Integration of electrochemistry in micro-total analysis systems for biochemical assays: Recent developments

Micro-total analysis systems (μTAS) integrate different analytical operations like sample preparation, separation and detection into a single microfabricated device. With the outstanding advantages of low cost, satisfactory analytical efficiency and flexibility in design, highly integrated and miniaturized devices from the concept of μTAS have gained widespread applications, especially in biochemical assays. Electrochemistry is shown to be quite compatible with microanalytical systems for biochemical assays, because of its attractive merits such as simplicity, rapidity, high sensitivity, reduced power consumption, and sample/reagent economy. This review presents recent developments in the integration of electrochemistry in microdevices for biochemical assays. Ingenious microelectrode design and fabrication methods, and versatility of electrochemical techniques are involved. Practical applications of such integrated microsystem in biochemical assays are focused on in situ analysis, point-of-care testing and portable devices. Electrochemical techniques are apparently suited to microsystems, since easy microfabrication of electrochemical elements and a high degree of integration with multi-analytical functions can be achieved at low cost. Such integrated microsystems will play an increasingly important role for analysis of small volume biochemical samples. Work is in progress toward new microdevice design and applications.     

Three-dimensional closed microfluidic channel fabrication by stepper projection single step lithography: the diabolo effect

Microfluidic devices are currently being used in many types of biochemical microsystems for liquid phase analysis in the frame of medical applications. This paper presents a new technique for the realization of microfluidic channels using SU-8, a commonly used epoxy-based negative photo-resist. These microchannels were fabricated by a single stepper UV-photolithography process. By changing the process parameters, e.g. the optical focus depth and the UV exposure dose, well-defined, covered microchannels with various dimensions and aspect ratios were realized and proven to be effective for the fluid transport by capillarity. This technique can easily be used for the fabrication of microfluidic devices in the microanalysis and lab-on-chip applications realm.     

Electrochemical techniques for microfluidic applications

Electrochemical principles provide key techniques to promote the construction of bio/chemical microsystems of the next generation. There is a wealth of technology for the microfabrication of bio/chemical sensors. In addition, microfluidic transport in a network of flow channels, pH regulation, and automatic switching can be realized by electrochemical principles. Since the basic components of the devices are electrode patterns, the integration of different components is easily achieved. With these techniques, bio/chemical assays that require the exchange of solutions can be conducted on a chip. Furthermore, autonomous microanalysis systems that can carry out necessary procedures are beginning to be realized. In this article, techniques developed in our group will be comprehensively introduced.     

Analytical-process supercritical fluid extraction: a synergestic combination for solving analytical and laboratory scale problems

Identical principles govern the theory and application of supercritical fluid extraction (SFE) whether they are applied in the field of chemical engineering or analytical chemistry. We have used these principles to develop instrumentation and methodology that can be used to solve a wide range of analytical and laboratory problems. The development of larger scale extractors for analytical use will be presented, including modules which allow the extraction of larger samples, multiple samples simultaneously, and highly viscous materials. Key components in the design of these extractors, such as fluid delivery systems, collection devices, and cosolvent addition schemes, will also be described. This equipment and the components have been integrated into a laboratory-wide extraction and processing system.     

Bulk electrochemical etching of semiconductor single-crystal silicon in HF-containing solutions

Effect of the component composition of an HF-containing electrolytic aqueous solution on the polishing electrochemical etching of semiconductor single-crystal silicon was studied. Propanol-2, SV-1017, and NH₄F served as additional components of solutions used for this purpose. The conditions in which this process can be employed to form elements with 3D structure in microsystems devices were determined. An analysis of the results obtained led to an assumption that the hydrogen passivation of the surface of semiconductor single-crystal silicon is the rate-determining factor affecting the development of a bulk polishing electrochemical etching of this material. Because the process of polishing electrochemical etching of silicon wafers is preserved during approximately 20 min, the method is acceptable for formation of shallow grooves in microsystems devices.     

Thermal lens detection device

A thermal lens detection device was developed to realize an easy-to-use, portable and sensitive detector for nonfluorescent molecules. Two laser diodes (658 nm for excitation and 785 nm for probe) were made coaxial in an optical unit and were coupled to a single-mode optical fiber. On a microfluidic chip, a small holder for the optical fiber was fixed, and micro-lenses (numerical aperture of 0.2) were also integrated inside the holder. The micro-lenses were designed to realize an adequate chromatic aberration (50 μm), which was essential for sensitive thermal lens detection. Compared with conventional thermal lens detection systems which required very laborious and accurate optical alignment with the microchannel, the new device needed just attachment-detachment of the optical fiber, which was important for practical application. The lower limit of detection was 10 nM for nickel(II) phthalocyaninetetrasulfonic acid tetrasodium salt solutions (model sample), and the absorbance was 9 × 10(-6) AU. The absolute number of molecules detected was less than 200 zmol. The coefficient of variance for 5-time attachment-detachment of the optical probe was as small as 3.6%. The technical development allowed integration of the thermal lens detection devices inside a microsystem (e.g. enzyme-linked immuno-sorbent assay system), and practical microsystems were realized with sensitivities several-orders higher than absorptiometry.     

