Rapid mixing of sub-microliter drops by magnetic micro-stirring
We demonstrate rapid mixing of sub-microliter droplets (250nl) using miniaturized magnetic stir bars (400 µm by 200 µm by 15 µm). The stir bars are fabricated using laser micromachining and placed on the substrate on which the drops are manipulated. They are activated by an externally applied magnetic field and used in combination with on-demand drop merging in enthalpy arrays. This technique results in a 10 fold increase in mixing rate, and a mixing time constant of about 2 seconds. Drop mixing times are measured by Förster resonance energy transfer (FRET) and verified by thermodynamic measurements of binding and enzymatic reactions.
De Bruyker, D.; Recht, M. I.; Bhagat, A.; Torres, F.; Bell, A. G.; Bruce, R. H. Rapid mixing of sub-microliter drops by magnetic micro-stirring. Lab on a Chip. 2011 October 7; 11 (19): 3313-3319.