Controlled FRET efficiency in nano-bio hybrid materials made from semiconductor quantum dots and bacteriorhodopsin

Forster resonance energy transfer (FRET) between CdSe/ZnS core/shell quantum dots (QDs) and the photochromic protein bacteriorhodopsin (bR) in its natural purple membrane (PM) has been modulated by independent tuning of the Forster radius, overlap integral of the donor emission spectrum and acceptor absorption spectrum, and the distance between the donor (QD) and acceptor (bR retinal). The results have shown that the observed energy transfer from QDs to bR corresponds to that predicted by a multiple-acceptors geometric model describing the FRET phenomenon for QDs quasi-epitaxied on a crystalline lattice of bR trimers. Linking of QDs and bR via streptavidin–biotin linkers of different lengths caused FRET with an efficiency reaching 82%, strongly exceeding the values predicted by the classical FRET theory. The data not only demonstrate the possibility of nano-bioengineering of efficient hybrid materials with controlled energy-transfer properties, but also emphasize the necessity to develop an advanced theory of nano–bio energy transfer that would explain experimental effects contradicting the existing theoretical models.