Improving the temporal stability of the preconcentrated analyte plug in ion concentration polarization in a microfluidic device for proteomics study

Description:
Ion concentration polarization (CP) is a preconcentration method actively used in microfluidic platforms for the analysis of biological and environmental samples. Applying an electric field across a negatively charged ion-permselective element (nanocapillary membrane) in a microchannel forms an ion depleted zone on the anodic side of the membrane and an ion enriched zone on the cathodic side. The movement of the ions in the microchannel is driven by electroosmotic flow (EOF) and electrophoresis. In an EOF dominated device, analytes can be enriched on the anodic side at the edge of the depleted zone with a counter EOF provided by an additional side channel. However, this preconcentrated plug is extremely difficult to recover for downstream analysis without dissipation due to temporal instability. In an electrophoresis dominant device, the analytes can be enriched on the cathodic side. When the mobility of the analyte is higher than the background electrolyte co-ions, the analyte will be enriched at the nanofluidic microfluidic interface (NMI). When the mobility of the analyte is lower than the background electrolyte co-ions, which is typically the case for proteins and peptides, the analyte will be enriched at the edge of the background electrolyte enrichment shock that propagates away from the NMI. The propagation of the enriched zone, which is driven by EOF, leads to a lower enrichment factor and the uncontrolled movement of the preconcentrated plug. Our studies of this enrichment process have revealed that low EOF through the ion permselective element and high current are needed for efficient and stable enrichment. Background electrolyte optimization, membrane pore density selection, and variation of pH at the anodic side of the membrane are performed to minimize EOF while maintaining a high current. An improvement in analyte preconcentration is achieved with a localized enrichment plug, which can be eluted for downstream mass spectrometry analysis.

Speaker: Dayi Chen - University of Pennsylvania
BS Peking University
PhD University of Utah