Hybrid Nano-Biosystems: A Study on the Effect of Quantum Dots on the Bacteriorhodopsin Photocycle
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Hybrid nano-biosystems are explored with the goal of optimizing the properties of an archaeal proton pump. These hybrid systems are composed of inorganic nanoparticles in biological settings and have been studied in a variety of applications, including bioimaging and drug delivery systems. One such hybrid system that has been investigated is quantum dots (QDs) coupled with the photoactive protein, bacteriorhodopsin (BR). Studies suggest that the coupling of QDs with BR enhances the quantum efficiency, wavelength coupling, and photovoltaic activity of the protein as a result of Förster Resonance Energy Transfer (FRET). However, these studies fail to address the effect QDs have on the photocycle of BR. Thus, the purpose of this work was to explore the effect of QDs on the photocycle by analyzing specific photointermediates in the cycle. Quantum dots were added incrementally to BR and the lifetimes of the bR, M, and O photointermediates were monitored using time-resolved UV/visible spectroscopy. It was hypothesized that as a result of FRET that occurs between the QDs and BR, an increase in the lifetimes of the photointermediates would be observed. The results obtained indicated an elongation in the M-state and a disappearance in the O-state. Moreover, it was concluded that the presence of the QDs varied photointermediate lifetimes, depending on the proportion of QDs to BR. However, further studies are needed to more fully characterize the mechanism by which the QDs mediate the photointermediates of the protein.