The electrochemical dissolution of single silver nanoparticles enlightened by hyperspectral dark-field microscopy

Nowadays, silver nanoparticles are extensively employed in several branches of industry and medicine. Hence, those particles are amongst the most studied class of nanomaterials, yet their reactivity and in particular their reactivity in biological systems is still poorly understood. This discrepancy leads to a huge demand for further insights into the reaction dynamics of electrochemical reactions. For this purpose, coupled opto- and spectro-electrochemical dark-field microscopy is used herein to study the electrochemical oxidation and dissolution process of individual silver nanoparticles in thiocyanate solutions. It is observed, that upon electrochemical oxidation of silver, a silver thiocyanate complex is formed. This is indicated by a change of both the measured plasmon resonance frequency and scattering intensity, simultaneous to the detection of an oxidative current. Subsequently, this silver pseudo-halide is chemically converted to a silver thiocyanate complex with higher solubility in the presence of high thiocyanate concentrations. This follow-up reaction is only detectable thanks to in situ spectroscopy as no current is associated with this chemical conversion but a distinct change in the spectroscopy response of the individual particles is seen. We were thus able to reveal that the total conversion of silver nanoparticles in the presence of thiocyanate is a multi-step process which lasts much longer than the electrochemical response suggests.