Mechanistic Aspects of Quantum Dot Based Probing of Cu (II) Ions: Role of Dendrimer in Sensor Efficiency
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Selective quenching of luminescence of quantum dots (QDs) by Cu2+ ions vis-à-vis other physiologically relevant cations has been reexamined. In view of the contradiction regarding the mechanism, we have attempted to show why Cu2+ ions quench QD-luminescence by taking CdS and CdTe QDs with varying surface groups. A detailed study of the solvent effect and also size dependence on the observed luminescence has been carried out. For a 13% decrease in particle diameter (4.3 nm →3.7 nm), the quenching constant increased by a factor of 20. It is established that instead of surface ligands of QDs, conduction band potential of the core facilitates the photo-induced reduction of Cu (II) to Cu (I) thereby quenching the photoluminescence. Taking the advantage of biocompatibility of dendrimer and its high affinity towards Cu2+ ions, we have followed interaction of Cu2+-PAMAM and also dendrimer with the CdTe QDs. Nanomolar concentration of PAMAM dendrimer was found to quench the luminescence of CdTe QDs. In contrast, Cu2+-PAMAM enhanced the fluorescence of CdTe QDs and the effect has been attributed to the binding of Cu2+-PAMAM complex to the CdTe particle surface. The linear portion of the enhancement plot due to Cu2+-PAMAM can be used for determination of Cu2+ ions with detection limit of 70 nM.
KeywordsCdTe Nanoparticles Cu2+ions PAMAM dendrimer Photoluminescence (PL)
The authors wish to thank Chemical Science Division, Saha Institute of Nuclear Physics, Kolkata for help in fluorescence lifetime measurement. One of the authors (A.P.) is thankful to University Grants Commission, Govt. of India, for the award of Senior Research Fellowship.
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