A Highly Sensitive Luminescent Upconversion Nanosensor for Turn-On Detection of As 3 .

A luminescent nanoprobe (N P ), MnO 2 -modified Er 3+ /Yb 3+ -codoped Ag 2 MoO 4 upconversion nanoparticles (UCNPs; cod-AMO-3/MnO 2 ), was constructed for rapid, sensitive, and selective "turn-on" detection of trace As 3+ . Herein, two kinds of luminescent N P s were developed based on luminescence resonance energy transfer (LRET) between cod-AMO-3 as the energy donor and MnO 2 as the energy acceptor. By using MnO 2 as the matrix in cod-AMO-3/MnO 2 fluorometric assay, the upconversion luminescence (UCL) intensity ( I UCL ) of the cod-AMO-3 probe was quenched significantly through LRET, illustrating MnO 2 as an efficient quencher for UCL. With the addition of As 3+ , a stable bidentate binuclear (BB) corner-sharing bridged complex (As 5+ -MnO 2 ) was probably formed, which alters the surface of the upconversion N P , leading to gradual separation between UCNPs and MnO 2 and subsequent recovery of I UCL . Interestingly, it possessed superior sensitivity, reaction kinetics, and also high selectivity toward As 3+ in aqueous solution. Our optimized cod-AMO-3/MnO 2 nanocomposite (NComp) demonstrated a linear range of 0-150 ppb and an ultrasensitive detection limit of 0.028 ppb for As 3+ , which is extremely below the regulatory level, signifying the promising practical usage of this system. To the best of our knowledge, such a surface-modified Ln 3+ -codoped Ag-based nanosensor being applied for As 3+ detection probably has not been reported yet, and it is rather unexplored. In a nutshell, the ability to monitor the As 3+ concentration may enable the rational design of a convenient platform for a diverse range of environmental monitoring applications.