Sensors and Actuators A 135 (2007) 28–33 Centrifugo-magnetic pump for gas-to-liquid sampling Stefan Haeberle a,∗ , Norbert Schmitt a , Roland Zengerle a,b , Jens Ducr´ ee a,b a Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Koehler-Allee 106, 79110 Freiburg, Germany b HSG-IMIT, Institute for Micromachining and Information Technology, Wilhelm-Schickard-Straße 10, 78052 Villingen-Schwenningen, Germany Received 28 February 2006; received in revised form 30 August 2006; accepted 6 September 2006 Available online 13 October 2006 Abstract This paper describes a novel gas micropump realized on a centrifugal microfluidic platform. The pump is integrated on a passive and microstruc- tured polymer disk which is sealed by an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid over a stationary magnet induces a designated sequence of volume displacements of the elastic lid, leading to a net transport of gas. The pumping pressure was determined as a function of the frequency of rotation, with a maximum observable pressure of 4.1 kPa without further optimization. The first application of this rotary device is the production of gas–liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The injected gas volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms. © 2006 Elsevier B.V. All rights reserved. Keywords: Centrifugal microfluidics; Micropump; Segmented flow; Gas–liquid sampling 1. Introduction The toolbox of centrifugal microfluidics has been continu- ously extended over the last decade. Up to now, a diverse set of unit operations such as cell-lysis [1], continuous micromix- ing [2–4], hematocrit determination [5] as well as applications in (bio-)analytics [6,7] and emulsification [8] for micro process engineering have been successfully implemented. However, the processing of gases in rotating microchannels still remains a challenge since the centrifugal field used for pumping scales with the fluid density, thus reducing the force density on gases by three orders of magnitude with respect to liquids. In particular the generation of gas–liquid flows is aggravated by the buoyancy of the gas under the strong “artificial-gravity” conditions of the centrifugal field. To access the interesting field of gas–liquid flows [9] with our centrifugal platform, the gas has to be additionally pressurized with respect to the liquid. To comply with the modular concept of the rotary system, the typically disposable disk should remain ∗ Corresponding author. Tel.: +49 761 203 7476; fax: +49 761 203 7539. E-mail address: haeberle@imtek.de (S. Haeberle). passive and the force transmission ought to be accomplished in a contact-free fashion. We chose a centrifugo-magnetical prin- ciple to displace movable, disk-based steel plates which are incorporated in the lid by permanent magnets aligned along the orbit of the pumping chamber [10]. Several magnetically driven micropumps were presented recently where external electro-magnets deflect permanent mag- nets integrated on elastic membranes [11–13]. Silicone elas- tomers, predominantly PDMS, are commonly used due to their simple handling, adjustable elastic properties as well as their cost-efficiency [14,15]. Compared to these approaches, our novel design significantly simplifies the setup by drawing the power for both, the centrifugal liquid pumping as well as the pressurization of the gas, quasi-independently from the same rotary power source. Therefore, no additional power supply is needed to operate the gas-processing part. The so realized centrifugo-magnetic pumping of gases supplements our recently presented centrifugal platform for continuous liquid-processing [2,8,16]. On this platform, liquid flows are propelled by the pulse-free centrifugal “artificial- gravity” field which is self-stabilized by the inertia associated with the spinning motion. The constant pumping force is of par- ticular benefit for the well-controlled formation of liquid–fluid 0924-4247/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2006.09.001