New Composite Materials for Biosensing: Gold Nanoparticles protected with Mesoporous Silica Films

PAULA C. ANGELOMÉ; PAULA ALDEANUEVA POTEL; RAMÓN ÁLVAREZ PUEBLA ; LUIS M. LIZ-MARZÁN

Workshop; Functionalized Plasmonic Nanostructures for Biosensing; 2010

Recent progress in colloid chemistry techniques for the synthesis of metal nanoparticles with tailored morphology has contributed to the development of a number of applications in several fields, including diagnostics and therapy. In particular, the use of metallic nanostructures as (bio)sensors based on the refractive index sensitivity of localized surface plasmon resonances or surface enhanced Raman spectroscopy (SERS) has advanced considerably. We report here the design and fabrication of a new nanocomposite material comprising two functional layers: a glass substrate with chemically attached gold nanoparticles covered with a thin mesoporous silica film. While the gold nanoparticles can be used as refractive index sensors or SERS enhancers, the mesoporous film has the double function of retaining the particles attached to the substrate and acting as a size-selective filter. As a consequence, this device can be used as a selective sensor where molecules bigger than the pore size will be excluded, thereby allowing the detection of a specific analyte in a complex sample solution. We have tested nanoparticles of several shapes (spheres with diameter of 15 and 60 nm, nanostars, decahedra) and three types of mesoporous silica films with different pore sizes (average diameters ca. 3, 6 and 12 nm). The stabilities of both the film and the particles were studied during the synthesis and processing of the material, demonstrating that, in most cases particles shape and porous order are not deteriorated. Particle shape and composition was additionally varied by immersing the composite material in an appropriate solution for seeded growth. This overgrowth procedure allowed us to obtain anisotropic gold or gold/silver particles whose shape is determined by the pore size and the arrangement of the mesoporous thin film. The obtained materials where characterized with UV-vis spectroscopy, electron microscopy and XPS. Finally, the sensitivity of the composite materials toward changes in the medium refractive index and the use as SERS substrates was tested with excellent results.