Direct coupling of a free-flow isotachophoresis (FFITP) device with electrospray ionization mass spectrometry (ESI-MS).

We present the online coupling of a free-flow isotachophoresis (FFITP) device to an electrospray ionization mass spectrometer (ESI-MS) for continuous analysis without extensive sample preparation. Free-flow-electrophoresis techniques are used for continuous electrophoretic separations using an electric field applied perpendicular to the buffer and sample flow, with FFITP using a discontinuous electrolyte system to concurrently focus a target analyte and remove interferences. The online coupling of FFITP to ESI-MS decouples the separation and detection timeframe because the electrophoretic separation takes place perpendicular to the flow direction, which can be beneficial for monitoring (bio)chemical changes and/or extensive MS(n) studies. We demonstrated the coupling of FFITP with ESI-MS for simultaneous concentration of target analytes and sample clean-up. Furthermore, we show hydrodynamic control of the fluidic fraction injected into the MS, allowing for fluidically controlled scanning of the ITP window. Future applications of this approach are expected in monitoring biochemical changes and proteomics.

From chip-in-a-lab to lab-on-a-chip: towards a single handheld electronic system for multiple application-specific lab-on-a-chip (ASLOC).

We present a portable, battery-operated and application-specific lab-on-a-chip (ASLOC) system that can be easily configured for a wide range of lab-on-a-chip applications. It is based on multiplexed electrical current detection that serves as the sensing system. We demonstrate different configurations to perform most detection schemes currently in use in LOC systems, including some of the most advanced such as nanowire-based biosensing, surface plasmon resonance sensing, electrochemical detection and real-time PCR. The complete system is controlled by a single chip and the collected information is stored in situ, with the option of transferring the data to an external display by using a USB interface. In addition to providing a framework for truly portable real-life developments of LOC systems, we envisage that this system will have a significant impact on education, especially since it can easily demonstrate the benefits of integrated microanalytical systems.

Protein-carbohydrate complex reveals circulating metastatic cells in a microfluidic assay.

Advances in carbohydrate sequencing technologies reveal the tremendous complexity of the glycome and the role that glycomics might have to bring insight into the biological functions. Carbohydrate-protein interactions, in particular, are known to be crucial to most mammalian physiological processes as mediators of cell adhesion and metastasis, signal transducers, and organizers of protein interactions. An assay is developed here to mimic the multivalency of biological complexes that selectively and sensitively detect carbohydrate-protein interactions. The binding of ß-galactosides and galectin-3--a protein that is correlated to the progress of tumor and metastasis--is examined. The efficiency of the assay is related to the expression of the receptor while anchoring to the interaction's strength. Comparative binding experiments reveal molecular binding preferences. This study establishes that the assay is robust to isolate metastatic cells from colon affected patients and paves the way to personalized medicine.

Bilayer microfluidic chip for diffusion-controlled activation of yeast species.

A bilayer microfluidic chip is used, in which multiple laminar streams are generated to define local microenvironments. The bilayer architecture of the microchip separates cell handling and positioning from cell activation by soluble chemicals. Cell activation is diffusion controlled through a porous membrane. By employing time-lapse fluorescence microscopy, gene expression of the enhanced green fluorescent protein (eGFP) in Saccharomyces cerevisiae is studied under various conditions. We demonstrate that the yeast cells remain viable in the microchip for at least 17 h, and that gene expression can be initiated by the supply of the inducer galactose at a spatial precision of a few micrometers.

Miniaturised nucleic acid analysis.

The application of micro total analysis systems has grown exponentially over the past few years, particularly diversifying in disciplines related to bioassays. The primary focus of this review is to detail recent new approaches to sample preparation, nucleic acid amplification and detection within microfluidic devices or at the microscale level. We also introduce some applications that have as yet to be explored in a miniaturised environment, but should benefit from improvements in analytical efficiency and functionality when transferred to planar-chip formats. The studies described in this review were published in commonly available journals as well as in the proceedings of three major conferences relevant to microfluidics (Micro Total Analysis Systems, Transducers and The Nanotechnology Conference and Trade Show). Although an emphasis has been placed on papers published since 2002, pertinent articles preceding this publication year have also been included.

An AC electroosmotic micropump for circular chromatographic applications.

