Metal nanoparticles associated with a spectroscopy-active (e.g., Raman-active) analyte and surrounded by an encapsulant are useful as sensitive optical tags detectable by surface-enhanced spectroscopy (e.g., surface-enhanced Raman spectroscopy)....http://www.google.com.au/patents/US7443489?utm_source=gb-gplus-sharePatent US7443489 - Surface enhanced spectroscopy-active composite nanoparticles
