A Highly Sensitive Luminescent Upconversion Nanosensor for Turn-On Detection of As³

A luminescent nanoprobe (N_P), MnO₂-modified Er³⁺/Yb³⁺-codoped Ag₂MoO₄ upconversion nanoparticles (UCNPs; cod-AMO-3/MnO₂), was constructed for rapid, sensitive, and selective "turn-on" detection of trace As³⁺. Herein, two kinds of luminescent N_Ps were developed based on luminescence resonance energy transfer (LRET) between cod-AMO-3 as the energy donor and MnO₂ as the energy acceptor. By using MnO₂ as the matrix in cod-AMO-3/MnO₂ fluorometric assay, the upconversion luminescence (UCL) intensity (I_UCL) of the cod-AMO-3 probe was quenched significantly through LRET, illustrating MnO₂ as an efficient quencher for UCL. With the addition of As³⁺, a stable bidentate binuclear (BB) corner-sharing bridged complex (As⁵⁺-MnO₂) was probably formed, which alters the surface of the upconversion N_P, leading to gradual separation between UCNPs and MnO₂ and subsequent recovery of I_UCL. Interestingly, it possessed superior sensitivity, reaction kinetics, and also high selectivity toward As³⁺ in aqueous solution. Our optimized cod-AMO-3/MnO₂ nanocomposite (NComp) demonstrated a linear range of 0-150 ppb and an ultrasensitive detection limit of 0.028 ppb for As³⁺, 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 Ln³⁺-codoped Ag-based nanosensor being applied for As³⁺ detection probably has not been reported yet, and it is rather unexplored. In a nutshell, the ability to monitor the As³⁺ concentration may enable the rational design of a convenient platform for a diverse range of environmental monitoring applications.