Temperature/pH dual-responsive poly (N-isopropylacrylamide)/chitosan-coated luminescent composite nanospheres: Fabrication and controllable luminescence

Thermo/pH dual-responsive luminescent composites consisting of lanthanide-polyoxometalates and Poly (N-isopropylacrylamide)/Chitosan were synthesized. The dual-responsive nanoparticles are characterized by the FT-IR, UV–vis, TEM , SEM , TGA, DLS and luminescence. The prepared composites exhibit the thermo/pH-responsive properties and the controllable and switchable luminescence in solution in response to the simple changes in temperature and pH values. For instance, the composite hydrogels exhibit intense red luminescence under UV irradiation below 34 °C, and the luminescence become much weaker in solution above 34 °C. Moreover, the hydrogel could not show red luminescence in the buffer solution with low pH value. However, it shows bright red luminescence in neutral and alkaline buffer solution. The possible reasons for controllable luminescence are discussed in the research. The results suggest that the multifunctional nanoparticles could be potentially used in biomedical fields such as luminescent switches, biological labeling and imaging.