Sidewall Electrodes in Microchannels for Dielectrophoretic Cell Separation and Electrochemical Detection

Microfluidics in biological and medical research has gained much attention in the past decade for the purposes of separation and analysis of components within a complex sample. However, electrically functional microfluidic devices for biological sensing and cell manipulation require the ability to modulate electric field profiles over the channel width and depth, which is especially challenging to fabricate with minimum lithography steps. Metal deposition is the most ubiquitous method for integrating electrodes in microchannels, but the traditional deposition method is limited to planar electrodes, which have low electric field extents along the depth of the channel, thereby making them unsuitable for applications wherein sensing and manipulation are required over the channel depth. To address the need for uniform measurements over channel depth without highly specialized sidewall metal deposition steps, alternative electrode fabrication methods have been explored, such as conductive liquid electrodes, Ag-PDMS electrodes, and liquid metal electrodes. Current methods based on liquid electrodes have been limited by stability of the conductive fluid, whereas conductive polymer composites (Ag-PDMS) do not exhibit sufficient electrical conductivity for field coupling and liquid metal lacks physical stability for portable device applications. Here, we present the design principles for facile microfabrication to integrate liquid metal electrodes that solidify at room temperature, thereby enabling a microdevice for dielectrophoretic cell separation and electrochemical detection over the entire depth of the microchannel. Specifically, an electrode and sample channel are co-fabricated in a single lithography step and sequentially filled to enable electrically functional microfluidic separation and detection. Three distinct confinement approaches are examined for creating electrode channels that are physically separated from biological sample channels, but electrically coupled for enabling dielectrophoretic separation and electrochemical detection.