Bulk Phase-Encoded Gold Nanoparticles: The Fourth-Generation Surface-Enhanced Raman Scattering Tag for Hg2+ Ion Detection

We report a bulk phase-encoded surface-enhanced Raman scattering (SERS) tag, which uses a thin pinhole-free bulk phase of a Raman-active polymer other than submonolayer molecules as the signal reporter. With a pinhole-free, highly cross-linked structure, the outer bulk phase shell not only offers ideal protection to the inner Au nanoparticles (signal amplifier) but also greatly limits their particle deformation and adverse surface process for reporter molecules. Furthermore, the thin bulk phase is within most of the long-ranged electromagnetic field of the Au nanoparticles so that it can fully use the field enhancement of the Au nanoparticles. Consequently, the SERS tags could offer strong, stable, and high-purity SERS signals for the detection of analytes, for example, Hg2+ ions, reaching a detection limit of 3.2 x 10(-10) M outperforming that of many conventional SERS tags.