Electrokinetic biased Deterministic Lateral Displacement for particle separation

Abstract

Microfluidics will lead to a revolution in the field of sample analysis and to the development of Labon-a-Chip platforms capable to perform complete analytical processes cheaper and faster than the current methods inside single tiny chips. Many biomedical and diagnostic analytical processes require micro/nanoparticle separation which means there is an increasing need for reliable particle separation techniques, suitable for integration within Lab-on-a-Chip systems.
This thesis introduces a novel microfluidic sorting technique that combines a well-established sizebased microfluidic separation technique known as Deterministic Lateral Displacement (DLD) with electrokinetic particle manipulation. This new approach to particle sorting expands the spectrum of potential applications and delivers precise, high-resolution and label-free separation and fractionation of particles in the range of micro and nanometres.
Coplanar parallel electrodes were integrated into a DLD microfluidic device in order to generate electric fields orthogonal to the fluid flow. These electrical forces enable fine tuning of particle trajectories within the DLD microchannels depending on particle structural and electrical properties. This turns a simple size-based separation DLD into a tunable technique capable of targeting a range of particle properties other than size, including particle polarisability and electrical charge. Proof-of-principle experiments demonstrate the potential of this new separation technique and investigate its working principles.
Characterisation experiments were performed to identify the scaling laws that govern behaviour under the action of alternating electric fields. The results were compared with a theoretical model together with numerical simulations to achieve a full understanding of the physical mechanisms that lead to particle sorting. The results showed two distinct working regimes that depend on the frequency of the applied AC electric field. At high frequencies (above 500 Hz), Dielectrophoresis (DEP) was identified as the force driving the separation. When a low frequency field is applied (below 500 Hz), the physical mechanism differs significantly, and experiments indicated the existence of new electrokinetic phenomena that drive the separation process.
Finally, the thesis also describes a refined design of a device that is capable of separation of nanoparticles. The experimental results demonstrate the potential of this technique for the extraction and purification of a wide range of micro and nanoparticles.

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Identifiers

ORCID for Hywel Morgan: orcid.org/0000-0003-4850-5676

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