The publication contains some information which are interesting for your investigation (preparation, surface characterisation, zeta potential). In general the not-modified surface of ZnO is positively charged. Hence modifications with amines aren't possible. But you can use a carboxylic group to attach nearly any group at the surface. Note that ZnO is photo reactive and wil destroy the modification.
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...