Ultrasensitive ratiometric detection of Pb using DNA tetrahedron-mediated hyperbranched hybridization chain reaction.

A fluorescent sensing strategy was developed for rapid, highly sensitive and specific detection of lead (II) ion (Pb) on the basis of Pb DNAzyme-controlled tetrahedral DNA nanostructure (TDN)-mediated hyper-branched hybridization chain reaction (hHCR). In this strategy, DNA hairpins used for HCR amplification are modified on the four vertexes of TDN, which are then used to perform rapid TDN-hHCR in the presence of an initiator strand, producing large-sized cross-linked reaction products and thus giving greatly improved fluorescence resonance energy transfer (FRET) signal output. Pb DNAzyme catalyzes the cleavage of the initiator strand, inhibiting the initiation of TDN-hHCR and giving decreased FRET signal. Synergetic signal amplification of Pb DNAzyme-catalyzed cleavage reaction and subsequent TDN-hHCR confers the sensing platform with ultrahigh sensitivity. As low as 0.25 pM Pb can be detected by using either signal "turn-on" or "turn-off" mode. The whole detection process can be finished within 20 min. Strong anti-interference capacity of FRET-based ratiometric detection and high specificity of Pb DNAzyme endow the sensing platform with great practical application potential, which was demonstrated by the accurate detection of Pb in real river water, fruit, vegetable and grain samples.