White cellulose discs (Watson Group) with a diameter of 10 mm were impregnated with 200 μL of RATU (100 μM) CH3CN solution and then dried in air at 25 °C to get the white dried discs containing RATU, namely the solid support sensors. After immersing the solid support sensors in 2 mL water solutions including increasing amounts of Hg2+ for 60 min, visual color changes from colorless to violet were clearly observed (Fig. 13 top). Therefore, RATU could be supported in low cost simple cellulose for monitoring Hg2+ in 100% aqueous solution by the naked eye. This method is really useful for the development of portable and convenient onsite detection of environmental Hg2+. In addition, the solid support RATU sensor binding different amounts of Hg2+ exhibited different fluorescent images under an ultraviolet analyzer (Fig. 13 bottom).