Digital magnetofluidics

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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 in the laboratory of Prof. Miguel Angel Rubio in Madrid, Spain by Professor Sonia Melle and Ana Gomez. Research to better understand the physics of digital magnetofluidics is currently being performed in collaboration with researchers in 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.

• Gomez, A., Melle, S., Garcia, A.A.,, Picraux, T., Taraci, J.L., Clement, T., Hayes, M., Gust, D., Marquez, M., Dominguez-Garcia, P. , Rubio, M.A., Discrete magnetic microfluidics, Applied Physics Letters 89, 034106 (2006).
• Solitaire Lindsay, Terannie Vázquez Ana Egatz-Gόmez, Suchera Loyprasert, Antonio A. Garcia, Joseph Wang, “Magnetic digital microfluidics with electrochemical detection”, Analyst, 132, 412 - 416 (2007).
• Antonio A. Garcia, Ana Egatz-Gómez, Solitaire A. Lindsay, P. Domínguez-García, Sonia Melle Manuel Marquez, Miguel A. Rubio, S. T. Picraux, Dongqing Yang, P. Aellad, Mark A. Hayes, Devens Gust, Suchera Loyprase, Terannie Vazquez-Alvarez, Joseph Wang, “Magnetic movement of biological fluid droplets”, Journal of Magnetism and Magnetic Materials 311, 238–243 (2007).