Redox-magnetohydrodynamic microfluidics

by Fritsch, I.; Weston, M. C.; Gerner, M. D.; Hooten, C. K.; Gonzales, C.; Sahore, V.; Isaac, K. M.; Leventis, N.

Manipulation of small fluid vols. (microfluidics) is essential to perform multi-step chem. anal., enhance the combination and mixing of solns. for reactions, and achieve small-scale sepns. Micro total anal. systems that employ microfluidics could revolutionize chem. anal. in genomics, environmental monitoring, medical diagnostics, and drug discovery. Microfluidics has largely been dominated by electrokinetic pumps that easily control direction and produce flat flow profiles in channels (~tens of micrometers), which are well-suited for sepns., and by mech. approaches such as syringe pumps that work well at larger dimensions. Other micropumps involve centrifugal and electrohydrodynamic phenomena. New challenges continue to arise in handling fluids at small dimensions and thus gaps in capabilities of more traditional approaches drive further development of existing methods and introduction of new ones. Recent advances in the understanding and development of redox-MHDs (MHD) as an alternative microfluidic approach that offers unique capabilities will be presented. The MHD body force, FB, acts on a fluid element where ion flux, j, generated by electrochem. oxidn. and redn. of redox species at electrodes on a chip in the presence of a magnetic field, B, in the direction detd. by the right hand rule: FB = j × B (where j, B, and FB are vectors). Stirring, pumping in a loop, and ease of changing flow direction are possible with redox-MHD, with the added feature that both aq. and non-aq. solvents may be used. Also, redox-MHD can "grab" a specific fluid element and move it around with or without the presence of a channel. Linear velocities of tens of micrometers to millimeters per s have been demonstrated. Because channels can be hundreds of micrometers to millimeters in size, vol. flow rates can be higher than for electrokinetic pumping.