Facile preparation of a multifunctional fluorescent nanosensor for chemical and biological applications

To prepare a versatile solid-state fluorescent sensor for chemical and biological applications is still a challenge. In this report, we describe a multifunctional fluorescent nanosensor that is capable of highly sensitive and selective detecting of the heavy metal ion Hg2+ in a range of pH from 4.0 to 6.6, sensitive probing of α-amino acids by a metal ion-mediated approach, turn-on sensing of the protein BSA under physiological conditions and in vitro monitoring of Hg2+ within living cells. This all-round smart sensor 1 has been designed by functionalizing highly ordered mesoporous SBA-15 nanoparticles with 3-isocyanatopropyltriethoxysilane and dansylcadaverine, followed by the characterization of the pore structure, textural property, microscopic morphology, molecular composition of grafted organic fluorophore and the colorimetric property of 1. The quenching fluorescence emission of 1 in the presence of Hg2+ could be attributed to the photoinduced electron transfer (PET) from the exited dansyl moiety to the proximate mercuric ion. The successful sensing of α-amino acids has been realized by an indirect approach, in which the quenched fluorescence of 1 by Hg2+ was recovered upon the addition of α-amino acids. The turn-on sensing of BSA under physiological conditions is based on the hydrophobic interaction between BSA and the naphthalene ring on the dansyl fluorophore of 1. This interaction also makes 1 become an efficient adsorbent for storing and retaining BSA. Finally, 1 has been demonstrated to have application in living cells by detecting intracellular Hg2+.