Silver hexacyanoferrate (II) nanocrystals as a new material to improve Raman scattering enhancement during silver surface oxidation

Raman spectroscopy is a powerful analysis technique that shows its full potential when a high amplification of the Raman signal is achieved. In this sense, Surface-Enhanced Raman scattering (SERS) has been the most widely used phenomenon for analysis. SERS provides the amplification of the Raman intensity due to the interaction of molecules with a plasmonic nanostructured surface. The enhancement of the Raman signal can be also obtained during the electrochemical oxidation of a metal electrode; this phenomenon was denoted as Electrochemical-Surface Oxidation Enhanced Raman Scattering (EC-SOERS) and yields a good Raman signal enhancement with high reproducibility. Until now, only chloride and bromide have been employed in EC-SOERS, using a silver electrode to generate silver chloride and silver bromide nanocrystals. In this work, a new EC-SOERS substrate based on the electrogeneration of silver hexacyanoferrate (II) nanocrystals is presented which provides a very sensitive Raman response. The electrogeneration of this new material can be easily followed using spectroelectrochemistry since the characteristic Raman bands of the nanocrystals lie outside of the fingerprint region used for the analysis where the detection of most of the target molecules is performed. Indigo Carmine has been selected as target molecule, obtaining a very good response at nanomolar level under Raman resonance and non-resonance conditions.