Miniaturized isothermal nucleic acid amplification, a review

Micro-Total Analysis Systems (μTAS) for use in on-site rapid detection of DNA or RNA are increasingly being developed. Here, amplification of the target sequence is key to increasing sensitivity, enabling single-cell and few-copy nucleic acid detection. The several advantages to miniaturizing amplification reactions and coupling them with sample preparation and detection on the same chip are well known and include fewer manual steps, preventing contamination, and significantly reducing the volume of expensive reagents. To-date, the majority of miniaturized systems for nucleic acid analysis have used the polymerase chain reaction (PCR) for amplification and those systems are covered in previous reviews. This review provides a thorough overview of miniaturized analysis systems using alternatives to PCR, specifically isothermal amplification reactions. With no need for thermal cycling, isothermal microsystems can be designed to be simple and low-energy consuming and therefore may outperform PCR in portable, battery-operated detection systems in the future. The main isothermal methods as miniaturized systems reviewed here include nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP), helicase-dependent amplification (HDA), rolling circle amplification (RCA), and strand displacement amplification (SDA). Also, important design criteria for the miniaturized devices are discussed. Finally, the potential of miniaturization of some new isothermal methods such as the exponential amplification reaction (EXPAR), isothermal and chimeric primer-initiated amplification of nucleic acids (ICANs), signal-mediated amplification of RNA technology (SMART) and others is presented.     

An integrative review on the applications of 3D printing in the field of in vitro diagnostics

Biomedicine is one of the fastest growing areas of additive manufacturing. Especially, in the field of in vitro diagnostics(IVD), contributions of 3D printing include ⅰ) rapid prototyping and iterative IVD proofof-concept designing ranging from materials, devices to system integration; ⅱ) conceptual design simplification and improved practicality of IVD products; ⅲ) shifting the IVD applications from centralized labs to point-of-care testing(POCT). In this review, the latest developments of 3D p...     

CMOS-Based Bio/Chemosensor and Bioelectronic Microsystems

Microfabrication techniques and, in particular, complementary-metal-oxide-semiconductor (CMOS) technology have been used to devise chemo/biosensors [1-3] as well as bioelectronic microsystems [4-7]. Examples of micromachined bio- or chemosensors, such as cantilevers or micoelectrode arrays, will be shown, and the electrical interfacing of CMOS microelectronics with biological entities or electrogenic cells, i.e., cells that react upon electrical stimulation and, in turn, produce electrical signals (heart cells or neurons) are detailed. CMOS-based, fully integrated microelectrode arrays for bidirectional communication (stimulation and recording) with electrogenic cells are presented. These devices are capable of monitoring relevant electrophysiological responses of cells to electrical stimuli or to pharmacological agents with prospective applications in the field of bio-inspired information processing or pharmascreening.     

Towards computer-supported management of analytical laboratories

In daily practice, the laboratory management must control several complex data flows in the analytical laboratory. Computer aids to support the management are discussed. Commercially available laboratory information management systems (LIMS) apply to the flow of data about the individual samples and the subsequent test results. Additional software modules are needed to deal with data about the performance of the laboratory as an organization, to provide decision support. Two modules for this purpose are presented: FEA for processing of historical laboratory data and LABGEN for application of digital simulation by the laboratory management.     

The liquid-liquid diffusive extraction of hydrocarbons from a North Sea oil using a microfluidic format

Extraction of a GC-amenable hydrocarbon fraction from oil by liquid-liquid diffusion across a laminar interface can be performed in a microfluidic format. Analysis of figures of merit, determined using standard analytical techniques, show this method to be an effective new tool for rapidly processing small quantities of oil and petroleum for GC analysis. Methods based upon similar microsystems devices could find widespread use in a variety of fields, including those associated with organic geochemistry and oil exploration and production, where the manipulation of petroleum constituents (greater than C14) is necessary for analytical purposes.     

