Microfluidics is the science and technology of manipulating fluids at small scales ranging from microlitres (10$\mathrm{<mrow\; data-mjx-texclass="ORD">-6</mrow>}$) to picolitres (10$\mathrm{<mrow\; data-mjx-texclass="ORD">-12</mrow>}$). The fundamental physics is distinct from fluid behaviour on bulk scales and laminar flow is the key characteristic on this scale. Microfluidic systems have a wide range of applications in many disciplines from engineering to physics, chemistry and biotechnology. In this thesis, I explore different strategies exploiting the capabilities of microfluidic devices for manipulating and analysing biomolecules.

A particular focus of the work is on the study of amyloid fibrils. These species are protein aggregates related to a wide range of human diseases and functional materials. In chapter 3 I demonstrate an efficient way to separate particles in different sizes based on a microfluidic diffusion method. This method enables us to explore the properties of amyloid fibrils, such as their growth kinetics and interaction with small molecules. Rapid binding information could be obtained with only microlitres of sample in tens of seconds time scale.

A further manipulation method for charged particles is introduced in chapter 4, based on the integration of microfluidics and free flow electrophoresis. I present a very effective and simple way to overcome one of the most critical problem in this situation. High electric filed can be applied through two streams of conductive solutions, with all the electrolysis by products, e.g., gas bubbles and other deposits, removed simultaneously without interfering with the system.

In addition to microfluidic devices made by soft lithography in PDMS, I also set up a hot embossing fabrication process with the Teflon material (chapter 5). Teflon has many advantages compared with PDMS, such as lower protein adsorption, higher mechanical strength and better chemical compatibility. With different materials and structures, microfluidic devices can be expanded to more applications.