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Glass-coated, analyte-tagged nanoparticles (GANs) are core−shell particles where a nanometer-scale Au or Ag core is functionalized with Raman active molecules and encapsulated in a glass shell. The glass shell provides the particle with mechanical and chemical stability. Specifically, the glass coating renders the particle amenable to use in many solvents without altering the Raman spectral response and makes agglomeration a nonfactor. The density and thickness of the glass shell are controllable through synthetic conditions; thus, the rate of diffusion through the silica network can be tuned and the metal cores kept sequestered from any exterior reaction. This will allow for the attachment of biomolecules to the glass shell without altering the Raman response. GANs can be identified by the Raman spectrum of the attached Raman tag, and two differently labeled samples are unambiguously identified. The scattering from the Raman tag is amplified through surface-enhanced Raman scattering. The narrow bandwidth (∼20 cm - 1 ) of the Raman peaks and fingerprint-like spectra will allow multiple Raman tags to be simultaneously evaluated with a single excitation source.
Mulvaney et al. (Sat,) studied this question.