Continuous and Digital Approaches to Manipulation and Detection of Analytes on Microfluidic Devices

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Mats, Lili
Microfluidics , Magnetic Actuation , EWOD , Digital Microfluidics
Microfluidic devices are extremely popular in the area of analytical research as they reduce sample input requirements, have low operational cost, fast analysis time, high separation resolution and low detection limits. A multitude of analytical techniques has been adapted to the microdevice format, including pre-treatment, separation, and detection. Depending on how the fluid is addressed and manipulated, microfluidics can be sub-divided into the “continuous-flow” and digital microfluidics (DMF) approaches. This thesis aims to demonstrate the versatility of microfluidic field of research, where a number of actuation approaches, fabrication methods and materials, on-chip operations and applications were explored. “Continuous-flow” microfluidics allows manipulating the bulk of the sample through the narrow channels under the applied force. Fabrication techniques unique to thermoplastics were utilized to fabricate a “continuous-flow” device capable of separating small drugs and large biological molecules, where a microstructured fibre served as an electrospray ionization mass spectrometry (ESI-MS) emitter. Interest in DMF, where discrete droplets are addressed and manipulated independently, has grown rapidly due to the versatility that arises from non-linear control of fluids. The most common approaches to droplet manipulation are based on either electrowetting-on-dielectric (EWOD) or magnetic interactions. EWOD devices were fabricated with standard photolithography procedures, where coatings with varying degrees of hydrophobicity were explored for EWOD actuation – natural leaf surface, Teflon® AF, and a series of fluorinated silica nanoparticle-based materials. The magnetic actuation approach is based on the interaction of an external magnetic field and magnetically susceptible material inside the droplet, which can be transported over a low-friction surface. Natural superhydrophobic leaf, hydrophobic Teflon, and a commercial superhydrophobic surface were compared for their suitability for the particle-based magnetic actuation. We demonstrated that a commercial coating has excellent compatibility with magnetic actuation, where high actuation speed was reproducibly achieved. We also developed a novel “particle-free” method of magnetic manipulation, where instead of magnetic particles, droplets contained paramagnetic salts with high magnetic susceptibilities were used. Droplets of five paramagnetic salts were efficiently actuated over the commercial superhydrophobic surface, where salts with higher magnetic susceptibility required lower concentrations and achieved higher actuation speed. The “particle-free” approach was used with online fluorescence detection of an anti-cancer drug.
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