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[Display omitted] • A dual-amplification strategy coupling ExoIII-assisted chain cycling with CHA reaction was used for TOB detection. • A Poly A structure was used to fix the probe and adjust the probe density on the electrode surface. • The biosensor has a regenerative characteristic. Based on ExoIII-assisted nucleic acid circulation and catalytic hairpin assembly (CHA) reaction, a dual-amplification electrochemical biosensors strategy for sensitive detection of tobramycin was presented. When the target was present, the trigger 1 (T1) was released to unfold hairpin DNA (H1), which allowed the ExoIII-assisted nucleic acid circulation to proceed smoothly and create a lot of trigger 2(T2). Following that, the CHA reaction between H2 and H3 proceeded under the catalysis of T2 and produced plenty of H2-H3 complex. Signal probe labeled with ferrocene was immobilized on the electrode ahead by adenine (PolyA). Finally, the H2-H3 complex combined with the probe and the DNA strand labeled with ferrocene (C2) fell off the electrode surface. The above process significantly reduced the electrochemical signal, so the biosensor has a low detection limit of 0.11 nM. Moreover, this biosensor has a satisfactory regenerability. [ABSTRACT FROM AUTHOR]

This work designed an artificial substrate peptide to synthesize peptide-hemin/G-quadruplex (peptide-DNAzyme) conjugates. In addition to enhancing catalytic activity of hemin/G-quadruplex, the peptide could also be induced and cleaved by prostate specific antigen (PSA). It was the first report on peptide-DNAzyme conjugates in application of the peptide biosensor. The polyethyleneimine-reduced graphene oxide@hollow platinum nanotubes (PEI-rGO@PtNTs) nanocomposites were cast on the glassy carbon electrode in order to form the interface of biocompatibility and huge surface area for bioprobes immobilization. In absence of PSA, the peptide-DNAzyme conjugates retained intact on the surface of the electrode to produce a strong response signal. But in presence of PSA, the peptide-DNAzyme conjugates were destroyed to release electron mediators, resulting in dramatical decrease of the electrochemicl signal. Therefore, the method had high sensitivity and super selectivity with the limit of detection calculated as 2.0 fg/mL. Furthermore, the strategy would be promising to apply for other proteases by transforming the synthetic peptide module of target. [ABSTRACT FROM AUTHOR]

In this work, a novel strategy for preparation of bipedal DNA walker (BDW) based on hybridization chain reaction (HCR) with the assistance of Exonuclease III (Exo III) was proposed. Based on this strategy, an electrochemical biosensor was constructed to achieve sensitive detection of CYFRA 21-1 DNA. Firstly, target recognition and circulation were achieved through a one-step catalytic hairpin assembly (CHA) reaction. For further amplification, hybridization chain reaction (HCR) was employed to form duplex-stranded DNA (dsDNA) nanostructure in homogeneous solution. In particular, the elongated single strand of the hairpin DNA for HCR was designed as the Mg2+ DNAzyme sequence. With the assistance of Exo III, dsDNA nanostructure can be digested and transformed into large amounts of BDW. These BDW can cleave the signal probe driven by Mg2+, which was modified on the electrode surface and thus achieved "signal-off" detection of target. This BDW preparation method based on HCR with the digestion of Exo III converted one target input into large amount of BDW. Coupled with the walking cleavage of BDW, a series of cascade amplification endowed high sensitivity with this biosensor and realized ultrasensitive detection of target DNA with the detection limit as low as 3.01 aM. [Display omitted] • The preparation of bipedal DNA walker (BDW) based on hybridization chain reaction (HCR) was firstly proposed. • One target input can be converted into large amount of BDW. • Triple signal amplification was achieved by integrating catalytic hairpin assembly (CHA), HCR and BDW. • This biosensor realized ultrasensitive detection of CYFRA 21-1 DNA with the detection limit as low as 3.01 aM. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensing strategy was proposed to detect cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA based on Exo III-assisted digestion of dsDNA polymer (EADDP) from hybridization chain reaction (HCR). Primarily, the presence of target can drive a catalytic hairpin assembly (CHA) reaction, which was aimed to achieve target recognition and circulation. Then the HCR can be triggered for further signal amplification and generate long dsDNA polymer with signal tags. Subsequently, the introduction of Exo III can digest the long dsDNA polymer to produce large amounts of double signal fragments (DSFs). The above experiments were all carried out in homogeneous solution. Finally, the released DSF can be captured onto the electrode directly by capture probe (CP) and a highly amplified electrochemical signal can be detected. The EADDP in homogeneous solution circumvented complex solid-liquid interface reaction and tedious operation steps on electrode. Besides, one target can be converted into abundant DSFs, which greatly improved the sensitivity. This biosensor exhibited a low detection limit (0.0348 fM) and wide linear range (5 fM ∼ 50 nM) for CYFRA 21-1 DNA biosensing with reliable specificity and stability. [Display omitted] • A novel strategy based on Exo III-assisted digestion of dsDNA polymer (EADDP) was proposed. • The Exo III was firstly used to digest dsDNA polymer to produce abundant double signal fragments (DSF). • The EADDP can convert one target into large amount of DSF in homogeneous solution. • EADDP in homogeneous solution and direct capture of DSF simplified the operation steps on electrode. • This biosensor achieved a low detection limit of 0.0348 fM for CYFRA 21-1 DNA detection. [ABSTRACT FROM AUTHOR]

