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The easy and rapid spread of bacterial contamination and the risk it poses to human health makes evident the need for analytical methods alternative to conventional time-consuming laboratory-based techniques for bacterial detection. To tackle this demand, biosensors based on isothermal DNA amplification methods have emerged, which avoid the need for thermal cycling, thus facilitating their integration into small and low-cost devices for in situ monitoring. This review focuses on the breakthroughs made on biosensors based on isothermal amplification methods for the detection of bacteria in the field of food safety and environmental monitoring. Optical and electrochemical biosensors based on loop mediated isothermal amplification (LAMP), rolling circle amplification (RCA), recombinase polymerase amplification (RPA), helicase dependent amplification (HDA), strand displacement amplification (SDA), and isothermal strand displacement polymerisation (ISDPR) are described, and an overview of their current advantages and limitations is provided. Although further efforts are required to harness the potential of these emerging analytical techniques, the coalescence of the different isothermal amplification techniques with the wide variety of biosensing detection strategies provides multiple possibilities for the efficient detection of bacteria far beyond the laboratory bench.

Isothermal amplification (IA) is a nucleic acid amplification technology (NAAT) that has contributed significantly to the healthcare system. The combination of NAAT with a suitable detection platform resulted in higher sensitivity, specificity, and rapid disease diagnosis. Traditional NAAT, such as polymerase chain reaction (PCR), is widely applied in the general healthcare system but is rarely accessed in resource-limited hospitals. Some IA methods provide a rapid, sensitive, specific, and simple method for disease diagnosis. However, not all IA techniques have been regularly used in clinical applications because different biomarkers and sample types affect either the enzyme in the IA system or sample preparation. This review focuses on the application of some IA techniques that have been applied in the medical field and have the potential for use at points of care.

Nucleic acid (DNA and RNA) detection and quantification methods play vital roles in molecular biology. With the development of molecular biology, isothermal amplification of DNA/RNA, as a new molecular biology technology, can be amplified under isothermal condition, it has the advantages of high sensitivity, high specificity, and high efficiency, and has been applied in various fields of biotechnology, including disease diagnosis, pathogen detection, food hygiene and safety detection and so on. This paper introduces the progress of isothermal amplification technology, including rolling circle amplification (RCA), nucleic acid sequence-dependent amplification (NASBA), strand displacement amplification (SDA), loop-mediated isothermal amplification (LAMP), helicase-dependent amplification (HDA), recombinase polymerase amplification (RPA), cross-priming amplification (CPA), and its principle, advantages and disadvantages, and application development are briefly summarized.

Arctic amplification (AA)—referring to the enhancement of near-surface air temperature change over the Arctic relative to lower latitudes—is a prominent feature of climate change with important impacts on human and natural systems. In this review, we synthesize current understanding of the underlying physical mechanisms that can give rise to AA. These mechanisms include both local feedbacks and changes in poleward energy transport. Temperature and sea ice-related feedbacks are especially important for AA, since they are significantly more positive over the Arctic than at lower latitudes. Changes in energy transport by the atmosphere and ocean can also contribute to AA. These energy transport changes are tightly coupled with local feedbacks, and thus their respective contributions to AA should not be considered in isolation. It is here emphasized that the feedbacks and energy transport changes that give rise to AA are sensitively dependent on the state of the climate system itself. This implies that changes in the climate state will lead to changes in the strength of AA, with implications for past and future climate change.

Loop-mediated isothermal amplification (LAMP), a newly developed gene amplification method, combines rapidity, simplicity, and high specificity. Several tests have been developed based on this method, and simplicity is maintained throughout all steps, from extraction of nucleic acids to detection of amplification. In the LAMP reaction, samples are amplified at a fixed temperature through a repetition of two types of elongation reactions occurring at the loop regions: self-elongation of templates from the stem loop structure formed at the 3′-terminal and the binding and elongation of new primers to the loop region. The LAMP reaction has a wide range of possible applications, including point-of-care testing, genetic testing in resource-poor settings (such as in developing countries), and rapid testing of food products and environmental samples.

The livestock industry has been deeply affected by African swine fever virus (ASFV) and Capripoxvirus (CaPV), which caused an enormous economic damage. It is emergent to develop a reliable detection method. Here, we developed a rapid, ultra-sensitive, and one-pot DNA detection method combining recombinase polymerase amplification (RPA) and CRISPR/Cas12a for ASFV and CaPV, named one-pot-RPA-Cas12a (OpRCas) platform. It had the virtue of both RPA and CRISPR/Cas12a, such as high amplification efficiency, constant temperature reaction, and strict target selectivity, which made diagnosis simplified, accurate and easy to be operated without expensive equipment. Meanwhile, the reagents of RPA and CRISPR/Cas12a were added to the lid and bottom of tube in one go, which overcame the incompatibility of two reactions and aerosol contamination. To save cost, we only need a quarter of the amount of regular RPA per reaction which is enough to achieve clinical diagnosis. The OpRCas platform was 10 to 100 times more sensitive than qPCR; the limit of detection (LOD) was as low as 1.2 × 10 −6  ng/µL (3.07 copies/µL by ddPCR) of ASFV and 7.7 × 10 −5  ng/µL (1.02 copies/µL by ddPCR) of CaPV with the portable fluorometer in 40 min. In addition, the OpRCas platform combined with the lateral flow assay (LFA) strip to suit for point-of-care (POC) testing. It showed 93.3% consistency with qPCR for clinical sample analysis. Results prove that OpRCas platform is an easy-handling, ultra-sensitive, and rapid to achieve ASFV and CaPV POC testing. Key points • The platform realizes one-pot reaction of RPA and Cas12a. • Sensitivity is 100 times more than qPCR. • Three output modes are suitable to be used to quantitative test or POC testing.

This paper demonstrates a 2-4 GHz wideband power amplifier (WPA) using Cree 10 W GaN HEMT CGH40010. Also a novel process to find the optimum impedances is presented, with which the gain flatness can be taken into account. A compact PCB has been fabricated and tested with continuous waves at 20 dBm and 28 dBm input power level. From the measured results, at low power level, the gain is 13.1 dB-14.1 dB across 2.0-3.9 GHz and 12.3-14.1 dB across 2.0-4.0 GHz. For large signals, power gain is 11.1 dB-12.6 dB with power-added efficiency 36.5%-53.4% while output power is around 40 dBm. Gain flatness keeps less than 1 dB beyond 95% of the band. For a 5 MHz WCDMA signal, the adjacent channel leakage ratio of the WPA with digital predistortion reaches -45.3 dBc with an average drain efficiency of 46.7%.

A helix travelling-wave tube for 825 GHz has been designed and its broadband amplification performance has been demonstrated with 3D particle-in-simulations. The design utilises a helix slow-wave structure with a square form and input/output couplers based on a transition from the helix to a coplanar waveguide and further to a rectangular waveguide with a through-substrate post coupler. A simulated small-signal gain of 18.3 dB with an output power of over 25 dBm at 1 dB compression point and a 3 dB instantaneous bandwidth of 8% have been obtained. [PUBLICATION ABSTRACT]

A vector-sum phase shifter that provides 90° phase control with a positive signal gain is successfully demonstrated at WR-3 band. The integrated circuit consists of input and output microstrip power dividers and two InP DHBT amplifiers with a 300 GHz gain of 14.8 dB. The measurements on a fabricated phase shifter show offset phases of - 46°, - 22°, 0°, 25°, 57° and signal gain of 7.7 to 10.1 dB at 300 GHz. [PUBLICATION ABSTRACT]