NiO/CuO@Graphene oxide-modified electrode for sensitive detection of an antidiabetic drug

A new, simple, and cost-effective electrochemical sensor was developed for the determination of Sitagliptin phosphate monohydrate (SP) in powder, pharmaceutical tablet form and biological fluids as spiked plasma. Electrochemical sensor used a chemically modified electrode (CME) based on a glassy carbon electrode (GCE) modified with graphene oxide (GO) and nickel/copper oxide nanoparticles (NiO/CuO NPs). The crystalline nature of GO/ (NiO/CuO NPs), the particle size of (NiO/CuO NPs) and the surface topography of the prepared surface were investigated using surface analysis techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDXA) and elemental mapping. Surface characterization revealed that NiO/CuO NPs had an average size of 27.5 ± 2 nm and were uniformly distributed homogenously on the surface of GO. This distribution increased the effective surface area and enhanced electron transfer, confirming the structural and electrochemical advantages of the modified electrode material. The sensor efficiency was validated by different electrochemical techniques such as differential pulse voltammetry (DPV), cyclic voltammetry (CV), and electrical impedance (EIS). The Voltammetric response of SP powder form toward sensor was observed at − 0.1 V in DPV and − 0.055 V in CV, using 0.1 M phosphate-buffered solution (PBS, pH 7.4) as the electrolyte. The linear concentration range for SP in powder form was 0.05–1.071 mM, with a limit of detection (LOD) of 0.0223 mM and a limit of quantification (LOQ) of 0.0677 mM while, for powder in spiked plasma linear range was 0.0295–0.2715 mM, with LOD of 0.0061 mM and LOQ of 0.0185 mM. The diffusion coefficient (D) of 0.614 mM SP in PBS (pH 7.4, 0.1 mol/L) was evaluated using CV at various scan rates and found to be 2.41 × 10⁻⁶ cm²/s, based on the Randles–Sevcik equation. The method was validated by detecting SP in both powder and tablet forms using an Agilent 1200 HPLC system equipped with a UV detector at 266 nm. Statistical calculations such as recovery and precision were carried out to validate the accuracy and reliability of the method. The recovery values for both the electrochemical and HPLC-UV methods ranged from 99% to 101%, while the repeatability and reproducibility of the electrochemical method showed RSD values below 1.5%. The sensor demonstrated good sensitivity and selectivity toward SP, even in the presence of potential interferents such as glucose, ascorbic acid, and metal ions.