  The focus of this article is based on the aqueous dispersed state properties
of inorganic ZnO nanoparticles (average size lessthan or equal to 4 nm), their
surface modification and bio-functionalization with folic acid at physiological
pH ~ 7.5, suitable for bio-imaging and targeted therapeutic application. While
TEM studies of the ZnO nano-crystallites have been performed to estimate their
size and morphology in dry state, the band gap properties of the freshly
prepared samples, the hydrodynamic size in aqueous solution phase and the wide
fluorescence range in visible region have been investigated to establish the
fact that the sol is particularly suitable for the bio-medical purpose in the
aqueous dispersed state.
  Key words: ZnO nanoparticle; folic acid; band gap; hydrodynamic size;
fluorescence.
