Assembly of binary colloidal structures via specific biological adhesion

We present a novel approach to the fabrication of binary colloidal materials where specific biomolecular cross-linking drives the self-assembly of bidisperse colloidal suspensions. In particular, we have employed low-affinity immune system carbohydrate-selectin interactions to mediate the heterotypic assembly of binary colloidal structures. Using small (0.94 mum) and larger (5.5 mum) diameter particles coated with complementary chemistry, we show that a progressive series of structures, such as colloidal micelles (a large particle coated with smaller particles), colloidal clusters, rings, and elongated chains, can be made by decreasing the number fraction, N-A/N-B, Of Small (A) to large (B) particles (200 greater than or equal to N-A/N-B greater than or equal to 2) at low total volume fraction (phir = 10(-4)-10(-3)). The assembly is due to specific molecular interactions, as control experiments in which the molecules are blocked or eliminated do not lead to the assembly of these structures. The size of the structures can be modulated by time or total volume fraction. Currently, our methods employ high molecular surface densities, such that the structures result from kinetically trapped, diffusion-limited assembly. Ultimately, with the ability to control the strength of the interaction (using different chemistries and molecular surface densities) as well as the lengths of the molecular tethering arms, particle number densities, and physical properties of the colloidal components, this colloidal assembly driven by specific interactions should yield new materials with many potential technological applications including optical filters, sensors, and separation media.