Surface modification is usually used to obtain reactive group
on silica nanoparticles, most of the recent literatures concerning
surface modification are based on surface grafting organosilanes
onto silica [23,24], and amine, vinyl, dendrime, and pyridine
especially amine group which has been applied extensively
in biomedical. However a very limited member of articles describes
the modification of carboxyl group to silica nanoparticle
surface. Carboxyl groups on silica surface were obtained by
trichlorocyanoethylsilane (TCES) [19], polymer [25] and succinic
anhydride [26,27] through different methods, especially
succinic anhydride converts amino groups into carboxyl groups
easily without higher temperature or additional catalyst [28,29].