Temperature and pH responsive behavior of antifouling zwitterionic mesoporous silica nanoparticles

Zwitterionic brush grafting is considered a serious strategy for surface modification on mesoporous silica nanoparticles (MSN) and a prominent alternative to polyethylene glycol films for antifouling applications. In this study, the solution behavior of poly(sulfobetaine methacrylate) (pSBMA) polymer brushes grafted on MSN (95 ± 15 nm particle diameter, 2.8 nm pore size) was evaluated. The layers increased their hydrodynamic diameter (d_H) with increasing temperature, indicating a conformational change from a surface-collapsed state to a fully solvated brush. This development was marked by a transition temperature, related to the molecular weight and the theoretical length of the polymer chains. Variation of d_H with pH values was studied and a zwitterionic range of 5–9 was established where the electric charges in the molecule were balanced. Zeta potential (ZP) values for all pSBMA-MSN products were also measured. A decreasing trend of ZP with pH and an isoelectric point around 5.5–6.5 was obtained for all dispersions. Furthermore, the influence of temperature was analyzed on ZP and a directly proportional correlation was found, with increasing rates of 0.50–0.87%/°C. Finally, ZP variation with electrolyte concentration was determined and a range of 40–60mM of NaCl concentration was established to reach an almost zero-charge point for all nanoparticles. It was demonstrated that the solution response of pSBMA-MSN can be modulated by temperature, pH, and ionic concentration of the media. These behaviors could be used as controlled release mechanisms for the application of pSBMA-MSN as carriers in biomedicine and nanophamaceutical fields in the future.