Interfacial Capacitance of Graphene Oxide Films Electrodes: Fundamental Studies on Electrolytes Interface Aiming (Bio)Sensing Applications

The understanding of bidimensional materials dynamics and its electrolyte interface equilibrium, such as graphene oxide (GO), is critical for the development of a capacitive biosensing platform. The interfacial capacitance (Ci) of graphene‐based materials may be tuned by experimental conditions such as pH optimization and cation size playing key roles at the enhancement of their capacitive properties allowing their application as novel capacitive biosensors. Here we reported a systematic study of Ci of multilayer GO films in different aqueous electrolytes employing electrochemical impedance spectroscopy for the application in a capacitive detection system. We demonstrated that the presence of ionizable oxygen‐containing functional groups within multilayer GO film favors the interactions and the accumulation of cations in the structure of the electrodes enhancing the GO Ci in aqueous solutions, where at pH 7.0 (the best condition) the Ci was 340 μF mg−1 at −0.01 V vs Ag/AgCl. We also established that the hydrated cation radius affects the mobility and interaction with GO functional groups and it plays a critical role in the Ci, as demonstrated in the presence of different cations Na+=640 μF mg−1, Li+=575 μF mg−1 and TMA+=477 μF mg−1. As a proof‐of‐concept, the capacitive behaviour of GO was explored as biosensing platform for standard streptavidin‐biotin systems. For this system, the Ci varied linearly with the log of the concentration of the targeting analyte in the range from 10 pg mL−1 to 100 ng mL−1, showing the promising applicability of capacitive GO based sensors for label‐free biosensing.