Energy Transfer Processes Under One-and Two-photon Excitation of Nano-biohybrid Structures based on Semiconductor Quantum Dots and Purple Membranes

In this work we present the results of the resonance energy transfer study in bio-nanohybrid structures, engineered on the basis of semiconductor quantum dots (QD) and photosensitive membrane protein bacteriorhodopsin (bR) in purple membranes (PM) under one- and two-photon excitation. We showed the formation of bio-nanohybrid complexes between QDs and PMs and we also showed the Forster resonance energy transfer (FRET) from QDs to bR under one-photon excitation. The measured two-photon absorption cross-section (TPACS) of QDs was about two orders of magnitude larger than TPACS of bR and consequently the two-photon excitation of QDs in hybrid structure is highly selective. It was found that FRET in bio-nanohybrid system of QDs and bR under two-photon excitation is possible and the FRET efficiency was sufficient to initiation of bR photocycle. Studying of energy transfer between QDs and bR gives the perspective of considerable improvement of bR light absorption and consequently extends the possible applications of this photo-converting material. Additionally we showed that the two-photon excitation of QDs in QD-bR hybrid material makes possible the initiating of bR photocycle in the infrared spectral range.