A novel tantalum pentoxide nanoparticle-electrochemically reduced graphene oxide nanocomposite-modified glassy carbon electrode (Ta₂O₅-ErGO/GCE) was developed for the detection of oxytetracycline in milk. The composition, structure and morphology of GO, Ta₂O₅, and Ta₂O₅-ErGO were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Oxytetracycline electrochemical behavior on the bare GCE, GO/GCE, ErGO/GCE, and Ta₂O₅-ErGO/GCE was studied by cyclic voltammetry. The voltammetric conditions (including scan rate, pH, deposition potential, and deposition time) were systematically optimized. With the spacious electrochemical active area, the Ta₂O₅-ErGO/GCE showed a great magnification of the oxidation signal of oxytetracycline, while that of the other electrodes (GCE, GO/GCE, ErGO/GCE) could not reach the same level. Under the optimum conditions, the currents were proportional to the oxytetracycline concentration in the range from 0.2 to 10 μM, and a low detection limit of 0.095 μM (S/N = 3) was detectable. Moreover, the proposed Ta₂O₅-ErGO/GCE performed practically with satisfactory results. The preparation of Ta₂O₅-ErGO/GCE in the current work provides a minor outlook of detecting trace oxytetracycline in milk.

In this study, we reported facile synthesis of Fe₃O₄/C composite and its application for the cost-effective and sensitive determination of tryptophan (Trp) in human serum samples. Fe₃O₄/C composites were prepared by a simple one-pot hydrothermal method followed by a mild calcination procedure, using FeCl₃∙6H₂O as Fe₃O₄ precursor, and glucose as reducing agent and carbon source simultaneously. The Fe₃O₄/C composite modified glassy carbon electrode (Fe₃O₄/C/GCE) was prepared by drop-casting method. The microstructure and morphology of Fe₃O₄/C composite was characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Due to large specific surface area and synergistic effect from Fe₃O₄ nanoparticles and carbon coating, Fe₃O₄/C composite showed excellent electrocatalytic activity toward the oxidation of Trp. As a result, the proposed Fe₃O₄/C/GCE displayed superior analytical performances toward Trp determination, with two wide detection ranges (1.0–80 μM and 80–800 μM) and a low detection limit (0.26 μM, S/N = 3). Moreover, successful detection of Trp in human serum samples further validate the practicability of the proposed sensor.