Chemicals and Apparatus: Conductive inks (Ag/AgCl and graphite) were acquired from Acheson (Italy). Hydrogen peroxide, uric acid, acetaminophen, dopamine hydrochloride, glucose, sodium acetate, potassium chloride, and potassium ferrocyanide were procured from Sigma Aldrich (Italy). Cobalt acetate tetrahydrate, platinum chloride, ammonia water, and ethanol were procured from Sigma Aldrich (Malaysia). All the chemicals used in this study were of analytical grade and used without additional processing or modification. Electrochemical analysis was executed employing a PalmSens portable potentiostat (Palm Instruments, The Netherlands). The complete electrochemical experiments were accomplished at room temperature. All the working solutions were prepared with double-distilled water from Millipore. In vitro cell culture and reagents: Mouse HL-1 cardiac muscle cells (Merck Millipore) were cultured in 75 cm² culture flasks (Falcon, Germany) that had been precoated with a solution of 0.02% gelatin (Sigma Chemical, cat. number: G-9391) and 5 μg/mL fibronectin (Sigma Chemical, cat. number: F-1141) to promote cell adhesion and ensure optimal growth conditions. The cells were maintained in Claycomb medium (cat. number 51800C, Sigma Aldrich), specifically formulated for HL-1 cell growth. This medium was supplemented with 2 mM glutamine (L-Glutamine, cat. number: A29168-01, Gibco), 100 U/mL penicillin, and 100 μg/ml streptomycin (PenStrep, cat. number: 15140-122, Gibco) to maintain sterility and prevent bacterial contamination. Additionally, 100 μM norepinephrine (Sigma Chemical) was added to support cellular function, and 10% Fetal Bovine Serum (FBS, cat. number: 16000044, Gibco) was included to provide necessary growth factors and nutrients. For cardiotoxicity experiments, DOX was sourced from Sigma-Aldrich, Segrate, Milan, Italy. It was dissolved in dimethyl sulfoxide (DMSO, Sigma-Aldrich, Segrate, Milan, Italy) to prepare a solution suitable for experimental use. DOX was employed as a model compound to study the cardiotoxic effects of chemotherapy drugs on cardiac cells. Manufacturing of polyester-based printed strips: Screen-Printed Electrodes (SPEs) were manufactured on a polyester substrate using a semi-automatic screen-printing system (Model GPE/2; Type AP05). The fabrication involved two main steps, conducted at 100°C for 30 minutes. First, a pseudo-reference electrode was printed using silver ink (Ag/AgCl, Electrodag 477 SS) and dried in an oven at 100 °C for 30 minutes. Next, the working and counter electrodes were printed with graphite ink (Elettrodag 421) under controlled environmental conditions. The working electrode featured a diameter of 0.4 cm, resulting in a geometric area of 0.07 cm². Prior to electrochemical experiments, adhesive tape was applied to define the contact area of the electrode and to insulate the electrical connections. Synthesis of rGO-Co₃O₄: Graphene oxide (GO) was prepared following a simplified version of Hummer's method, as described in the previous work . For the synthesis of reduced graphene oxide-cobalt oxide (rGO-Co₃O₄), 1 mmol of cobalt acetate tetrahydrate was dissolved in 10 mL of deionized (DI) water and then gradually added to a 20 mL suspension of GO (1 mg/mL) under constant stirring. Subsequently, 5 mL of a platinum chloride solution was introduced into the mixture while stirring continuously. After stirring for 30 minutes, 15 mL of ammonia solution was added dropwise with continuous stirring. The mixture was then stirred for an additional 30 minutes and transferred to a 100 mL Teflon-lined autoclave for a microwave-assisted hydrothermal reaction at 180 °C for 10 minutes, with a heating rate of 5 °C per minute. The resulting precipitate was collected, thoroughly washed with DI water and ethanol, and freeze-dried. The same procedure was applied for synthesizing rGO-Co₃O₄ and Co₃O₄, both with and without the addition of platinum salt and GO, respectively. Characterization: The morphological characteristics of the individual specimens-Co₃O₄, rGO-Co₃O₄, and the rGO-Co₃O₄-Pt nanocomposite-were analyzed using a Hitachi TEM system integrated with an energy-dispersive X-ray spectrometer (EDX/EDS). X-ray diffraction (XRD) measurements were conducted on a PANalytical X'Pert3 powder diffractometer, utilizing Cu-Kα radiation (λ = 0.15406 nm) at 40 kV and 30 mA, covering a 2θ range of 5-80°. The surface properties of the rGO-Co₃O₄-Pt nanocomposite were characterized using a Thermo Scientific K-Alpha XPS system, maintained at a chamber pressure below 5 × 10 -9 mbar. The instrument operated in large-area XL magnetic lens mode with pass energies set at 150 eV for survey scans and 20 eV for high-resolution scans. Spectra were acquired at a 90° electron takeoff angle relative to the surface plane, with high-resolution peaks fitted using the algorithms provided in the ThermoVG Avantage software. Binding energies were determined by referencing the internal C1s signal at 284.9 eV. Preparation of rGO-Co₃O₄-Pt nanocomposite dispersion: DI was used to prepare rGO-Co₃O₄-Pt nanocomposite aliquots at a concentration of 1 mg/mL. These aliquots were subsequently employed to modify the working electrode for further electrochemical studies. A 8 µL from each aliquot was applied onto the taped SPEs to fabricate the electrode. Electrochemical measurements: The PalmSens4 portable potentiostat/galvanostat/impedance analyzer was used for conducting electrochemical measurements using a 100-µL drop of the working solution. First the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments were conducted to evaluate the electrochemical performance of the bare SPEs, rGO/SPEs, Co3O4/SPEs, Pt/SPEs, rGO-Co3O4/SPEs, and rGO-Co3O4-Pt/SPEs. The electrolyte used for these tests was a 5 mM solution of potassium ferricyanide/potassium ferrocyanide [Fe(CN)6 ]3-/4 -in 0.1 M KCl. Additionally, square wave voltammetry (SWV) experiments were performed with rGO-Co3O4-Pt/SPEs in 0.1 M KCl containing up to 2.5 µM hydrogen peroxide.