Dielectrophoretic liquid actuation on nano-textured super hydrophobic surfaces

Nano-textured super hydrophobic (SH) surfaces can achieve very high droplet contact angles (typically >150°) and are furthermore associated with reduced surface adsorption of enzymes and other macro-molecules. The advantages of such SH surfaces have already been explored for electrostatic based digital microfluidic (DMF) devices where the high CA and the reduced surface adsorption largely benefits the handling and manipulation of complex bio-chemical samples/reagents. Liquid dielectrophoresis (LDEP) based digital microfluidic (DMF) technology has demonstrated its capability for achieving combinatorial assays on standard hydrophobic surfaces. However, such devices suffer from similar issues as DMF devices when it comes to handling bio-reagents/samples where off-chip sample handling steps (washing/buffer exchange) are often required prior to the on-chip bio-assay. In this work, we have optimized a comprehensive fabrication protocol to develop a nano-textured SH surface topology for LDEP device applications. The static and transient behavior of LDEP actuation over the SH surface has been investigated using an improved lumped model and furthermore experimentally verified using specifically tailored liquid samples. The developed SH surface has also been analyzed for liquid actuation of TAQ DNA polymerase enzyme which is a key component of most nucleic acid amplification assays. The performance of LDEP actuation of tailored liquid samples is analyzed and compared for both hydrophobic and SH surfaces. The reported work demonstrates that specific textured SH surfaces can successfully achieve reliable LDEP actuation and furthermore dispense/manipulate TAQ DNA polymerase enzyme and various other aqueous samples.