Ultrasensitive electrochemical detection of trace copper using iron oxide—expanded graphite and its applications

Abstract Access to clean water is a critical global challenge, requiring reliable, low-cost, and sensitive technologies for pollutant monitoring. This study presents the development of an ultrasensitive electrochemical sensor for detecting trace amounts of copper ions in aqueous and biological samples. The sensor is based on an iron oxide-expanded graphite (FeO-EG) composite synthesised via a rapid and energy-efficient microwave-assisted method. The resulting material, combining the high conductivity of graphite with the redox-active properties of iron oxide, was thoroughly characterised using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS). The composite was used to modify a glassy carbon electrode, and its electrochemical performance was evaluated using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The sensor demonstrated excellent sensitivity with a detection limit of 0.14 ppb, along with high selectivity and stability. Its practical utility was confirmed through the successful detection of copper in untreated seawater and artificial urine, without the need for sample pre-treatment. These findings highlight the potential of the proposed sensor as a portable, low-cost, and efficient solution for real-time water quality assessment and non-invasive clinical monitoring.