In this work, we have identified key parameters for controlling the surface density of ferritin on metal oxides
and observed a conformational change of the protein shell of ferritin occurring exclusively at pH 4. The
quartz crystal microbalance with dissipation (QCM-D) monitoring technique was used to examine protein
adsorption on gold and Ti-, Si-, Ta-, Al-, and Nb-oxide surfaces. A comparative study of the adsorption to
Ti-oxide was made using atomic force microscopy (AFM). The surface density of ferritin was controlled by
a variation in the solution pH (from 2 to 8) and the isoelectric point (Ip) of the surface. On the basis of these
findings, clear trends in the effect of electrostatic interactions between the ferritin proteins and between ferritin
and the surface were found, making it possible to tune the surface density of ferritin through the choice of
solution pH and the Ip of the surface. Furthermore, the influence of the pH on the viscoelastic properties of
the adsorbed ferritin layer was examined using QCM-D. Conformational changes of the protein shell of ferritin
were found to occur at pH 4, which is close to the Ip of ferritin (4.6), but not for lower or higher values of
the pH. This conformational change of ferritin was seen clearly in dissipation per frequency value obtained
from the QCM-D technique.
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