Digital magnetofluidics
Digital magnetofluidics is a method for moving, combining, splitting, and controlling drops of water or biological fluids using magnetic fields. This is accomplished by adding superparamagnetic particles to a drop placed on a superhydrophobic surface. Normally this type of surface would exhibit a lotus effect and the drop of water would roll or slide off. But by using magnetic fields, the drop is stabilized and its movements and structure can be controlled.
Drop movement is possible due to the influence of an applied magnetic field. The paramagnetic particles inside the water drops become magnetized. The consequent magnetic dipole interactions among the particles cause them to form chain-like clusters, which follow the magnetic field lines and aggregate further to form long filaments. When the magnet is displaced, the clusters move and drive the motion of the drop.
Multiple drops can be moved simultaneously using different local magnetic fields. By moving the fields together, drops can be combined. This is useful as a method of adding a biological or chemical detection agent to the drop.
Drops may also be split through the action of separate magnetic fields. First, two separate fields are brought together. Then as the fields are moved apart, separate particle clusters are formed and push against the surface tension of the drop eventually ripping the drop into two separate drops.
The first demonstration of this method was done under the direction of Dr. Antonio Garcia (Arizona State University) and Dr Sonia Melle (Universidad Complutense de Madrid, Spain), by doctoral student Ana Egatz-Gomez (Arizona State University), who worked at the laboratory generously provided by Dr Miguel Angel Rubio (Universidad Nacional de Educacion a Distancia, Madrid, Spain). Research to better understand the physics of digital magnetofluidics and to develop biomedical applications is currently being performed in collaboration with researchers at Arizona State University and Los Alamos National Laboratory.
It is believed that this method can lead to the development of so-called "Open Drop Assays" where individual drops of blood and other biological fluids can be rapidly analyzed to diagnose and treat diseases.
References
[1] A. Egatz-Gomez, S. Melle, A.A. García, S. Lindsay, M.A. Rubio, P. Domínguez, T. Picraux, J. Taraci, T. Clement, and M. Hayes, “Superhydrophobic Nanowire Surfaces for Drop Movement Using Magnetic Fields,” in Proc. NSTI Nanotechnology Conference and Trade Show, 2006, pp. 501–504.
[2] A. Egatz-Gómez, S. Melle, A.A. García, S.A. Lindsay, M. Márquez, P. Domínguez-García, M.A. Rubio, S.T. Picraux, J.L. Taraci, and T. Clement, “Discrete magnetic microfluidics,” Applied Physics Letters, vol. 89, pp. 034106, 2006.
[3] A. Egatz-Gómez, J. Schneider, P. Aella, D. Yang, P. Domínguez-García, S. Lindsay, S.T. Picraux, M.A. Rubio, S. Melle, and M. Marquez, “Silicon nanowire and polyethylene superhydrophobic surfaces for discrete magnetic microfluidics,” Applied Surface Science, vol. 254, (no. 1), pp. 330–334, 2007.
[4] A.A. García, A. Egatz-Gómez, S.A. Lindsay, P. Domínguez-García, S. Melle, M. Marquez, M.A. Rubio, S.T. Picraux, D. Yang, and P. Aella, “Magnetic movement of biological fluid droplets,” Journal of Magnetism and Magnetic Materials, vol. 311, (no. 1), pp. 238–243, 2007.
[5] S. Lindsay, T. Vázquez, A. Egatz-Gómez, S. Loyprasert, A.A. Garcia, and J. Wang, “Discrete microfluidics with electrochemical detection,” The Analyst, vol. 132, (no. 5), pp. 412–416, 2007.
[6] J. Schneider, A. Egatz-Gómez, S. Melle, S. Lindsay, P. Domínguez-García, M.A. Rubio, M. Márquez, and A.A. García, “Motion of viscous drops on superhydrophobic surfaces due to magnetic gradients,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007.
[7] S. Melle Hernandez, A. Gomez, T. Picraux S, J. Gust, M. Hayes, S. Lindsay, A. Garcia, J. Wang, and T. Vazquez-Alvarez, “DIGITAL MAGNETOFLUIDIC DEVICES AND METHODS,” US Patent WO/2007/101174