The Application of Graphene Field-Effect Transistor Biosensors in COVID-19 Detection Technology: A Review.

Coronavirus disease 2019 (COVID-19) is a disease caused by the infectious agent of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). The primary method of diagnosing SARS-CoV-2 is nucleic acid detection, but this method requires specialized equipment and is time consuming. Therefore, a sensitive, simple, rapid, and low-cost diagnostic test is needed. Graphene field-effect transistor (GFET) biosensors have become the most promising diagnostic technology for detecting SARS-CoV-2 due to their advantages of high sensitivity, fast-detection speed, label-free operation, and low detection limit. This review mainly focus on three types of GFET biosensors to detect SARS-CoV-2. GFET biosensors can quickly identify SARS-CoV-2 within ultra-low detection limits. Finally, we will outline the pros and cons of the diagnostic approaches as well as future directions.

Fabrication and enhanced visible-light photocatalytic H2production of B-doped N-deficient g-C3N4/CdS Hybrids with robust 2D/2D hetero-interface interaction.

2D layered photocatalysts with proper electronic structure have sparked much attention in the field of visible-light photocatalysis for H2production. Herein, by simply calcining the mixture of ultrathin g-C3N4(CNN) and NaBH4, heteroatom B and N defect were simultaneously introduced into g-C3N4. The obtained modified g-C3N4(BDCNN) was further coupled with 2D flower-like CdS nanosheet. The optimal 2D/2D BDCNN/CdS-15% heterojunction behaved ideal photocatalytic activity for H2revolution by water splitting, and the highest H2revolution rate was as high as 1013.8µmol g-1h-1, which was 6.7 times, 2 times, and 5.8 times of the corresponding values of pristine CNN, BDCNN and CdS respectively. It was evidenced that the band structure of 2D/2D BDCNN/CdS-15% was well tuned for better visible-light adsorption and higher separation efficiency of photo-induced carriers for enhancing H2revolution performance. The achievement in this study provided informative principles for exploring g-C3N4based heterojunctions with higher H2-production performance.

Three-Component Synthesis of Dioxaphosphorane-Fused Diphosphacycles Exhibiting Unique Dynamic Fluorescence "On/Off" Properties.

Rigidly planar polycyclic phosphacycles featuring an internal dioxaphosphorane are promising photofunctional materials. However, the lack of efficient synthetic methods resulted in limited structural diversities which significantly hampered extensive study. Herein, we report a straightforward three-component synthesis of novel dioxaphosphorane-fused diphosphacycles with distinctive photophysical properties. Control experiments and theory calculations were performed to account for a plausible reaction mechanism. We also systematically investigated the structure-property relationships of these unprecedented platforms by combining experiments (X-ray analysis, optical and redox properties) and theoretical computations. Based on their unique structure and properties, a novel fluorescent switch for pH sensing was revealed by a dynamic ring-opening/ring-closing process.

Multi-response gelation based on the molecular assembly of Sudan I dye derivatives for phase selective gelators and chemosensors.

Sudan I dye-based smart low molecular weight gelators with/without a perfluoroalkyl group have been successfully synthesized and characterized by rheological measurements, scanning electron microscopy (SEM), IR, and NMR spectroscopies. The gelation behaviors in response to temperature, pH changes, metal cations, and UV-vis light irradiation are investigated. Compounds 1 and 2 could selectively sense the Cu2+ cation in the presence of other metal cations. Moreover, compound 2 with a perfluoroalkyl group shows phase selective gelation ability. This work also provides a valuable reference for exploiting photosensitive materials as chemosensors.

In situself-assembly fabrication of ultrathin sheet-like CuS modified g-C3N4heterojunction and its enhanced visible-light photocatalytic performance.

Photocatalysts with heterojunction structure have been widely used for organic degradation. In this study, CuS/g-C3N4heterojunction was formed byin situself-assembly via a simply hydrothermal method. A series of characterizations were applied to analyzing the morphology, structure, optical properties and photo-induced electron transfer of the samples. The effect of CuS mass ratio in the CuS/g-C3N4composite on methyl blue (10 mg l-1) degradation under visible-light illumination was discussed. When CuS mass ratio was 60%, CuS/g-C3N4behaved the highest photocatalytic efficiency which is 17 times higher than that of pure g-C3N4, and the optimal heterojunction exhibited promising photocatalytic stability as well. The synthesized CuS/g-C3N4with intimate contact and promising photocatalytic performance provides important implications on analogous researches on g-C3N4-based heterojunctions for photocatalytic applications.

