Escherichia coli O157:H7 has been reported as an important pathogenic bacteria causing serious infection and economic loss. However, detection of Escherichia coli O157:H7 needs improvement, given its current complexity and sensitivity. Herein, we attempt to build a fluorescence sensing method to detect Escherichia coli O157:H7 with easy operation and high efficiency. The target virulence gene sequences are recognized and cleaved by the CRISPR-Cas9 system, and trigger strand displacement amplification and rolling circle amplification. After amplification reactions, massive products can hybridize with the probes, the fluorescence of which are quenched based on a metal–organic framework platform, leading to the fluorescence recovery at typical excitation/emission wavelengths of 480/518 nm. This method exhibits high sensitivity with the detection limit at 4.0 × 101 CFU mL–1 and a wide range from 1.3 × 102 CFU mL–1 to 6.5 × 104 CFU mL–1. Meanwhile, this assay also shows significant specificity and applies to practical samples with high accuracy. Therefore, our method would have great potential application in bacterial detection, food safety monitoring, or clinical diagnostics.

A novel, sensitive chemiluminescence (CL) immunoassay for Escherichia coli O157:H7 detection with signal dual-amplification using glucose oxidase (GOx) and laccase was investigated. The method was based on the characterization of a luminol-H2O2-laccase reaction. Compared with the horseradish peroxidase-based biosensor, laccase exhibited high catalytic activity in strong alkaline medium, which was compatible with the luminol system. The capture antibody was immobilized onto the magnetic bead (MB) surfaces. The detection antibody was linked with GOx through biotin-avidin recognition. Accordingly, the bioconjugation of MB-caputure antibody- E. coli O157:H7-detection antibody-GOx catalyzed the substrate glucose, thereby generating H2O2. E. coli O157:H7 was then detected by measuring the CL intensity after H2O2 formation. Under optimal conditions, the calibration plot obtained for E. coli O157:H7 was approximately linear from 4.3 × 10(3) colony-forming unit (CFU) mL(-1) to 4.3 × 10(5) CFU mL(-1), and the total assay time was <2.0 h without any enrichment. The limit of detection for the assay was 1.2 × 10(3) CFU mL(-1) (3σ), which was considerably lower than that of enzyme-linked immunosorbent assay method (1.0 × 10(5) CFU mL(-1)) (3σ). A series of repeatability measurements of using 1.7 × 10(4) CFU mL(-1) E. coli O157:H7 exhibited reproducible results with a relative standard deviation (RSD) of 3.5% (n = 11). Moreover, the proposed method was successfully used to detect E. coli O157:H7 in synthetic samples (spring water, apple juice, and skim milk), which indicated its potential practical application. This protocol can be applied in various fields of study.

[1] Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three-dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler-mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group-velocity cone angle for the whistler wave regime of reconnection.

Supersaturated NaClO4 aerosols have been studied using a Fourier transform infrared (FTIR) spectrometer coupled with an aerosol flow tube (AFT). Compared with previous Raman results, the water O-H stretching envelope in the supersaturated solutions of NaClO4 aerosols was more structured in response to changing RH, revealing at the same time the existence of water monomers weakly hydrogen-bonded with ClO4- at extremely high concentrations. Due to enhanced ion interactions in the supersaturated solutions of NaClO4 aerosols, the formation of contact ion pairs (CIPs) could be observed without component decomposition for the nondegenerate nu1 band of ClO4-, and the degenerate nu3 band of ClO4- was successfully related to the formation of CIPs in NaClO4 solutions. Based on these observations, a new mechanism featured by the attack of ClO4- upon hydrated Na+ for CIPs formation in the supersaturated solutions of NaClO4 aerosols was further proposed. The anhydrous NaClO4, characterized by the upper limit deliquescence relative humidity (DRH) of approximately 43% and the disappearance of the nu1 band of ClO4- in the infrared spectra, was observed to form on the silicon windows at low RHs.

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