Deposition and conformational control of Poly-L-lysine spontaneous deposition on glass

Polylysine is a cationic polyelectrolyte (pKa ~ 10,5) extensively used to promote interactions with negatively charged molecules.[1] Despite the use of polylysine treated glass is generally used to promote cell adhesion, a systematic study aimed to investigate the role played by dispersive forces to achieve an effective spontaneous deposition (in water) is not largely discussed. In particular, we focus on the role of the secondary structure of poly-L-lysine (PLL), extensively studied in solution, on both deposition on solid surfaces and following interactions with negatively charged porphyrins (H2TPPS). Glass slides have been treated with PLL in different conditions, to demonstrate the possibility to trigger glass surface charge by controlling and rationalizing PLL deposition. In fact, because oxide surfaces develop a surface charge in water (depending on the pH), [2] electrostatic interactions play an important role when absorbing molecules bear a charge. In water, a complex tuning of many factors, among them molecular solubility and solvophobicity, surface chemical and morphological complexity, overall charge distribution in solid and liquid phase and molecular conformation control is required to attain a successful (non-covalent) surface functionalization. The presented non-covalent deposition allows for a process reproducibility and control as well as robustness of the assembled layers.