Resonance energy transfer from quantum dots to bacteriorhodopsin affects the saturation of two-photon absorption under a pulsed femtosecond excitation

摘要

Semiconductor quantum dots (QDs) have high two-photon absorption cross-sections and long photoluminescence (PL)lifetimes, which make them a promising photosensitive part for fabrication of QD-based hybrid materials for two-photonbio-imaging, bio- and optoelectronics. In these areas, mode-locked femtosecond lasers are often used for two-photonexcitation of QDs because of the high peak intensity of the laser pulse. However, the QD radiative lifetime usuallyexceeds the period between the laser pulses of such laser systems, which can affect the absorption and PL properties ofQDs. In this work, we investigated the PL properties of CdSe/ZnS QDs under two-photon excitation. We have shownthat using femtosecond laser excitation at a wavelength of 790 nm with a pulse repetition rate of 80 MHz and a peakintensity of more than 10 GW/cm2, the two-photon absorption in QD is saturated. However if QDs were in complexeswith purple membranes (PM) containing the photosensitive protein bacteriorhodopsin (bR), saturation was not observedup to an intensity of about 27 GW/cm2. It was concluded that the difference in the saturation of two-photon absorptionbetween QDs and QD-PM material is associated with the F?rster resonance energy transfer from QD to bR and thecorresponding shortening of the PL lifetime. The results obtained will allow to optimize the two-photon excitationregime of QD-PM nano-bio hybrid material which will expand the possible areas of its application in bio-imaging, bioandoptoelectronics.