Abstract
Interaction between porphyrins and quantum dots (QD) via energy and/or charge transfer is usually accompanied by reduction of the QD luminescence intensity and lifetime. However, for CdSe/ZnS-Cys QD water solutions, kept at 276 K during 3 months (aged QD), the significant increase in the luminescence intensity at the addition of meso-tetrakis (p-sulfonato-phenyl) porphyrin (TPPS4) has been observed in this study. Aggregation of QD during the storage provokes reduction in the quantum yield and lifetime of their luminescence. Using steady-state and time-resolved fluorescence techniques, we demonstrated that TPPS4 stimulated disaggregation of aged CdSe/ZnS-Cys QD in aqueous solutions, increasing the quantum yield of their luminescence, which finally reached that of the fresh-prepared QD. Disaggregation takes place due to increase in electrostatic repulsion between QD at their binding with negatively charged porphyrin molecules. Binding of just four porphyrin molecules per single QD was sufficient for total QD disaggregation. The analysis of QD luminescence decay curves demonstrated that disaggregation stronger affected the luminescence related with the electron-hole annihilation in the QD shell. The obtained results demonstrate the way to repair aged QD by adding of some molecules or ions to the solutions, stimulating QD disaggregation and restoring their luminescence characteristics, which could be important for QD biomedical applications, such as bioimaging and fluorescence diagnostics. On the other hand, the disaggregation is important for QD applications in biology and medicine since it reduces the size of the particles facilitating their internalization into living cells across the cell membrane.
Highlights
Colloidal semiconductor nanocrystals or quantum dots (QD) due to their specific characteristics, intense broad absorption and narrow luminescence spectra with the sizedependent maximum position and high thermal and photostability [1, 2], find applications in various fields of modern technology, such as medical imaging and diagnostics, modern computing nanodevices, fluorescent probes for bioanalytical applications, photoelectrochemicalParra et al Nanoscale Research Letters (2018) 13:40[7, 11]
Basing on the obtained data, we can assert that the long storage of CdSe/ZnS-Cys QD in aqueous solutions even at low temperatures induces their aggregation, which reduces the luminescence quantum yield and lifetimes
The addition of TPPS4 porphyrin stimulates disaggregation of aged CdSe/ZnS-Cys QD which is pronounced via increase of the QD luminescence quantum yield and the contribution of electron-hole annihilation in the QD shell in the total QD luminescence
Summary
Colloidal semiconductor nanocrystals or quantum dots (QD) due to their specific characteristics, intense broad absorption and narrow luminescence spectra with the sizedependent maximum position and high thermal and photostability [1, 2], find applications in various fields of modern technology, such as medical imaging and diagnostics, modern computing nanodevices, fluorescent probes for bioanalytical applications, photoelectrochemicalParra et al Nanoscale Research Letters (2018) 13:40[7, 11]. The observed increase of the aged QD luminescence intensity at interaction with TPPS4 cannot be explained via reverse energy transfer from TPPS4 to QD, since the TPPS4 fluorescence spectrum is localized in the range λ > 600 nm where QD absorption is weak (Additional file 1: Figure S3). We associate the observed increase in the QD luminescence intensity and lifetimes in the presence of TPPS4 with QD disaggregation, stimulated by TPPS4 at its binding with the aggregate.
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