Organic semiconductor polymer nanodots as a new kind of off-on fluorescent probe for sulfide

The authors describe a fluorescent probe for sulfide that is based on carboxy-functionalized semiconducting polymer dots (P-dots). The dots were prepared from carboxy-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′-3-thiadiazole)] (referred to as COOH-PFBT) via co-precipitation. The P-dots aggregate on addition of Cu(II) ions and their green fluorescence (with excitation/emission peaks at 455/540 nm) is then quenched. Fluorescence is restored on addition of sulfide to the aggregates due to the formation of CuS. This quenching-recovery (“off-on”) mechanism forms the basis for a new sulfide detection scheme. Fluorescence increases linearly in the 1.25 to 75.0 μM sulfide concentration range, with a 0.45 μM detection limit. Good selectivity over other anions is demonstrated. The method shows recoveries ranging between 98.6% and 105.7% when applied to the determination of sulfide in spiked real water samples. Schematic of a fluorescent off-on sensor for (hydrogen) sulfide based on the use of semiconducting polymer dots (PFBT-COOH) whose fluorescene is quenched by Cu(II) ion but restored on addition of (hydrogen) sulfide.