High-Density PEO-b-DNA Brushes on Polymer Particles for Colloidal Superstructures

Abstract

We demonstrate a method to create high-density DNA coatings on colloidal particles that can be used for DNA-mediated self-assembly of single- and multiple-component colloidal crystals. First, we modify an amphiphilic diblock copolymer consisting of a hydrophobic polystyrene (PS) block and a hydrophilic poly(ethylene oxide) (PEO) block with azide functional groups at the end (poly(ethylene oxide)-N3). Then, we introduce the diblock copolymers into an aqueous suspension of colloidal polymer particles swollen with a solvent. The hydrophobic PS anchoring block is incorporated into the swollen polymer spheres and physically trapped when the solvent is removed, resulting in a dense PEO polymer brush with azide functional end groups. Finally, single-stranded DNA strands with sticky ends are attached to the azide groups using strain-promoted azide-alkyne cycloaddition (SPAAC, a copper-free click chemistry). This procedure results in a high areal coverage of up to 225-000 DNA strands on 1-μm-diameter particles. The ssDNA-coated particles with sticky ends can readily form either face-centered-cubic (fcc) or cesium chloride (CsCl) crystal structures when annealed just below the melting temperature of the DNA-coated particles.