Monolithic surface micromachined fluidic devices for dielectrophoretic preconcentration and routing of particles

Abstract

We describe a batch fabrication process for producing encapsulated monolithic microfluidic structures. The process relies on sacrificial layers of silicon oxide to produce surface micromachined fluid channels. Bulk micromachined interconnects provide an interface between the microchannels and meso-scale fluidics. The full integration of the fabrication processing significantly increases device reproducibility and reduces long-term costs. The design and fabrication of dielectrophoresis (DEP) gating structures configured in both batch-flow and continuous-flow modes are detailed. Highly efficient microparticle preconcentration (up to ∼100× in 100 s) and valving (97% particle routing efficiency) are demonstrated using ac DEP and an accompanying phase separation. The low aspect-ratio fluid channels with integrated microelectrodes are well suited for µm and sub-µm particle manipulation with electric fields.

Sample preconcentration in microfluidic devices

“…It has also been used for on-chip sample preconcentration. For example, a highly efficient preconcentration microchip based on nDEP gating was reported (James et al 2006). In this study, the DEP gate spans the width of the channel and low polarizability particles such as latex beads with an initial concentration of c 1 are hydrodynamically directed toward the gate.…”

“…In electric field gradient focusing (EFGF), the electrophoretic force that drives charged analytes in a region with a changing electric field is equal and opposite to the force generated by a constant pressure-driven flow, resulting in a focused band (Kelly and Woolley 2005;Koegler and Ivory 1996;Tolley et al 2002;Wang et al 2002). nDEP-based focusing is performed on the basis of the balance between the repulsive force generated by the DEP electrode and the counter force generated by the hydrodynamic flow in the channel (James et al 2006). …”

“…For example, a microchip-based enzymatic assay platform for bioactivity screening was reported (de Boer et al 2005). In this study, the microchip featured two Liu et al (2006a, b) Latex particles (1 lm) nDEP 100 s 100 James et al (2006) microreactors in which an enzyme inhibition and a substrate conversion reaction were performed. The microchipbased assay was coupled on-line to a SPE column for preconcentration and extraction while a capillary reversedphase HPLC column, serving as an analytical column, was connected in series between the SPE column and the microchip.…”

Microfluidics Based Point‐of‐Care Diagnostics

“…The different techniques for the fabrication of silicon‐based MF devices include bulk micromachining, buried‐channel, or surface micromachining . Among these techniques, the bulk micromachining is most prevalent, where channels are created on a silicon wafer by eradication of the material which is then enclosed with another wafer via chemical bonding or by physical adherence .…”

Microfluidic impedance‐based flow cytometry

“…However, the throughput can be relatively low at the cost of high power consumption (128). DEP gates have been used to divert and concentrate particles at flow rates $52 nl/min and high concentration factor (129), and DEP switches have been used to sort particles at a rate of 300/s (130). DEP has also been used to sort dropletencapsulated cells in a microfluidic fluorescence-activated sorter (131) at a rate of 2,000/s.…”