DEVELOPMENT OF NEW ELECTROCHEMICAL SENSORS FOR DETERMINATION OF BIOLOGICAL INDICATORS FOR DISEASES

Abstract

This dissertation aims to develop new electrochemical sensing platforms using modified screen-printed graphene electrodes (SPGEs) for the determination of significant biological indicators. This research was divided into two sections. The first section is split into two subprojects: the first deals with the electrochemical sensors for tyramine detection and the other with the simultaneous detection of levodopa (L-DOPA) and L-Tyrosine (L-Tyr), respectively. The first subproject focused on the use of poly(histidine)-based SPGE electrocatalytic activity towards tyramine oxidation, yielding greater sensitivity than bare SPGEs. This developed platform showed two wide linear ranges of 0.5–20 µM and 50–300 µM with a limit of detection (LOD) of 0.065 µM. The next subproject reports on a new electrochemical platform using poly(L-proline)-linked nanodiamonds on SPGEs. To be highlighted, this platform can unlock interfering substances from printing ink components and improve L-DOPA and L-Tyr signals. Broad working ranges of 0.075–50 µM with a low LOD of 0.021 µM for L-DOPA and 2.5–120 µM with a LOD of 0.74 µM for L-Tyr were obtained. The as-prepared sensor demonstrated good reproducibility and long-term stability, lasting up to five weeks. The second section focused on the modification of SPGEs with biocatalyst materials based on a hemin matrix assembled on carbonaceous material for measuring hydrogen peroxide (H2O2) levels by amperometry. The combination of these modifiers produced synergistic effects that provided for a wide detection range of 1–10 µM and 30–1000 µM with a LOD of 0.11 µM. This non-enzymatic sensor offers the capacity to function as an even more effective electrocatalyst for H2O2 reduction, which opens up its potential uses in exhaled breath analysis. Therefore, it is possible to draw the conclusion that the key results of all the sensing platforms developed for this dissertation were user-friendliness, practicality, and the ability to provide sufficient analytical performance in practical applications.

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