A cost-effective electrochemical sensor based on L-cysteine-functionalized NiFe2O4@NiCoFe LDH/MLG for Pb2+ screening in class III-V surface waters

Herein, a cost-effective and user-friendly electrochemical sensor was fabricated via a straightforward surface functionalization strategy using L-cysteine-functionalized NiFe 2 O 4 @NiCoFe LDH/MLG nanocomposites, specifically designed for on-site screening of Pb 2+ in Class III-V surface waters. The fabrication process involved the in-situ one-step hydrothermal growth of NiFe 2 O 4 @ternary NiCoFe layered double hydroxide (LDH) nanomaterials on a multilayer graphene (MLG) scaffold, followed by functionalization with L-cysteine (L-Cys) to yield the Cys/NiFe 2 O 4 @NiCoFe LDH/MLG/SPE sensor. Benefiting from the excellent electrical conductivity of MLG, the synergistic enhancement effect of the ternary LDH, and the multiple coordination active sites of L-Cys, the as-prepared sensor exhibits reliable sensing performance for Pb 2+ detection. Under optimal conditions, the sensor achieved a linear dynamic range of 0.1–3 mg/L and a limit of detection (LOD) of 30 μg/L, which is sufficient to discriminate Pb 2+ concentrations exceeding the regulatory threshold for Class III surface water (50 μg/L, GB 3838–2002). The sensor also demonstrated excellent selectivity against common coexisting ions (Co 2+ , Fe 3+ , Cu 2+ , and Zn 2+ ) and satisfactory repeatability (RSD = 4.42%). In real water sample analysis, recoveries ranged from 94.1% to 113%, confirming its practical applicability. Overall, the Cys/NiFe 2 O 4 @NiCoFe LDH/MLG/SPE composite electrode offers a cost-effective, robust, and operationally simple analytical platform, showing great promise for rapid on-site risk-level screening of Pb 2+ contamination in heavily impacted surface waters, particularly in resource-limited regions.