Critical importance of the junction in touching Ag particles for single molecule sensitivity in SERS

An elastic scattering peak at ca. 600 nm was extinguished during inactivation process of enormous Surface Enhanced Raman Scattering (SERS) of Ag touching particles with adsorbates. Numerical simulations using three dimensional Finite Difference Time Domain (FDTD-3D) method proved that this peak originates from implicit electromagnetic coupling between the localized surface plasmon (LSP) of the Ag particles and absorption of dye located at their junction. Correspondingly, the blinking that the SERS intensity fluctuates with time and is an evidence of the single molecule detection was attributed to thermal diffusion of individual molecules in and out of the junctions based on its suppression at low temperature. Thus, critical importance of the junctions of Ag particles was evidenced with respect to single molecule sensitivity in SERS.