Pairwise interactions between thermal emulsion droplets functinalized with sticky DNA strands that are mobile along the surface

DNA functionalization of particles and droplets has recently emerged as a new tool to achieve programmable sequential self-assembly of colloidal structures. The hybridization of complementary DNA strands is temperature-dependent, and above its melting temperature, the bonds unbind. The temperature-dependent binding allows for tempering and control over the binding strength. Moreover, DNA strands' recruitment on a mobile interface renders the interaction between droplet surface time and history-dependent. We present results on the interaction between DNA-mediated emulsion droplets using time-shared optical tweezers. To this end, we trap two droplets with the optical tweezers and move them close to contact. Then the interaction potential between the droplets is measured by tracking their center-to-center distance. We find a weak, short-range attraction between droplets with complementary DNA strands at higher temperatures. The attraction strength increases when lowering the temperature from 50 to 25°C. In some measurements, we observe that the droplets form a "permanent bond" that cannot be broken by the optical tweezer force.