Flow rates of up to 50 microm s(-1) have been successfully achieved in a closed-loop channel using an AC electroosmotic pump. The AC electroosmotic pump is made of an interdigitated array of unequal width electrodes located at the bottom of a channel, with an AC voltage applied between the small and the large electrodes. The flow rate was found to increase linearly with the applied voltage and to decrease linearly with the applied frequency. The pump is expected to be suitable for circular chromatography for the following reasons: the driving forces are distributed over the channel length and the pumping direction is set by the direction of the interdigitated electrodes. Pumping in a closed-loop channel can be achieved by arranging the electrode pattern in a circle. In addition the inherent working principle of AC electroosmotic pumping enables the independent optimisation of the channel height or the flow velocity.

Electrophoretic manipulation of single DNA molecules in nanofabricated capillaries.

We demonstrate the use of nanofabricated capillaries, integrated as part of a microfluidic structure, to study the electrophoretic behaviour of single, fluorescently-labelled, molecules of DNA as a function of capillary size. The nanocapillaries, fabricated using a focused ion beam, have cross-sections down to 150 x 180 nm. Control of single-molecule direction and velocity was achieved using voltage manipulation. DNA mobility was found to increase with decreasing cross-section, which we interpret in terms of reduced electro-osmotic counter-flow. Such nanofabricated capillaries as part of larger fluidic structures have great potential for biotechnology, particularly single molecule manipulation and analysis.

Poly(dimethylsiloxane) electrospray devices fabricated with diamond-like carbon-poly(dimethylsiloxane) coated SU-8 masters.

This study presents coupling of a poly(dimethylsiloxane) (PDMS) micro-chip with electrospray ionization-mass spectrometry (ESI-MS). Stable electrospray is generated directly from a PDMS micro-channel without pressure assistance. Hydrophobic PDMS aids the formation of a small Taylor cone in the ESI process and facilitates straightforward and low-cost batch production of the ESI-MS chips. PDMS chips were replicated with masters fabricated from SU-8 negative photoresist. A novel coating, an amorphous diamond-like carbon-poly(dimethylsiloxane) hybrid, deposited on the masters by the filtered pulsed plasma arc discharge technique, improved significantly the lifetime of the masters in PDMS replications. PDMS chip fabrication conditions were observed to affect the amount of background peaks in the MS spectra. With an optimized fabrication process (PDMS curing agent/silicone elastomer base ratio of 1/8 (w/w), curing at 70 degree C for 48 h) low background spectra were recorded for the analytes. The performance of PDMS devices was examined in the ESI-MS analysis of some pharmaceutical compounds and amino acids.

Synchronized cyclic capillary electrophoresis using channels arranged in a triangle and low voltages.

Synchronized cyclic capillary electrophoresis (SCCE) makes use of a closed loop separation channel by which the same sample can be separated during many cycles. This enables the repeated use of the same voltage for separations such that a high total voltage, and thus high efficiency, is obtained for the synchronized components. This can be accomplished by using any type of polygon geometry for the separation channel; and calculations of the available field and number of connections needed for polygons from 3 to 5 sides are presented. Triangular designs have the advantage of using the lowest number of wells. Such designs are described, with two additional features compared to that of earlier work: 1. voltage connections that are much shallower than the separation channel, to reduce losses and dispersion at the intersections; and 2. corners that are narrower than the separation channels to reduce dispersion in the turns. Experimental data is presented for the separation of a mixture of amino acids, and for a DNA separation in a polymeric sieving matrix. The DNA separation is most sensitive to the corner dispersion problem, which reduces the observed efficiency for that separation.

Shah convolution differentiation Fourier transform for rear analysis in microchip capillary electrophoresis.

This paper first reports the application of Shah convolution differentiation Fourier transform for rear analysis. Rear analysis eliminates the need to create a well-defined and reproducible sample plug, thus making the operation simpler. The number of solution reservoirs, for microchip capillary electrophoresis (CE), could be reduced from the usual four to three. Sample bias in CE could be avoided too. The separation channel was first filled with the fluorescent sample solution, and subsequently flushed out with the buffer. The rear of each analyte zone gives rise to its flight of sigmoid-shaped steps in the time-domain. The time-domain detector signal was first differentiated and then Fourier transform was performed. The Fourier transform results were represented in the form of a magnitude plot. It is proposed that this would be as equally applicable to other separation techniques (e.g., chromatography) and detection methods (e.g., absorption).

A wireless electrochemiluminescence detector applied to direct and indirect detection for electrophoresis on a microfabricated glass device.

