Time resolved temperature switchable excitation energy transfer processes between CdSe/ZnS nanocrystals and phycobiliprotein antenna from Acaryochloris marina

Hybrid systems were self-assembled in solution from surface treated CdSe/ZnS quantum dots (QDs) and isolated phycobiliprotein (PBP) complexes from the cyanobacterium Acaryochloris marina. The excitation energy transfer (EET) from the QDs to attached PBPs was analyzed by time correlated single photon counting and time integrated fluorescence measurements at different temperatures. It was found:(1)The green emission of the QDs (3.3 nm diameter of the CdSe core) in solution at 530 nm becomes strongly quenched after addition of PBPs.(2)The functional connection between QDs and PBPs via EET interrupts at temperatures below 273 K (0 °C)(3)This temperature dependent effect is fully reversible(4)EET from QDs to PBPs occurs with a time constant of about 140 ps and an efficiency of 85–90% for coupled QDs/PBP hybrid complexes.A model of the EET steps is presented which is based on data evaluation of the time integrated fluorescence emission and the time resolved measurement results via decay associated emission spectra (DAS). According to the theory of Förster Resonance Energy Tranfer (FRET) the average distance between the center of the QDs and the nearest neighbouring chromophore is estimated to be 3.2 nm.