• A novel structural of DNA nanotweezer is designed to construct electrochemical DNA biosensor. • Split G-rich sequences on the periphery of DNT is not only used as signal generator but also can reduce the background signal to improve sensitivity. • The preparation of this biosensor is convenient and inexpensive. • This DNA biosensor has high sensitivity, well stability and reproducibility for circulating tumor DNA detection. In this work, a label-free electrochemical biosensor for DNA assay was constructed based on a novel structural DNA nanotweezer (DNT) coupled with split G-quadruplex. The novel DNT consists of a long single strand with two hairpin structures in the middle as a recognition element and two short single strands with split G-rich sequences at outsides as a signal reporter. The target triggered two hairpin structures hybridized with each other, it caused the DNT transformation from "open" to "close". The "closed" DNT facilitated the split G-rich sequences combined together and provided electrochemical signals. Here, the hairpin structures were not only used for specific target identification but also avoided the false positive signals and improved the sensitivity. Additionally, the split G-rich sequences were put at outsides instead of insides, which significantly improved the signal-background ratio. Moreover, the construction of this biosensor was convenient and easy to control, which was beneficial to reduce the error generated by the operation process and improve stability and reproducibility. Under the optimal conditions, the proposed assay achieved a low detection limit (22 aM) and a wide linear range (1 fM to 1 nM) for circulating tumor DNA determination. This efficient and convenient DNT can be used as a template in electrochemical biosensors fabrication. [ABSTRACT FROM AUTHOR]

Herein, a robust and highly ordered three-dimensional electrochemical DNA (3D E-DNA) biosensor was proposed, and its orientation was controlled from top down by poly adenine oligonucleotides (polyA-ODNs)-mediated rolling motor (PRM) and graftable tetrahedron DNA (GTD). The GTD with a grafting domain was immobilized on the electrode surface to construct a well-organized sensing interface and controlled the orientation and distribution of the whole system at the "bottom" of this biosensor. The polyA-ODNs regulated the direction and density of the leg DNA attached on PRM at the "top" of the biosensor. The motion was achieved through the target induced cyclic cleaving, which triggered the motor rolling rather than walk. Impressively, the duplex strand DNA (dsDNA) formed after grafting, as a girder, provided a stable support to the soft long single strand (ssDNA), which facilitated the formation of the catalytic center, elevated the efficiency of the rolling cleavage. Under the optimal conditions, the designed biosensor exhibited a lower limit of 0.17 nM and wide linear range from 0.5 nM to 1.5 μM for adenosine rapid detection. Unique dual orientation regulated characteristics of the system increased the probability hybridization enormously and improved the motion efficiency significantly, which offered new avenue of DNA nanomachines development in biosensor platform. • The 3D electrochemical DNA biosensor is highly ordered with the density and orientation are well controlled from top down. • The rolling motor is well-designed and triggered rolling by target induced cyclic cleaving. • A distinctive graftable tetrahedron DNA is proposed to constructed 3D sensing surface regulated the density of the whole system. • The graftable tetrahedron can be used to simultaneously construct different sensing strategies without re-synthesizing according to the target. • Poly adenine prompts the substrate DNA of rolling motor to adopt an upright conformation and program the direction and density of substrate DNA precisely. [ABSTRACT FROM AUTHOR]