Diamond based electrodes for the design of electrochemical microsystems for biological applications
Boron doped diamond (BDD) electrodes are extremely promising in the field of biomedical applications as they exhibit a unique combination of properties. The thesis aims at developing new types of BDD microelectrodes and exploring their interests for electro-analytical and electrophysiological applications. Despite their superior electro-analytical properties, BDD electrodes are prone to fouling, which leads to a loss of electrode reactivity when used in biological fluids such as urine, waste waters, drinks, blood plasma, etc. A novel electrochemical treatment was developed to clean the electrode surface and to retrieve the initial reactivity, thereby enabling the use of BDD electrodes to long periods of measurements without degradation of the signal, thus significantly extending the field of monitoring and surveying applications up to domains where continuous analysis is required. The real novelty of the technique is that it does not require the use of a specific media and thus can be directly performed in the probed (bio-)fluid. Microelectrodes in comparison with macro-electrodes offer higher sensitivity, lower background current, lower ohmic losses and higher signal-to-noise ratio. A robust, high-yield, reliable, and reproducible process for fabricating a thin-film BDD micro and ultra-microelectrode arrays (MEA) was developed using a novel lithographic technique, based on clean room processing on 4 inch substrates, thus offering wide flexibility. For example, among other prototypes, BDD microelectrodes were developed as biosensors to quantify uric acid in human urine in quasi-real time. Although diamond film possesses good biocompatibility and excellent electrochemical properties, the low double-layer capacitance limits its application in electrophysiological applications. Increasing the charge injection limit was investigated by surface modification and nano-structuring. These include the synthesis of hybrid diamond-polypyrrole electrodes and nanograss BDD MEAs. Such high aspect ratio materials appear as excellent candidates for neurointerfacing applications such as for retinal implants.