Showing papers by "Jörg Peter Kutter published in 2011"

Nanofluidic devices with two pores in series for resistive-pulse sensing of single virus capsids.

Abstract: We report fabrication and characterization of nanochannel devices with two nanopores in series for resistive-pulse sensing of hepatitis B virus (HBV) capsids. The nanochannel and two pores are patterned by electron beam lithography between two microchannels and etched by reactive ion etching. The two nanopores are 50-nm wide, 50-nm deep, and 40-nm long and are spaced 2.0-μm apart. The nanochannel that brackets the two pores is 20× wider (1 μm) to reduce the electrical resistance adjacent to the two pores and to ensure the current returns to its baseline value between resistive-pulse events. Average pulse amplitudes differ by <2% between the two pores and demonstrate that the fabrication technique is able to produce pores with nearly identical geometries. Because the two nanopores in series sense single particles at two discrete locations, particle properties, e.g., electrophoretic mobility, are determined from the pore-to-pore transit time.

On-chip electro membrane extraction with online ultraviolet and mass spectrometric detection.

Abstract: Electro membrane extraction was demonstrated in a microfluidic device. The device was composed of a 25 μm thick porous polypropylene membrane bonded between two poly(methyl methacrylate) (PMMA) substrates, each having 50 μm deep channel structures facing the membrane. The supported liquid membrane (SLM) consisted of 2-nitrophenyl octyl ether (NPOE) immobilized in the pores of the membrane. The driving force for the extraction was a 15 V direct current (DC) electrical potential applied across the SLM. Samples containing the basic drugs pethidine, nortriptyline, methadone, haloperidol, loperamide, and amitriptyline were used to characterize the system. Extraction recoveries were typically in the range of 65−86% for the different analytes when the device was operated with a sample flow of 2.0 μL/min and an acceptor flow of 1.0 μL/min. With the sample flow at 9.0 μL/min and the acceptor flow at 0.0 μL/min, enrichment factors exceeding 75 were obtained during 12 min of operation from a total sample volume of o...

Carbon nanotube based separation columns for high electrical field strengths in microchip electrochromatography

Abstract: Electrically insulated carbon nanotube (CNT) based separation columns have been fabricated that can withstand an electrical field strength of more than 2.0 kV cm−1 without bubble formation from electrolysis. The carbon nanotubes were grown in a pillar array defined by photolithographic patterning of the catalyst layer used for synthesis of the nanotubes. Multiwall carbon nanotubes are inherently electrically conductive and cannot be used as a continuous layer in the microfluidic channels, without short circuiting the electrical field in the separation column, when the field strength is more than a couple of 100 V cm−1. Here, the carbon nanotubes are grown in an array of hexagonal pillars, where the nanotubes in the individual pillars are not in direct electrical contact with the nanotubes of the adjacent pillars. This makes it possible to increase the electrical field strength from around 100 V cm−1 to more than 2.0 kV cm−1 and thereby to use the CNT columns for electrokinetic separations with the high electrical field strengths that are typically used in this application. An electrochromatographic separation of two Coumarin dyes was demonstrated on the CNT column with an acetonitrile content of 90%.

Microfluidics and Miniaturization

Abstract: The special issue on Microfluidics and Miniaturization is becoming a ‘‘trusted veteran’’ in the publication schedule of Electrophoresis. For more than a decade, it has been published towards the end of the year and often comes with the first snow in the countries of the two editors. This year is no exception, and the issue you are reading collects 26 original articles covering Fundamentals, New Technology and Applications of Microfluidic Systems. As microfabrication technology becomes more accessible to interdisciplinary research, it is interesting to see the directions of its practical use. With more than one-third of the papers dealing with Cell Analysis, this issue points to one of the most important applications of microfluidic technology. This trend is also well documented by the two special issues focused on dielectrophoresis, which were published earlier this year. On behalf of the coeditors, it is my pleasure to thank all the contributors as well as the Editor-in-Chief, Ziad El Rassi, for his support. Last but not least, I wish all the best to Jörg Kutter, my Co-Editor, who was getting married at the time of writing of this text. Wishing you joy and happiness, today and always.

Automated microfluidic sample-preparation platform for high-throughput structural investigation of proteins by small-angle X-ray scattering

Abstract: A new microfluidic sample-preparation system is presented for the structural investigation of proteins using small-angle X-ray scattering (SAXS) at synchrotrons. The system includes hardware and software features for precise fluidic control, sample mixing by diffusion, automated X-ray exposure control, UV absorbance measurements and automated data analysis. As little as 15 µl of sample is required to perform a complete analysis cycle, including sample mixing, SAXS measurement, continuous UV absorbance measurements, and cleaning of the channels and X-ray cell with buffer. The complete analysis cycle can be performed in less than 3 min. Bovine serum albumin was used as a model protein to characterize the mixing efficiency and sample consumption of the system. The N2 fragment of an adaptor protein (p120-RasGAP) was used to demonstrate how the device can be used to survey the structural space of a protein by screening a wide set of conditions using high-throughput techniques.

Anti-stiction coating of PDMS moulds for rapid microchannel fabrication by double replica moulding

Abstract: In this paper, we report a simple and precise method to rapidly replicate master structures for fast microchannel fabrication by double replica moulding of polydimethylsiloxane (PDMS). A PDMS mould was surface-treated by vapour phase deposition of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS), which resulted in an anti-stiction layer for the improved release after PDMS casting. The deposition of FDTS on an O2 plasma-activated surface of PDMS produced a reproducible and well-performing anti-stiction monolayer of fluorocarbon, and we used the FDTS-coated moulds as micro-masters for rapid replication of micro-structures, avoiding the necessity to have to use other, more costly and fragile master materials. Our protocol has been shown to reliably fabricate PDMS-based microfluidic devices in a low-cost and efficient manner. The replicas were further employed as micro-contract stamps to fabricate polymer-based waveguides.

