A novel route to photoluminescent, water-soluble Mn-doped ZnS quantum dots via photopolymerization initiated by the quantum dots

We design a photopolymerization, in which Mn-doped ZnS quantum dots (ZnS:Mn2+) initiate the polymerization of acrylic acid, to convert the non-cytotoxic quantum dots to water-soluble ones for biological chromophores The prepared quantum dots are nearly monodispersed in water and the resulting solution shows long-term stability for months. The water-soluble ZnS:Mn2+ quantum dots exhibit high quantum efficiency of fluorescence. The polymerization of acrylic acid is ruled by a free-radical mechanism and results in a polymer with a random configuration. Raman scattering shows that, in the water-soluble quantum dots, the vibration modes of surface optical phonons, transverse optical phonons and longitudinal optical phonons are changed in frequencies. Results of model calculations correlate these changes to the polymerization occurring at the surface of QDs.