Guided assembly of colloidal particles on patterned substrates

Mica substrates decorated with a periodic array of gold squares are used to guide the growth of two-dimensional colloidal crystals of charged polystyrene particles. For polystyrene spheres (90 nm in diameter) suspended in pure water, the attractive interaction between the solvent and the hydrophilic mica surface leads to selective deposition of the colloidal particles on the mica surface, where two-dimensional monolayers are formed. In contrast, by addition of a dilute surfactant (5 mM sodium dodecylsulfate) to the colloidal suspension, the self-assembly process of colloidal monolayers is completely changed. The polystyrene spheres are preferentially attached to the gold terraces in the form of ordered monolayers, confined laterally by the boundaries of the prefabricated gold terraces. This method provides an efficient route to guided growth of novel colloidal monolayers, with potential applications in, for example, biosensing and photonics.