Digital Fabrication of Transparent Electrodes for Simultaneously Optical and Electrochemical Biosensor Applications

This dissertation proposes a pioneering biosensor for detecting cancer biomarkers that combines electrochemical and optical recognition in the same analyzing spot, by taking advantage of laser direct writing to pattern transparent and flexible electrodes. The bi-omarker, the carcinoembryonic antigen (CEA), is detected by an antibody-like biomi-metic material as recognizing agent. The sensing film over indium tin oxide (ITO) coated glass substrate consisted of a molecularly imprinted layer of polypyrrole (PPy). The im-printed film is assembled on a three-dimensional photonic crystal composed of silica na-noparticles (NPs), allowing optical detection. The molecularly imprinted polymer was obtained through electropolymerization of pyrrole in the presence of the biomarker as template. The interaction between the biomarker and the sensing material produces elec-trochemical signals generating quantitative data. In addition, it triggers a difference in the reflectance of the sensing photonic film matrix. The analytical features of the biosensor were assessed in PBS buffer by electrochemical impedance spectroscopy (EIS) and by reflectance of the opal-based photonic crystal. The response of the proposed biosensor was in the range of physiological relevant levels of CEA (from 2.5 ng/mL to 10 ng/mL). This sensor was assembled on an ITO substrate as proof of concept, the best substrate among the several conductive material produced on glass support, even if the first part of the work focuses on the preparation of aluminum doped zinc oxide (AZO) thin films by RF sputtering and laser direct writing. These processes were optimized for the fabrication of a highly conductive and transparent oxide capable of replacing ITO in the future as a main component in most transparent and flexible electronics applications. The developed sensing device showed promising features to become a much simpler, faster and low-cost point-of-care (POC) portable solution for the detection of CEA when compared to conventional immunoassay approaches, due to its high sensitivity, stability and dual detection method. At the same time, it may open new doors for other applications and foreseen improvement concerning the early diagnosis of diseases