Engineering a high-performance Mil101(Fe)-CQD-TiO₂ aptasensor platform for trace-level quantification of hazardous metal ions in real water systems

Heavy metal pollution in water systems has increased significantly due to large-scale industrialisation worldwide. This study highlights the monitoring and trace detection of heavy metals (Cd 2 + , AS 5+ , Cu 2+ , As 3+ and Pb 2+ ) in river samples. The ternary composite was synthesized hydrothermally, and the morphological and structural characterisation was examined using physicochemical characterisation techniques to confirm the integration of the ternary composite. The synergy between the Mil101(Fe)-CQD-TiO 2 (metallic organic framework (101)-iron- carbon quantum dot- titanium dioxide) system has rarely been documented in the literature. In this work, it has been shown to enhance the reaction kinetics and electron mobility of the newly developed aptasensor. The improved electron transport, large electroactive surface area, and high conductivity of this ternary composite have significantly increased the electrode's adsorption affinity for heavy metal ions. The new aptasensor platform was examined in both phosphate buffer solutions and water samples using anodic stripping voltammetry (ASV), achieving lower detection limits (LOD) of 1.0 × 10 −4 µM for Cd 2+ , 1.3 × 10 −4 µM for As 5+ , 3.0 × 10 −4 µM for Pb 2+ , and 1.0 × 10 −4 µM for Cu 2+ , and 1.0 × 10 −3 µM for As 3+ . The aptasensor demonstrated excellent anti-interference capability, high reliability, and impressive performance in water analysis, with recoveries ranging from 88 % to 112 %. • The Mil101(Fe)–CQD–TiO₂ ternary composite shows ∼3 × enhanced charge transfer and electroactive surface area. • The aptasensor achieves ultra-low detection limits for Cd²⁺, As⁵⁺, Pb²⁺, Cu²⁺, and As³ ⁺. • Excellent real-sample performance is demonstrated, with 88–101 % recoveries in river water.