Thioglycolic acid-capped CdS quantum dots modified with ${\text{Co}}^{2+}$ as a fluorescent sensor for dopamine

A new selective fluorescent sensor for detection of dopamine (DA) using ${\text{Co}}^{2+}$ -decorated thioglycolic acid-capped CdS QDs (${\text{Co}}^{2+}$@TGA–CdS QDs) was proposed. Basically, the fluorescent intensity of TGA–CdS QDs can be quenched by ${\text{Co}}^{2+}$. However, with the addition of dopamine into the solution of ${\text{Co}}^{2+}$@TGA–CdS QDs, the fluorescent intensity was efficiently quenched due to the formation of the efficient quencher (${\text{Co}}^{2+}$–dopamine complex). Thus, the concentration of dopamine can be determined by tracking the decrease in the fluorescent intensity of the ${\text{Co}}^{2+}$@TGA–CdS QDs. The proposed sensor showed high selectivity towards the detection of dopamine over other catecholamine derivatives and related compounds. Under optimal conditions, the quenching efficiency of dopamine on the ${\text{Co}}^{2+}$@TGA–CdS QDs system was linearly proportional to the concentration of dopamine in the range of $20-100\mu \text{mol}{\text{l}}^{-1}$. The limits of detection and quantification were 1.8 and $12.7\mu \text{mol}{\text{l}}^{-1}$, respectively. This sensor system was demonstrated to detect dopamine in real urine samples with satisfactory results.