He Lifang,Bao Zhijun,Zhang Kui,Yang Danting,Sheng Bingbing,Huang Rui,Zhao Ting,Liang Xiaochen,Yang Xingjie,Yang Annan,Zhang Cheng,Cui Ping,Zapien Juan Antonio,Zhou Haibo
A ratiometric probe is described for the fluorometric determination of Cu(II) ions based on their quenching effect on the luminescence of dually-emitting quantum dots (QDs). ZnS QDs were doped with Mn(II) and subsequently modified with mercaptopropionic acid to give the QD probe which consists of a sole fluorophore but has two emission peaks (at 430 and 590 nm under 310 nm excitation, respectively). On addition of Cu(II) ions, the 590 nm band is quenched while the 430 nm band exhibits a little change. The changes in the intensity ratios of the yellow and the purple bands increases linearly in the 0 to 3.0 μM Cu(II) concentration range, and the detection limit reached 14 nM. The QD probe was validated and successfully applied to the determination of Cu(II) in spiked real water samples.
Mn-doped ZnS (ZnS:Mn(II)) quantum dots were synthesized with yellow fluorescence. After the modification of 3-mercaptopropionic acid (MPA), ZnS:Mn(II) was transferred to aqueous phase and became MPA modified Mn-doped ZnS (MPA- ZnS:Mn(II)). The fluorescence was changed to purple upon the addition of copper ions because the yellow band was largely quenched while the purple band only changed a little.
High-quality glutathione (GSH) capped ZnS : Mn/ZnS core/shell doped quantum dots (d-dots) with pure dopant emission band and excellent stability have been synthesized directly in aqueous media. The influences of experimental variables on the luminescent properties of the ZnS : Mn/ZnS nanocrystals have been investigated. The quantum yield of the dopant Mn photoluminescence in the as-prepared ZnS : Mn/ZnS core/shell d-dots can be up to 27.4%. The value is the highest reported to date for ZnS : Mn d-dots via the direct aqueous synthetic method. Their optical features and structure have been characterized by UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in detail. Additionally, the stability study against UV irradiation indicated that the obtained d-dots possess excellent photostability. Furthermore, the MTT assay demonstrated that the ZnS : Mn QDs do not exhibit any cytotoxicity toward HeLa cells up to a concentration of 600 μg mL−1. Using the Con A-mannose recognition system as a model, Con A functionalized ZnS : Mn/ZnS nanocrystals were prepared and successfully used for targeted mannosyl groups expression on the HeLa cells surface. Our investigation clearly shows that the GSH capped ZnS : Mn QDs are promising candidates as biological fluorescent labels.
Wang Jiangru,Yu Jialuo,Wang Xiaoyan,Wang Liyan,Li Bowei,Shen Dazhong,Kang Qi,Chen Lingxin
Manganese-doped ZnS quantum dots (ZnS:Mn(II) QDs) were synthesized and modified with L-cysteine (L-Cys) and 6-mercaptonicotinic acid (MNA). This prevents the aggregation of the QDs and makes them available for the interaction with Cu(II) ions via Cu(II)-S interaction. As a result, the fluorescence of the QDs is quenched by Cu(II) due to an electron transfer mechanism. The QDs display two emission peaks under 325 nm excitation, one (being red) peaking at 593 nm, the other (blue) at 412 nm. The red fluorescence is strongly quenched, while the blue fluorescence is not affected. An easily distinguishable color change from orange red to purple can be observed in fluorescence as the concentration of Cu(II) is increased. The probe is selective over commonly encountered other ions. The ratio of fluorescence intensities at 593 and 412 nm increases linearly in the 5 to 500 nM Cu(II) concentration range, and the detection limit is 1.2 nM.
Schematic of the preparation of manganese-doped quantum dots functionalized with L-cysteine and 6-mercaptonicotinic acid for selective and sensitive visual detection of copper ions.
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