G-quadruplex DNAzyme molecular beacon for amplified colorimetric biosensing of Pseudostellaria heterophylla.

With an internal transcribed spacer of 18 S, 5.8 S and 26 S nuclear ribosomal DNA (nrDNA ITS) as DNA marker, we report a colorimetric approach for authentication of Pseudostellaria heterophylla (PH) and its counterfeit species based on the differentiation of the nrDNA ITS sequence. The assay possesses an unlabelled G-quadruplex DNAzyme molecular beacon (MB) probe, employing complementary sequence as biorecognition element and 1:1:1:1 split G-quadruplex halves as reporter. In the absence of target DNA (T-DNA), the probe can shape intermolecular G-quadruplex structures capable of binding hemin to form G-quadruplex-hemin DNAzyme and catalyze the oxidation of ABTS2- to blue-green ABTS•- by H(2)O(2). In the presence of T-DNA, T-DNA can hybridize with the complementary sequence to form a duplex structure, hindering the formation of the G-quadruplex structure and resulting in the loss of the catalytic activity. Consequently, a UV-Vis absorption signal decrease is observed in the ABTS2--H(2)O(2) system. The "turn-off" assay allows the detection of T-DNA from 1.0 × 10-9 to 3.0 × 10-7 mol·L-1 (R2 = 0.9906), with a low detection limit of 3.1 × 10-10 mol·L-1. The present study provides a sensitive and selective method and may serve as a foundation of utilizing the DNAzyme MB sensor for identifying traditional Chinese medicines.