Ultrasensitive and Regenerative Transistor Sensor Based on Dynamic Covalent Chemistry.

Field-effect transistor (FET) sensors require not only high sensitivity but also excellent regeneration ability before widespread applications are possible. Although some regenerative FETs have been reported, their lowest limit of detection (LoD) barely achieves 10-15 mol L-1. Here, we develop a graphene FET with a regenerative sensing interface based on dynamic covalent chemistry (DCvC). The LoD down to 5.0 × 10-20 mol L-1 remains even after 10 regenerative cycles, around 4-5 orders of magnitude lower than existing transistor sensors. Owing to its ultra-sensitivity, regeneration ability, and advantages such as simplicity, low cost, label-free and real-time response, the FET sensor based on DCvC is valuable in applications such as medical diagnosis, environment monitoring, etc.

Enhanced H2evolution performance by carbonized SiC/g-C3N4heterojunction under visible-light illumination.

In this study, carbonized silicon carbide/graphitic carbon nitride ((SiC/C)/g-C3N4) composites were fabricated via a facile calcination method. The optimal SiC/C/g-C3N4composite shows an excellent visible-light photocatalytic activity for water splitting, with the highest hydrogen evolution amount being 200.2µmol, which is four times higher than that of pure g-C3N4when triethanolamine and platinum (1.0 wt%) are used as the sacrificial agent and cocatalyst, respectively. With an intimate interface between SiC/C and g-C3N4, the energy band structure of g-C3N4was well engineered for photocatalytic H2production. This study provides a novel method for fabricating g-C3N4-based heterojunctions for application in environmental conservation.

Ultraprecise Antigen 10-in-1 Pool Testing by Multiantibodies Transistor Assay.

Effective screening of infectious diseases requires a fast, cheap, and population-scale testing. Antigen pool testing can increase the test rate and shorten the screening time, thus being a valuable approach for epidemic prevention and control. However, the overall percent agreement (OPA) with polymerase chain reaction (PCR) is one-half to three-quarters, hampering it from being a comprehensive method, especially pool testing, beyond the gold-standard PCR. Here, a multiantibodies transistor assay is developed for sensitive and highly precise antigen pool testing. The multiantibodies capture SARS-CoV-2 spike S1 proteins with different configurations, resulting in an antigen-binding affinity down to 0.34 fM. The limit of detection reaches 3.5 × 10-17 g mL-1SARS-CoV-2 spike S1 protein in artificial saliva, 4-5 orders of magnitude lower than existing transistor sensors. The testing of 60 nasopharyngeal swabs exhibits ∼100% OPA with PCR within an average diagnoses time of 38.9 s. Owing to its highly precise feature, a portable integrated platform is fabricated, which achieves 10-in-1 pooled screening for high testing throughput. This work solves the long-standing problem of antigen pool testing, enabling it to be a valuable tool in precise diagnoses and population-wide screening of COVID-19 or other epidemics in the future.

Total synthesis of a marine alkaloid--rigidin E.

In the present paper, we report an efficient total synthesis of a marine alkaloid, rigidin E. The key tetrasubstituted 2-amino-3-carboxamidepyrrole intermediate was synthesized by cascade Michael addition/intramolecular cyclization between N-(2-(4-(benzyloxy)phenyl)-2-oxoethyl)methanesulfonamide and 3-(4-(benzyloxy)phenyl)-2-cyano-N-methylacrylamide. Subsequent carbonylation with triphosgene catalyzed by I(2) and deprotection of benzyl groups afforded rigidin E in 21% overall yield. This strategy has the merits of metal-free reactions, low cost, mild reaction protocols, and easy access to diversity-oriented derivatives for potential structure-activity relationship investigation.

Synthesis of thioethers via metal-free reductive coupling of tosylhydrazones with thiols.

A metal-free procedure for the synthesis of thioethers is described via the base-promoted reductive coupling of tosylhydrazones with thiols through an insertion of a carbene into the S-H bond.

Silica gel-promoted tandem addition-cyclization reactions of 2-alkynylbenzenamines with isothiocyanates.

Tandem addition-cyclization reactions of 2-alkynylbenzenamines with isothiocyanates promoted by silica gel are described. This reaction proceeds smoothly at 80 degrees C under metal- and solvent-free conditions, which provides an efficient and practical route for the generation of 2,4-dihydro-1H-benzo[d][1,3]thiazines. The recovered silica gel could be reused for several times.