In this work, we prepare plexcitonic nanoparticles composed by plasmonic nanoparticles, Au@Ag@mSiO2 nanorattles, and J-aggregates of TDBC cyanine dye to be used as ultra-efficient SERS-tags. The methodology used here allowed us to improve the colloidal stability of the plexcitonic nanoparticles. The optical properties have been characterised by UV-vis-NIR and Surface-Enhanced Raman Scattering (SERS) spectroscopies. Besides, finite-difference time-domain (FDTD) calculations revealed that the electromagnetic field is strongly confined into the J-aggregate deposited over the surface of the plasmonic nanoparticle at wavelengths near the upper plexciton. However, for the lower plexciton mode, the electromagnetic field decays through the J-aggregate/water interface. In summary, the plexcitonic nanoparticles showed high SERS efficiency for 532 nm and 633 nm laser lines, even reaching single-nanoparticle detection. The results obtained showed us the significance of strong coupling effect which might lead new possibilities for ultrasensitive biosensing and bioimaging.
We investigated the interactions between localized plasmons in gold nanorods and excitons in J-aggregates and were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy we showed that nonmagnetic organic molecules exhibit magnetooptical response due to binding to a plasmonic nanoparticles. In our experiments we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states
Strong coupling of plasmons and excitons can form hybrid states, the so called “plexcitons”. Especially with molecular J-aggregated dye molecules strong interaction becomes observable even under ambient conditions. In our work we investigate the nature of plexcitonic states formed in gold nanorods coated with a cyanine dye by transient absorption spectroscopy. We demonstrate that plexcitons show tunable plasmonic and excitonic non-linear optical behaviour. Our experimental data can be explained on the basis of a simple Lorentz oscillator model. We find that both the quality factor and the coupling strength between plasmons and excitons can be optically manipulated on an ultrashort time scale.
T. Simon, D. Melnikau, A. Sánchez-Iglesias, M. Grzelczak, L. Liz-Marzán, Y. Rakovich, J. Feldmann and A. Urban, Exploring the optical non-linearities of plasmon-exciton hybrid resonances in coupled colloidal nanostructures, submitted (2016)
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