Dopamine functionalized CuInS2 quantum dots as a fluorescence probe for urea

In this paper, a simple, convenient and selective urea-biosensing system with dopamine-functionalized CuInS2 quantum dots (QDs) as the fluorescence probe was developed. Water-soluble CuInS2 QDs capped by 3-mercaptopropionic acid (MPA) was directly synthesized in aqueous solution, and then it was linked to dopamine to form the dopamine-functionalized CuInS2 QDs (DA-CuInS2 QDs) fluorescence probe. When the pH value of DA-CuInS2 QDs solution was adjusted from neutral to alkalinity, the dopamine on the surface of QDs would change into quinone, which would lead to the fluorescence quenching of DA-CuInS2 QDs due to the charge transfer interactions between QDs and the proximal quinone. Based on the fact that the hydrolysis of urea in the presence of urase would release OH− to change the pH value of the solution, so the fluorecence intensity of DA-CuInS2 QDs could be linked to the enzymatic degradation of urea. The novel urea-biosensing system could effectively probe urea in the dynamic concentration range from 0.2 to 6 mmol/L.