Energy transfer in hybrid CdSe quantum dots vs. labelled molecular chaperone systems by imaging microscopy

Abstract

Resonant energy transfer in hybrid CdSe quantum dot (QD) conjugated with Cy5‐labelled molecular chaperone systems is observed with single molecule imaging technique. Photonic QDs are the core‐shell type nanocrystals covered with organic surfactants on the outermost surfaces, i.e. CdSe/ZnS/TOPO's, and prefoldin (PFD) is used as prototype molecular chaperons. PFD is a jellyfish‐shaped hexameric co‐chaperone of group II chaperonins, which recognize hydrophobic portion of denatured proteins and encapsulate them within its central cavity. So the CdSe/ZnS/TOPO QDs can also be captured be cause of its surface similarity to the denatured proteins. We have found one possible reaction pathway to get such artificial complex in aqueous solutions with keeping bioactivities of the proteins. Performance of the complex is evaluated by TIRF imaging microscopy. As the proteins are transparent in visible wavelength region, labeling dyes, Cy5, which also work as acceptors, are connected to detect their behaviors microscopically. Förster type energy transfer is observed from the QD donors to Cy5‐labeled PFD acceptors in single molecule level, which can be a distinct evidence for the complex formation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single molecule FRET detection in CdSe-QD donor and Cy5-labeled molecular chaperone acceptor complex by imaging microscopy

“…In the case of nano-conjugate QD-PFD-Cy5 systems, however, the characteristic size is much smaller than wavelength, so the LDOS effect should be negligible and Förster transfer simply competes with spontaneous emission and works as an increase of nonradiative decay rate. Indeed, we have already detected that the time trajectories of photoemission intensity from single conjugated QDs are roughly one-third to one-forth decreased if compared to those from the isolated QDs [4]. In order for further elucidation, it is more preferable to detect directly single molecule emission spectra of QD-Cy5 DA-system in its Förster regime.…”

“…Such complex of the QDs and Cy5-labeled molecular chaperones can actually be prepared [3] and their photophysical investigations are ongoing. Among them, detection of resonant energy transfer (FRET) from the donor QDs to the acceptor Cy5-labeled proteins [4] is significant and also a most direct evidence for complex formation. In this work, we report our recent preliminary results on single QD-PFD spectral observation in FRET regime with single molecule imaging technique, which would eventually deduce the dynamics in the bioactive functions of the complex.…”

Nitrated Fluorophore Formation upon Two-Photon Excitation of an Azide with Extended Conjugation

“…As mentioned before, due to their high atom densities, QDs possess large two-photon absorption (2PA) coefficients ,, and are able to transfer the respective exciton energy to the species attached to the surface. − This feature makes them suitable biphotonic antennas for our purpose. With the intention of testing this idea in the phototransformation of hCy–N 3 , appropriate nanocrystal CdS quantum dots (QDs) were chosen in order to the enhance two-photon induced hCy–N 3 transformation.…”