Surface enhanced Raman scattering in the near infrared using metal nanoshell substrates

A metal nanoshell is a composite nanoparticle consisting of a dielectric co re coated by a thin metal shell; its peak plasmon resonance wavelength is d etermined by the ratio of the core diameter to the shell thickness. When p- mercaptoaniline (p-MA) is in solution with gold nanoshells that have their plasmon resonance near a 1.06 mu m excitation source, significant surface e nhanced Raman scattering (SERS) is observed. The strongest Raman enhancemen ts are obtained when enough gold is deposited on the silica cores to form a nearly complete metal shell. Correlations between transmission electron mi croscopy (TEM)-defined structure, ultraviolet (UV)-visible spectra, SERS si gnal strength, and electromagnetic theory show that the SERS signal is due to both the local enhancement of the dielectric field via the plasmon reson ance of the nanostructure and to the localized regions of high field intens ity provided by the nearly completed gold shell. Comparison with SERS enhan cements on completed nanoshell structures indicates the relative contributi on of these two effects. (C) 1999 American Institute of Physics. [S0021-960 6(99)70733-6].