Signal-on aptamer-based lateral flow test strip for sensitive cadmium detection

Cadmium (Cd²⁺) contamination poses severe environmental and public health risks due to its toxicity and persistence in water sources. Conventional heavy metal detection methods, including lateral flow test strips (LFTSs), often suffer from signal-off mechanisms, requiring complex interpretation and exhibiting limited sensitivity for trace-level detection in environmental matrices. To address these challenges, we developed a signal-on aptamer-based lateral flow test strip (ATS) for rapid and reliable Cd²⁺ detection. The ATS leverages a cadmium-specific aptamer (apCd) and aptamer-conjugated gold nanoparticles (apAuNPs) as signal probes, providing direct visual interpretation where the appearance of the T-line correlates with Cd²⁺ presence. The test strip design and assay conditions were optimized to enhance sensitivity and specificity, including apCd concentration, T-probe concentration, surfactant type, apAuNPs conjugation volume, and incubation time. The ATS demonstrated a limit of detection (LOD) of 0.02 ppb (3SD/slope) and a visual detection threshold of 1.0 ppb, both exceeding the World Health Organization's (3 ppb) and Thailand's (5 ppb) drinking water standards. Stability testing confirmed functionality for over 35 days at room temperature. Application to real water samples, including drinking, tap, and river water, showed accurate detection of Cd²⁺, highlighting the robustness and field applicability of the ATS. Combining simplicity, portability, and high sensitivity, this signal-on ATS provides an innovative solution for decentralized monitoring of heavy metal contamination, addressing critical gaps in current environmental sensing technologies and advancing efforts in water quality management.