Silver nanoclusters capped silica nanoparticles as a ratiometric photoluminescence nanosensor for the selective detection of I⁻ and S²⁻

A novel and efficient approach has been established for the synthesis of silver nanoclusters capped silica nanoparticles (SiO₂@AgNCs). These nanoclusters (AgNCs) capped silica nanoparticles were utilized as a novel ratiometric photoluminescence (PL) nanosensor for extremely sensitive and selective detection of I⁻ and S²⁻ ions. The AgNCs were prepared in situ on the silica nanoparticles through polyethyleneimine (PEI) template approach. While dual PL emissions of AgNCs (at 500 nm) and luminescent silica nanoparticles (at 602 nm) formed the basis for the ratiometric sensing. The PL emission of AgNCs was strongly quenched by I⁻ (or S²⁻), while that of luminescent silica nanoparticles was hardly affected. The PL emission intensity ratio of AgNCs and the luminescent silica nanoparticles was defined as I₅₀₀/I₆₀₂. A good linear relationship between the I₅₀₀/I₆₀₂ value and the concentration of I⁻ (or S²⁻) was observed, and the limit of detection (LOD) was estimated to be 57 nM for I⁻ and 62 nM for S²⁻. In addition, the fluorescence images of the SiO₂@AgNCs nanosensor changed from white to orange upon exposure to different concentrations of I⁻ (or S²⁻) (0–250 μM), which could be clearly distinguished by the naked eye. The SiO₂@AgNCs nanosensor exhibited good selectivity against other analytes, and I⁻ or S²⁻ ions could be separately detected via the introduction of proper masking agents. Furthermore, the detection of I⁻ and S²⁻ in real water samples was also demonstrated.