Switchable Wettability on Cooperative Dual-Responsive Poly-L-lysine Surface

A cooperative dual-responsive polypeptide surface switching between superhydrophilic and superhydrophobic states is presented. This macroscopic phenomenon of surface originates from the combination of the cooperative unfolding/aggregation of the poly-L-lysine (PLL) immobilized on the substrate with micro/nanocomposite structure in response to pH and temperature. At pH lower than the pK(a) of PLL (similar to 11.0), PLL mainly adopts a random coil conformation, which corresponds to the superhydrophilic state on the rough surface substrate. Raising the pH to higher than the pK(a) allows the appearance of alpha-helix conformation, which also corresponds to the hydrophilic state. However, heating up the surface at pH higher than the pK(a) destabilizes the alpha-helix conformation and induces the formation of aggregated beta-sheet structures, which represents the superhydrophobic state. Lowering the pH and temperature simultaneously switches a reversible conversion from superhydrophobic to superhydrophobic states. In the switching process, the hydrophobicity and hydrophilicity can be memorized due to the cooperative pH and temperature stimuli-induced unfolding/aggregation behaviors or PLL. This provides a new exciting prospect for understanding Surface propel-ties of polypeptides and the design of smart material surfaces with potential applications in nanodevices, bioseparation, and biosensors.