Turn-ON [5]helicene-based fluorescence sensor with very large Stokes shift for highly selective detection of Ag+ and AgNPs

Novel Ag+ fluorescence sensor (HC4) based on 2-(4-(2-aminoethylsulfanyl) butylsulfanyl)ethanamine and [5]helicene dye, was successfully synthesized with high yield. The optical studies of HC4 showed the intense fluorescence signal and significantly large Stokes shift of 187 nm. The sensor exhibited high sensitivity and selectivity turn-on fluorescence response for Ag+ over competitive metal ions such as Cu2+, Hg2+, Pb2+, Ca2+, Cd2+, Co2+, Fe2+, Na+, K+, Ba2+, Al3+, Ni2+, Mn2+, Li+, Mg2+ and Zn2+ in aqueous methanol solution. The detection limit of HC4 for Ag+ was 10 ppb, which was lower than the recommended value for the U.S. EPA. NMR spectroscopy, Job's plot, and molecular modeling indicated that sulfur atoms in HC4 played an important role in the selective binding to Ag+. The stoichiometry between HC4 and Ag+ was 1:1. In addition, HC4 could be applied for detection of silver nanoparticles (AgNPs) with simply one-step sample pretreatment, thus the sensor could be used for determining of AgNPs in the consumer products and environment. (C) 2017 Elsevier B.V. All rights reserved.