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African swine fever virus (ASFV) causes hemorrhagic infectious disease in pigs with a fatality rate of nearly 100%. In this study, we developed a visual strand exchange amplification detection assay for ASFV. In the presence of ASFV, DNA amplification products containing multimeric G-quadruplex sequences were amplified by strand exchange amplification. These G-quadruplexes, assembled with hemin to form DNAzyme, displayed enhanced significant "turned-on" colorimetric signals to indicate detection results. The results showed that dimeric DNAzyme had the best visualization effect. Under the optimal reaction parameters, there was a linear relationship between the absorbance of the reaction solution at 417 nm and the logarithm of ASFV concentration ranged from 1 × 10

Cronobacter sakazakii is an important opportunistic food-borne pathogen, and it can cause severe diseases with main symptoms including neonatal meningitis, necrotizing enterocolitis, and sepsis. For the achievement of practical and convenient detection of viable C. sakazakii, a simple and robust strategy based on the cascade signal amplification of RT-PCR triggered G-quadruplex DNAzyme catalyzed reaction was firstly used to develop an effective and sensitive DNAzyme electrochemical assay. Without viable C. sakazakii in the samples there are no RT-PCR and DNAzyme products, which can cause a weak electrochemical response. Once viable C. sakazakii exists in the samples, an obvious enhancement of the electrochemical response can be achieved after the target signal is amplified by RT-PCR and the resulting DNAzyme, which catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 with the assistance of the cofactor hemin. Our novel assay can be performed in a range of 2.4 × 107 CFU mL-1 to 3.84 × 104 CFU mL-1 (R2 = 0.9863), with a detection limit of 5.01 × 102 CFU mL-1. Through the assay of 15 real samples, electrochemical detection assay provided the same results as conventional detection methods. Therefore, detection of viable C. sakazakii based on G-quadruplex DNAzyme electrochemical assay with RT-PCR demonstrates the significant advantages of high sensitivity, low cost and simple manipulation over existing approaches and offers an opportunity for potential application in pathogen detection.

Understanding the underlying mechanism of HBV maturation and subviral particle production is critical to control HBV infection and develop new antiviral strategies. Here, we demonstrate that deoxycholic acid (DCA) plays a central role in HBV production. HBV infection increased DCA levels, whereas elimination of DCA-producing microbiome decreased HBV viral load. DCA can bind to HBs antigen via LXXLL motif at TM1 and TM2 region to regulate HBs-HBc interaction and the production of mature HBV. Plasma DCA levels from patients undergoing antiviral therapy were significantly higher in those with positive HBV viral load. These results suggest that intestinal DCA-producing microbiome can affect the efficiency of antiviral therapy and provide a potential novel strategy for HBV antiviral therapy.One Sentence SummaryWe demonstrate that DCA-promoted HBs-HBc interaction and contributes to HBV maturation.

Chloramphenicol (CAP) is a kind of broad-spectrum antibiotic, which has been forbidden in food by most countries because of its side effects. In this study, a simple and low-cost biosensor for CAP detection in food was developed. The biosensor consisted of an aptamer specific to CAP and a pair of split probes that could self-assemble as DNAzyme. The detection result could be identified by the naked eye and the visual limit was 10 nM CAP. The absorbance of final reaction products at 417 nm had a linear relationship with the logarithm of the CAP concentration in a range from 10 to 200 nM, and the limit of detection was 87.3 pM. The visual analysis by imageJ also showed a linear detection range between 25 and 200 nM. The entire detection procedure could be completed in about 1.5 h at a cost of about 0.16 dollars per reaction. We believe that the biosensor shows great potential in the rapid and sensitive detection of CAP in food.

Listeria monocytogenes is a kind of foodborne pathogen, which can cause meningitis, septicemia, gastroenteritis, and abortion with a fatality rate of up to 30%. Rapid, sensitive, and convenient detection of L. monocytogenes in food is an important strategy for controlling contamination and infection. In this study, an enhanced visual detection assay for L. monocytogenes based on an isothermal amplified peroxidase-mimicking catalytic beacon was developed. When L. monocytogenes existed, G-quadruplex sequences were amplified together with targeted gene sequence by polymerase spiral reaction (PSR). G-quadruplex adequately formed DNAzyme with hemin to have an enhanced peroxidase-like bioactivity with help of Nb. BbvCI nicking endonuclease, which could display significant colorimetric signals for indicating positive results qualitatively. The sensitivity test results determined that our assay enabled the quantitative detection of L. monocytogenes ranging from 10 to 105 CFU mL−1, as well as had a detection limit of 3.1 CFU mL−1, which was lower than previous visual detection assays for L. monocytogenes. Besides, it was notable that this assay could detect L. monocytogenes with the concentration of 2.0 lg CFU/g in artificially contaminated pork samples within about 4 h, with the advantages of high sensitivity, simple operation, and good visual signal output. We believed the improved visual detection assay based on isothermal amplified peroxidase-mimicking catalytic beacon showed great potential for food safety analysis.

Cronobacter sakazakii is a typical food-borne bacterium that causes clinical symptoms including necrotizing enterocolitis, bacteremia, and meningitis with a mortality rate of 40 %–80 %. In this study, a pair of split G-rich DNA probes was assembled into the DNAzyme capable of mimicking peroxidase. The assembly was utilized to provide a simple, low-cost, highly specific, and sensitive method for rapid detection of viable C. sakazakii. In the absence of viable C. sakazakii, the two split G-rich DNA probes formed DNAzyme, mimicked the activity of peroxidase and displayed colorimetric signals to indicate detection results. In the presence of viable C. sakazakii, specific recognition by the aptamer results in the destruction of the DNAzyme-aptamer complex, and subsequently the colorimetric signal is “turned-off” due to the decrease in DNAzyme bioactivity. Under the optimal reaction conditions, there is a linear relationship between absorption intensity at 418 nm and logarithmic concentration of C. sakazakii in the range of 2–1200 CFU/mL (R2 = 0.9839), with a detection limit of 1.2 CFU/mL. This is the highest sensitivity ever reported for viable C. sakazakii detection. Artificially contaminated samples were assayed by this novel sensor, and numerous advantages were discovered, including ultra-low sensitivity, low-cost, simple operation, and good performance, compared to existing methods. We believe the DNAzyme shows great potential for food safety applications.