Heavy Metal-Induced Assembly of DNA Network Biosensor from Double-Loop Hairpin Probes for Ultrasensitive Detection of UO₂²⁺ in Water and Soil Samples

The uranyl ion (UO₂²⁺) is the most stable form of uranium, which exhibits high toxicity and bioavailability posing a severe risk to human health. The construction of ultrasensitive, reliable, and robust sensing techniques for UO₂²⁺ detection in water and soil samples remains a challenge. Herein, a DNA network biosensor was fabricated for UO₂²⁺ detection using DNAzyme as the heavy metal recognition element and double-loop hairpin probes as DNA assembly materials. UO₂²⁺-activated specific cleavage of the DNAzyme will liberate the triggered DNA fragment, which can be utilized to launch a double-loop hairpin probe assembly among H_ab, H_bc, and H_ca. Through multiple cyclic cross-hybridization reactions, hexagonal DNA duplex nanostructures (n[H_ab•H_bc•H_ca]) were formed. This DNA network sensing system generates a high fluorescence response for UO₂²⁺ monitoring. The biosensor is ultrasensitive, with a detection limit of 2 pM. This sensing system also displays an excellent selectivity and robustness, enabling the DNA network biosensor to work even in complex water and soil samples with excellent accuracy and reliability. With the advantages of enzyme-free operation, outstanding specificity, and high sensitivity, our proposed DNA network biosensor provides a reliable, simple, and robust method for trace levels of UO₂²⁺ detection in environmental samples.