Control ling Droplet Motion on an Organogel Surface by Tuning the Chain Length of DNA and Its Biosensing Application

Controllable droplet motion has attracted extensive attention but still faces the challenges of an uncontrollable sliding speed and a slow response rate. Here, controllable sliding speed and critical sliding angle (CSA) of a droplet on an oil-swollen organogel surface are achieved with a fast response rate via modulation of the DNA chain length. Comprehensive investigations ranging from macroscopic wetting behavior to molecular mechanism suggest that short single-stranded DNA (ssDNA) could act as a hydrotrope to interact with oil molecules via interfacial hydrophobic interactions while increasing the interfacial thickness and adhesion, thus hindering the movement of droplets. Conversely, long ssDNA generated from rolling-circle amplification tend toward a curled conformation, minimizing nucleobase exposure and leading to weak interfacial adhesion, allowing the droplets to slide easily. With a significant CSA gradient, biosensing applications for ATP, microRNA, and thrombin detection are demonstrated, indicating the potential for the detection of a broad range of targets.