Probing charge transfer through antifouling polymer brushes by electrochemical methods: supporting self-assembled monolayer chain length matters Judita Anthi 1,2 , Eva Vaněčková 3 , Monika Spasovová 1 , Milan Houska 1 , Markéta Vrabcová 1 , Eva Vogelová 1 , Barbora Holubová 2 , Hana Vaisocherová-Lísalová 1* and Viliam Kolivoška 3* 1 Institute of Physics of the Czech Academy of Sciences, Czech Republic 2 Department of Biochemistry and Microbiology, University of Chemistry and Technology Prague, Czech Republic 3 J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Czech Republic Ultrathin surface-tethered polymer brushes represent attractive platforms for a wide range of sensing applications in vital areas such as medicine, forensics, or security. The recent trends towards adjusting these platforms to “real world conditions” highlighted the role of zwitterionic poly(carboxybetaine) (pCB) brushes, which provide excellent antifouling properties combined with bio-functionalization capacity. These pCB brushes need to be highly dense in order to achieve the best antifouling properties, and such highly dense brushes are usually prepared by the “grafting from” polymerisation triggered by initiators on self-assembled monolayers (SAMs). Here, we present a multi-methodological experimental study to elucidate the impact of varying the alkanethiolate SAM chain length (C 6 , C 8 and C 11 ) on structural and functional properties of antifouling poly(carboxybetaine methacrylamide) (pCBMAA) brush. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a custom-made 3D printed cell employing [Ru(NH 3 ) 6 ] 3+/2+ redox probe were used to investigate penetrability of pCBMAA brushes for small molecules and interfacial charge transfer characteristics. The bio-fouling resistance of pCBMAA brushes was characterized by surface plasmon resonance; ellipsometry and FT-IRRAS spectroscopy were used to determine swelling and relative density of the synthesized brushes. The SAM length was found to have a substantial impact on all studied characteristics; the highest value of charge transfer resistance ( R ct ) was observed for denser pCBMAA on longer-chain (C 11 ) SAM when compared to shorter SAMs. The observed high value of R ct for C 11 implies a limitation of the analytical performance of electrochemical sensing methods. At the same time, the pCBMAA brushes on C 11 SAM exhibited the best bio-fouling resistance amongst inspected systems. Taken together, these two findings highlight how critical it is to properly select supporting structures for brushes in order to use these assemblies effectively in biosensing applications. References 1. Vaisocherová, H., et al., Ultralow Fouling and Functionalizable Surface Chemistry Based on a Zwitterionic Polymer Enabling Sensitive and Specific Protein Detection in Undiluted Blood Plasma. Analytical Chemistry, 2008. 80 (20): p. 7894-7901. 2. Visova, I., et al., Tuning of Surface Charge of Functionalized Poly(Carboxybetaine) Brushes Can Significantly Improve Label-Free Biosensing in Complex Media. Advanced Materials Interfaces, 2022. 9 (33). 3. Víšová, I., et al., Modulation of Living Cell Behaviorwith Ultra Low Fouling Polymer Brush Interfaces. Macromolecular Bioscience, 2020. 20 (3). 4. Anthi, J., et al., Probing polymer brushes with electrochemical impedance spectroscopy: a mini review. Biomaterials Science, 2021. 5. Vaněčková, E., et al., Electrochemical Reduction of Carbon Dioxide on 3D Printed Electrodes . ChemElectroChem, 2021. 8(11): p. 2137-2149. 6. Sebechlebská, T., et al., 3D Printed Platform for Impedimetric Sensing of Liquids and Microfluidic Channels . Analytical Chemistry, 2022. 94(41): p. 14426-14433.
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