A visual physiological temperature sensor developed with gelatin-stabilized luminescent silver nanoclusters. 
A visual physiological temperature sensor was successfully developed with newly hydrothermally prepared fluorescent silver nanoclusters (AgNCs) at room temperature using gelatin as the protective and reducing agent.  The as-prepared gelatin-stabilized AgNCs was water-soluble, uniform and exhibited a narrow distribution with an average size of 1.16 nm, showing a maximum emission band at 552 nm (2.45 eV) when excited at 445 nm (2.79 eV).  The large Stokes shift of 110 nm of the gelatin-stabilized AgNCs makes it actually applicable with very low background and light scattering interferences.  It was found that the as-prepared gelatin-stabilized AgNCs is temperature-sensitive over the range from 5°C to 45°C, and thus a visual physiological temperature sensor could be developed with the gelatin-AgNCs as under the irradiation of visible light.