Cage-like silsesequioxanes bearing rhodamines as fluorescence Hg2+ sensors

Abstract

Polyhedral oligomeric silsesquioxane (POSS) was ultilized as a core and functionalized with the rhodamine hydrazide receptors for incresing the sensitivity of Hg2+ sensing. The POSS sensor (T10Rh) was synthesised, and its sensing behaviors toward metal ions were investigated by UV/Vis and fluorescence spectroscopy. The sensor provided chromogenic and fluorogenic changes upon Hg2+ detection as well as served as a “naked-eye” indicator by a noticeable color change of the aqueous solutions (from colorless to pink-red color). The selective binding resulted in the change in the structures from the spirolactams (non-fluorescent forms) to the non-cyclic forms (fluorescent forms) of T10Rh as indicated by the OFF-ON fluorescence signal upon Hg2+ binding and was shown to discriminate Cu2+, Ag+, Pb2+, Al3+, Cd2+, Mg2+, Ni2+, Fe2+, Co2+, Mn2+, Zn2+, Li+, Na+, Ba2+, Ca2+ and K+, with ultra detection limit of 0.63 ppb which was lower than drinking water permission concentrations by the United States Environmental Protection Agency (U.S. EPA) and World Health Organization (WHO).