Colloids, broadly defined as particles small enough to not sediment under gravitational force while dispersed in a continuous medium, are of great scientific and industrial importance. They are present in foods, cosmetics, paints and other materials, often in a jammed or a gelled state. This dissertation explores the self-assembly of hard and soft colloidal particles into mesoscopic structures through modification and control of their surface potentials. Due to its selective binding properties and thermal reversibility, deoxyribonucleic acid (DNA) was used to coat spherical polymeric colloids and subsequently have them assemble into high density colloidal gels. The formation and morphology of one- and two-component colloidal gels was investigated; the use of in-house synthesised fluorinated latex colloids (n = 1.36) allowed for refractive indexmatching of such systems in aqueous solutions, greatly aiding the imaging process deep inside dense gels. Additionally, the diffusion of tracer particles in the confinement of the gel structure was investigated. Furthermore, using the same coating technique, oil droplets (ODs) were functionalised with DNA: various sizes and configurations of DNAcoated ODs were investigated with the goal of creating functional oil-in-water emulsions for possible industrial and biotechnological applications. Taking a different assembly approach, 200 nm diameter fluorinated latex particles without any DNA coating were assembled into photonic crystals which, rather than showing iridescence, displayed strong single colour reflectance along with high transmittance, with the reflection colour varying with interparticle distance. Jumping back to colloidal assembly via DNA, rod-sphere structures made from DNA-coated gold nanoparticles and long DNA-coated virions were explored, demonstrating how anisotropic building blocks could create composite structures with increased porosity. Finally, an external magnetic field was shown to aid the assembly of superparamagnetic DNA-coated colloids into long linear constructs, while an additional coating of colloids was shown to stabilise the constructs after the magnetic field had been switched off.