Transition metal oxide (TMO)-based nanomaterials are effectively utilized to fabricate clinically useful ultra-sensitive sensors. Different nanostructured nanomaterials of TMO have attracted a lot of interest from researchers for diverse applications. Herein, we utilized a hydrothermal method to develop porous nanosheets of cobalt oxide. This synthesis method is simple and low temperature-based. The morphology of the porous nanosheets like cobalt oxide was investigated in detail using FESEM and TEM. The morphological investigation confirmed the successful formation of the porous nanosheet-like nanostructure. The crystal characteristic of porous cobalt oxide nanosheets was evaluated by XRD analysis, which confirmed the crystallinity of as-synthesized cobalt oxide nanosheets. The uric acid sensor fabrication involves the fixing of porous cobalt oxide nanosheets onto the GCE (glassy carbon electrode). The non-enzymatic electrochemical sensing was measured using CV and DPV analysis. The application of DPV technique during electrochemical testing for uric acid resulted in ultra-high sensitivity (3566.5 µAmM⁻¹cm⁻²), which is ~7.58 times better than CV-based sensitivity (470.4 µAmM⁻¹cm⁻²). Additionally, uric acid sensors were tested for their selectivity and storage ability. The applicability of the uric acid sensors was tested in the serum sample through standard addition and recovery of known uric acid concentration. This ultrasensitive nature of porous cobalt oxide nanosheets could be utilized to realize the sensing of other biomolecules.

Early-stage uric acid (UA) abnormality detection is crucial for a healthy human. With the evolution of nanoscience, metal oxide nanostructure-based sensors have become a potential candidate for health monitoring due to their low-cost, easy-to-handle, and portability. Herein, we demonstrate the synthesis of puffy balls-like cobalt oxide nanostructure using a hydrothermal method and utilize them to modify the working electrode for non-enzymatic electrochemical sensor fabrication. The non-enzymatic electrochemical sensor was utilized for UA determination using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The puffy balls-shaped cobalt oxide nanostructure-modified glassy carbon (GC) electrode exhibited excellent electro-catalytic activity during UA detection. Interestingly, when we compared the sensitivity of non-enzymatic electrochemical UA sensors, the DPV technique resulted in high sensitivity (2158 µA/mM.cm²) compared to the CV technique (sensitivity = 307 µA/mM.cm²). The developed non-enzymatic electrochemical UA sensor showed good selectivity, stability, reproducibility, and applicability in the human serum. Moreover, this study indicates that the puffy balls-shaped cobalt oxide nanostructure can be utilized as electrode material for designing (bio)sensors to detect a specific analyte.

Enzymeless sensors have been known as highly stable, fast, and reliable devices for the detection of several biomolecules and for use in early disease diagnosis. Hence, it is crucial to fabricate enzymeless sensors with high sensitivity. Herein, we describe the synthesis of hexagonal cobalt oxide nanosheets using a hydrothermal method. The crystalline phase of the as-synthesised cobalt oxide nanosheets was examined using X-ray diffraction (XRD), and the morphology was observed using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The cobalt oxide nanomaterials were synthesised in a large quantity and showed a uniform and hexagonal nanosheet like morphology. To investigate their application, the nanosheet nanomaterial was utilised to fabricate an ultra-sensitive enzymeless electrochemical-based uric acid (UA) sensor on a screen-printed carbon electrode (SPCE). A paste of hexagonal cobalt oxide nanosheets in a conductive binder was drop-casted onto the working electrode of the SPCE. The cobalt oxide nanosheet-based UA sensor showed a good response for UA detection. Under optimal conditions, the cobalt oxide/SPCE UA sensor showed linearity up to 200 μM of UA with ultra-sensitivity (1560 μA mM⁻¹ cm⁻²) and a limit of detection of ∼5 μM. Furthermore, the fabricated UA sensor was subjected to reproducibility, storage stability, and selectivity tests, which confirmed good stability, reproducibility, and specificity for UA. The developed ultra-sensitive enzymeless UA sensor is expected to be useful for the sensing of UA in real samples.

Electrolyte-gated transistor (EGT)-based biosensors are created with nanomaterials to harness the advantages of miniaturization and excellent sensing performance. A cholesterol EGT biosensor based on iron oxide (Fe ₂ O ₃ ) nanoparticles decorated ZnO nanorods is proposed here. ZnO nanorods are directly grown on the seeded channel using a hydrothermal method, keeping in mind the stability of nanorods on the channel during biosensor measurements in an electrolyte. Most importantly, ZnO nanorods can be effectively grown and modified with Fe ₂ O ₃ nanoparticles to enhance stability, surface roughness, and performance. The cholesterol oxidase (ChOx) enzyme is immobilized over Fe ₂ O ₃ nanoparticles decorated ZnO nanorods for cholesterol detection. With cholesterol addition in buffer solution, the electro-oxidation of cholesterol on enzyme immobilized surface led to increased the biosensor’s current response. The cholesterol EGT biosensor detected cholesterol in wide-linear range (i.e., 0.1 to 60.0 mM) with high sensitivity (37.34 μ A mM ⁻¹ cm ⁻² ) compared to conventional electrochemical sensors. Furthermore, we obtained excellent selectivity, fabrication reproducibility, long-term storage stability, and practical applicability in real serum samples. The demonstrated EGT biosensor can be extended with changing enzymes or nanomaterials or hybrid nanomaterials for specific analyte detection.

Hydrothermally prepared grain-like CeO₂ nanostructures were useful for creating a high-performance and non-enzymatic sensor for uric acid detection.