Optical metamaterials offer new ways of manipulating electromagnetic wave. We develop optical metamaterials with colloidal nanoparticles as building blocks (known as meta-atoms). Colloidal nanoparticles exhibit rich properties that are tailorable down to atomic level. Opto-thermal tools are developed to manipulate and assemble colloidal particles into desired configurations. Inline optical metrology is developed to measure structures, dynamics and properties of metamaterials at single-particle resolution. Optical phenomena of nanoparticles at molecules and two-dimensional materials are also explored, enabling the developments of active metamaterials and new optical nano-tools such as reactive bubble printing and optical scissors.