DNAzyme-mediated CHA-HCR cascade amplification enabling dual-mode electrochemical/colorimetric sensing of ultra-trace lead ions with smartphone readout.

Trace lead ions (Pb2+) can seriously damage ecosystems and human health. Thus, it is urgent to develop reliable detection methods with high sensitivity and selectivity. This work constructs an electrochemical/colorimetric dual-mode biosensor for ultra-trace Pb2+ detection. The sensor combines Pb2+-specific DNAzyme recognition with enzyme-free catalytic hairpin assembly-hybrid chain reaction (CHA-HCR) cascade signal amplification technology. The experimental results indicate that this dual-mode sensing platform exhibits exceptional detection performance. The limit of detection (LOD) reaches 1.76 pM (electrochemical mode) and 32.17 pM (colorimetric mode). The corresponding linear ranges are 0.005 - 5000 nM and 0.1 - 10000 nM respectively. Moreover, the sensor demonstrates high selectivity against interfering metal ions. It maintains good storage stability, retaining over 84 % of its initial activity after being stored at 4 °C for 3 weeks. It also achieves satisfactory detection reliability for real water samples collected from the Pinglu Canal, with recovery rates ranging from 97.5 % to 99.3 %. This work provides a novel, sensitive, and robust technical solution for aquatic Pb2+ monitoring. It shows great application potential for on-site environmental detection and public health protection.