A novel electrochemiluminescence (ECL) detector is presented in this article. The detector is applied for micellar electrokinetic chromatographic separation of dichlorotris(2,2'-bipyridyl)ruthenium(II) hydrate [Ru-(bpy)] and dichlorotris(1,10-phenanthroline)ruthenium-(II) hydrate [Ru(phen)] on a microfabricated glass device. It consists of a microfabricated "U"-shape floating platinum electrode placed across the separation channel. The legs of the U function respectively as working and counter electrode. The required potential difference for the ECL reaction is generated at the Pt electrode by the electric field available in the separation channel during electrophoretic separation. Initial experiments demonstrate a micellar electrokinetic separation and direct ECL detection of 10(-16) mol of Ru(phen) (10(-6) M) and 4.5 x 10(-16) mol of Ru(bpy) (5 x 10(-6) M). Also, preliminary results show the indirect detection of three amino acids. The high voltage at the location of detection does not interfere with the electrochemistry.

[Home transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin and beta-hexachlorocyclohexane?]. / Heimübertragungen von 2,3,7,8-Tetrachlordibenzo-p-dioxin und beta-Hexachlorcyclohexan?

Persons living together with workers who have been exposed to dioxins, furans or hexachlorocyclohexane, accumulate increased concentrations of these molecules in the blood and in fatty tissue, in comparison with normal people. This result is based on an investigation of 14 workers and their female partners. The workers had been contaminated with high concentrations of 2,3,7,8-TCDD and moderate concentrations of beta-HCH, respectively, in contrast with their female partners who had never been exposed to these poisons. Nevertheless, the female partners accumulated a significant amount of these molecules, corresponding to 10% of the concentrations of their male partners. The origin of this correlation is still unknown. As a working hypothesis, we discuss the possibility of molecular transfer by clothing and underwear. The clinical consequences of these findings are still unclear. Further observations are needed.

Narrow sample channel injectors for capillary electrophoresis on microchips.

In microchip CE, sample injection is generally achieved through cross, double-tee, or tee injector structures. In these reported approaches, channel width and depth are uniform at the injection intersection. Here, we present cross and tee injectors having narrow sample channels. Using a cross injector with reduced sample channel width, resolution, column efficiency, and sensitivity are remarkably improved. Furthermore, no leakage control is required in both injection and separation phases, making the microchip CE system more user-friendly. Good resolution can also be obtained using tee injectors with narrow sample channels, which would otherwise be impossible using conventional tee injectors. Using the narrow sample channel tee injector instead of conventional cross and double-tee injectors, the number of reservoirs in multiplexed systems can be reduced to N + 2 (N, the number of paralleled CE systems), the real theoretical limit. The virtues of the novel injectors were demonstrated with poly(dimethylsiloxane)-glass chips incorporating eight parallel CE channels.

Velocity measurement of particles flowing in a microfluidic chip using Shah convolution Fourier transform detection.

A noninvasive radiative technique, based on Shah convolution Fourier transform detection, for velocity measurement of particles in fluid flows in a microfluidic chip, is presented. It boasts a simpler instrumental setup and optical alignment than existing measurement methods and a wide dynamic range of velocities measurable. A glass-PDMS microchip with a layer of patterned Cr to provide multiple detection windows which are 40 microns wide and 70 microns apart is employed. The velocities of fluorescent microspheres, which were electrokinetically driven in the channel of the microfluidic chip, were determined. The effects of increasing the number of detection windows and sampling period were investigated. This technique could have wide applications, ranging from the determination of the velocity of particles in pressure-driven flow to the measurement of electrophoretic mobilities of single biological cells.

Shah convolution Fourier transform detection: multiple-sample injection technique.

For the direct measurement of electrophoretic mobility, multiple-point (Shah function) detected, time-domain detector signals were converted into frequency-domain plots by means of Fourier transformation. Multiple sample plugs (up to a maximum of three) were introduced into the separation channel and the resultant time-domain signals were then Fourier-transformed. The multiple-sample injection technique has been successfully demonstrated for a one-component system and a separation. Though the number of fluorescing zones flowing through the illuminated length of the channel is greater than the number of analytes in the solution, Shah convolution Fourier transform detection (SCOFT) is able to identify the number of fluorescent species in the solution based on their migration velocities. The height of the fundamental peak increases as the number of injected sample plugs is increased. More importantly, the signal-to-noise ratio (S/N) is found to be proportional to the number of injected sample plugs. With these findings, the multiple-sample injection technique certainly has got many potential applications in trace analysis. The technique would be equally applicable to other separation techniques (e.g., high-performance liquid chromatography) and detection methods (e.g., absorption, refractive index).

Microfabricated devices for fluid mixing and their application for chemical synthesis.

