DNA-driven assembly of bidisperse, micron-sized colloids

Oligonucleotides are unique chemical moieties that can serve as a useful assembly tool. Unlike most bioadhesion molecules that bind together with high affinity, the attraction between complementary DNA strands can vary greatly depending on strand characteristics (e.g., length and sequence choice) and solution conditions (e.g., ionic strength and temperature). We have studied DNA-mediated assembly of micron-sized, bidisperse mixtures using primarily optical and confocal microscopy. To increase hybridization efficiency between complementary strands, DNA sequences were designed to have a low self-affinity that minimizes intrastrand loop and hairpin formations. Single strands of biotinylated DNA were tethered to NeutrAvidin-coated 1.10 and 1.87 micron beads. The resulting oligonucleotide density on the large bead surface was quantified using flow cytometry. In binary mixtures, we found we could vary the degree of binding between complementary beads depending on the number of matching pairs and the ionic strength of the solution. We have also observed a variety of colloidal structures such as chains of alternating large and small particles by exploring additional experimental variables such as particle number ratio and volume fraction.