Time-resolved determination of Fe(II) ions using cysteine-bridged Mn-doped ZnS quantum dots as a phosphorimetric probe.

Abstract

A time-resolved phosphorescence (TRP) is applied to the highly sensitive determination of Fe(II) ions. The method is based on the use of a phosphorescent probe consisting of cysteine-bridged Mn-doped ZnS quantum dots (Mn/ZnS QDs). The presence of cysteine enhances the phosphorescence of the QDs and alsoincreases the efficiency ofquenching caused by Fe(II) ions. This results in strongly improved selectivity for Fe(II). The linear response is obtained in the concentration range of 50-1000nM with a 19nM detection limit. Phosphorescence is recorded at excitation/emission peaks of 301/602nm. The interference of short-lived fluorescent and scattering background from the biological fluids is eliminated by using the TRP mode with a delay time of 200μs. The determination of Fe(II) in human serum samples spiked at a 150nM level gave a 92.4% recovery when using the TRP mode, but only 52.4% when using steady-state phosphorescence. This demonstrates that this probe along with TRP detection enables highly sensitive and accurate determination of Fe(II) in serum. Graphical abstract Schematic of a novel phosphorescent method for the detection of Fe2+ ions based on cysteine-bridged Mn-doped ZnS quantum dots. The sensitivity of this assay greatly increases due to the addition of cysteine. Interferences by short-lived auto-fluorescence and the scattering light from the biological fluids is eliminated by using time-resolved phosphorescence mode.