Disposable Miniaturized Screen‐Printed pH and Reference Electrodes for Potentiometric Systems

Abstract: This work describes the development of a miniaturized potentiometric system comprising a miniaturized quasi-reference electrode (QRE) coupled to a solid-state ion-selective electrode (ISE) for the monitoring of pH. We describe the optimization of materials and fabrication processes including screen-printing (SP), electrode treatments (thermal and electrochemical) and the formulation and deposition of an ion-selective membrane (ISM), to obtain a system compliant with biomedical specifications. We developed a potentiometric system composed of an Ag/AgCl QRE and a pH-electrode (ISM deposited on a graphite electrode) that can be used continuously for a period of not less than 7 days in aqueous solutions. Curing the Ag/AgCl pastes during 20 minutes at 120 °C after printing allowed the QREs to display excellent potential stability, as demonstrated by an open-circuit-potential standard deviation of ±1.2 mV over a period of 7 days (n=3 samples). Promoting adhesion of the pH membrane over graphite electrodes improved the pH-electrode performance. This was achieved through a combination of thermal treatment and electrochemical activation of the electrodes by cyclic voltammetry (CV). The final device integrated both the QRE and the pH-electrode, and displayed an average pH sensitivity of −60.8±1.7 mV per pH unit, over a pH range of 7.00 to 7.63.

Polymer microvalve with pre-stressed membranes for tunable flow–pressure characteristics

Abstract: A novel, inexpensive, polymer-based valve approach is presented that offers the combination of a check valve’s rectifying properties with the possibility to actively control the flow rate in the forward (open) direction. An elastic membrane with an incision is clamped between two rigid polymer plates and expands when pressure is applied in the forward direction allowing fluid to pass. In the backward direction, expansion of the membrane is not possible and flow is prevented. Varying the clamping force influences the expansion capability of the membrane due to its elasticity and thus enables control of the flow rate.

Fiber-free coupling between bulk laser beams and on-chip polymer-based multimode waveguides.

Abstract: In this paper, we demonstrate the design of a virtually alignment-free optical setup for use with microfluidic applications involving a layered glass/SU-8/PDMS (polydimethylsiloxane) chip. We show how inexpensive external lenses combined with carefully designed on-chip lenses can be used to couple light from a bulk beam to on-chip waveguides and back into a bulk beam again. Using this setup, as much as 20% of the light coming from the source can be retrieved after passing through the on-chip waveguides. The proposed setup is based on a pin-aided alignment system that makes it possible to change chips in the optical train in only a few seconds with a standard deviation of about 2% in the transmitted power. Furthermore, we demonstrate how these optical setups can be combined with microfluidics to create an on-chip flow cytometer enabling detection and counting of polystyrene particles down to 1 μm at a rate of 100 Hz.

Simplified Monolithic Flow Cytometer Chip With Three-Dimensional Hydrodyanmic Focusing And Integrated Fiber-Free Optics

Abstract: A miniaturized flow cytometry incorporating both fluidic and optical systems has a great possibility for portable biochemical sensing or point-of-care diagnostics. This paper presents a simple microfluidic flow cytometer combining reliable 3D hydrodynamic focusing and optical detection without optical fibers in a monolithic architecture fabricated by a single photolithographic process. The vertical flow focusing is achieved by the optimized inlet geometry in a PDMS lid onto the substrate with detection channel and integrated optics. The simplified approach indicates the possibility to be applied as a portable platform of cytometer chip.

Gold nanoparticle-based microfluidic sensor for mercury detection

Abstract: The contamination of natural resources by human activity can have severe socio-economical impacts. Conventional methods of environmental analysis can be significantly improved by the development of portable microscale technologies for remote/field sensing. A gold nanoparticle-based lab-on-a-chip device was developed for the rapid, in-field detection and quantification of mercury in aquatic environments. Rhodamine 6G functionalized gold nanoparticles allowed the on-chip fluorescence detection of mercury in aqueous samples with a limit of detection of 7 nM.

Electrical insulation of carbon nanotube separation columns for microchip electrochromatography

Abstract: Carbon nanotubes (CNT) have been grown in microfluidic glass channels for chemical analysis based on electrokinetic separations. A limitation of CNTs for this type of application is their high conductivity, which prevent them from being used for electroosmotic pumping with electrical field strengths in the range of 0.5–1.0 kV/cm. This range of field strength is desirable for most electrokinetic separation systems in order not to have excess band broadening from diffusion due a too low mobile phase velocity. Here, we have approached this limitation by patterning the CNTs into micrometer sized regions in order to significantly lower the conductivity of the carbon nanotube layer. By this approach, the electrical field strength that can be sustained by the column is increased from around 100 V/cm to more than 2 kV/cm. This is more than one order of magnitude higher than previous reports [1–3].

Nanochannels with two pores in series for single particle sensing and characterization

Abstract: We report the fabrication and use of nanochannels with multiple nanopores in series for resistive-pulse sensing and characterization of virus capsids. Two pores in series permits single particles to be probed multiple times to improve counting statistics and to determine physical properties. To fabricate the nanochannels, we combined electron beam lithography with reactive ion etching to confine both the channel width and depth to the nanoscale.