Free radical sensor based on CdSe quantum dots with added 4-amino-2,2,6,6-tetramethylpiperidine oxide functionality.
The association and resulting fluorescence quenching of CdSe quantum dots by 4-amino-2,2,6,6-tetramethylpiperidine oxide (4-amino-TEMPO), a persistent nitroxide, have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. EPR data suggest binding constants around (8 +/- 4) x 10(6) M(-1) for green (2.4-2.5 nm) nanoparticles, and the application of Job's method indicates that the preferred mode of binding involves one or two quencher molecules per quantum dot, although more quenchers could bind at high concentrations of 4-amino-TEMPO. Fluorescence quenching by 4-amino-TEMPO is at least 3 orders of magnitude more efficient than by TEMPO itself, reflecting the strong binding confirmed by the EPR data. Stern-Volmer plots are nonlinear and in light of the EPR data probably reflect ready accessibility of the CdSe surface to one or two 4-amino-TEMPO molecules, while additional quenchers can only bind if they displace trioctylphosphine oxide ligands. Quantum dot-4-amino-TEMPO complexes can be used as free radical sensors, since the fluorescence (quenched by the nitroxide) is readily restored when radicals are trapped to form alkoxyamines.
Maurel
Vincent
V
Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
Laferrière
Marie
M
Billone
Paul
P
Godin
Robert
R
Scaiano
J C
JC
D019187:Cadmium Compounds / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005456:Fluorescent Dyes; D005609:Free Radicals / Q000032:analysis / Q000737:chemistry; D015394:Molecular Structure; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
D019187:Cadmium Compounds; D003497:Cyclic N-Oxides; D005456:Fluorescent Dyes; D005609:Free Radicals; D018036:Selenium Compounds; C015527:4-amino-TEMPO; C058667:cadmium selenide