A fiber-optic fluorescent biosensor based on DNAzyme-mediated multitag-regulated hybridization chain reaction for the detection of lead(II).

Portable yet ultrasensitive and accurate detection of trace Pb2+ in real environmental samples remains challenging. A rapid-response evanescent wave fluorescent biosensor with a reusable sensing surface offers significant advantages for in-situ and real-time measurements. Herein, we first report a reliable DNAzyme-based biosensor that leverages universal enzyme-free autonomous hybridization chain reaction (HCR)-integrated evanescent wave fluorescence, enabling accurate and facile detection of trace Pb2+. Target recognition activates the metal ion-responsive RNA cleavage activity of DNAzyme, which releases the initiator chain to trigger downstream HCR amplification circuits. The multitagged HCR products (dual-labeled with biotins and fluorophores) are detected through a two-step mechanism: (i) affinity-directed immobilization on streptavidin-functionalized optical fiber surfaces, followed by (ii) evanescent field-induced fluorescence readout. Under the optimal detection conditions, the evanescent wave fluorescent biosensing platform coupling DNAzyme recognition with multitag-regulated HCR amplification achieves a limit of detection of 0.09 nM and a linear response range of 1 to 500 nM. With the optical fiber sensing surface being regenerable for more than 100 cycles, this biosensor enables cost-effective repeated detection. Pb2+ spike-recovery validation in negative environmental water samples confirms the reliability of this technique in complex matrices. The robust detection performance of this technique demonstrates its promising potential for the on-site quantification of metal ion contaminants in the environment.