Advances in Synthetic-Biology-Based Whole-Cell Biosensors: Principles, Genetic Modules, and Applications in Food Safety

A whole-cell biosensor based on synthetic biology provides a promising new method for the on-site detection of food contaminants. The basic components of whole-cell biosensors include the sensing elements, such as transcription factors and riboswitches, and reporting elements, such as fluorescence, gas, etc. The sensing and reporting elements are coupled through gene expression regulation to form a simple gene circuit for the detection of target substances. Additionally, a more complex gene circuit can involve other functional elements or modules such as signal amplification, multiple detection, and delay reporting. With the help of synthetic biology, whole-cell biosensors are becoming more versatile and integrated, that is, integrating pre-detection sample processing, detection processes, and post-detection signal calculation and storage processes into cells. Due to the relative stability of the intracellular environment, whole-cell biosensors are highly resistant to interference without the need of complex sample preprocessing. Due to the reproduction of chassis cells, whole-cell biosensors replicate all elements automatically without the need for purification processing. Therefore, whole-cell biosensors are easy to operate and simple to produce. Based on the above advantages, whole-cell biosensors are more suitable for on-site detection than other rapid detection methods. Whole-cell biosensors have been applied in various forms such as test strips and kits, with the latest reported forms being wearable devices such as masks, hand rings, and clothing. This paper examines the composition, construction methods, and types of the fundamental components of synthetic biological whole-cell biosensors. We also introduce the prospect and development trend of whole-cell biosensors in commercial applications

Radiolysis of aqueous solution containing copper ions

Copper and copper alloys are widely used in the field of nuclear materials. The effects of aqueous solutions that have undergone copper ion radiolysis on the generation of H2O2, O2, and H2 must be considered for material corrosion control and hydrogen explosion risk assessment. In this study, a γ-radiolysis experiment of an aqueous solution containing copper ions was conducted to explore the effects of different absorbed doses, absorption dose rates, and Cu2+ concentrations on the generation of H2O2, O2, and H2. The results showed that with an increase in the absorbed dose (0-1.80 kGy), the concentrations of H2O2 and H2(g) firstly increased and then tended to stabilize under steady-state concentrations of 5.41×10-6 and 7.91×10-5 mol/L, respectively, whereas the concentration of O2(g) remained at 9.04×10-4 mol/L. The presence of Cu2+ enhanced the equilibrium concentrations of H2 and H2O2 by one and two orders of magnitude, respectively, which in turn promoted the generation of H2O2 and H2; however, it had a negligible effect on O2 generation. The equilibrium concentrations of H2O2 and H2 increased with an increase in the absorption dose rate. Specifically, when the absorption dose rate was increased from 1.40 to 46.93 Gy/min, the equilibrium concentrations of H2O2 and H2 increased from 4.56×10-6 and 1.78×10-5 mol/L to 2.46×10-5 and 3.81×10-4 mol/L, respectively, whereas O2 remained essentially unaffected within this absorption dose rate range. In addition, based on the kinetics of water radiolysis and two-film theory of gas-liquid mass transfer, we constructed a calculation model for the radiolysis of aqueous solutions containing copper ions. Compared with the experimental data, the absolute values of the normalized mean bias in the simulation results were mostly between 1% and 7%, with a maximum of approximately 24%, thereby demonstrating the effectiveness and correctness of the calculation model. Accordingly, the model was used to calculate the radiolytic behavior of an aqueous solution containing copper ions under C6+ ion irradiation, and the simulation results matched well with the experimental data reported in the literature, indicating that the model can be expanded to other applications

γ-Radiolysis of the aqueous ammonia solution saturated by N2

In some reactors, ammonia and its radiolytic product (H2) are used to scavenge the oxidizing species (H2O2, O2, and •OH). A reducing chemical environment is thus created and the pH of the coolant is regulated simultaneously. In the present study, the radiolytic behaviors of deoxygenated ammonia solution were studied in the γ-ray field. The impacts of N2 pressure, gas-liquid volume ratio, and temperature on deoxygenated ammonia solution radiolysis were investigated. The pH and the concentrations of residual ammonia, H2, and nitrogen oxides (NO2- and NO3-) were analyzed. The results revealed that the variation of N2 pressure (0.5~5.0 MPa) and gas-liquid volume ratio had no influence on the concentrations of residual ammonia and nitrogen oxides. NO2- and NO3- concentrations were approximately 1 mg/L at room temperature when the absorbed dose was 28.8 kGy. However, the apparent concentration of H2 significantly decreased with the N2 pressure and gas-liquid volume ratio. The loss fraction of ammonia considerably declined from 26.5% to 8.4% when the temperature increased from 25 to 200 ℃, demonstrating that the radiolysis of ammonia was suppressed at the elevated temperature. However, the concentrations of NO2- and NO3- increased to 34 and 3 times, respectively, at 200 ℃ compared to those at 25 ℃. In addition, a radiolysis model of ammonia-containing coolant was established in the present study. The maximum relative error between experimental data and calculation results at any temperature was 4.1%. The model was thereafter used to calculate residual ammonia concentration with the absorbed dose under different initial ammonia concentrations. The results revealed that it was necessary to replenish ammonia regularly when using it alone to inhibit oxidizing species

Diagnosing and tracing the pathogens of infantile infectious diarrhea by amplicon sequencing

Abstract Background Metagenomic methods have been widely applied to study the relationship between gut microbiota and human health. To test whether metagenomic amplicon sequencing could be an effective method to diagnose and trace the pathogens of infantile infectious diarrhea, the fecal samples of 20 diarrheic and 13 healthy infants were collected. After 16S rDNA amplicon sequencing, diversity analyses were carried out. The relationship between the pathogens of the gut microbiota and geography of patients was analyzed. Results The diversity of the gut microbiota in diarrheic infants was significantly lower than that of the gut microbiota in healthy ones and that, the composition of gut microbiota in the diarrheic group was significantly different than that of the gut microbiota in the healthy group. The results also indicated that in some of the patients, the amounts of Escherichia coli were significantly increased in the diarrheic infants, which was in agreement with the result of the qPCR analysis. Using a geographical map, we found some patterns between pathogen source and geographical location. This is helpful for an early warning of the disease. Conclusions The method of using high-throughput DNA sequencing and a comprehensive and deep data analysis can be a new strategy to detect and trace pathogens in infantile infectious diarrhea. Trial registration Diagnosing and tracing the pathogens of infantile infectious diarrhea by amplicon sequencing, ChiCTR-DDD-1701088, Registered 16 March 2017-Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=1847