration systems and novel composite materials.
Following the trend towards smaller channel inner diameter for better separation performance and shorter channel length for shorter transport time, a modular construction of a miniaturized 'total chemical analysis system' is proposed. The theoretical performances of such systems based on flow injection analysis, chromatography and electrophoresis, are compared with those of existing chemical sensors and analysis systems.
This report describes a UV laser photoablation method for the production of miniaturized liquid-handling systems on polymer substrate chips. The fabrication of fluid channel and reservoir networks is accomplished by firing 200 mJ pulses from an UV excimer laser at substrates moving in predefined computer-controlled patterns. This method was used for producing channels in polystyrene, polycarbonate, cellulose acetate, and poly(ethylene terephthalate). Efficient sealing of the resulting photoablated polymer channels was accomplished using a low-cost film lamination technique. After fabrication, the ablated structures were observed to be well defined, i.e., possessing high aspect ratios, as seen by light, scanning electron, and atomic force microscopy. Relative to the original polymer samples, photoablated surfaces showed an increase in their hydrophilicity and rugosity as a group, yet differences were noted between the polymers studied. These surface characteristics demonstrate the capability of generating electroosmotic flow in the cathodic direction, which is characterized here as a function of applied electric field, pH, and ionic strength of common electrophoretic buffer systems. These results show a correlation between the ablative changes in surface conditions and the resulting electroosmotic flow. The effect of protein coatings on ablated surfaces is also demonstrated to significantly dampen the electroosmotic flow for all polymers. All of these results are discussed in terms of developing liquid-handling capability, which is an essential part of many μ-TAS and chemical diagnostic systems.
Microfabricated electrophoretic separation devices have been produced by an injection-molding process. The strategy for producing the devices involved solution-phase etching of a master template on a silicon wafer, followed by electroforming more durable injection-molding masters in nickel from the silicon master. One of the nickel electroforms was then used to prepare an injection mold insert, from which microchannel chips in an acrylic substrate were mass-produced. The microchannel devices were used to demonstrate high-resolution separations of double-stranded DNA fragments with total run times of less than 3 min. Run-to-run and chip-to-chip reproducibility was good, with relative standard deviation values below 1% for the run-to-run data and in the range of 2-3% for the chip-to-chip comparisons. Such devices could lead to the production of low-cost, single-use electrophoretic chips suitable for a variety of separation applications, including DNA sizing, DNA sequencing, random primary library screening, and rapid immunoassay testing.
Microfluidic devices have been fabricated on poly(methyl methacrylate) substrates by two independent imprinting techniques. First-generation devices were fabricated using a small-diameter wire to create an impression in plastics softened by low-temperature heating. The resulting devices are limited to only simple linear channel designs but are readily produced at low cost. Second-generation devices with more complex microchannel arrangements were fabricated by imprinting the plastic substrates using an inverse three-dimensional image of the device micromachined on a silicon wafer. This micromachined template may be used repeatedly to generate devices reproducibly. Fluorescent analtyes were used to demonstrate reproducible electrophoretic injections. An immunoassay was also performed in an imprinted device as a demonstration of future applications.
In the past year, microchips as applied to miniaturised total analysis systems, or microTAS, have benefited from technological improvements in their fabrication and been applied to analysis in many different biological areas. From a technological perspective, salient work includes fast, cheap and easy micromachining in polymers and integrated optical detection. From the bioapplications perspective, advances in DNA and protein separations, cell manipulations, immunoassays and polymerase chain reaction using on-chip electrophoretic separation stand out.
- L E Locasico
L.E. Locasico, Anal. Chem 69 (1997), 4783-4789.
- M A Roberts
- J S Rossier
- P Bercier
- H Girault
M.A.Roberts, J.S.Rossier, P.Bercier, H.Girault, Anal. Chem. 69 (11) (1997) 2035-2042.
- W Ehrfeld
- D Münchmeyer
W.Ehrfeld, D.Münchmeyer, Nucl. Instrum. Methods A303 (1991), 523-532.
- C S Effenhauser
- G J M Bruin
- A Paulus
- M Ehrat
C.S. Effenhauser, G.J.M. Bruin, A.Paulus, M.Ehrat, Proceedings -TAS '96, Anal.
Methods Instrum. Special Issue (1996), 124-125.
- A Manz
- W Graber
- H Widmer
A.Manz., W.Graber, H.N Widmer, Sensors and Actuators, B1 (1990), 244-248.