Preparation, characterization and evaluation of water-soluble l-cysteine-capped-CdS nanoparticles as fluorescence probe for detection of Hg(II) in aqueous solution

Water-soluble l-cysteine-capped-CdS nanoparticles were prepared in aqueous solution at room temperature through a straightforward one-pot process by using safe and low-cost inorganic salts as precursors, and characterized by transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry, spectrofluorometry and ultraviolet-visible spectrometry. The prepared l-cysteine-capped-CdS nanoparticles were evaluated as fluorescence probe for Hg(II) detection. The fluorescence quenching of the l-cysteine-capped-CdS nanoparticles depended on the concentration and pH of Hg(II) solution. Maximum fluorescence quenching was observed at pH 7.4 with the excitation and emission wavelengths of 360 nm and 495 nm, respectively. Quenching of its fluorescence due to Hg(II) at the 20 nmol l⁻¹level was unaffected by the presence of 5 × 10⁶-fold excesses of Na(I) and K(I), 5 × 10⁵-fold excesses of Mg(II), 5 × 10⁴-fold excesses of Ca(II), 500-fold excesses of Al(III), 91-fold excesses of Mn(II), 23.5-fold excesses of Pb(II), 25-fold excesses of Fe(III), 25-fold excesses of Ag(I), 8.5-fold excesses of Ni(II) and 5-fold excesses of Cu(II). Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of Hg(II) ranging from 16 nmol l⁻¹ to 112 nmol l⁻¹. The limit of detection for Hg(II) was 2.4 nmol l⁻¹. The developed method was applied to the detection of trace Hg(II) in aqueous solutions.