In this paper, we demonstrated a versatile approach for fabricating water-dispersible nanoparticle (NP)–polymer composite microspheres from amphiphilic poly(ethylene glycol) diglycidyl-grafted poly(maleic anhydride-alt-octadecene) (PMAO-g-PEG) and various NPs with specific functionalities. Depending on the surface polarity of the NPs, the microspheres were fabricated either via two step phase transfers for water soluble NPs or one step phase transfer for oil-soluble ones. For example, aqueous luminescent CdTe NPs were first transferred to chloroform by dimethyldioctadecylammonium bromide modification, and subsequently transferred back to water using PMAO-g-PEG, thus producing luminescent microspheres. Due to the protection of the polymer, the luminescence stability of the NPs under acidic conditions was significantly improved, permitting the detection of Ag⁺ and Cu²⁺ over a broader pH range.