Change search
ReferencesLink to record
Permanent link

Direct link
Dark states in ionic oligothiophene bioprobes-evidence from fluorescence correlation spectroscopy and dynamic light scattering
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
Show others and affiliations
2014 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 22, 5924--5933 p.Article in journal (Refereed) Published
Abstract [en]

Luminescent conjugated polyelectrolytes (LCPs) can upon interaction with biological macromolecules change their luminescent properties, and thereby serve as conformation- and interaction-sensitive biomolecular probes. However, to exploit this in a more quantitative manner, there is a need to better understand the photophysical processes involved. We report studies of the conjugated pentameric oligothiophene, derivative p-FTAA, which changes optical properties with different p-FTAA concentrations in aqueous buffers, and in a pH and oxygen saturation dependent manner. Using dynamic light scattering, luminescence spectroscopy and fluorescence correlation spectroscopy, we find evidence for a monomer dimer equilibrium, for the formation of large clusters of p-FTAA in aqueous environment, and can couple aggregation to changed emission properties of oligothiophenes. In addition, we observe the presence of at least two dark transient states, one presumably being a triplet state. Oxygen was found to statically quench the p-FTAA fluorescence but also to promote molecular fluorescence by quenching dark transient states of the p-FTAA molecules. Taken together, this study provides knowledge of fluorescence and photophysical features essential for applying p-FTAA and other oligothiophene derivatives for diagnostic purposes, including detection and staining of amyloid aggregates.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014. Vol. 118, no 22, 5924--5933 p.
Keyword [en]
National Category
Physical Chemistry
Research subject
Biological Physics
URN: urn:nbn:se:kth:diva-144060DOI: 10.1021/jp501324eISI: 000337011400013ScopusID: 2-s2.0-84901982083OAI: diva2:710747
Knut and Alice Wallenberg Foundation, KAW 2011.0218Swedish Research Council, VR-NT, 2012-3045

Updated from "Manuscript" to "Published article". QC 20140707

Available from: 2014-04-08 Created: 2014-04-08 Last updated: 2016-03-10Bibliographically approved
In thesis
1. Fluorescence-based methods to probe long-lived transient states for biomolecular studies
Open this publication in new window or tab >>Fluorescence-based methods to probe long-lived transient states for biomolecular studies
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fluorescence spectroscopy and imaging are wide-spread tools in life science. Themain read-out parameters are still fluorescence intensity and wavelength, but given thebenefits of multi-parameter characterization there are also good reasons to consideradditional fluorescence-based read-out parameters. A major focus of this thesis is toextend the use of transient, non-fluorescent states as additional parameters forbiomolecular studies. To-date, such states (including mainly triplet states, isomerizedstates and photo-ionized states) have been exploited to a very limited extent for thispurpose. Their use has been limited because they show very weak, or no luminescence atall, and absorption measurements require relatively complex instrumentation which aretypically not applicable for studies under biologically relevant conditions. Moreover, thelong lifetime of these transient states make any readout signal very sensitive to changes inthe micro-environment, e.g. presence of small amounts of quenchers, like oxygen. Thosetransient states can be accessed by fluorescence correlation spectroscopy (FCS) and thenewly developed transient state (TRAST) monitoring technique. In this thesis, FCS andTRAST have been applied to demonstrate the use of transient state monitoring forbiomolecular studies.

In Paper I, we demonstrated that due to the low brightness requirements ofTRAST, also autofluorescent molecules like tryptophan can be studied, making externallabeling of molecules redundant. The photo-physical transient states of tryptophan andtryptophan-containing proteins could be analyzed and were found to provide informationabout protein conformational states and about the influence of pH and buffers on singletryptophan molecules. In Paper II investigations of the transient states of theoligothiophene p-FTAA with FCS as well as with dynamic light scattering andspectrofluorimetry revealed a pH dependent aggregation behavior and a very efficientfluorescence quenching by oxygen could be identified and analyzed. In Paper III, FCSand TRAST were used to monitor the isomerization kinetics of Merocyanine 540incorporated in lipid membranes. Because isomerization of cyanine dyes strongly dependson the viscosity of the local environment, the isomerization kinetics could be used tocharacterize membrane fluidity in artificial lipid vesicles and in cellular membranes. InPaper IV, a new approach was developed, based on a combination of TRAST and FCS todetermine the stoichiometry of a fluorescently labeled sample. Finally, in Paper V, FCSand TRAST were employed to demonstrate that triplet states of fluorophores can provide auseful readout for Förster Resonance Energy Transfer (FRET) reflecting intra- orivintermolecular distances between two fluorophores. The sensitivity of the triplet statemade it possible to monitor distances larger than 10 nm, which is often stated as the upperlimit of FRET interactions.

Taken together, the studies presented in this thesis show that there is a wealth ofinformation that can be revealed by studying long-lived transient states. Both FCS andTRAST combine a sensitive readout via the fluorescence signal with the sensitivity of thelong-lived transient states monitored via the fluorescence changes. It can therefore bepredicted that these approaches will find additional applications in the future.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xii, 49 p.
TRITA-FYS, ISSN 0280-316X ; 2014:14
National Category
Natural Sciences
Research subject
urn:nbn:se:kth:diva-144063 (URN)978-91-7595-104-1 (ISBN)
Public defence
2014-04-29, FA31, Roslagstullsbacken 21, Stockholm, 09:00 (English)

QC 20140408

Available from: 2014-04-08 Created: 2014-04-08 Last updated: 2014-04-08Bibliographically approved

Open Access in DiVA

Hevekerl et al J Phys Chem B 2014(1406 kB)14 downloads
File information
File name FULLTEXT01.pdfFile size 1406 kBChecksum SHA-512
Type fulltextMimetype application/pdf

Other links

Publisher's full textScopusPublisher's website

Search in DiVA

By author/editor
Hevekerl, HeikeWidengren, Jerker
By organisation
Experimental Biomolecular Physics
In the same journal
Journal of Physical Chemistry B
Physical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 14 downloads
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: 83 hits
ReferencesLink to record
Permanent link

Direct link