Target-activated multivalent sensing platform for improving the sensitivity and selectivity of Hg2+ detection.

Sensitivity and selectivity are critical parameters to evaluate the performance of sensors. For trace detection, it remains a challenge to design a new sensor that achieves high sensitivity and selectivity simultaneously. Here, we present a target-activated dual Mg2+-dependent DNAzyme (MNAzyme) that served as a simple sensing model to explore the multivalency in improving the analytical sensitivity and selectivity for target detection. Mercury ion (Hg2+), a notorious toxic metal ion, was selected as a model target. In the presence of Hg2+, the thymine-rich regions of the hairpin probe and primer could hybridize to form a stable duplex via the thymine-Hg2+-thymine structure. Then, an intact enzyme sequence was exposed and two separate enzyme fragments were close to each other, generating a dual MNAzyme. Benefiting from the localized high-concentration of the enzyme strand, the dual MNAzyme showed a remarkable improvement in binding stability. The catalytic rate constant of the dual MNAzyme was theoretically 1.60 times higher than that of the monomeric counterpart, and the sensitivity and selectivity had 4.50 and 1.44-fold enhancement, respectively. When the dual MNAzyme was used for sensor applications, the limit of detection was determined to be 0.04 and 0.2 nM via UV-vis spectrophotometer and naked eye, respectively. Meanwhile, the method offered desirable selectivity toward Hg2+ against other metal ions. With the advantages of simple operation, high sensitivity, and desirable selectivity, the developed multivalent sensing platform could be easily expanded in the future for the on-site detection of other low-abundance analytes.

Colorimetric aptasensor for the sensitive detection of ochratoxin A based on a triple cascade amplification strategy.

Ochratoxin A(OTA), a highly toxic mycotoxin commonly found in food, poses a serious threat to health even at low concentrations. Developing a sensitive, accurate, simple, and cost-effective detection method is of great significance for food safety and quality control. Herein, a triple cascade amplification strategy was used to construct the colorimetric assay for the detection of OTA, where the amplification process consists of an entropy-driven DNA circuit (EDC), a catalytic hairpin assembly (CHA), and Mg2+-assisted DNAzyme catalysis (MNAzyme). Through the specific binding of ochratoxin A (OTA) and its aptamer, an initiator strand is released to initiate upstream EDC and then produce a new trigger unit that motivates downstream CHA to generate MNAzyme, which further cleaves the substrate strand to induce the formation of G-quadruplex/hemin DNAzyme as a signal readout. The aptasensor was shown to detect OTA, with a low detection limit of 8.7 fM and good selectivity. The developed method could be used as a highly colorimetric aptasensor for the detection of OTA in spiked rice samples.