Composite aerogels for sensing applications

Composite aerogels are nanoscale mesoporous materials that retain both the meso- and nanoscopic properties of each component. Colloidal metal-silica aerogels (in which the colloidal metal is Au or Pt) exhibit both the transparency and porosity of silica aerogel and the optical behavior of the metal colloid. The silica aerogel essentially acts as a transparent matrix for the isolated metal colloids, which remain accessible to external reagents. Sensing elements adsorbed to the surface of the metal in colloidal Au-silica aerogels are also addressable. For dyes with absorption spectra complementary to that of the metal plasmon resonance, spectral changes due to alteration of the dye environment may be optically monitored. By dispersing the metal colloid in an about-to-gel silica sol, the properties of the metal colloid (i.e. size, which determines the position and FWHM of the plasmon resonance) can be tailored prior to immobilization., The ability to modify the colloidal metal surface either prior to or following gelation in the silica matrix coupled with gentle processing conditions permit modification of the metal surface with, for example, temperature-sensitive biomolecules. Composite colloidal metal-silica aerogels therefore provide a novel method for the nanoscale engineering of optical sensors with rapid response times due to the high mesoporosity of the silica matrix.