3-Aminophenylboronic acid-functionalized CuInS2 quantum dots as a near-infrared fluorescence probe for the detection of dicyandiamide

Abstract

In this paper, a simple and highly selective method for the determination of dicyandiamide (DCD) was developed based on the fluorescence quenching of functionalized CuInS₂ quantum dots (QDs). Water-soluble CuInS₂ QDs, capped by mercaptopropionic acid, were directly synthesized in aqueous solution and then covalently linked to 3-aminophenylboronic acid molecules to form the 3-aminophenylboronic acid-functionalized CuInS₂ QDs (F-CuInS₂ QDs) that had a fairly symmetric fluorescence emission centered at 736 nm. Based on the cyclization of the guanidine group of DCD with 2,3-butanedione and 3-aminophenylboronic acid, the fluorescence of the F-CuInS₂ QDs is quenched by DCD in the presence of 2,3-butanedione. This method effectively distinguishes DCD from other amino acids and nitrogen pollutants, such as melamine, in real milk samples. Under optimum conditions, there was a good linear relationship between the fluorescence intensity of F-CuInS₂ QDs and the concentration of DCD in the range of 2.0 × 10⁻⁶ to 2.0 × 10⁻³ mol L⁻¹, with a detection limit of 0.6 μmol L⁻¹.