Inkjet printing of nanomaterials and electrodes for electroanalytical sensing applications

Metal thin film electrodes and metal nanoparticle (MNPs)-modified electrodes are widely used in electroanalytical sensing. The fabrication of metal thin film electrodes is traditionally performed by a multi-step process, in which the deposition of pre-synthesized MNP-containing inks on a conductive or insulating substrate via drop-casting, screen-printing and other coating techniques is followed by a thermal treatment to eliminate auxiliary ink components and sinter the MNPs. Recently, inkjet printing of metal precursor inks coupled with the light-induced formation of MNPs, known as Print-Light-Synthesis (PLS), gained interest in reducing the number of fabrication steps, by synthesizing MNPs directly during device fabrication. The most powerful PLS systems contain a bulky and costly flash lamp, converting metal precursors after the timely separated printing step. In this thesis, a mercury UV lamp was integrated into an inkjet printer to achieve true single-step PLS. Gold, ruthenium oxide and copper oxide electrodes were successfully prepared. Particular attention was made to generate well-adhered, reproducible, and fully converted electrode thin films during the very limited time frame of the printing duration, i.e., seconds to minutes, differentiating PLS substantially from photochemical MNP syntheses in bulk solution that can take hours. This led to the use of secondary processes, such as photothermal metal precursor conversion. This effect became more important in the order Au, Ru and Cu, as predicted by their decreasing standard potentials. Key advantages of PLS in view of industrial applications are the absence of material waste (100% of precursor ink is used), device miniaturization and high control of material loadings in µg/cm2. Electrodes containing metal films or separated MNPs on graphene of all three metals were successfully used for electroanalytical applications, in particular pH sensing in cancer cell cultures with RuO2 electrodes and the monitoring of bacterial bio-assimilation of bioplastic monomers with a dual Au electrode-CuOx electrode platform.