Electrolysis-reducing electrodes for electrokinetic devices

Direct current electrokinetic systems generally require Faradaic reactions to occur at a pair of electrodes to maintain an electric field in an electrolyte connecting them. The vast majority of such systems, e.g. electrophoretic separations (capillary electrophoresis) or electroosmotic pumps (EOPs), employ electrolysis of the solvent in these reactions. In many cases, the electrolytic products, such as H+ and OH? in the case of water, can negatively influence the chemical or biological species being transported or separated, and gaseous products such as O? and H? can break the electrochemical circuit in microfluidic devices. This article presents an EOP that employs the oxidation/reduction of the conjugated polymer poly(3,4-ethylenedioxythiophene), rather than electrolysis of a solvent, to drive flow in a capillary. Devices made with poly(3,4-ethylenedioxythiophene) electrodes are compared with devices made with Pt electrodes in terms of flow and local pH change at the electrodes. Furthermore, we demonstrate that flow is driven for applied potentials under 2?V, and the electrodes are stable for potentials of at least 100?V. Electrochemically active electrodes like those presented here minimize the disadvantage of integrated EOP in, e.g. lab-on-a-chip applications, and may open new possibilities, especially for battery-powered disposable point-of-care devices.     

Microfluidic routing of aqueous and organic flows at high pressures: fabrication and characterization of integrated polymer microvalve elements

This paper presents the first systematic engineering study of the impact of chemical formulation and surface functionalization on the performace of free-standing microfluidic polymer elements used for high-pressure fluid control in glass microsystems. System design, chemical wet-etch processes, and laser-induced polymerization techniques are described, and parametric studies illustrate the effects of polymer formulation, glass surface modification, and geometric constraints on system performance parameters. In particular, this study shows that highly crosslinked and fluorinated polymers can overcome deficiencies in previously-reported microvalve architectures, particularly limited solvent compatibility. Substrate surface modification is shown effective in reducing the friction of the polymer-glass interface and thereby facilitating valve actuation. A microchip one-way valve constructed using this architecture shows a 2 x 10(8) ratio of forward and backward flow rates at 7 MPa. This valve architecture is integrated on chip with minimal dead volumes (70 pl), and should be applicable to systems (including chromatography and chemical synthesis devices) requiring high pressures and solvents of varying polarity.     

Improved resolution with microchip-based enhanced field inversion electrophoresis

We present an improvement of the field inversion electrophoresis (FIE) method in which the passage of sample such as DNA back and forth within a short length of a microchannel can provide a similar resolution to that of a significantly longer microchannel. In constant field FIE the application of an alternating potential (e.g., +/- V) over short periods of time (e.g., several Hz) can provide enhanced separations of DNA fragments. In contrast, the present method consists of a series of separations, each of much longer duration, under high and low fields in such a way that the resolution is enhanced. This method is readily modeled and allows improved resolution to be obtained from extremely short microchannels (e.g., 8 mm) while requiring relatively low applied voltages (e.g., less than 600 V). An additional advantage is that this method can allow for the same equipment to be used in a rapid, low-resolution mode or in a slower, high-resolution mode through what might be referred to as an automated "zoom" capability. We believe that this method may facilitate the integration of microfluidic devices and microelectronic devices by allowing these devices to be of a similar small scale (< 1 cm).     

Dual-frequency electrowetting: application to drop evaporation gauging within a digital microsystem

This paper addresses a method to estimate the size of a sessile drop and to measure its evaporation kinetics by making use of both Michelson interferometry and coplanar electrowetting. From a high-frequency electrowetting voltage, the contact angle of the sessile droplet is monitored to permanently obtain a half-liquid sphere, thus complying perfectly with the drop evaporation theory based on a constant contact angle (Bexon, R.; Picknett, R. J. Colloid Interface Sci. 1977, 61, 336-350). Low-frequency modulation of the electrowetting actuation is also applied to cause droplet shape oscillations and capillary resonance. Interferometry allows us to measure a time-dependent capillary spectrum and, in particular, the shift in natural frequencies induced by drop evaporation. Consequently, diffusive kinetics of drop evaporation can be properly estimated, as demonstrated. Because of coplanar electrode configuration, our methodology can be integrated in open and covered microsystems, such as digital lab-on-a-chip devices.     

Microfluidic tectonics platform: A colorimetric, disposable botulinum toxin enzyme-linked immunosorbent assay system

A fabrication platform for realizing integrated microfluidic devices is discussed. The platform allows for creating specific microsystems for multistep assays in an ad hoc manner as the components that perform the assay steps can be created at any location inside the device via in situ fabrication. The platform was utilized to create a prototype microsystem for detecting botulinum neurotoxin directly from whole blood. Process steps such as sample preparation by filtration, mixing and incubation with reagents was carried out on the device. Various microfluidic components such as channel network, valves and porous filter were fabricated from prepolymer mixture consisting of monomer, cross-linker and a photoinitiator. For detection of the toxoid, biotinylated antibodies were immobilized on streptavidin-functionalized agarose gel beads. The gel beads were introduced into the device and were used as readouts. Enzymatic reaction between alkaline phosphatase (on secondary antibody) and substrate produced an insoluble, colored precipitate that coated the beads thus making the readout visible to the naked eye. Clinically relevant amounts of the toxin can be detected from whole blood using the portable enzyme-linked immunosorbent assay (ELISA) system. Multiple layers can be realized for effective space utilization and creating a three-dimensional (3-D) chaotic mixer. In addition, external materials such as membranes can be incorporated into the device as components. Individual components that were necessary to perform these steps were characterized, and their mutual compatibility is also discussed.     

