We have fabricated and characterized a polymethylmethacrylate (PMMA) valveless micropump. The pump consists of two diffuser elements and a polydimethylsiloxane (PDMS) membrane with an integrated composite magnet made of NdFeB magnetic powder. A large-stroke membrane deflection ($200 lm) is obtained using external actuation by an electromagnet. We present a detailed analysis of the magnetic actuation force and the flow rate of the micropump. Water is pumped at flow rates of up to 400 ll/min and backpressures of up to 12 mbar. We study the frequency-dependent flow rate and determine a resonance frequency of 12 and 200 Hz for pumping of water and air, respectively. Our experiments show that the models for valveless micropumps of A. Olsson et al. (J Micromech Microeng 9:34, 1999) and L.S. Pan et al. (J Micromech Microeng 13:390, 2003) correctly predict the resonance frequency, although additional modeling of losses is necessary.

The study of the electrical properties of DNA has aroused increasing interest since the last decade. So far, controversial arguments have been put forward to explain the electrical charge transport through DNA. Our experiments on DNA bundles manipulated with silicon-based actuated tweezers demonstrate undoubtedly that humidity is the main factor affecting the electrical conduction in DNA. We explain the quasi-Ohmic behavior of DNA and the exponential dependence of its conductivity with relative humidity from the adsorption of water on the DNA backbone. We propose a quantitative model that is consistent with previous studies on DNA and other materials, like porous silicon, subjected to different humidity conditions.

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We present the microfabrication and characterization of a ball valve micropump in glass, which is magnetically actuated using the sinusoidal current of an external electromagnet. We employ the use of a simple powder blasting technology for microstructuring the glass substrates and fusion bonding for assembly of the multi-layered microfluidic chip. The use of a polymer membrane with embedded permanent magnet gives rise to a large actuation stroke, making the micropump bubble-tolerant and self-priming. The micropump exhibits a backpressure as high as 280 mbar and water flow rates up to 5 mL/min thanks to the large magnetic actuation force and the use of high-efficiency ball valves. The frequency-dependent characteristics are in excellent agreement with a hydrodynamic damped oscillator model.

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We present a valveless micropump in glass, which is magnetically actuated using the sinusoidal current of an external electromagnet. We employ a powder blasting microerosion process for microstructuring the glass substrates and fusion bonding for assembly of the multi-layered microfluidic chip. The reciprocating type micropump contains two nozzle/diffuser elements and a poly(dimethylsiloxane) membrane with embedded permanent magnet. The micropump is self-priming and exhibits a backpressure of 50 mbar and water flow rates up to 1 mL/min. The flow resonance frequency is in excellent agreement with the model of Olsson et al.

Abstract-In-plane linear displacements of microelectromechanical systems are measured with subnanometer accuracy by observing the periodic micropatterns with a charge-coupled device camera attached to an optical microscope. The translation of the microstructure is retrieved from the video by phase-shift computation using discrete Fourier transform analysis. This approach is validated through measurements on silicon devices featuring steep-sided periodic microstructures. The results are consistent with the electrical readout of a bulk micromachined capacitive sensor, demonstrating the suitability of this technique for both calibration and sensing. Using a vibration isolation table, a standard deviation of σ = 0.13 nm could be achieved, enabling a measurement resolution of 0.5 nm (4σ) and a subpixel resolution better than 1/100 pixel. Microelectromechanical systems (MEMS) comprise integrated devices made by batch-fabrication techniques, like those adopted from silicon-based integrated circuit technology. MEMS sensors and actuators have typical feature sizes ranging from a few tens of nanometers to several hundreds of micrometers. Mechanical transducers fabricated using silicon micromachining technology have to be characterized or even calibrated and possibly trimmed electronically before being used in an instrument. To mention only a few examples, the spring constant of an atomic force microscopy (AFM) cantilever, the voltage-displacement quadratic response of a comb-drive electrostatic actuator, or the sensitivity of a differential capacitive sensor are all parameters that are highly dependent on the microfabrication. Hence, at micro-and nanometer scales, precise and accurate dimensions can be difficult to guarantee because of process limitations. However, there are geometric parameters that are process independent, like the pitch of a periodic micropattern that is determined solely by the design. Thus, the periodicity can be used advantageously for precise and accurate position measurements.Optical measurements are noninvasive in nature and constitute an alternative or a complement to solid-state sensors, which can be challenging to miniaturize and integrate. However, most optical techniques proposed for the characterization of static displacements, motion, and vibrations were developed to quantify the out-of-plane motion of MEMS structures, often relying on complex interferometric techniques [1]. In contrast, only very few approaches were demonstrated for high-resolution in-plane displacement measurements. With continuous illumination, the displacement of the moving part of a We introduce here an extremely simple and robust method for measuring the in-plane linear displacement of MEMS microstructures with a subnanometer resolution. It is applicable to any transducer that shows a translational displacement and features periodic microstructures. Apart from the MEMS device, the setup consists of a charge-coupled device (CCD) camera attached to a bright field optical microscope and a computer for the analysis of th...

This paper presents a systematic method to isolate and trap long single DNA segments between integrated electrodes in a microfluidic environment. Double stranded lambda-DNA molecules are introduced in a microchip and are isolated by electrophoretic force through microfluidic channels. Downstream, each individual molecule is extended and oriented by ac dielectrophoresis (900 kHz, 1 MV m(-1)) and anchored between aluminium electrodes. With a proper design, a long DNA segment (up to 10 microm) can be instantly captured in stretched conformation, opening way for further assays.