Temperature-modulated adsorption of poly(N-isopropylacrylamide)-grafted ferritin on solid substrate

Ferritin grafted with temperature-responsive poly(N-isopropylacrylamide) (PIPAAm-ferritin) was synthesized by a coupling reaction using PIPAAm and ferritin for obtaining stimuli-responsive biomaterials. The hydrodynamic diameter of PIPAAm-ferritins in aqueous solution increased at 37 degrees C at a higher protein concentration (>0.2 mg/mL) because of the intermolecular aggregation through the hydrophobic interaction of PIPAAm chains. On the other hand. PIPAAm-ferritins at a lower concentration (<0.2 mg/mL) were unable to increase their size even at 37 degrees C. The adsorption kinetics of PIPAAm-ferritins on hydrophobically modified Si substrate were evaluated with a quartz crystal microbalance in 10 mmol/L Bis-Tris/HCl buffer (pH 5.8) with and without poly(oxyethylene) sorbitan monolaurate (TWEEN 20) (0.05 wt%) as a surfactant. Although the adsorption of PIPAAm-ferritins on hydrophobic Si substrate at 25 degrees C in the buffer with TWEEN 20 was hardly observed. PIPAAm-ferritins were considerably adsorbed on the substrate at 37 degrees C, indicating that the hydrophobic interaction between the substrate and PIPAAm grafts on the ferritins after the destruction of the hydrophobic interaction between the protein and the substrate by TWEEN 20. (C) 2012 Elsevier B.V. All rights reserved.