Electrode fouling is one of the main challenges encountered during electrochemical measurements of biological material. This process takes place at the electrode surface and negatively affects analytical parameters of the sensors[1]. The impermeable layer is formed through nonspecific adsorption and polymerization or precipitation of fouling agents, such as: proteins, lipids, phenols or neurotransmitters. There are several antifouling strategies employed to protect the surface based on the hydrophobic or zwitterionic molecules, formation of a physical barrier or chemical modification of the surface with self-assembled monolayers, polymers or hydrogels[2,3]. Antifouling material should be biocompatible, naturally inert and continuously protect the electrode in a complex environment as blood, urea, sweat or wastewater[2].

Electrochemical sensors can be used for monitoring of oxygen and glucose consumption in cell cultures. In long term measurement, where sensors are permanently incorporated into cell culture matrix, oxygen and glucose sensors provide information about cell viability that can be translated to toxicity during tests of new drugs. For such systems electrodes need to withstand prolonged (at least 3-4 weeks) contact with the cell culture matrix and the surrounding medium, thus biofouling is a major issue.

We have tested antifouling layers including major strategies: coating with polymers (e.g. Nafion®, phenylenediamine, polyvinyl chloride, polysilicate matrix), hydrogels (e.g. polyhydroxyethyl methacrylate), proteins (e.g. albumin), polyethylene glycol and poly-L-lactic acid. Electrodes were first coated with syringaldazine, which is easily adsorbed on carbon surfaces and provides facile to interpret response towards pH changes[4]. It is also very stable in buffer solutions but quickly desorbs in more complex media, thus making it an excellent probe for measurement of beneficial impact of antifouling layers. Tests were first conducted on macro- glassy carbon electrodes and later on low-cost pencil based sensors (250 µm diameter) as it was shown that some layers are less stable due to the big size of the electrode surface. It was revelated that polysilicate matrix, poly-L-lactic acid, polyhydroxyethyl methacrylate are suitable candidates for antifouling layers for electrochemical sensors. All three were tested as sensors in HELA cell culture, assessing cell growth on the layers and around the electrodes. Stability of the layers was evaluated during three weeks of cell culture.

References:

1. Lin PH., Li BR., Analyst, 2020, 145, 1110
2. Hassen B.L., Siraj S., Wong D.K.Y., Rev. Anal. Chem., 2016; 35(1): 1–28
3. Campuzano S. et al., Int. J. Mol. Sci. 2019, 20, 423
4. M. Michalak, M. Kurel, J. Jedraszko, D. Toczydlowska, G. Wittstock, M. Opallo, W. Nogala, Analytical Chemistry, 2015, 87, 23, 11641–11645

Authors acknowledge financial support of the National Centre for Research and Development under the grant LIDER/38/01381/L-9/17/NCBR/2018, and EWN would like to also thank the Foundation for Polish Science (FNP), from which she was supported through START programme and National Science Centre Poland for the MINIATURA grant NCN 2017/01/X/ST4/00463