FRD - Investigación - Ciencia y Tecnología
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Item High resolution imaging using nanoparticle based probes(2018) Scarpettini, Alberto; Bragas, AndreaNew plasmonic probes, based on silica microspheres decorated with metal nanoparticles (Figure 1), are built and used to confine and enhance the electric field in their interaction with the sample, giving ultra-high optical resolution in a wide variety of samples [1]. The coverage and aggregation processes of nanoparticles on plane and spherical substrates were systematically studied [2]. These probes present red shifted resonances, dominated by the formation of small nanoparticle clusters [3]. Approach curves with the new probes show clearly field enhancement at very short probe-sample distances, and depend strongly on the incoming wavelength and polarization. Optical contrast was achieved in flat samples composed by materials of different dielectric constants, and images were obtained using optical feedback.Item Nanorod-based plasmonic substrates with predefined optical resonances(2018) Scarpettini, Alberto; Gutierrez, MarinaTo design and fabricate plasmonic substrates to be used in ultrasensitive chemical sensing or surfaceenhanced spectroscopies, it is important to achieve control on the morphology, dimensions and surface density of metallic nanostructures on the substrate, and therefore to achieve control on their optical resonances. In this direction, monodisperse colloidal gold nanorods were synthesized in a seed-mediated growth [1] with a longitudinal surface plasmon resonance tunable in wavelengths from 600 to 1000 nm. These nanorods with well-controlled size and aspect ratio were used as plasmonic building blocks. Glass substrates were chemically modified and the synthesized gold nanorods were adsorbed through a dipping process [2]. The nanostructured coverage dynamics of these substrates was characterized by spectrophotometry and electron microscopy (Fig. 1). A nanoparticle surface aggregation was observed during the coverage process at long times. This aggregation is dominated by the mobility of the isolated nanorods, which first join in dimers and, further in time, in clusters of higher number of nanorods, changing from well-defined longitudinal plasmons to more complex coupling resonances. Evolution of amplitudes of resonance peaks in extinction spectra and nanorod counting statistics were used to model both coverage and aggregation processes [3]. Their characteristic times and saturation values were analyzed and related with kinetic parameters and nanorod extinction coefficients. This work can be used as a predictive tool to prepare plasmonic substrates with desired optical resonances.Item Fabricación y Caracterización de Sustratos Plasmónicos Basados en Nanobastones de Oro(2015) Scarpettini, Alberto; Gutierrez, MarinaSe fabricaron sustratos plasmónicos mediante el recubrimiento controlado de superficies de vidrio y películas delgadas de oro con nanobastones de oro. Estos sustratos nanoestructurados poseen resonancias ópticas en el rango visible e infrarrojo cercano del espectro electromagnético, y producen grandes intensificaciones de campo, llamados puntos calientes, en regiones muy localizadas de su superficie. El control de estas propiedades ópticas y la posibilidad de sintonizar la respuesta espectral de un sustrato son fundamentales para el diseño y construcción de sensores moleculares ultrasensibles y de sondas de microscopía óptica de altísima resolución. Se sintetizaron nanobastones de oro utilizando métodos de crecimiento mediado por semillas, con un preciso control de sus dimensiones finales. Se obtuvieron suspensiones monodispersas y con alta eficiencia. Se modificaron químicamente superficies de vidrio y películas de oro para adsorber nanobastones de oro. Se controló la densidad de recubrimiento superficial mediante el tiempo de inmersión de los sustratos en la solución coloidal. Se caracterizaron los sustratos fabricados mediante espectros de extinción e imágenes de microscopía electrónica. Se obtuvieron recubrimientos homogéneos con bandas de absorción dadas por el acoplamiento de las resonancias de los nanobastones con el material del sustrato.