Nanoparticles such as extracellular vesicles, liposomes, DNA, gold nanorods and small biomolecules have been widely used for various applications in medicine, analytical chemistry, agriculture and pharmaceutical industries. The most common techniques used for nanoparticles isolation are ultracentrifugation and gel electrophoresis. Although these techniques are effective for nanoparticle sorting, they require large sample volume, have poor reproducibility, low purity, are time-consuming, and batch limited. Meanwhile, microfluidic sorting techniques have gained much attention for separating nanoparticles, overcoming most challenges faced with conventional techniques. Inertial microfluidics and acoustophoresis are non-invasive to bioparticles, label-free and can be used for continu...[ Read more ]

Nanoparticles such as extracellular vesicles, liposomes, DNA, gold nanorods and small biomolecules have been widely used for various applications in medicine, analytical chemistry, agriculture and pharmaceutical industries. The most common techniques used for nanoparticles isolation are ultracentrifugation and gel electrophoresis. Although these techniques are effective for nanoparticle sorting, they require large sample volume, have poor reproducibility, low purity, are time-consuming, and batch limited. Meanwhile, microfluidic sorting techniques have gained much attention for separating nanoparticles, overcoming most challenges faced with conventional techniques. Inertial microfluidics and acoustophoresis are non-invasive to bioparticles, label-free and can be used for continuous-flow sorting of nanoparticles. However, the former shows low sorting efficiency when used in highly dense particle concentration, while in the latter, sorting efficiency can be compromised as the required acoustic frequency streaming can disrupt laminar flow. Also, magnetophoresis has high sorting efficiency; however, it requires labelling antibodies with magnetic beads. However, dielectrophoresis provides a label-free technique used for sorting nanoparticles, but most reports are batch limited.

This thesis presents a microfluidic device with microfabricated 3D electrodes, which uses dielectrophoresis and electrohydrodynamic drag to manipulate and enrich nanoparticles under continuous-flow and in a label-free manner. The devices present a pair of unique 3D electrode with sidewall contours, separated by a channel with a downstream junction featuring electrode bridges on both sides. It was demonstrated that the device could be applied for nanoparticle manipulation based on numerical analysis of particle trajectories against the device channel width and the applied voltage. Furthermore, we experimentally demonstrated railing and enrichment of 500 nm polystyrene beads in both high and low conductive media, under pressure-driven flow to a downstream junction where microelectrodes (tracks) act as bridges, keeps nanoparticles on course within the main channel. We also report on nanoparticle oscillations under strong AC electroosmosis. Specifically, nanoparticles in deionized water can be seen bouncing off tracks or circulating with convective rolls in and out of space beneath tracks at an oscillation frequency and amplitude depending on the activation frequency. These results collectively draw attention to the functional use of electrode sidewall contours for continuous-flow manipulation of nanoparticles, which are rarely explored in microfluidics and yet could lead to more effective designs for nanoparticle separation and enrichment. Further work will be directed at the optimization of the devices for applications such as the enrichment and detection of sub-micrometre pathogens in freshwater (low-conductive medium) and the isolation and recovery of extracellular vesicles like exosomes in blood plasma (high-conductive medium).