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In this work, we first conjugated a short peptide to thrombin binding aptamer (TBA) and bond hemin to the hybrid, effectively rendering hemin/G4-peptide more active over the original hemin/G4, so that a highly sensitive electrochemical thrombin (TB) aptasensor was developed based on it and PtNTs@rGO nanocomposite. It was the first report on the application of hemin/G4-peptide in electrochemical aptasensor. PtNTs@rGO with large surface area served as excellent nanocarrier for high loading of hemin/G4-peptide hybrids, resulting in the formation of hemin/G4-peptide–PtNTs@rGO bioconjugate as the secondary aptamer and further signal enhancement. The specific affinity of aptamer for target TB made the secondary aptamer go into the sensing interface, and then a noticeable current signal was obtained from hemin without additional redox mediators. Due to the collaborative electrocatalysis of hemin/G4-peptide and PtNTs toward H 2 O 2 , which was formed in situ during the process of hemin/G4-peptide-catalyzed oxidation of NADH with dissolved O 2 , the current intensity increased dramatically. Such an electrochemical aptasensing system could be used to detect TB with a linear range of 0.05 pM–60 nM and very lower detection limit of 15 fM. Notably, this method exhibited a higher sensitivity than that of many hemin/G4-based electrochemical strategies for TB detection due to the improvement of the catalytic activity of hemin/G4-peptide. The present works opened a new way for expanding the application of hemin/G4 in biological detection. With the mediator-free, proteinous enzyme-free yet high-sensitivity advantages, this electrochemical aptasensor held great promise for other biomarker detections in clinical diagnostics. [ABSTRACT FROM AUTHOR]

Abstract Herein, a label-free and double recognition–amplification (LDRA) strategy for carcinoembryonic antigen (CEA) detection was developed, based on a new designed dual-function messenger probe (DMP) coalescing with DNA tetrahedron probes (DTPs) and hybridization chain reaction (HCR). The DMP possess dual-function to replace CEA for specific interface hybridization and initiate hybridization chain reaction. The interfacial hybridization event was quantitatively converted to an electrochemical signal by using hemin/G-quadruplex (h-Gx) formed after the hybridization chain reaction. Self-assembled DNA tetrahedron probes, which were readily decorated on an electrode surface as a scaffold with rigid support and ordered orientation, enabled the highly efficient strands hybridization and greatly increased target accessibility as well as significantly decreased noise. The proposed assay integrated dual recognition processes and HCR signal amplification processes, achieving the identification of low concentration of CEA as detection limit of 18.2 fg mL−1 (S/N = 3) and wider linearity range of 0.0001 ng mL−1–50 ng mL−1. A new electrochemical sensing method was proposed for CEA detection and used in real clinical samples. The obtained results were good consistency with those of clinical diagnosis. Highlights • A new dual-function messenger probe (DMP) was designed for specific interface hybridization and initiate HCR. • The employment of DNA tetrahedron probes increased the probability of hybridization and reduced the background signal. • The synergetic combination of DMP and hybridization chain reaction (HCR) improved the sensitivity of the detection. • The proposed strategy was used to analysis CEA in real sample and achieved a detection limit as low as 18.2 fg/mL. [ABSTRACT FROM AUTHOR]

Rapid and effective diagnosis of communicable disease is one of the critical issues of the modern society, especially for detecting different targets at the same time. In this work, a grafting homogenous electrochemical biosensing strategy is proposed by integrating of reverse proximity ligation and exonuclease III (Exo III) assisted target circulation to analyze hepatitis B (HBV) and human immunodeficiency (HIV). Specially, a two-wing nanodevice (TWD) with two detection paths is elaborately designed based on analogous proximity ligation assay. The reverse proximity ligation process provides a new way of signal conversion and amplification, what accomplished by demolishing the TWD in the presence of targets. Meanwhile, a vast number of signal probes are released via Exo III assisted target circulation. Then the signal probes are grafted on the universal sensing interface, which is decorated with graftable tetrahedron DNA (GTD). These lead to a highly amplified electrochemical signal. Compared with the conventional strategies, the grafting homogenous electrochemical biosensing strategy not only achieves convenient sensitive detection of multiple communicable diseases DNA simultaneously, but also performs well in the detection of sole target. This strategy effectively decreases the background, homogenizes the distribution of probes, and avoids the complex and time-consuming modification process of the working electrode, which holds great potential application in early diagnosis for communicable disease in the future. • A two wing nanodevice is constructed by using the principle of analogous proximity ligation assay. • By using the principle of reverse proximity ligation assay, a new manner for conversing and amplifying the electrochemical signal is demonstrated for the first time. • The graftable tetrahedron DNA is immobilized on the electrode to construct a universal grafting sensing interface. • This strategy can be used to detect multiple targets simultaneously, and can also perform well in detection of sole target. [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]

In this study, a highly ordered three dimensional (3D) DNA nanostructure was self-assembled by label-free DNA nanotweezers, which was used as recognized probe to interact with target. Once the target was recognized by the 3D DNA nanoprobe (3D DNT), DNA nanotweezers opened to release target analog (T1). This recognition process was proceeded in homogeneous solution, which can avoid complex electrode modification and improve reaction efficiency. Then these target analogs were captured by the signal DNA probes (E1) modified on the electrode. In the assistance of Exo III, E1 was digested and the T1 was released to participate in the next cycle to realize signal amplification. Finally, an ultrasensitive carcinoembryonic antigen (CEA) electrochemical biosensing with a detection limit of 4.88 fg mL−1 was developed. • Label-free 3D DNA nanoprobe based on DNA tweezers was firstly developed in electrochemical biosensing. • Homogeneous biorecognition strategy simplified experiment procedure and improved reaction efficiency. • Exo III assisted recycling amplification technology improved the sensitivity of biosensor. [ABSTRACT FROM AUTHOR]

A novel signal on-off type photoelectrochemical (PEC) biosensing system was designed for sensitive detection of carcinoembryonic antigen (CEA) based on tin disulfide nanosheets loaded on reduced graphene cxide (SnS 2 -GR) as the photoactive material and gold nanoparticles coated on reduced graphene oxide-functionalized copper sulfide (Au@CuS-GR) for signal amplification. It's the first time for SnS 2 -GR was exploited as a sensing matrix. Here, the photocurrent signals of SnS 2 were amplified attributed to the sensitization effect of graphene. As signal amplifier, Au@CuS-GR could quench the photocurrents of SnS 2 -GR not only through the p-n type semiconductor quenching effect as well as the steric hindrance effect, but also as peroxidase mimetics to catalyze the oxidation of 4-Chloro-1-naphthol (4-CN) to produce insoluble product on the electrode surface. Based on the multiple signal amplification ability of Au@CuS-GR, CEA was detected sensitively with a linear range from 0.1 pg mL−1 to 10 ng mL−1 and limit of detection down to 59.9 fg mL−1 (S/N = 3). Meanwhile, the PEC biosensor displayed excellent performance in the assay of human serum sample, showing good application prospects for various target analysis. • This is the first time that SnS 2 -GR and Au@CuS-GR was used to constructed PEC biosensor. • Au@CuS-GR had several quenching effects on the photocurrent of SnS 2 -GR/ITO. • The PEC biosensor showed a low detection limit of 0.0559 pg mL−1 for CEA.. [ABSTRACT FROM AUTHOR]