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An immobilization-free electrochemical impedance biosensor for microRNA detection was developed in this work, which was based on both the duplex-specific nuclease assisted target recycling (DSNATR) and capture probes (Cps) enriched from the solution to electrode surface via magnetic beads (MBs). In the absence of miR-21, Cps cannot be hydrolyzed due to the low activity of duplex-specific nuclease (DSN) against ssDNA. Therefore, the intact Cps could be attached to the surface of magnetic glass carbon electrode (MGCE), resulting in a compact negatively charged layer as well as a large charge-transfer resistance. While in the presence of miR-21, it hybridized with Cp to form a DNA–RNA heteroduplex. Due to the considerable cleavage preference for DNA in DNA–RNA hybrids, DSN hydrolyzed the target-binding part of the Cp while liberating the intact miR-21 to hybridize with a new Cp and initiate the second cycle of hydrolysis. In this way, a single miR-21 was able to trigger the permanent hydrolysis of multiple Cps. Finally, all Cps were digested. Thus, the negatively charged layer could not be formed, resulting in a small charge-transfer resistance. By employing the above strategy, the proposed biosensor achieved ultrahigh sensitivity toward miR-21 with a detection limit of 60 aM. Meanwhile, the method showed little cross-hybridization among the closely related miRNA family members even at the single-base-mismatched level. Successful attempts were made in applying the approach to detect miR-21 in human serum samples of breast cancer patients. [ABSTRACT FROM AUTHOR]

The simultaneous detection of various mycotoxins is indispensable for food safety since the agricultural products are often contaminated by multiple mycotoxins. Herein, we report a signal-enhancement fluorescent aptasensor based on DNA-scaffolded silver nanoculsters (DNA/AgNCs) for simultaneous detection of Ochratoxin A (OTA) and Aflatoxin B 1 (AFB 1 ). The OTA aptamer (Ap1) and the AFB 1 aptamer (Ap2) immobilized on magnetic beads surface hybridize with signal probe1 (Sp1) and signal probe2 (Sp2), respectively. In the presence of these two mycotoxins, the single-strand Sps are released after Aps binding with mycotoxins due to the higher stability of mycotoxin-Ap. Through the magnetic separation, the Sps in the supernatant liquid are acted as the corresponding scaffolds to synthesize AgNCs with different photoluminescence emission bands. Intriguingly, we find that the fluorescence intensity is obviously increased after adding Zn(II)-ion into the system, leading to a linear range from 0.001 ng/mL to 0.05 ng/mL both for OTA and AFB 1 with the detection limit of 0.2 pg/mL for OTA and 0.3 pg/mL for AFB 1 . The proposed fluorescent aptasensor shows excellent performance towards the analytical application in real samples, providing a new model for the simultaneous detection for other mycotoxins by simple change of the aptamer. [ABSTRACT FROM AUTHOR]

• Differences in major chemical constituents existed in different dark teas. • Dark tea promoted gastrointestinal transit in normal mice. • Dark tea restored antibiotic-induced dysbiosis of intestinal microflora. Processing of dark tea varieties, such as Fu brick tea, Liupao tea, Qianliang tea, and Qing brick tea, includes solid-state fermentation involving microorganisms. In this study, we analyzed the major chemical constituents of dark tea extracts and evaluated their modulatory effect on the gastrointestinal function in normal mice, including the improvement of gastrointestinal transit and intestinal microbial, as well as the attenuation of intestinal microbial dysbiosis and intestinal pathological damage, and the adjustment of immune function in antibiotic-treated mice. Substantial differences in major chemical constituents, including total polyphenols, total organic acids, water extract content, 18 free amino acids, gallic acid, and six tea catechins, were observed among Fu brick tea, Qianliang tea, Qing brick tea, and Liupao tea extracts. Extracts from the four dark tea varieties significantly promoted gastrointestinal transit and colonization of beneficial Bifidobacterium and Lactobacillus , and inhibited the growth of harmful Escherichia coli and Enterococcus in normal mice. In addition, Qianliang tea, Qing brick tea, and Liupao tea extracts significantly accelerated the reversal of the ampicillin sodium-induced pathological damage in the ileum, intestinal bacterial dysbiosis (Bifidobacterium , Lactobacillus , E. coli , and Enterococcus), and low immunity. [ABSTRACT FROM AUTHOR]