Lateral flow strip biosensor for visual detection of heavy metal ions based on feedback circuit with trigger DNA...

The on-site and visual detection of trace levels of heavy metal ions in resource-limited settings is still a big challenge. Herein, using chromium ions (Cr³⁺) as a model target, we developed a lateral flow strip biosensor for visual detection of Cr³⁺ on the basis of a feedback circuit with trigger DNA regeneration strategy. Cr³⁺-specific DNAzyme was used to recognize Cr³⁺. The free trigger DNA (T) after the cleavage reaction can initiate the assembly of hairpin probes H1, H2, and H3. The resulting H1-H2-H3 products contain a freshly regenerated T fragment, which can continuously drive the operation of feedback DNA circuit, thereby yielding abundant H1-H2-H3 assemblies. Compared with the no T regeneration strategy, the feedback circuit with T regeneration method exhibits superior signal amplification capability. The strip biosensor achieves a visual detection limit of 10 pM. Moreover, the sensing platform exhibits favorable robustness and performs reliably when applied to practical water samples. Using Cr³⁺ and cadmium ion (Cd²⁺) as two inputs, we further constructed INHIBIT and XOR strip logic gates that open new avenues for intelligent detection of different heavy metal ions in resource-poor environments.