Determination of arsenic in water using fluorescent ZnO quantum dots

Stabiliser-free zinc oxide (ZnO) quantum dots (QDs) have been synthesised by refluxing zinc acetate dihydrate in methanol under alkaline conditions and were re-dispersed into water by centrifugation. The ultrasmall particles so obtained have been characterised by absorption and fluorescence spectroscopy, transmission electron microscopy and selected area electron diffraction studies. The as-prepared fluorescent ZnO QDs have been employed as a greener indicator for selective and ultrasensitive detection of highly toxic arsenic in aqueous solution. Since fluorescence spectroscopy is a very sensitive technique, fluorescence quenching behaviour of ZnO QDs upon addition of arsenic compounds has been utilised as a sensing platform for the quantification of arsenic at the parts-per-billion (ppb) level. The interaction of the arsenic species with the ZnO QDs has been elucidated by Fourier transform infrared spectroscopy, zeta potential measurements and dynamic light scattering studies. Three different calibration curves of arsenic(III), arsenic(V) and total arsenic [arsenic(III) + arsenic(V)] have been set up in the dynamic range of 10–100 ppb and the corresponding limit of detection is 27, 7 and 28 ppb, respectively. The method is free from common interference and applicable for real sample analysis.