Retraction Note: Microchimica Acta (2020) 187:247

https://doi.org/10.1007/s00604-020-4216-9

The Editors-in-Chief have retracted this article. After publication the editors were alerted to irregularities within the SERS spectra presented in figures 2C and 3B. The authors were informed of this and while addressing these concerns the authors conducted further experiments and concluded after detailed evaluation of the original experimental procedures that possible misinterpretation of the original spectra leading to the “atto-molar” claim cannot be excluded, and most likely was caused by a combination of three (unintentional) procedural issues: (1) The “blank” measurement was carried out on the "as-fabricated" substrate without exposing it to the solvent; (2) The solvent used was not of the highest possible purity grade; and (3) There are indications on the presence of impurities /contaminants on the deposited silver layer. The Editors-in-Chief have therefore lost confidence in the reliability of the results of this article. All authors agree to this retraction.