Microfluidics involves the confinement of fluid to small length scales, which makes it possible to conduct experiments which have no corollary in the bulk regime. In this thesis, microfluidic technology is used to enable quantitative measurements of proteins and other biomolecules. In addition, microfluidics is used to create otherwise inaccessible structures, designed to modulate biological systems in a controlled way.

More specifically, this thesis studies the effect of shear in the microfluidic devices on the structure of a protein and its reactivity. Using a microfluidic device for kinetics measurements, I show that low levels of shear can induce changes in biomolecular structure, dynamics, and reactivity. In addition, a multidimensional strategy for labelling free and total cysteine residues within proteins is presented. I expect that these results will have implications in the development of new biomarker assays, and further, may suggest ways in which reactions on biomolecules, for example, post-translational modifications, can be modulated within living systems.

In the final part of the thesis, I utilised protein self-assembly and silica precipitation in the creation of protein nanoparticles and silica microparticles for continuous flow enzyme microreactors. The protein nanoparticles were produced with microfluidic co-flow and were used to encapsulate a lipophilic drug while achieving an increased solubility and decreased cell toxicity of the compound. Moreover, by harnessing silica precipitation with droplet microfluidics, extremely homogenous microcapsules containing enzymes were formed, which feature an inorganic silica shell that forms a semi-permeable barrier. I show that the porous shell permits selective diffusion of the substrate and product while protecting the enzymes from degradation by proteinases and maintaining their functionality over multiple reaction cycles. These results demonstrate a robust, accessible and modular approach for the formation of microcapsules containing active but protected enzymes for molecular sensing applications and potential novel diagnostic platforms.

Using these examples, I aim to emphasize the variety of applications and research areas, in which microfluidics can be applied in a quantitative manner.