On-chip intermediate potential measurements for the control of electromigration in multi-channel networks in case of time-dependent potential changes

Abstract

One of the greatest challenges in multi-channel networks for electromigrative separation techniques is the control of the leakage of sample constituents and band broadening at the channel intersections in microfluidic devices or capillary-chip interfaces, which can be achieved using fixed bias or pullback potentials. These may be implemented as the first separation dimension in a 2D setup, where the electric potential at the interface to the second dimension changes with time. Thus, a dynamic control via on-line potential measurement in combination with a feedback system is needed to control electromigration into the side channels. We here present for the first time a prototype for in-channel potential measurements using a low working current in combination with a Si3N4 passivated Ti/Pt electrode at the intersection of the channels in a microfluidic interface. Exemplarily we chose capillary electrophoresis and isotachophoresis as model applications with constant vs. dynamic potential. Parallel on-chip intersection potential measurements were successfully conducted without disturbing capillary zone electrophoretic and isotachophoretic analysis regarding separation and peak performance of amino acids chosen as model analytes. This was possible due to a Si3N4 passivation layer, but also due to an ad-hoc developed high impedance instrumentation, resulting in a very low measuring electric current. Simulations of the detected isotachophoretic cross-section potential allowed a deeper understanding of the potential development during the separation.