Synergistic design of electric field and membrane in facilitating continuous adsorption for cleanup and enrichment of proteins in direct ESI-MS analysis

We designed and fabricated a novel microdevice to facilitate continuous adsorption phenomena for biological sample preparation. Using the device, we also developed an online, highly integrated, multifunctional strategy, with a promise of accepting a large volume of crude tissue extracts with the end point generation of a reliable MS identification within 20 min. Under an external electric field, charged membranes can adsorb multiple layers of proteins, which exceed the capacity limit of common resins or membranes. It enlarges sample loading and trapping efficiency, thus bypasses the tradeoff between sample capacity and downstream detection sensitivity. This integrated approach, formed by synergistic utilization among electric field, membrane, and fluidic handling at the microscale, reduces the overall complexity of crude samples in one step for direct MS analysis. The sample preparation goals, including enrichment, desalting, removal of noncharged contaminants, and initial fractionation, can be rapidly performed in a single device. The strategy facilitates reproducible MS quantification by circumventing traditional laborious and time-consuming sample preparation steps. In addition, MEPD extended the ion trap linear dynamic range from 2 to at least 4 orders of magnitude by eliminating ion suppression effect, enriching target analyte(s), and decreasing sample loss during integrated sample preparation.