Long range self-organisations of small metallic nanocrystals for SERS detection of electrochemical reactions

Abstract

Gold electrodes were modified by silver and gold nanocrystals (NCs) that self-organize onto the surface. Their optical properties were explored by measuring electroreflectance spectra as a function of electrode potential. Below their oxidation potential, no shift of the reflectance maximum was observed for Ag NCs. This can be explained by a low interfacial capacitance resulting from the impossibility for the electrolyte to penetrate into the hydrophobic layer created by the NCs dodecanethiol ligands. Conversely, a non-monotonous evolution was observed with the electrode potential for oleylamine capped Au NCs. This behavior is suggesting a less dense hydrophobic layer, allowing significant electrolyte penetration. Next, electroactive compounds were adsorbed on the the Au NCs assemblies and characterized by Raman spectroelectrochemistry. In the first system displaying a single electron transfer with no coupled chemical reaction, only the spectrum intensity changed, because oxidation generated a Raman resonant radical cation. The second study considered 4-nitrothiophenol, for which up to 6 electrons and 6 protons may be transferred. In this case, the nitro band disappeared upon reduction, and the spectrum displayed typical features of the formed 4-aminothiophenol.

Recent advances in Raman and surface enhanced Raman spectroelectrochemistry

“…Raman spectroscopy can be adopted to monitor the real-time electrochemical redox process of the molecule under test in situ (e.g., the oxidative polymerization of poly (EDOT-OH), the electroreduction process of ruthenium, iron, as well as 4-NTP) (Martín-Yerga et al, 2018a;Perales-Rondon et al, 2018;Regina et al, 2018;Tsai et al, 2019). It also helps clarify the electrocatalytic reaction mechanism, including by studying the position of the binding point and coordination of the molecule to be measured and the electrode (e.g., AMP/ATP and silver ion electrode) to explore the growth mechanism of different molecular growth orientations (parallel or vertical) (nekrasov et al, 2017;Fato et al, 2018;Groni et al, 2020).…”