Highly efficient and toxicologically safe ZnO(NP)@GO nanocomposite in the simultaneous detection of Cd²⁺, Hg²⁺, Pb²⁺, and Zn²⁺ in aqueous medium

• Highly efficient and safe ZnO(NP)@GO thin film electrode in trace and simultaneous detection of Cd²⁺, Hg²⁺, Pb²⁺, and Zn²⁺. • The thin film electrode has a relatively higher shelf life and is stable for repeated uses. • The electrode is promising in the simultaneous and trace-level detection of these heavy metal ions from hospital wastewater. Miniaturised devices for trace, simultaneous and off-site detection are the need of the hour for protecting public health and the environment at large. Using sustainable and greener approach, the current study explores using Acmella oleracea extract to derive zinc oxide nanoparticles. Further, ZnO incorporates graphene oxide to obtain the nanocomposite material (ZnO(NP)@GO). The thin film electrode using the ZnO(NP)@GO efficiently detects potential heavy metal ions viz. , Cd²⁺, Hg²⁺, Pb²⁺, and Zn²⁺ individually and simultaneously at trace level concentrations. The thin film electrode using the ZnO(NP)@GO showed significantly enhanced electroactive surface area and reduced electron transfer resistance compared to the unmodified glassy carbon electrode. The calibration curve for detecting Cd²⁺, Hg²⁺, Pb²⁺, and Zn²⁺ shows the limits of detection of 0.026, 0.03, 0.010 and 0.020 µgL⁻¹, respectively, in their simultaneous detection. The ZnO(NP)@GO thin film electrode possesses good shelf life and stability for repeated detections of these heavy metal toxic ions. Furthermore, the thin film electrode detects simultaneously these ions at trace levels in the hospital effluent waters with real implications. Moreover, the acute toxicity of ZnO(NP)@GO towards D. magna shows an EC 50 value of 115.7 mgL⁻¹ after 48 hrs, proving the safety and environmental sustainability of the modified electrode.