title: Mechanistic aspects of quantum dot based probing of Cu (II) ions: role of dendrimer in sensor efficiency.
abstract: 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.
authors: UGC-DAE Consortium for Scientific Research, Kolkata Centre, III/LB-8, Bidhananagar, Kolkata 700098, India.
authors: Srabanti
authors: S
authors: Ghosh
authors: Amiya
authors: A
authors: Priyam
authors: Subhash C
authors: SC
authors: Bhattacharya
authors: Abhijit
authors: A
authors: Saha
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D050091:Dendrimers; D005456:Fluorescent Dyes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008024:Ligands; D049449:Luminescence; D010316:Particle Size; D011073:Polyamines / Q000737:chemistry*; D045663:Quantum Dots; D013440:Sulfides / Q000737:chemistry*; D013499:Surface Properties; D013691:Tellurium / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D050091:Dendrimers; D005456:Fluorescent Dyes; D007477:Ions; D008024:Ligands; C104700:PAMAM Starburst; D011073:Polyamines; D013440:Sulfides; C034939:cadmium sulfide; D003300:Copper; D013691:Tellurium; C028337:cadmium telluride