Zwitterionic Phenyl Layers: Finally, Stable, Anti-Biofouling Coatings that Do Not Passivate Electrodes

Abstract

Organic coatings on electrodes that limit biofouling by proteins but are of sufficiently low impedance to still allow Faradaic electrochemistry to proceed at the underlying electrode are described for the first time. These organic coatings formed using simple aryl diazonium salts present a zwitterionic surface and exhibit good electrochemical stability. The layers represent a low impedance alternative to the oligo (ethylene glycol) (OEG)-based anti-biofouling coatings and are expected to find applications in electrochemical biosensors and implantable electrodes. Two different zwitterionic layers grafted to glassy carbon surfaces are presented and compared to a number of better-known surfaces, including OEG-based phenyl-layer-grafted glassy carbon surfaces and OEG alkanethiol SAMs coated on gold, to allow the performance of these new layers to be compared to the body of work on other anti-biofouling surfaces. The results suggest that phenyl-based zwitterionic coatings are as effective as the OEG SAMs at resisting the nonspecific adsorption of bovine serum albumin and cytochrome c, as representative anionic and cationic proteins at physiological pH, whereas the impedance of the zwitterionic phenyl layers are two orders of magnitude lower than OEG SAMs.

Investigation of the Antifouling Properties of Phenyl Phosphorylcholine‐Based Modified Gold Surfaces

“…Interfacial impedance and antifouling nature of the newly developed (1), (2), and (3) surfaces were investigated and were compared with the conventional (4) antifouling surface with high impedance, (5) fouled surface and (6) a previously developed antifouling surface with low impedance from our group in Ref. 17.…”

“…Gold electrodes were soaked for 12 h in 1 mM OEG and C12 solutions in ethanol to form OEG and C12 SAMs on the surfaces, respectively (scheme , surface 4 and 5). The construction of GC/PPC (Scheme , surface 6) involved the electrochemical reduction of 4‐aminophenyl phosphorylcholine diazonium salts 17. The modification process of GC/PPC was similar to that for Au/PPC, but the potential range from 0.6 to −0.8 V was used during the electrochemical adsorption process.…”

“…Later the molecular wire was replaced with nanoparticles at the distal end of the OEG monolayer to provide conduits to facilitate electron transfer 15, 16. In attempts to obviate the complexity of fabricating electrode surfaces with these components, our interest has been drawn to develop low impedance antifouling layers comprising zwitterionic molecules 17. Furthermore, zwitterions are preferred for modifying implantable electrodes as PEGs/OEGs face considerable biocompatibility issues due to the oxidation of hydroxyl groups within the molecular chain 18, 19.…”

“…Aryl diazonium salts derived layers to anchor antifouling moieties have just started to be explored 32, 33. Recently, we have shown the utility of modification of GC electrode surface in resisting protein adsorption using different low impedance aryl diazonium salts bearing zwitterion molecule 17. It has been shown that aryl diazonium salt derivatives can form stable layers, with efficient electron transfer kinetics on different surfaces 30, 34–38.…”

Investigation of Antifouling Properties of Surfaces Featuring Zwitterionic α‐Aminophosphonic Acid Moieties

“…But also zwitterionic polymers, such as poly(sulfobetaine methacrylate) (PSBMA), have been found to provide non‐fouling properties. Polymers incorporating zwitterionic moieties, for example, phosphorylcholine and carboxybetaine are excellent candidates for the creation of antifouling surfaces due to their anionic and cationic terminal groups, which form a strong hydration layer as an effect of the solvation of the charged groups …”