Multibody interactions of actuated magnetic particles used as fluid drivers in microchannels

R. J. S. Derks 0 1 2 3 A. J. H. Frijns 0 1 2 3 M. W. J. Prins 0 1 2 3 A. Dietzel 0 1 2 3 0 M. W. J. Prins Philips Research Europe , High Tech Campus 12, 5656 AE Eindhoven, The Netherlands 1 M. W. J. Prins Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2 R. J. S. Derks (&) A. J. H. Frijns A. Dietzel Mechanical Engineering, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands 3 A. Dietzel Holst Centre , High Tech Campus 31, 5605 KN Eindhoven, The Netherlands The forced motion of superparamagnetic particles and their multibody interactions are studied in view of the application as integrated fluid drivers in microchannel systems. Previous studies on particle manipulation in open fluid volumes serve as our starting point for the analysis of particle dynamics and interplay effects in confined fluid volumes. An experimental setup is designed that offers a constant force field on all individual particles dispersed in a microchannel. Distinguishable multi-particle configurations are observed and analyzed on the basis of magnetic and hydrodynamic particle interaction mechanisms. The fluid driving performance and the efficiency of the particles are evaluated on system level by means of numerical simulation models. 1 Introduction The current trend in lab-on-a-chip devices involves the miniaturization and integration of a wide range of functions (Haeberle and Zengerle 2007). For biosensors, a main challenge lies in achieving a high functional performance with respect to sensitivity, specificity, and speed (Bruls et al. 2009). Devices for biochemical analysis therefore often contain elements with a large surface area to enhance binding capacity and allow parallel screening. For instance, porous DNA hybridization microarrays have become an effective form of screening technology and allow the analysis of hundreds to thousands of genes simultaneously (Chen et al. 2007; Grasso et al. 2006). A concern in these high-surface area systems is the limited accessibility of the reactive surfaces for the fluid and analyte, which slows down the effective reaction rate (Vanderhoeven et al. 2005; Yuen et al. 2003). As an example, we consider a porous structure with microchannels of length L of several hundreds of micrometers. Assuming molecular diffusion only, the time s required to travel the distance L can be estimated using Einsteins law of diffusion (Vanderhoeven et al. 2005): s L2=2 D. A DNA molecule or protein with a typical diffusion coefficient D of 10-11 m2/s needs hours to travel from the channel inlet to the outlet. Furthermore, only a fraction of the molecules is able to enter the pore that holds the specific capture molecules on its surface. Active transportation of fluid and analyte within and through micropores is therefore essential to enable accelerated reaction rates. Several actuation methods have already been discussed in literature, but each having one or more crucial shortcomings. External mechanical pumps typically require large sample volumes (Vanderhoeven et al. 2005; Yuen et al. 2003; Laser and Santiago 2004). Open systems such as droplet-based actuation are sensitive to evaporation (Gutmann et al. 2005). Systems based on capillary or electro kinetic flows have a strong dependence on the chemical properties of the sample (Vanderhoeven et al. 2005; Laser and Santiago 2004). In fact, a fluid actuation system for high-surface-area elements should be fully integrated and suited for small samples of complex biological fluids (Chen et al. 2007). Superparamagnetic particles can be used for different functions in lab-on-a-chip applications (Gijs 2004; Pamme 2006; Bruls et al. 2009). Their electromagnetic motion control is very flexible and can even be combined with the self-assembly and alignment of particle chains (Derks et al. 2007; Petousis et al. 2007). As biological materials are essentially non-magnetic, functions such as sample filtering, analyte transport, mixing, labeling, or detection can be applied in complex samples without undesired side effects and high reproducibility. In this paper, we propose a novel way for integrated fluid transport in porous high surface area systems based on the hydrodynamic momentum transfer by magnetic particles. By means of applied magnetic fields, the particles are actuated in the microchannels in a non-contact approach. The fluid is driven by the forced motion of the particles to create a net flow through the pores, as illustrated in Fig. 1. Such integrated driving mechanism can be applied in a porous system for large as well as small sample volumes, without generating dead fluid volumes. Several papers have addressed the use of magnetic particles for fluidic pumping on the microscale (Hatch et al. 2001; Hartshorne et al. 2004). These discuss irreversibly aggregated plugs of enormous numbers of Fig. 1 A sketch of the fluid driving concept in microchannels by confined actuated superp (...truncated)