Metal-enhanced fluorescence arises from the near-field interaction between fluorophores and metal nanostructure when a dye molecule is placed very closely to the surface of a metallic nanoparticle. The fluorescence enhancement is thought to be associated mainly with the increased radiative decay rate of the nearby fluorophores, but recent reports have suggested that strong coupling between the surface plasmon and the photon emitted by the emitter can take place when the electromagnetic field enhancement is very high. In such cases, the resonant exciton-plasmon interactions modify exciton wave functions and surface plasmon modes, leading to changes of exciton and surface plasmon resonance energies that are much larger than the cases with increased radiative decay rate alone. Here, we report a new experimental system that exhibit the strong coupling between exciton-plasmon interactions. Water-soluble CdSe/ZnS core/shell QDs were chemically bonded to popcorn-shaped gold nanoparticles (PS-AuNPs). The separation distance between QD and PS-AuNP was fixed at 6 nm. The strong exciton-plasmon coupling in our system resulted in >100 times fluorescence enhancement, the highest reported so far for the QD-metallic nanoparticle construct. Finite difference time-domain (FDTD) simulations were conducted to investigate the enhanced electric field near QD at various excitation wavelengths. A linear relationship with the measured fluorescence enhancement was achieved. As the fluorescence enhancement is highly sensitive to the local electric field environment, we attached biomolecules onto the PS-AuNP-QD and investigated how such change can influence the fluorescence enhancement.

Strong coupling between exciton and plasmon in gold-quantum dot nanoconjugates for protein detection

244th National Meeting (2012)

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