Hybrid microfluidics: A digital-to-channel interface for in-line sample processing and chemical separations

Microchannels can separate analytes faster with higher resolution, higher efficiency and with lower reagent consumption than typical column techniques. Unfortunately, an impediment in the path toward fully integrated microchannel-based labs-on-a-chip is the integration of pre-separation sample processing. Although possible in microchannels, such steps are challenging because of the difficulty in maintaining spatial control over many reagents simultaneously. In contrast, the alternative format of digital microfluidics (DMF), in which discrete droplets are manipulated on an array of electrodes, is well-suited for carrying out sequential chemical reactions. Here, we report the development of the first digital-channel hybrid microfluidic device for integrated pre-processing reactions and chemical separations. The device was demonstrated to be useful for on-chip labeling of amino acids and primary amines in cell lysate, as well as enzymatic digestion of peptide standards, followed by separation in microchannels. Given the myriad applications requiring pre-processing and chemical separations, the hybrid digital-channel format has the potential to become a powerful new tool for micro total analysis systems.