Magnetic colloidal assemblies and their applications in bioscience.
Date of Issue2010
School of Physical and Mathematical Sciences
Colloidal assemblies have many applications in science and technology, ranging from optics and photonics devices to bioscience and biotechnologies. For paramagnetic colloids, the interactions between colloidal particles can be manipulated by adjusting the magnitude of an external magnetic field. This thesis investigates the assemblies of micrometer-sized magnetic colloids and their applications in bioscience. The phase ordering phenomena in a two-dimensional (2D) colloidal system by tuning the electro- and magnetostatic interparticle interactions were studied. A subtle competition between the repulsive interparticle interactions and the thermal excitations of the particles was found to determine the crystallization of the colloidal system. The order-disorder transition (from 2D to 3D) of the colloidal system was also observed, when the magnetic interaction between colloids was higher than a critical value. The formation of 2D clusters of protein-coated colloids in evaporating aqueous droplets was observed, indicating the presence of attractive interactions between colloidal particles. The dynamical evolution of the cluster formation and the effects of different experimental parameters (e.g. magnetic field and salt concentration) on this process were quantitatively characterized by using the radial distribution function. The magnetic colloidal chains bridged by short biotin-ended single-stranded DNA, and guided by the magnetic interactions between colloidal particles were fabricated. The relationship between the length of colloidal chains and different experimental parameters (e.g. magnetic field, time under magnetic field, DNA density on colloids’ surface) was established. The conditions for protein adsorption on glass substrates were investigated and protein patterns were successfully created using colloidal lithography. The experimental results indicated that the adsorption of bovine serum albumin (BSA) protein on glass substrates can be controlled by (i) adjusting the pre-coated polyelectrolyte layer of poly (allylamine-hydrochloride) (PAH) molecules and (ii) adding the surfactant sodium dodecyl sulphate (SDS) or salt in the BSA solution.