Sustainable incorporation of waste toner derived Fe ₃ O ₄ into reduced graphene oxide for electrochemical dopamine sensing

The improper disposal of electronic waste (e-waste) poses significant environmental challenges but also presents an opportunity for sustainable material recovery. Simultaneously, dopamine (DA) is a vital neurotransmitter involved in numerous physiological processes, and its sensitive detection is essential for diagnosing neurological disorders. In this study, we report a cost-effective and environmentally friendly strategy to synthesize a reduced graphene oxide-magnetite (rGO-Fe₃O₄) nanocomposite from e-waste-derived precursors for DA sensing. Graphite was recovered from spent lithium-ion battery (LIB) anodes <i>via</i> ultrasonication, while Fe₂O₃ was obtained from waste toner powder (WTP) through thermal decomposition. Graphene oxide (GO) was synthesized from the purified graphite using an improved Hummers' method and subsequently reduced in the presence of Fe₂O₃ to form the rGO-Fe₃O₄ nanocomposite. The resulting materials were characterized by FTIR, SEM-EDS, and XRD analyses. The rGO-Fe₃O₄-modified glassy carbon electrode (GCE) exhibited excellent electrocatalytic performance for DA detection, as evaluated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometry. The sensor demonstrated a wide linear detection range (10-450 µM), high sensitivity (42.35 µA mM^-1), and a low detection limit (0.0639 µM). It also showed outstanding selectivity, repeatability, and stability, along with successful DA quantification in human urine samples. This work presents a circular materials approach for converting e-waste into functional nanocomposites and underscores their potential in the development of affordable, high-performance electrochemical biosensors.