Threaded 3D microfluidic paper analytical device-based ratiometric fluorescent sensor for background-free and visual detection of organophosphorus pesticides.

With the increasing concerns of food safety and environmental protection, it is desirable to develop reliable, effective, and portable sensors for detection of organophosphorus pesticides (OPs). Here, a cascade reaction system integrated with threaded 3D microfluidic paper analytical device (3D µPAD) was firstly developed for background-free and visual detection of OPs in agricultural samples. Butyrylcholinesterase (BChE) hydrolyzed acetylcholine into thiocholine (TCh), which reduced MnO2 nanosheets into Mn2+. With addition of OPs, BChE activity was irreversibly inhibited, and the generation of TCh and the reduction of MnO2 nanosheets were prevented. Then the remaining MnO2 nanosheets oxidized o-phenylenediamine into 2,3-diaminophenazine with yellow-emission fluorescence, which quenched the fluorescence intensity of red-emission carbon dots (RCDs) via inner-filter effect. Based on above mechanism, a ratiometric fluorescent system was established for OPs detection. Threaded 3D µPAD consisted of 4 layers, which allowed to load and/or add reagents to trigger the cascade reaction system for OPs detection. The fluorescent images presented distinguishable color variations from red to yellow with dichlorvos concentrations ranging from 2.5 to 120 µg L-1, and the limit of detection was 1.0 µg L-1. In the practical samples testing, threaded 3D µPAD can eliminate background influence on fluorescent signal for OPs detection. Threaded 3D µPAD integrated with ratiometric sensing platform has merits of accuracy response, facile operation, and background-free detection, which supplies a new alternative approach for on-site pesticide detection.

A dual-emission carbon dots-based nonenzymatic fluorescent sensing platform for simultaneous detection of parathion-methyl and glyphosate.

Simultaneous and high-performance detection of pesticides is still a considerable challenge and urgent need. Herein, a dual-emission carbon dots (CDs)-based nonenzymatic fluorescent sensing platform has been developed, which shows excellent sensitivity and selectivity in simultaneously detecting parathion-methyl (MP) and glyphosate. CDs with emissions at 440 nm (bCDs) and 660 nm (rCDs) were prepared by hydrothermal treatment of mulberry leaves and sodium hydroxide. bCDs response to hydrolyzed MP via inner filter effect, while rCDs sense glyphosate with the aid of Cu2+ by static quenching effect. Excellent linear correlations were found for MP (0.3-65.0 µM) and glyphosate (1.0-110.0 µM) with limits of detection at 0.14 and 0.60 µM. Notably, the presented dual-channel strategy was successfully applied in simultaneously detecting MP and glyphosate in food/herbal samples with acceptable recoveries, good precision, and high selectivity. Moreover, an ORlogicgatewas achieved for estimating food, herbal, or environmental safety.

A novel co-production of cadaverine and succinic acid based on a thermal switch system in recombinant Escherichia coli.

BACKGROUND: Polyamide (nylon) is an important material, which has aroused plenty of attention from all aspects. PA 5.4 is one kind of nylon with excellent property, which consists of cadaverine and succinic acid. Due to the environmental pollution, bio-production of cadaverine and succinic acid has been more attractive due to the less pollution and environmental friendliness. Microbes, like Escherichia coli, has been employed as cell factory to produce cadaverine and succinic acid. However, the accumulation of cadaverine will cause severe damage on cells resulting in inhibition on cell growth and cadaverine production. Herein, a novel two stage co-production of succinic acid and cadaverine was designed based on an efficient thermos-regulated switch to avoid the inhibitory brought by cadaverine. RESULTS: The fermentation process was divided into two phase, one for cell growth and lysine production and the other for cadaverine and succinic acid synthesis. The genes of ldhA and ackA were deleted to construct succinic acid pathway in cadaverine producer strain. Then, a thermal switch system based on pR/pL promoter and CI857 was established and optimized. The fermentation conditions were investigated that the optimal temperature for the first stage was determined as 33 â„ƒ and the optimal temperature for the second stage was 39 â„ƒ. Additionally, the time to shifting temperature was identified as the fermentation anaphase. For further enhance cadaverine and succinic acid production, a scale-up fermentation in 5 L bioreactor was operated. As a result, the titer, yield and productivity of cadaverine was 55.58 g/L, 0.38 g/g glucose and 1.74 g/(L·h), respectively. 28.39 g/L of succinic acid was also obtained with yield of 0.19 g/g glucose. CONCLUSION: The succinic acid metabolic pathway was constructed into cadaverine producer strain to realize the co-production of succinic acid and cadaverine. This study provided a novel craft for industrial co-production of cadaverine and succinic acid.

Weaving microscale wool ball-like hollow covalent organic polymers from nanorods for efficient adsorption and sensing.

Microscale covalent organic polymers with a unique 3D hollow wool ball-like morphology have been woven from 1D nanorods by a cascade emulsion strategy with a large surface area (284 m2 g-1), which showed great potential for simultaneous removal (Qmax, 358.15 mg g-1) and fluorescent detection (detection limit, 8.0 µg L-1) of bisphenol A.

Mathematical model of salt cavern leaching for gas storage in high-insoluble salt formations.

A mathematical model is established to predict the salt cavern development during leaching in high-insoluble salt formations. The salt-brine mass transfer rate is introduced, and the effects of the insoluble sediments on the development of the cavern are included. Considering the salt mass conservation in the cavern, the couple equations of the cavern shape, brine concentration and brine velocity are derived. According to the falling and accumulating rules of the insoluble particles, the governing equations of the insoluble sediments are deduced. A computer program using VC++ language is developed to obtain the numerical solution of these equations. To verify the proposed model, the leaching processes of two salt caverns of Jintan underground gas storage are simulated by the program, using the actual geological and technological parameters. The same simulation is performed by the current mainstream leaching software in China. The simulation results of the two programs are compared with the available field data. It shows that the proposed software is more accurate on the shape prediction of the cavern bottom and roof, which demonstrates the reliability and applicability of the model.