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A simple fluorescence biosensor is developed based on the enzyme-assisted cascade amplification strategy. The amplification system consists of a hairpin-structure DNA (H-DNA) and exonuclease III. The target DNA can hybridize with the H-DNA and initiate exonuclease III-assisted target recycling amplification to generate abundant G-rich DNA (G-DNA). One region of G-DNA is designed to possess the same sequence as target DNA. Thus, the G-DNA can also hybridize with H-DNA and initiate the digestion of H-DNA. The cascade strategy in this amplification system causes the concentration of G-DNA to grow exponentially. The fluorescence intensity of N-methylmesoporphyrin IX (NMM) is highly enhanced due to the formation of G-quadruplex configuration. Under optimal conditions, the cascade system could achieve an admirable sensitivity with a detection limit of 52 fM for HIV DNA, and guarantees a satisfactory specificity. Moreover, the cascade system could be implemented for other target DNA detections by substituting the recognition region of the H-DNA. In this way, a detection limit of 65 fM for HBV DNA could be achieved by the cascade system. The target DNA analysis in a real serum sample further indicates that this biosensor has potential for future application in clinical diagnosis. Graphical abstract A simple and label-free cascade amplification strategy is developed by exploiting hairpin DNA and EXO III for sensitive DNA detection.

Taking advantage of the homogeneous and heterogeneous electrochemical biosensors, a simple, sensitive, and selective electrochemical biosensor is constructed by combining entropy-driven amplification (EDA) with DNA walker. This electrochemical biosensor realizes the biorecognition and EDA operation in homogeneous solution, which is beneficial to improve the recognition and amplification efficiency. A two-leg DNA walker generated by EDA can walk on the surface of gold electrode for cleaving the immobilized substrate DNA and releasing the electroactive labels, giving rise to a significant decrease of the electrochemical signal. The immobilization of the electroactive labels ensures the reproducibility and reliability of the biosensor. The present cascade amplification assay can be applied to detect target DNA with a detection limit of 0.29 fM, and base mutations can be easily distinguished. Moreover, the proposed electrochemical biosensor shows a satisfactory performance for the detection of target DNA in human serum. Thus, the novel electrochemical biosensor holds promising potential for a future application in disease diagnosis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

DNA can be modified to function as a scaffold for the construction of a DNA nanomachine, which can then be used in analytical applications if the DNA nanomachine can be triggered by the presence of a diagnostic DNA or some other analyte. We herein propose a novel and powerful DNA nanomachine that can detect DNA via combining the tandem strand displacement reactions and a DNA walker. Three different DNA sensing platforms are described, where the whole DNA machine was constructed on a gold electrode (GE). This cascade multiple amplification strategy exhibited an excellent sensitivity. Under optimal conditions, the electrochemical sensor could achieve a detection limit of 36 fM with a linear range from 50 to 500 fM. In particular, the electrochemical sensor could easily distinguish the base mutations. More interestingly, the DNA nanomachine could be used to construct analog AND and OR logic gates. We demonstrate that electrochemical signals generated from the different input combinations can be used to distinguish multiple target DNAs. The practical applicability of the present biosensor is demonstrated by the detection of target DNA in human serum with satisfactory results, which holds great potential for a future application in clinical diagnosis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

• A simple sensing platform based on 3D DNA nanospheres was developed for miRNA-141 detection with an enzyme-free amplification strategy. • The DNA nanosphere constructed with high-ordered assembly of the ssDNA enhanced emission by 69 % compared to the monodisperse one. • The biosensing platform shows high selectivity and good sensitivity. • The biosensing platform can be used in human serum samples and potentially applied to early clinical diagnosis. Detection of microRNAs (miRNAs) by using precise and convenient biosensing methods is desired in biochemical study and early clinical diagnosis. We constructed an innovative programmed all-DNA biosensing platform by using homogeneous 3D DNA nanospheres as signaling reporter and entropy-driven enzyme-free amplification strategy to detect miRNA-141. The self-assembly 3D DNA nanosphere was obtained by the highly ordered aggregation of two kinds of single strand of DNA (ssDNA) labeled with 6-carboxyfluorescein (FAM) and two kinds of linker DNA strands in terms of Watson-Crick base pairing rule. The highly ordered aggregation of the ssDNA resulted in an enhancement of fluorescence signal by 69 % compared to that of monodisperse one, which significantly improved the sensitivity of the biosensor. Target microRNA triggered the release of bulk BHQ1-DNA from the quencher complex, leading to the fluorescence quenching of the DNA nanosphere. The present biosensing platform achieves a detection limit of 0.2 nM with a linear range from 0.4 nM to 4.0 nM. The results based on human serum samples indicate that the developed DNA biosensing platform could be potentially applied to early clinical diagnosis. [ABSTRACT FROM AUTHOR]