Rational Design of Amperometric Sensor Based on Magnesium Oxide and Reduced Graphene Oxide Hybrid for Ultralow Detection of Cephalexin in Complex Biological Matrices

Cephalexin (CEX) is the first-generation β-lactam antibiotic drug used to treat urinary, respiratory, and skin infections. However, the overtherapeutic use of CEX necessitates its accurate and low-level monitoring in biological and clinical applications. In the current work, an amperometric electrochemical sensor based on a magnesium oxide/reduced graphene oxide (MgO/rGO) nanocomposite was successfully prepared for reliable and sensitive determination of CEX in biological samples. First, the MgO/rGO hybrid was comprehensively characterized. The XRD patterns revealed an excellent crystalline structure and an average crystallite size of 20.6 nm. The FTIR spectra manifested the disappearance of GO peaks and the emergence of MgO peaks, confirming the successful synthesis of MgO/rGO hybrid nanocomposite. The SEM images exhibited highly exfoliated GO sheets after incorporating MgO, offering a broad electroactive surface area, and the EDX images confirmed the elemental composition and uniform distribution of Mg and O within the rGO matrix. The electrochemical characterization of MgO/rGO-modified glassy carbon electrode (MgO/rGO/GCE) was carried out on cyclic voltammetry and electrochemical impedance spectroscopy, which revealed excellent redox response and charge-transfer kinetics. Under the optimal conditions, e.g., scan rate of 80 mV·s^-1, PBS electrolyte (pH 3), and potential window from 0.4 to 1.8 V, the fabricated sensor exhibited a low limit of detection calculated as 1.3 nM. The prepared sensor detected CEX in human urine and serum samples with good recovery values, confirming its capability for real biological and clinical samples.