Multiplexed electrothermal vaporization sample introduction system for inductively coupled plasma spectrometry

A multiplexed electrothermal vaporization (ETV) system for sample introduction into an inductively coupled plasma was designed in an effort to increase sample turn-around time. Tungsten filaments (300 W), originally designed for overhead projectors, were chosen for use as ETVs to avoid the high power requirements associated with other ETV devices, e.g. graphite furnaces (2–3 kW). In short, we have multiplexed the thermal stages have been multiplexed such that a vaporization event can take place every 20 s. This represents a significant increase in the throughput typically associated with ETV-ICPMS, which is normally approximately 20–30 samples/h. Evaluated with respect to common figure of merit criteria, the performance of the multiplexed ETV system is similar to that seen with conventional graphite furnace ETV systems. However, several mass spectral interferences can be introduced by the presence of W into the plasma, which hinder the analysis of certain metals (Hg, Mo, etc.). Thus, other low power vaporizers (e.g. Re, Ta) should be considered for use in future systems.     

Thermal analysis of starch for realizing embedded channel in low temperature co-fired ceramic

The rapidly developing biotechnology, automotive industry, chemical and environmental fields have increasing needs for analytical systems with desires such as smaller sizes, lower sample volumes. Reduction in size results in further requirements in functionalities such as multi-sensor devices with low cost. These microsystems usually contain three-dimensional structures. In the fabrication of microfluidic devices ensuring a well-shaped channel is a challenge. During firing of the low temperature co-fired ceramic (LTCC) substrate, these embedded structures tend to deform and sag because the green glass–ceramic material is very weak. Starch was used as sacrificial volume material (SVM) to support the embedded structures of the LTCC during lamination and sintering. As a consequence of burnout, the increased fraction of evolving gases from SVM requires an adequate adaptation of the firing process to control starch degradation and provide a residue-free burnout. Using thermal analysis techniques and describing degradation kinetics of SVM, a new heating profile is demonstrated which insures complete starch burnout without damaging the LTCC structures.     

Spintronic platforms for biomedical applications

Since the fundamental discovery of the giant magnetoresistance many spintronic devices have been developed and implemented in our daily life (e.g. information storage and automotive industry). Lately, advances in the sensors technology (higher sensitivity, smaller size) have potentiated other applications, namely in the biological area, leading to the emergence of novel biomedical platforms. In particular the investigation of spintronics and its application to the development of magnetoresistive (MR) biomolecular and biomedical platforms are giving rise to a new class of biomedical diagnostic devices, suitable for bench top bioassays as well as point-of-care and point-of-use devices. Herein, integrated spintronic biochip platforms for diagnostic and cytometric applications, hybrid systems incorporating magnetoresistive sensors applied to neuroelectronic studies and biomedical imaging, namely magneto-encephalography and magneto-cardiography, are reviewed. Also lab-on-a-chip MR-based platforms to perform biological studies at the single molecule level are discussed. Overall the potential and main characteristics of such MR-based biomedical devices, comparing to the existing technologies while giving particular examples of targeted applications, are addressed.     

Terminally Chlorinated and Thiophene-linked Acceptor-Donor-Acceptor Structured 3D Acceptors with Versatile Processability for High-efficiency Organic Solar Cells

To exploit the potential of our newly developed three-dimensional (3D) dimerized acceptors, a series of chlorinated 3D acceptors (namely CH8-3/4/5) were reported by precisely tuning the position of chlorine (Cl) atom. The introduction of Cl atom in central unit affects the molecular conformation. Whereas, by replacing fluorinated terminal groups (CH8-3) with chlorinated terminal groups (CH8-4 and CH8-5), the red-shift absorption and enhanced crystallization are achieved. Benefiting from these, all devices received promising power conversion efficiencies (PCEs) over 16 % as well as decent thermal/photo-stabilities. Among them, PM6:CH8-4 based device yielded a best PCE of 17.58 %. Besides, the 3D merits with multi alkyl chains enable their versatile processability during the device preparation. Impressive PCEs of 17.27 % and 16.23 % could be achieved for non-halogen solvent processable devices prepared in glovebox and ambient, respectively. 2.88 cm² modules also obtained PCEs over 13 % via spin-coating and blade-coating methods, respectively. These results are among the best performance of dimerized acceptors. The decent performance of CH8-4 on small-area devices, modules and non-halogen solvent-processed devices highlights the versatile processing capability of our 3D acceptors, as well as their potential applications in the future.