Revisiting preparation routes of SERS materials

For the first time, a systematic study of a background noise to signal ratio is given for various preparation histories of consolidated silver nanoparticles and artificially prepared nanostructures to rate the best and the worst routes of deposition of surface-enhanced Raman spectroscopy (SERS) active layers. It is shown that most of common preparation schemes face with a high intensity of extra peaks in the ca. 900–1100 and 1400–1700 cm$^{-1}$ range as related to residual adsorbed / chemosorbed nitrate, nitrite ions and organic oxidation products of various pollutants formed in the course of Ag$^+$ redox reactions. Finally, Leopold-Lendl and the original USR (Ultrasonic Silver Rain) methods would be recommended for the highly sensitive SERS analysis of diluted solutions and impurities.