Recent progress on rapid diagnosis of COVID-19 by point-of-care testing platforms.

The outbreak of COVID-19 has drawn great attention around the world. SARS-CoV-2 is a highly infectious virus with occult transmission by many mutations and a long incubation period. In particular, the emergence of asymptomatic infections has made the epidemic even more severe. Therefore, early diagnosis and timely management of suspected cases are essential measures to control the spread of the virus. Developing simple, portable, and accurate diagnostic techniques for SARS-CoV-2 is the key to epidemic prevention. The advantages of point-of-care testing technology make it play an increasingly important role in viral detection and screening. This review summarizes the point-of-care testing platforms developed by nucleic acid detection, immunological detection, and nanomaterial-based biosensors detection. Furthermore, this paper provides a prospect for designing future highly accurate, cheap, and convenient SARS-CoV-2 diagnostic technology.

Photo-Enhanced Chemo-Transistor Platform for Ultrasensitive Assay of Small Molecules.

Compared with traditional assay techniques, field-effect transistors (FETs) have advantages such as fast response, high sensitivity, being label-free, and point-of-care detection, while lacking generality to detect a wide range of small molecules since most of them are electrically neutral with a weak doping effect. Here, we demonstrate a photo-enhanced chemo-transistor platform based on a synergistic photo-chemical gating effect in order to overcome the aforementioned limitation. Under light irradiation, accumulated photoelectrons generated from covalent organic frameworks offer a photo-gating modulation, amplifying the response to small molecule adsorption including methylglyoxal, p-nitroaniline, nitrobenzene, aniline, and glyoxal when measuring the photocurrent. We perform testing in buffer, artificial urine, sweat, saliva, and diabetic mouse serum. The limit of detection is down to 10-19 M methylglyoxal, about 5 orders of magnitude lower than existing assay technologies. This work develops a photo-enhanced FET platform to detect small molecules or other neutral species with enhanced sensitivity for applications in fields such as biochemical research, health monitoring, and disease diagnosis.

Self-Expanding Molten Salt-Driven Growth of Patterned Transition-Metal Dichalcogenide Crystals.

Transition-metal dichalcogenides (TMDs) have been considered potential materials for the next generation of semiconductors. Realizing controllable growth of TMD crystals is a prerequisite for their future applications, which remains challenging. Here, we reveal a new mechanism of self-expanding molten salt-driven growth for a salt-assisted method and achieve the patterned growth of TMD single-crystal arrays with a size of hundreds of micrometers. Time-of-flight secondary ion mass spectroscopy and other spectroscopy characterizations identify the component of the molten salt solution. Microscopic characterizations reveal the existence of salt solution as an interlayer between a TMD monolayer and the silicon substrate as well as particles along the crystal edge. The edged salt solution serves as a self-expanding liquid substrate, which confines the reactive sites to the localized liquid surface, thus avoiding random nucleation. The surface reaction also assures monolayer crystal formation due to self-limiting growth. Besides, the liquid substrate affords sources and spreads itself continuously owing to the nonwetting effect on TMD crystals, thereby facilitating the continuous extension of the TMD monolayer. This work provides novel insights into the controllable synthesis of TMD monolayers and paves the way for the fabrication of TMD-based integrated functional devices.