Temperature induced conformational changes in hybrid complexes formed from CdSe/ZnS nanocrystals and the phycobiliprotein antenna of Acaryochloris marina

In hybrid systems which are self-assembled in solution from surface treated CdSe/ZnS quantum dots (QDs) and isolated phycobiliprotein (PBP) complexes from the cyanobacterium Acaryochloris marina, excitation energy transfer (EET) from the QDs to the PBP complexes was observed. The EET from the QDs to attached PBPs was analyzed with time integrated fluorescence spectroscopy and time-correlated single photon counting (TCSPC) at different temperatures. This functional connection between QDs and PBPs via EET is interrupted at temperatures below 273 K (0 °C) (Schmitt et al 2010 Photon. Nanostruct. submitted). The evaluation of the temperature-dependent fluorescence spectra of the QDs showed that the change of the excitation energy transfer efficiency at temperatures below 273 K cannot be explained by the change of the spectral overlap integral alone. Therefore the value of κ2/R126 must change at 273 K. We assume that micro crystals of water, formed in between the QDs and the PBP antenna structures, lead to a structural change of the hybrid complex. Our results show that TCSPC is suitable to distinguish strongly coupled and weakly coupled QD-PBP complexes at different temperatures