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A novel competitive aptasensor for thrombin detection is developed by using a tetrahedral DNA (T-DNA) probe and hybridization chain reaction (HCR) signal amplification. Sulfur and nitrogen co-doped reduced graphene oxide (SN-rGO) is firstly prepared by a simple reflux method and used for supporting substrate of biosensor. Then, T-DNA probe is modified on the electrode by Au-S bond and a competition is happened between target thrombin and the complementary DNA (cDNA) of aptamer. The aptamer binding to thrombin forms an aptamer-target conjugate and make the cDNA remained, and subsequently hybridizes with the vertical domain of T-DNA. Finally, the cDNAs trigger HCR, which results in a great current response by the catalysis of horseradish peroxidase to the hydrogen peroxide + hydroquinone system. For thrombin detection, the proposed biosensor shows a wide linearity range of 10 –13 –10 −8 M and a low detection limit of 11.6 fM (S/N = 3), which is hopeful to apply in biotechnology and clinical diagnosis. [ABSTRACT FROM AUTHOR]

MicroRNAs (MiRNAs) play multiple crucial regulating roles in cell which can regulate one third of protein-coding genes. MiRNAs participate in the developmental and physiological processes of human body, while their aberrant adjustment will be more likely to trigger diseases such as cancers, kidney disease, central nervous system diseases, cardiovascular diseases, diabetes, viral infections and so on. What's worse, for the detection of miRNAs, their small size, high sequence similarity, low abundance and difficult extraction from cells impose great challenges in the analysis. Hence, it's necessary to fabricate accurate and sensitive biosensing platform for miRNAs detection. Up to now, researchers have developed many signal-amplification strategies for miRNAs detection, including hybridization chain reaction, nuclease amplification, rolling circle amplification, catalyzed hairpin assembly amplification and nanomaterials based amplification. These methods are typical, feasible and frequently used. In this review, we retrospect recent advances in signal amplification strategies for detecting miRNAs and point out the pros and cons of them. Furthermore, further prospects and promising developments of the signal-amplification strategies for detecting miRNAs are proposed. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemical biosensor for detecting microRNAs is fabricated based on hollow molybdenum disulfide (MoS 2 ) microcubes. Duplex-specific nuclease, enzyme and electrochemical–chemical–chemical redox cycling are used for signal amplification. Hollow MoS 2 microcubes constructed by ultrathin nanosheets are synthesized by a facile template-assisted strategy and used as supporting substrate. For biosensor assembling, biotinylated ssDNA capture probes are first immobilized on Au nanoparticles (AuNPs)/MoS 2 modified electrode in order to combine with streptavidin-conjugated alkaline phosphatase (SA-ALP). When capture probes hybridize with miRNAs, duplex-specific nuclease cleaves the formative duplexes. At the moment, the biotin group strips from the electrode surface and SA-ALP is incapacitated to attach onto electrode. Then, ascorbic acids induce the electrochemical–chemical–chemical redox cycling to produce electrochemical response in the presence of ferrocene methanol and tris (2-carboxyethyl) phosphine. Under optimum conditions, the proposed biosensor shows a good linear relationship between the current variation and logarithm of the microRNAs concentration ranging from 0.1 fM to 0.1 pM with a detection limit of 0.086 fM (S/N=3). Furthermore, the biosensor is successfully applied to detect target miRNA-21 in human serum samples. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new chemiluminescent plant tissue-based biosensor for diamine detection was presented by employing sequential injection analysis (SIA), which facilitates precise fluidic handling and lower consumption of sample and reagents. Pea-seedling tissue acted as the molecular recognition element and was packed in a mini-PTFE column and further incorporated in the SIA system. The analysis of diamines, such as putrescine and cadaverine, is based on an enzymatic conversion which takes place in the plant tissue column to produce hydrogen peroxide. The formed hydrogen peroxide was detected by a chemiluminescence reaction involving luminol and Co2+. Under the optimal conditions, the linear calibration graphs were obtained within 0.2–80μM (putrescine) and 0.5–100μM (cadaverine). The detection limits of 0.03 and 0.06μM were achieved for putrescine and cadaverine, respectively, along with the relative standard deviations of 2.14% and 3.08% (n =11) and a sampling frequency of 40h−1. The present biosensor has been used for the analysis of diamine in fish samples with an acceptable accuracy. [Copyright &y& Elsevier]

An ultrasensitive electrochemical biosensor for microRNA (miRNA) is developed based on tungsten oxide-graphene composites coupling with catalyzed hairpin assembly target recycling and enzyme signal amplification. WO 3 -Gr is prepared by a simple hydrothermal method and then coupled with gold nanoparticles to act as a sensing platform. The thiol-terminated capture probe H1 is immobilized on electrode through Au–S interaction. In the presence of target miRNA, H1 opens its hairpin structure by hybridization with target miRNA. This hybridization can be displaced from the structure by another stable biotinylated hairpin DNA (H2), and target miRNA is released back to the sample solution for next cycle. Thus, a large amount of H1-H2 duplex is produced after the cyclic process. At this point, a lot of signal indicators streptavidin-conjugated alkaline phosphatase (SA-ALP) are immobilized on the electrode by the specific binding of avidin-biotin. Then, thousands of ascorbic acid, which is the enzymatic product of ALP, induces the electrochemical-chemical-chemical redox cycling to produce a strongly electrochemical response in the presence of ferrocene methanol and tris (2-carboxyethyl) phosphine. Under the optimal experimental conditions, the established biosensor can detect target miRNA down to 0.05 fM (S/N=3) with a linear range from 0.1 fM to 100 pM, and discriminate target miRNA from mismatched miRNA with a high selectivity. [ABSTRACT FROM AUTHOR]