A finite-cluster phase in λ-DNA-coated colloids

We studied the aggregation of 1 µm colloids bridged by DNA with 32 µm contour length. We mixed two species of particles with grafted double-stranded λ-DNA displaying short, complementary single-stranded 'overhangs' as free binding-ends. Confocal microscopy showed the formation of stable, size-limited clusters in which the two species of particles were at touching contact. Simulations suggest that the observed close contact and the limitation to grow both result from entropic exclusion of the bridging DNA from the space between nearby particle surfaces.