This paper focuses on metal nanoparticles dimer with a molecular bridge for highly sensitive trace detection by Surface Enhanced Raman Spectroscopy (SERS). We clarified Raman intensity was determined from a concentration of particle dimers in mixing of a nanoparticle and a molecule solutions by characterization of SERS with the experimental and the analytical studies. This is because the particle dimer gives us higher enhancement factor of SERS intensity than the conventionally-used larger cluster of nanoparticles. Furthermore we proposed a multilayered mixing of nanoparticles and molecule solutions to achieve a higher concentration of the particle dimer in an entire laser spot of a portable Raman spectroscope. © 2013 IEEE.