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Abstract Smartly coupling exonuclease-induced target recycling signal amplifications with β-cyclodextrin host-guest recognition, a novel "signal-on" aptamer sensor for sensitive determination of ochratoxin A (OTA) was proposed for the first time. Firstly, the formation of double-strand DNA (dsDNA) was occurred by hybridizing OTA aptamer with its complementary DNA (cDNA) and as the probe DNA the cDNA at its 3′ terminal was labeled with methylene blue (MB). Next, when OTA was present, the aptamer tended to form aptamer-OTA complex with conformation of G-quadruplex instead of aptamer-cDNA duplex, leading to thus the probe DNA separating from dsDNA complex. Then the RecJf exonuclease was added, demolishing partially G-quadruplex structure and releasing a certain number of OTA. Sequentially, those released OTA would continue to react with the rest of aptamer in dsDNA, drawn into development of a new round of G-quadruplex complex, where the target cycling was realized. Meanwhile, as a signal molecule, MB modified on cDNA was liberated along with the cDNA being digested into monoucleotides by RecJf exonuclease, capable of diffusing onto the electrode surface due to host-guest recognition with β-cyclodextrin, whereupon the signal was enriched and yielded. In this way, cycles of target with continuous output of signal indicators were undergone, in which the detection of target was in return fulfilled with signal amplification owing to the joint endeavor of exonuclease and β-cyclodextrin. Under the optimal conditions, the raising signal maintained a linear relation with the logarithm of the target concentrations ranging from 10 pg/mL to 10.0 ng/mL and the detection limit reached as low as 3 pg/mL. This brand-new strategy was simple and low-cost but satisfactory in terms of detection limit, range and sensitivity, in all possibility to be applied extensively for diverse targets detection by easily alternating the corresponding aptamers. Highlights • A well-performed ochratoxin A aptasensor was proposed using exonucleases and β-cyclodextrin. • The employment of RecJf exonuclease triggered the target cycling and signal amplification. • The host-guest recognition with β-cyclodextrin facilitated capturing signal molecules, enabling the signal enrichment. • The selectivity was ensured by the adoption of aptamer. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensor for highly sensitive and selective detection of glutathione (GSH) was developed coupled thymine-Hg 2+ -thymine (T-Hg 2+ -T) coordination with mesoporous silica nanoparticles (MSN). Hg 2+ ions could specifically interact with thymine bases to form strong and stable T-Hg 2+ -T complexes. And the electroactive molecules-methylene blue (MB) was sealed in the inner pores of MSN with a unique sequential thymine (T)-rich DNA in the presence of Hg 2+ . After the target was added, the formed duplex DNA T-Hg 2+ -T complex could deform into single-stranded DNA by a competitive displacement reaction, leading to the release of MB entrapped in the MSN. Thus the target-dependent amount of released MB could be conveniently monitored with an n -dodecanethiol modified screen-printed gold electrode. Using GSH as a model target, the proposed assay showed a wide detection ranging from 1.0 nM to 1.0 μM with a detection limit of 0.6 nM. This strategy was simple and universal for various analytes with different competitive displacement ligands, possessing a great potential for convenient biotools testing and commercial application. [ABSTRACT FROM AUTHOR]

Incorporating elements of triple-helix aptamer probes (TAP), catalyzed hairpin assembly (CHA) signal amplification and host-guest recognition, a novel "signal-on" sensing strategy for sensitive electrochemical quantification of tetracycline (TC) was reported unprecedentedly. TAP was formed involving an aptamer loop, two-segment stems and a triplex oligonucleotide serving as trigger probe. Then, the trigger probe would be released from TAP once the target presented due to the conformational variation of TAP induced by aptamer binding event, sparking off the upcoming CHA amplification reaction, in which two coexisting DNA hairpins (H1 and H2 both modified with the electroactive molecules) would hybridize into plentiful H1–H2 double helices. Afterwards, the Exonuclease III was added, demolishing double helices and simultaneously releasing plentiful electroactive molecules which were capable of diffusing onto the electrode surface under the assistance of β-cyclodextrin due to host-guest recognition, where appreciable signals were enriched and generated. As thus, considerably slight amounts of targets though, emitted trigger probes, yet efficiently engining spectacular CHA cycles of reactions through which amplified signals were yielded, and in turn progressively enabling the sensitive target detection done. Under optimal conditions, the growing signal stayed a linear relation along with the logarithm of the target concentrations ranging from 0.2 nM to 100 nM, the detection limit reaching as low as 0.13 nM. This approach was desirable regarding to sensitivity, detection limit and range, prospectively rendering a service for diverse targets detection by easily replacing the matched aptamer loop of TAP. 1. A sensitive electrochemical sensor for tetracycline detection was developed. 2. A novel TAP switch and CHA probes were designed. 3. The elements of TAP, CHA and host-guest recognition were used for signal amplification. 4. This approach was desirable regarding to sensitivity, detection limit and range. [ABSTRACT FROM AUTHOR]