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We present three concepts for centrifugal microfluidics reducing ethanol carry-over in magnetic bead-based nucleic acid (NA) extraction. Ethanol carry-over is critical regarding inhibition of downstream NA amplification. We identified two possible carry-over pathways: Liquid co-transport within bead-clusters and vapor diffusion. For the first time, we integrated magnetic bead handling in centrifugal microfluidics at continuous rotation aiming to avoid liquid co-transport within bead-clusters. Consequently, no significant contribution to ethanol carry-over could be assigned anymore to liquid co-transport. Major carry-over was attributed to diffusive transport of ethanol vapor. Countermeasures reduced this from 9.7 % (v/v) to 0.4 % (v/v), below the critical level for inhibition of downstream amplification reactions. more...

We present a novel approach for the fully automated generation of dilution series using a disposable microfluidic cartridge. Fluids are metered, mixed and routed without active valving by defined rotational speed only. As a processing device, a standard lab centrifuge can be used. The dilution ratio can be freely choosen by loading the corresponding volume of sample into the cartridge without the need for changes in the microfluidic layout. Dilution series of Fluorescein in PBS buffer with ratios of 1∶3 and 1∶5 are shown with each dilution series comprising 5 single dilution steps. Reproducibility was determined by fluorescence measurement. more...