Salahi A, Varhue WB, Farmehini V, Hyler AR, Schmelz EM, Davalos RV, et al. Self- aligned microfluidic contactless dielectrophoresis device fabricated by single-layer imprinting on cyclic olefin copolymer. Anal Bioanal Chem. 2020;412: 3881–3889. doi:10.1007/s00216-020-02667-9
The trapping and deflection of biological cells by dielectrophoresis (DEP) at field nonuniformities in a microfluidic device is often conducted in a contactless dielectrophoresis (cDEP) mode, wherein the electrode channel is in a different layer than the sample channel, so that field penetration through the interceding barrier causes DEP above critical cut-off frequencies. In this manner, through physical separation of the electrode and sample channels, it is possible to spatially modulate electric fields with no electrode-induced damage to biological cells in the sample channel. However, since this device requires interlayer alignment of the electrode to sample channel and needs to maintain a thin interceding barrier (~15 pm) over the entire length over which DEP is needed (~1 cm), variations in alignment and microstructure fidelity cause wide variations in cDEP trapping level and frequency response across devices. We present a strategy to eliminate interlayer alignment by fabricating self-aligned electrode and sample channels, simultaneously with the interceding barrier layer (14 pm width and 50 pm depth), using a single-layer imprint and bond process on cyclic olefin copolymer. Specifically, by designing support structures, we preserve fidelity of the high aspect ratio insulating posts in the sample channel and the interceding barrier between the sample and electrode channels over the entire device footprint (~ 1 cm). The device operation is validated based on impedance measurements to quantify field penetration through the interceding barrier and by DEP trapping measurements. The presented fabrication strategy can eventually improve cDEP device manufacturing protocols to enable more reproducible DEP performance.
(a) Cross-section of the sequence of process steps (i-v) to fabricate self-aligned electrode and sample channels with an interceding barrier (v). Scanning electron micrograph (SEM) images of the imprinted COC replica: (b) Top view (15 keV, 300x) and (c) tilted view (15 keV, 150x) to show the membrane and post morphology, (d) Device cross-section determined using a stylus profilometry scan shows depths of 50 μm; (e) the bonded device shows no discernible leaks between the electrode and sample channels through the 14 μm interceding barrier layer over the entire device footprint (> 1 cm).