Solid-phase Extraction and Detection Techniques for Digital Microfluidics

Digital microfluidics (DMF) is a microscale fluid handling technology in which discrete liquid droplets are individually actuated in two dimensions over an array of dielectric-coated electrodes. DMF is gaining popularity as a platform for the development of micro-total analysis systems because of its ease of automation, portability, and ability to perform multiple processes simultaneously. A key step for the analysis of complex samples is extraction for clean-up, fractionation and preconcentration. Previously, the only extraction methods available for DMF were sample drying and re-dissolution, and liquid-liquid extraction. In this thesis, the first methods for performing solid-phase extraction (SPE) on DMF are introduced, along with a complementary optical detection system for on-chip absorbance and fluorescence interrogation of droplets. In Chapters 2 and 3, the formation of porous polymer monoliths with reverse-phase and strong cation exchange functionalities are demonstrated. Using these solid phases, small molecules, peptides and proteins are purified and enriched on DMF chips via SPE. In Chapter 4, an optical fibre-based absorbance and fluorescence detection system is presented, using a custom manifold to allow easy adjustment of absorbance pathlength with droplet stretching for sensitivity enhancement. Liquid lensing further enhances measurements, resulting in significant increases in sensitivity and limits of detection. In Chapter 5, an automated DMF elution solvent optimization protocol using design of experiments is developed, and applied to perform on-chip SPE with C18 beads. This method enables clean-up and fractionation of small molecule and peptide samples, with on-the-fly adjustment of solid phase volume. The advancements presented herein represent the first techniques allowing SPE to be performed with DMF. These methods promise to support the development of micro-total analysis systems for complex samples, including analyses for proteomics and clinical applications.Ph.D