A centrifugal microfluidic chip with integrated solid-phase extraction for separation and detection of Cd²⁺ and Cu²

The on-site monitoring of trace cadmium (Cd²⁺) and copper (Cu²⁺) ions in environmental waters is crucial for risk assessment but remains challenging due to the limitations of conventional methods, which often involve complex pretreatment and laboratory-bound instrumentation. Herein, we present an integrated centrifugal microfluidic chip that incorporates solid-phase extraction (SPE) for the efficient enrichment and subsequent detection of these heavy metal ions. The disc-shaped chip, fabricated with a multilayer polymer structure, automates the entire "load-adsorb-elute" sequence via centrifugal and Coriolis forces, using embedded capillary valves for precise fluidic control. Multi-walled carbon nanotubes were packed into the adsorption chamber, and alizarin complexone was added to the sample solution prior to adsorption to enhance selective complexation. The eluted analytes were quantified through two complementary modalities. Cd²⁺ was detected via a chemiluminescence inhibition assay, while Cu²⁺ was determined colorimetrically using bis-cyclohexanone oxalyl dihydrazone. Under optimized conditions, the chip achieved high enrichment factors of 100 for Cd²⁺ and 150 for Cu²⁺, with detection limits of 0.42 µg L^-1 and 2.0 µg L^-1, respectively. Linear ranges spanned 0.5-10 µg L^-1 for Cd²⁺ and 5-500 µg L^-1 for Cu²⁺. The method showed good reproducibility and was applied to the analysis of environmental water samples. This work demonstrates a portable and automated microfluidic platform that combines efficient SPE preconcentration with dual-mode detection, offering a practical solution for rapid on-site detection of trace heavy metal ions.