Probing nanoscale interactions between DNA-coated colloids using total internal reflection microscopy

DNA-coated colloids are our most versatile tool for the targeted self-assembly of colloidal materials. However, control of disorder, defects, melting, and crystal growth is hindered by the lack of a microscopic understanding of DNA-mediated colloidal interactions. Here we use total internal reflection microscopy (TIRM) to measure the interaction potential between DNA-coated colloids with nanometer resolution and the macroscopic melting behavior. The range and strength of the interaction are measured and linked to key material design parameters, including DNA sequence, polymer length, grafting density, and complementary fraction. We build a first-principles model that quantitatively reproduces our experimental data without fitting parameters over a wide range of DNA ligand designs. Our work identifies a subtle competition between DNA binding and steric repulsion and accurately predicts adhesion and melting at a molecular level.