An electrochemical immunosensor based on a nanostructured lanthanum oxide-substituted reduced graphene oxide interface for ultralow ciprofloxacin detection in milk samples

Abstract

In the present work, we have reported a nanostructured lanthanum oxide nanoparticle-decorated reduced graphene oxide nanocomposite (nLa₂O₃ NPs@rGO)-based biosensing platform for efficient and label-free determination of ciprofloxacin (CPX) antibiotic. A facile hydrothermal method was utilized for the synthesis of the nLa₂O₃ NPs@rGO composite, followed by functionalization with 3-aminopropyltriethoxysilane (APTES) and attachment on an indium tin oxide (ITO)-coated substrate electrophoretically. The CPX monoclonal antibodies (anti-CPX) and bovine serum albumin (BSA) were immobilized using a drop-casting approach. The morphological, structural, and electrochemical characterization of nLa₂O₃ NPs@rGO and other developed immunoelectrodes was done through contact angle, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Here, rGO's large surface area assists in enhancing the nLa₂O₃ NPs dispersibility, which provides synergistic effects to the nLa₂O₃ NPs@rGO nanocomposite leading to electron transfer process acceleration. Hence, the developed immunoelectrode (BSA/anti-CPX/APTES/nLa₂O₃ NPs@rGO/ITO) effectively determines CPX having a broad linear detection range from 10⁻⁶ to 600 μg mL⁻¹ with a lower detection limit of 0.055 μg mL⁻¹ and good durability of 25 days. Furthermore, the immunosensor showed good selectivity towards CPX and was used in real samples of processed milk. Thus, the nLa₂O₃ NPs@rGO composite could emerge as a potential material for the determination of other antibiotics also.