Over the last few decades, the processes of miniaturization, integration, and automation have revolutionized the world of science and industry. Within a chemical reaction process the unit operations, mixing, heating, and cooling, can be regarded as key steps. In microreactors, enhanced heat and mass transport, due to small characteristic dimensions together with large surface to volume ratios, are expected to open up a whole range of new possibilities. Increase in reaction yield, reduction of reaction time as well as byproduct formation, inherent process safety, and even completely new process routes are some of the advantages associated with microTAS (micro Total Analysis Systems) or microSYNTAS (micro SYNthesis Total Analysis Systems). This article aims to describe the development of microfabricated devices for fluid mixing, so-called micromixers, and their application for chemical synthesis.

Modular approach to fabrication of three-dimensional microchannel systems in PDMS-application to sheath flow microchips.

A modular approach to fabrication of three-dimensional microchannel systems in polydimethylsiloxane (PDMS) is presented. It is based on building blocks with microstructuring on up to three faces. The assembled 3D-microchip consists of three building blocks in two layers. For assembly of the bottom layer two building blocks are joined horizontally, whereby the side structuring of the first is sealed against the flat side surface of the other. This results in the formation of a vertical interconnection opening between the building blocks to supplement the microstructuring on the lower faces. The 3D microchannel system is completed by placing a third building block, with microstructuring only on its lower face, on top of the assembled layer. While plasma assisted bonding is used between the two building blocks of the bottom layer, inherent adhesion is sufficient between the layers and for attaching the assembled 3D-microchip to a substrate. This modular approach was applied to the fabrication of a 3D-sheath flow microchip. It comprises a 20 microm deep microchannel system with sample inlet, open sensing area and outlet in the bottom layer and sheath flow inlet in the top layer. 100 microM fluorescein at 6 microL min(-1) was used as sample flow and water at increasing flow rates as sheath flow. With ratios of sheath to sample flow up to 20:1 sample layers down to 1 microm thickness could be generated. Sample layer thickness was determined via volume detection on an epi-fluorescence microscope followed by image analysis.

Wavelet transform for Shah convolution velocity measurements of single particles and solutes in a microfluidic chip.

Wavelet transform analysis is applied to determine the speed of fluorescent polystyrene microspheres and fluorescent solutes in a microchip. The data analysed consist of the periodical signal (Shah convolution) obtained when fluorescent particles or solute plugs move in a channel that is covered with a chromium grid pattern. This setup converts velocity into a (fluorescence emission) frequency, and previous analyses therefore used Fourier transform to extract the frequency information. In this paper it is shown that wavelet transform has some advantages over Fourier transform. With wavelet transform, time information can be obtained in addition to frequency information. Thus the speed of individual particles was determined together with their moments of appearance and disappearance in the system. With solutes small changes of velocity during the analysis were detected, and an improvement in peak frequency resolution was obtained.

Inhibitory control in children with traumatic brain injury (TBI) and children with attention deficit/hyperactivity disorder (ADHD).

The behavioural and cognitive sequelae of traumatic brain injury (TBI) have features in common with attention deficit/hyperactivity disorder (ADHD), best characterized by deficits in response inhibition.The performance was, therefore, examined of 27 children with TBI, 31 children with developmental ADHD, and 26 matched controls aged 8-12, on two inhibition tasks: the Stop-Signal Task and a Delayed-Response-Task. Children with TBI and children with ADHD showed a pervasive deficit in their inhibitory control processes with respect to inhibition of both pre-potent and on-going responses. In addition, children with TBI were found to suffer from a general slowing of their information processing, which was not correlated with the inhibition deficit. TBI children with and without a secondary ADHD differed only tendentially in their Mean Go-Reaction time in the stop-task. However, subdividing TBI children according to actigraph data into hypo-, hyper- and normokinetic subgroups revealed that the hyperactive TBI children had inhibitory deficit patterns that were similar to children with developmental ADHD. It is concluded that slowing of information processing speed seems to be a general consequence of TBI in childhood, whereas slowing of the stop-processes or inhibitory deficits, specifically, are associated with post-injury hypo- or hyperactivity.

Integrated potentiometric detector for use in chip-based flow cells

A new kind of potentiometric chip sensor for ion-selective electrodes (ISE) based on a solvent polymeric membrane is described. The chip sensor is designed to trap the organic cocktail inside the chip and to permit sample solution to flow past the membrane. The design allows the sensor to overcome technical problems of ruggedness and would therefore be ideal for industrial processes. The sensor performance for a Ba2+-ISE membrane based on a Vogtle ionophore showed electrochemical behavior similar to that observed in conventional electrodes and microelectrode arrangements.