Semiconductor quantum dots (QDs) have been intensively used to study the optical properties of biological, chemical and metallic hybrid nanosystems because their excitation energy is tunable to optical properties by simply changing their size. Recently, there has been considerable interest in studying energy transfer in QD-metallic nanostructure hybrid systems. Metallic nanostructures greatly enhance a variety of optical processes which are due to the interaction between an exciton in the QD and the enhanced local electromagnetic .eld of a metal-surface plasmon. Light-harvesting, photovoltaics, and surface plasmon enhanced fluorescence have also been studied in these hybrid systems.
The photoluminescence (PL) spectrum of QDs, in contrast to conventional organic dyes, possess high quantum yield, narrow and stable fluorescence, and size-dependent absorption and emission6. They have been used as excellent florescent labels for biological imaging and sensing QDs have broad absorption and narrow emission spectra and hence they are used as donors of fluorescence resonance energy transfer. QD based hybrid systems have also been used for bio-sensing8, solar cells9, and light harvesting. These hybrid systems employ resonant energy transfer to generate energy low from donor QD to acceptor QD. The energy transport occurs on the nanoscale range via dipole-dipole interactions which depends on spectral overlap in the emission spectrum of the donor with the absorption spectrum of the acceptor and the distance between the donor and acceptor. Based on energy transfer mechanisms a series of QDs-based biosensors have been developed.