ETD

• creatinine
• electrochemical sensor
• kidney disease
• nanomaterial
• sweat
• urea

The growing demand for non-invasive, rapid, and wearable diagnostic technologies has positioned sweat as a promising alternative biofluid capable of reflecting an individual’s physiological state in real time. Among clinically relevant biomarkers for renal function, creatinine and urea hold fundamental diagnostic value and are traditionally quantified in serum or urine through laboratory-based analytical methods. This thesis was carried out within the framework of the European project KERMIT, which aims to develop a wearable patch integrating microfluidics, electrochemical sensors, and wireless communication modules for real-time monitoring of renal biomarkers in human sweat. The work focuses on the optimization and validation of non-enzymatic, nanomaterial-based electrochemical sensors for creatinine and urea detection, as well as on the exploration of miniaturized, printed electrode platforms suitable for wearable applications. The first part of the research addresses the development of a creatinine sensor based on graphene quantum dots (GQDs) modified with Cu(NO₃)₂, exploiting the coordination chemistry between copper ions and creatinine. The GQDs–Cu nanomaterial was synthesized via citric acid pyrolysis in the presence of Cu²⁺ ions and subsequently incorporated into a crosslinked chitosan matrix to improve its adhesion to gold screen-printed electrodes (SPGEs). Electrochemical characterization through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated a measurable and concentration-dependent variation in charge-transfer resistance, confirming the suitability of this nanocomposite as a functional sensing layer. The second part of the study focuses on the development of a non-enzymatic urea sensor employing a bimetallic nickel–cobalt hydroxide catalyst supported on hydrotalcite (NiCo–OH/HT). Because the electrocatalytic oxidation of urea requires strongly alkaline conditions, several formulations were explored to identify a stable film capable of maintaining high pH and ensuring uniform catalyst deposition. Low-melting agarose gel, prepared in phosphate buffer at pH 12, was found to provide optimal mechanical stability and reproducibility. Sensors fabricated with this formulation exhibited clear electrochemical responses associated with the Ni(OH)₂/NiOOH redox transition, with both CV and EIS confirming sensitivity toward physiologically relevant urea concentrations. Both sensors were validated using human sweat samples, obtained through iontophoretic stimulation and spiked at different analyte concentrations following the standard addition method. These experiments confirmed the stability of the sensing layers under realistic conditions and demonstrated the potential of the proposed nanomaterials for non-invasive renal monitoring, while also highlighting aspects requiring improvement, particularly in selectivity and response amplitude at low concentrations. The thesis further investigates the design and electrochemical behaviour of miniaturized carbon-based screen-printed electrodes (SPCEs), produced via scalable screen-printing techniques. Working electrode diameters ranging from 4 mm to 1 mm were evaluated to quantify how geometric reduction affects the electroactive surface area, impedance, and faradaic response. Experiments using ferricyanide and hexaammineruthenium redox probes revealed the crucial balance between electrode size, ohmic losses, and sensitivity, providing useful guidelines for future integration of the sensing layers into fully printed wearable devices. Finally, the work explores the development of MXene-based conductive inks for Direct Ink Writing (DIW) printing. Aqueous formulations combining Ti₃C₂Tₓ MXene with cellulose nanocrystals were optimized to achieve appropriate rheology and conductivity required for high-resolution additive manufacturing. Preliminary printed electrodes exhibited promising structural integrity and electrochemical activity, supporting the feasibility of MXene-based materials as next-generation printable conductors for wearable sensors. Overall, this thesis contributes to the advancement of non-enzymatic, nanomaterial-assisted electrochemical sensing for sweat analysis, bridging materials engineering, electrochemical characterization, and printed electronics. The results provide a solid foundation for the future development of fully integrated, flexible, and reliable wearable platforms for continuous monitoring of renal biomarkers.