Investigation of the Stability and Biocompatibility of Commonly Used Electrode Materials in Organic Neurooptoelectronics

Engineering optoelectronic devices for operation in liquid environments requires a comprehensive understanding of the consequences of exposing electrode materials to an aqueous environment. For this reason, we have investigated the stability of electrooptical properties (namely conductivity, work function, and transmittance) of several commonly used electrode materials for organic optoelectronics. As a potential means of improving the long-term performance of the electrodes in solution, we further characterized the stability of the electrodes following their deposition on a transparent SU-8 adhesion interlayer. As such, Indium-Tin Oxide, Gold, Gold-SU8, Silver, Silver-SU8, Aluminum, and Aluminium-SU8 were immersed in three different media of varying ionic composition (DI water, Phosphate-Buffered Saline and Dulbecco's Modified Eagle Medium) as well as a control “air immersion” condition. By comparing the electrode materials side by side, we aimed to identify their advantages and drawbacks for use in solid/liquid devices, as well as the benefits of an adhesion layer for applications requiring long-term aqueous immersion. Our findings indicate that metals show severe delamination when deposited on glass, as indicated by decreased conductance and increased optical transmittance upon immersion in media. The use of an SU8 adhesion layer was effective in bonding Silver and Gold to enhance the film lifetime. Finally, since in many applications the electrode must make direct contact with biological species, we also investigated their biocompatibility by evaluating cytotoxicity of HEK293 cells cultured on the candidate materials, the results of which indicate positive biocompatibility profile for the materials investigated.