Change search
ReferencesLink to record
Permanent link

Direct link
Blinking, Flickering, and Correlation in Fluorescence of Single Colloidal CdSe Quantum Dots with Different Shells under Different Excitations
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-3915-300X
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0007-0394
KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.ORCID iD: 0000-0003-0578-4003
Show others and affiliations
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 9, 4844-4851 p.Article in journal (Refereed) Published
Abstract [en]

We studied the fluorescence spectra from single CdSe core-CdS/ZnS and CdS/CdZnS/ZnS shell colloidal quantum dots (QDs) (different shell thicknesses and different surface ligands) under different optical excitations. It was found that the single QD blinks (on and off) at low excitation and flickers (without distinguishable on and off) under high excitation. Theoretical analysis suggests that under low excitation the single QD blinks due to transfer of the photogenerated electron and hole between QD core states and surface states, and the transfer rate is inversely proportional to the shell thickness, as demonstrated experimentally. Under high excitation, the photogenerated electron and hole via interband excitation are further excited via intraband excitation, which will keep the electron and hole from relaxing to the ground exciton state, therefore significantly suppressing the radiative interband recombination, resulting in QD flickering. It was further observed experimentally that the fluorescence events from two neighboring QDs under high excitation are correlated. The correlation can be most possibly understood that one QD, which is kept at the excited state by the high excitation, radiatively recombines under the stimulation of the emission from its neighboring QD.

Place, publisher, year, edition, pages
2013. Vol. 117, no 9, 4844-4851 p.
Keyword [en]
Semiconductor Nanocrystals, Thickness, Photoluminescence, Cells
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-120287DOI: 10.1021/jp311975hISI: 000315707600056ScopusID: 2-s2.0-84874838216OAI: diva2:614548
Swedish Research Council

QC 20130405

Available from: 2013-04-05 Created: 2013-04-04 Last updated: 2015-03-06Bibliographically approved
In thesis
1. Time-Resolved Optical Properties of Colloidal CdSe-CdS/ZnS Core-Multishell Quantum Dots in Bioimaging
Open this publication in new window or tab >>Time-Resolved Optical Properties of Colloidal CdSe-CdS/ZnS Core-Multishell Quantum Dots in Bioimaging
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semiconductor quantum dots (QDs) have attracted great attention as a novel fluorescent material in the last twenty years. Their superior optical properties such as high brightness and photostability, broad absorption spectrum, narrow and size-tunable emission spectrum, enable them great application in bioimaging.

However, the fluorescence from single QDs shows irregular on (bright) and off (dark) switches under continuous irradiation which is known as blinking. QD blinking may lead to information loss in single particle tracking and lower brightness in other bioimaging applications. We studied the blinking behavior and its mechanism by using CdSe-core QDs with different shell thicknesses under different excitations. We observed two types of fluorescence behavior, blinking with apparent on and off states and flickering without distinguishable on and off states under low (1.8 and 3.9 W/cm2) and high (12.1 and 25 W/cm2) excitations, respectively. The transfer of photoexcited electron or hole from CdSe core to the QD surface is responsible for QD blinking under low excitations. And further intraband excitation of photoexcited electron and hole is responsible for QD flickering under high excitations.

Ca2+ serves as the second messenger in signal transduction. Monitoring Ca2+ concentration in live cell is a key technique in biological research especially in neuroscience. Most of the commercial Ca2+ indicators are organic dyes which are easy to be photobleached. In order to develop QD-based Ca2+ indicator, we investigated the effect of Ca2+ on the QD fluorescence. We found that the fluorescence intensity, lifetime, and on-state ratio in single QD fluorescence were all decreased by Ca2+ ion. Theoretical study shows that one free Ca2+ could attach stably to the surface of one QD, attracting the photogenerated electron and repel the photogenerated hole, suppressing the radiative recombination between them, and resulting in the reduction of fluorescence intensity, lifetime and on-state ratio.

Overexpression of vascular adhesion molecule-1 (VCAM-1) in endothelial cells is a hallmark of inflammation-induced activation of endothelium and may serve as a target for evaluation atherogenesis in early stages. We conjugated VCAM-1 binding peptide to amino-coated QDs and employed the functionalized QDs (VQDs) to specifically image activated endothelial cells. Upon the interaction between VQDs and endothelial cells, a blue-shift of about 30 nm in the QD fluorescence peak was observed. We anticipate that the VQDs and the blue-shift phenomenon could be very useful for VCAM-1 detection in vitro and in vivo.

Furthermore, we studied the fluorescence of QDs embedded in a porous alumina membrane which is widely used as biomolecule and cell filter for biological research. We found that the fluorescence spectrum has small peaks superimposed on the principle curve. Theoretical study identifies that this modulation is due to the photonic band structure introduced by the membrane pores. This work could supply information about the interaction between QD fluorescence and porous membrane structure which would be useful when applying QDs to image biomolecules or cells filtered by the porous alumina membrane.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xvi, 69 p.
TRITA-FYS, ISSN 0280-316X ; 2015:11
National Category
Physical Sciences
Research subject
Biological Physics
urn:nbn:se:kth:diva-160939 (URN)978-91-7595-473-8 (ISBN)
Public defence
2015-03-27, Seminar room Air på SciLifeLab, Science for Life Laboratory, Tomtebodavägen 23A, Solna, 13:00 (English)

QC 20150306

Available from: 2015-03-06 Created: 2015-03-04 Last updated: 2015-03-06Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Li, LiTian, GuangjunLuo, YiBrismar, HjalmarFu, Ying
By organisation
Applied PhysicsTheoretical Chemistry and BiologyCell Physics
In the same journal
The Journal of Physical Chemistry C
Physical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 101 hits
ReferencesLink to record
Permanent link

Direct link