A Guide for the Electrochemical Stability of Thiolate Self-Assembled Monolayers on Gold in Various Electrolytes

Abstract

Self-assembled monolayers (SAMs) are widely used in surface chemistry to modify surfaces for various applications such as biosensing1, electronics2, and electrocatalysis3. SAMs are attractive due to their high surface coverage and stability. Although studies have been conducted to test the effects of temperature, air exposure, and solvent degradation on SAMs stability 4,5, the electrochemical stability of SAMs has not been as extensively studied. Existing literature on this topic mainly focuses on the reductive desorption limits of thiolate SAMs in alkaline conditions6,7. Recent work by Ramos et al. demonstrated pH-dependent stable potential windows in which SAMs remained intact on electrode surfaces of different metals8. However, there is still a need to verify and expand on this work.To address this need, we aim to create a comprehensive guide on the electrochemical stability of thiolate SAMs on gold electrodes. We will use cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and electrochemical surface plasmon resonance (EC-SPR) to probe and verify the stable electrochemical potential windows in both aqueous and non-aqueous electrolytes. We have conducted studies on three aqueous solutions at three distinct pH, perchloric acid, potassium hydroxide, and sodium chloride. For non-aqueous solvents we tested a wide range of different organic solvents including acetonitrile, dimethylformamide, propylene carbonate, and various alcohols. Our findings demonstrate that the main factor for SAM stability in aqueous and non-aqueous electrolytes is the pH and solubility of the SAM, respectively. Our poster will present our current work and outlook on this topic.(1) Dauphin-Ducharme, P.; Ploense, K. L.; Arroyo-Currás, N.; Kippin, T. E.; Plaxco, K. W. Electrochemical Aptamer-Based Sensors: A Platform Approach to High-Frequency Molecular Monitoring In Situ in the Living Body. In Biomedical Engineering Technologies: Volume 1; Ossandon, M. R., Baker, H., Rasooly, A., Eds.; Methods in Molecular Biology; Springer US: New York, NY, 2022; pp 479–492. https://doi.org/10.1007/978-1-0716-1803-5_25.(2) Hatton, R. A.; Willis, M. R.; Chesters, M. A.; Rutten, F. J. M.; Briggs, D. Enhanced Hole Injection in Organic Light-Emitting Diodes Using a SAM-Derivatised Ultra-Thin Gold Anode Supported on ITO Glass. J. Mater. Chem. 2003, 13 (1), 38–43. https://doi.org/10.1039/B208169P.(3) Shang, H.; Wallentine, S. K.; Hofmann, D. M.; Zhu, Q.; Murphy, C. J.; Baker, L. R. Effect of Surface Ligands on Gold Nanocatalysts for CO2 Reduction. Chem. Sci. 2020, 11 (45), 12298–12306. https://doi.org/10.1039/D0SC05089J.(4) Schlenoff, J. B.; Li, M.; Ly, H. Stability and Self-Exchange in Alkanethiol Monolayers. J. Am. Chem. Soc. 1995, 117 (50), 12528–12536. https://doi.org/10.1021/ja00155a016.(5) Laibinis, P. E.; Whitesides, G. M. Self-Assembled Monolayers of n-Alkanethiolates on Copper Are Barrier Films That Protect the Metal against Oxidation by Air. J. Am. Chem. Soc. 1992, 114 (23), 9022–9028. https://doi.org/10.1021/ja00049a038.(6) Salvarezza, R. C.; Carro, P. The Electrochemical Stability of Thiols on Gold Surfaces. J. Electroanal. Chem. 2018, 819, 234–239. https://doi.org/10.1016/j.jelechem.2017.10.046.(7) Beulen, M. W. J.; Kastenberg, M. I.; van Veggel, F. C. J. M.; Reinhoudt, D. N. Electrochemical Stability of Self-Assembled Monolayers on Gold. Langmuir 1998, 14 (26), 7463–7467. https://doi.org/10.1021/la981031z.(8) Ramos, N.; Medlin, J. W.; Holewinski, A. Electrochemical Stability of Thiolate Self-Assembled Monolayers on Au, Pt, and Cu; preprint; Chemistry, 2022. https://doi.org/10.26434/chemrxiv-2022-dt7dk. Figure 1