Determination of Pb²⁺ in Water by Fluorescence Sensing System Based on Amplification Strategy of Hairpin DNA Dynamic Self-Assembled Dendrimer

A novel enzyme free and highly sensitive fluorescence sensing system for detecting Pb²⁺ was constructed based on the specific recognition of GR-5 deoxyribozyme (GR-5 DNAzyme) for Pb²⁺ and the signal amplification strategy of hairpin DNA dynamic self-assembled dendrimer. The sequence extended GR-5 DNAzyme complex (GR-5E-S, synthesized from GR-5 DNAzyme enzyme chain GR-5E and substrate chain GR-5S) and Y-shaped skeleton (synthesized from skeleton chains Y1, Y2, and Y3) were synthesized by incubating at a constant temperature of 95 ℃. Hairpin trimers (synthesized from Y-shaped skeleton and hairpin chains H1, H2 and H3, in which fluorescent and quenching groups modified on hairpin H1) were synthesized by incubating at a constant temperature of 25 ℃. Water sample（4 μL）was added into 96 μL of the reaction solution containing 400 nmol·L^-1 GR-5E-S and 400 nmol·L^-1 hairpin trimers, and the mixed solution was incubated at 25 ℃ for 40 min. When Pb²⁺ was present in the water sample, GR-5E-S recognized Pb²⁺, and the substrate chain was cleaved. The enzyme chain and substrate chain were separated, and the target chain T was released. Target chain T hybridized with hairpin chain H1 to trigger a dynamic self-assembly process, generating the dendrimer. Fluorescence intensity was measured at 520 nm. It was shown that the established fluorescence sensing system could complete detection within 40 min. Linear relationship between values of the concentration of Pb²⁺ and the fluorescence intensity of the corresponding sensing system was kept in the range of 0.1-10.0 nmol·L^-1, with detection limit (3s/k) of 19 pmol·L^-1. Test for recovery was made according to the standard addition method, giving recoveries in the range of 98.0%-108%, and RSDs (n=5) of the determined values was not more than 15%.