A colorimetric biosensor for cadmium ion detection based on aptamer coupling G-quadruplex DNAzyme signal amplification

Cadmium ion (Cd 2+ ) is a highly toxic heavy metal ion that poses serious risks to environmental safety and human health. Its accumulation through food chains and drinking water can result in renal dysfunction, neurological damage, and carcinogenic effects. Therefore, the development of simple, sensitive, and field-deployable detection methods for Cd 2+ is of great importance. In this study, a novel approach was employed using graphene oxide–systematic evolution of ligands by exponential enrichment (GO-SELEX) to screen aptamer specific to Cd 2+ . The method reduced the screening time by 30%–50% compared with conventional SELEX methods. The selected aptamer was subsequently integrated with catalytic hairpin assembly (CHA) and a G-quadruplex DNAzyme to construct a colorimetric biosensor for Cd 2+ detection. Signal transduction was achieved via the peroxidase-like catalytic oxidation of ABTS in the presence of hydrogen peroxide, enabling visual and spectrophotometric readout without the need for complex instrumentation or sample pretreatment. Under optimized conditions, the biosensor exhibited a linear detection range from 0.1 to 20 μM with a detection limit of 57 nM. The assay demonstrated excellent selectivity toward Cd 2+ over other common metal ions and satisfactory performance in spiked environmental water samples. The findings of the study demonstrate that the proposed biosensor provided a cost-effective and practical platform for on-site monitoring of Cd 2+ . It holds strong potential for real-world applications, such as assessments of water quality at riverbanks or evaluations of industrial effluents, offering a seamless transition from laboratory research to field deployment.