Synthesis, properties and applications of hybrid plasmonic nanostructures

Resumo

Plasmonic capsules have been designed as submicron hollow silica capsules with gold nanoparticles supported over the inner walls of a mesoporous shell. This configuration shows morphological distinctive features that turn them into attractive nanostructures for different applications related to sensing, catalysis and biomedicine. These capsules have been used as nanoreactors capable of concentrating light for the simultaneous performance and optical realtime monitoring of thermally activated reactions. They behave as nanosources upon external illumination, promoting the conversion of reactants into products. The thermal effect was induced by the excitation of the LSPR inside the reactors and the electromagnetic field generated was exploited simultaneously for in situ SERS monitoring of the process. The estimated temperature achieved inside the capsule was 90 ºC. Diels-Alder cycloaddition reaction was carried out in the presence of capsules under NIR laser irradiation probing the capsules efficacy as nanoreactors by thermal activation. A remarkable increase in the reaction yield (¿300 %) was achieved without significant temperature alterations of the bulk solution. Another application consisted of using these plasmonic nanocapsules as biocompatible nanoprobes for quantitative in situ real-time optical monitoring of the dynamic of NO in living cells. The mesoporous silica shell facilitates the diffusion of small molecules and protects the active optical material (AuNPs) from the interaction with lysosomal macromolecules preventing the enzymatic degradation of the sensor. A large electromagnetic field confinement was generated inside plasmonic capsules upon illumination with a NIR laser, which contributes to amplify the Raman scattering, making these structures ideal for monitoring NO generation inside living cells through SERS spectroscopy. The intense optical absorption at the SPR frequency is responsible for a strong heat generation inside the capsule through an efficient photo-heat conversion, which favors the diffusion of NO between the exterior and the interior of the capsule. Intracellular NO was detected through its capacity to promote diazotization of ABT to finally obtain HBT. The rate of diazotization increases at high temperatures and it was determined that diazotization inside the capsules can only be considered quantitatively at pH <5. Both conditions were achieved inside of irradiated capsules (interior at 90 ºC) only when they were located exclusively in the lysosome (pH <4). NO generation was induced by the addition of hydrogen peroxide, demonstrating the ability of this sensor to detect the dynamic concentration of intracellular NO in a basically non-invasive way. It was probed that the design of this plasmonic capsules makes them ideal intracellular reporters allowing multiplexed on-line detection and showing stable SERS signals over time. It was designed a new hybrid system based on the impregnation of the hollow plasmonic mesocapsules with rhodamine 6G molecules. It was probed that this system has the capacity for mitigate the inherent optical losses of plasmonic materials involving a large portion of the visible spectrum. In the hollow cavity of the mesocapsule, the electric field is spatially uniform and, consequently, the nonradiative energy transfer takes place between chromophoric donors (R6G) present in this region and the surrounding plasmonic acceptors (AuNPs), giving rise to a broadband attenuation of losses. This loss-compensating mechanism was proved through an ultrafast pump-probe experiment. Mesocapsules can be considered an effective loss-mitigation model system in between a single nanoresonator and a bulk material. A new hybrid nanostructure has been designed taking advantage of the fluorophore-metal interactions. Highly luminescent, chemically stable and biocompatible optical nanoprobes have been fabricated based on a multistep synthesis which consists of a quantum dot core covered with a silica shell, all surrounded by a dense layer of gold nanoparticles. This architecture allows controlling the QD-metal interactions by modifying the thickness of the dielectric spacer. The shell thickness was optimized at the nanometer scale in order to increase the enhanced photoluminescence. This brighter biocompatible material comprises good qualities for bioimaging applications since it requires smaller acquisition times to yield better imaging results and smaller powers with the subsequent protection of the sample from photodegradation.