Thioglycolic acid-capped ZnSe quantum dots as nanoprobe for cobalt(II) and iron(III) via measurement of grey level, UV-vis spectra and dynamic light scattering.

Thioglycolic acid-functionalized ZnSe quantum dots (QDs) as a colorimetric nanoprobe were prepared and applied to the determination of cobalt(II) and iron(III). Test strips were obtained by a dipping-drying process. On exposure to Co(II), they undergo a color change from white to brown, and on exposure to Fe(III) from white to pink. The limits of detection (LOD) are 2.6 mg L-1 for Co(II) and 2.2 mg L-1 for Fe(III). Test strips introduce a low-cost, portable, rapid and convenient tool for determination of Co(II) and Fe(III). In addition, two other analytical methods have been studied for detection of Co(II) and Fe(III) at low concentration. The first is UV-vis spectrometry which has a LOD as low as 0.14 mg L-1 for Co(II) (at 412 nm) and 0.12 mg L-1 for Fe(III) (at 400 nm). The second is dynamic light scattering (DLS) with a LOD of 3.0 μg L-1 for Co(II) and 2.5 μg L-1 for Fe(III). Graphical abstract Thioglycolic acid-functionalized ZnSe quantum dots (TGA-ZnSe QDs) show high sensitivity and low detection limits for Co2+ and Fe3+.