L-Cysteine-capped core/shell/shell quantum dot–graphene oxide nanocomposite fluorescence probe for polycyclic aromatic hydrocarbon detection

Abstract

Environmental pollutants, such as the polycyclic aromatic hydrocarbons (PAHs), become widely distributed in the environment after emission from a range of sources, and they have potential biological effects, including toxicity and carcinogenity. In this work, we have demonstrated the analytical potential of a covalently linked l-cysteine-capped CdSeTe/ZnSe/ZnS core/shell/shell quantum dot (QD)–graphene oxide (GO) nanocomposite fluorescence probe to detect PAH compounds in aqueous solution. Water-soluble l-cysteine-capped CdSeTe/ZnSe/ZnS QDs were synthesized for the first time and were covalently bonded to GO. The fluorescence of the QD–GO nanocomposite was enhanced relative to the unconjugated QDs. Various techniques including TEM, SEM, HRSEM, XRD, Raman, FT-IR, UV/vis and fluorescence spectrophotometry were employed to characterize both the QDs and the QD–GO nanocomposite. Four commonly found priority PAH analytes namely; phenanthrene (Phe), anthracene (Ant), pyrene (Py) and naphthalene (Naph), were tested and it was found that each of the PAH analytes enhanced the fluorescence of the QD–GO probe. Phe was selected for further studies as the PL enhancement was significantly greater for this PAH. A limit of detection (LOD) of 0.19µg/L was obtained for Phe under optimum conditions, whilst the LOD of Ant, Py and Naph were estimated to be ~0.26µg/L. The fluorescence detection mechanism is proposed.