Carbon and Platinum Nanostructured Electrodes on Miniaturized Devices for Biomedical Diagnostics

Nowadays, medical devices face several limitations concerning rapid, reliable and simultaneous quantification of a set of ions and metabolites from a micro-nanoliter volume of undiluted samples. The development of minimally-sized devices is, therefore, of key importance. In such a context, electrochemical sensors are particularly advantageous because of the simple, low cost and reproducible fabrication procedures and the rapid analytical measurements. Moreover, they provide easy possibilities for continuous monitoring. However, sensitive and selective detection of molecules in the physio-pathological concentration range is very challenging when conventional electrochemical devices are employed, especially for long-term use. Nanostructured electrodes are considered as one of the most promising strategies to overcome issues of sensitivity because of their large surface area and their excellent electrocatalytic properties. They could also address in part the problem of selectivity due to shifts in potential of the measured Faradic currents. In addition, nanomaterials could provide stable and reproducible potential responses when used as solid-contact materials of ion-selective electrodes. Inappropriate nanointegration methods could decrease the sensor performance so that the development of tailored nanostructuration protocols is extremely important to boost the sensor sensitivity, selectivity and stability over time. Objective of this thesis was to design and electrochemical characterise novel carbon and metal nanostructures for medical sensors. First of all, the integration of carbon nanomaterials on specific sensing sites of a microfabricated sensor was considered. Time-consuming, expensive and hardly-reproducible nanostrucuturation approaches contemplate the co-immobilization of carbon nanomaterials and additives whose presence inevitably masks the nanomaterial promising properties and compromises the time-stability in aqueous environments. The selective CVD growth of carbon nanomaterials was considered as a promising method to enable the coupling nanomaterial-electrode. Deposition parameters were optimised to make the process compatible with CMOS temperatures. Then, new protocols based on rapid electrodeposition methods were developed to integrate differently shaped and sized Pt and Pt-Au nanostructures on electrochemical platforms. Template-free electrodeposition was selected because of the durably-anchored and the contaminant-free coatings resulting after the process. Both nanostructuration approaches generated highly-sensitive electrodes to detect human metabolites as compared with the bare counterparts. Unprecedented sensing performance were obtained by both direct and enzyme-mediated detection mechanisms. Selective sensing was achieved thanks to the capability of the proposed nanostructured electrodes to discriminate the detection potentials of biomarkers from those of interfering species. The developed nanostructures were also excellent solid contacts between an electrode and an ion-selective membrane resulting in stable and reliable solid-contact ion-selective electrodes. To prove their stability and reproducibility for long operating lifetimes, these ion-selective electrodes have been successfully used as standard for continuous acute cell death monitoring.

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