An In Situ Study on Nanozyme Performance to Optimize Nanozyme-Strip for Aß Detection.

The nanozyme-strip is a novel POCT technology which is different from the conventional colloidal gold strip. It primarily utilizes the catalytic activity of nanozyme to achieve a high-sensitivity detection of target by amplifying the detection signal. However, previous research has chiefly focused on optimizing nanozyme-strip from the perspective of increasing nanozyme activity, little is known about other physicochemical factors. In this work, three sizes of Fe3O4 nanozyme and three sizes of CoFe2O4 nanozyme were used to investigate the key factors of nanozyme-strip for optimizing and improving its detection performance. We found that three sizes of Fe3O4 nanozyme all gather at the bottom of the nitrocellulose (NC) membrane, and three sizes of CoFe2O4 nanozyme migrate smoothly on the NC membrane, respectively. After color development, the surface of NC membranes distributed with CoFe2O4 peroxidase nanozymes had significant color change. Experimental results show that CoFe2O4 nanozymes had better dispersity than Fe3O4 nanozymes in an aqueous solution. We observed that CoFe2O4 nanozymes with smaller particle size migrated to the middle of the NC membrane with a higher number of particles. According to the results above, 55 ± 6 nm CoFe2O4 nanozyme was selected to prepare the nanozyme probe and achieved a highly sensitive detection of Aß42Os on the nanozyme-strip. These results suggest that nanozyme should be comprehensively evaluated in its dispersity, the migration on NC membrane, and the peroxidase-like activity to determine whether it can be applied to nanozyme-strip.

Additively Manufactured Scaffolds with Optimized Thickness Based on Triply Periodic Minimal Surface.

Triply periodic minimal surfaces (TPMS) became an effective method to design porous scaffolds in recent years due to their superior mechanical and other engineering properties. Since the advent of additive manufacturing (AM), different TPMS-based scaffolds are designed and fabricated for a wide range of applications. In this study, Schwarz Primitive triply periodic minimal surface (P-TPMS) is adopted to design a novel porous scaffold according to the distribution of the scaffold stress under a fixed load with optimized thickness to tune both the mechanical and biological properties. The designed scaffolds are then additively manufactured through selective laser melting (SLM). The micro-features of the scaffolds are studied through scanning electron microscopy (SEM) and micro-computed tomography (CT) images, and the results confirm that morphological features of printed samples are identical to the designed ones. Afterwards, the quasi-static uniaxial compression tests are carried out to observe the stress-strain curves and the deformation behavior. The results indicate that the mechanical properties of the porous scaffolds with optimized thickness were significantly improved. Since the mass transport capability is important for the transport of nutrients within the bone scaffolds, computational fluid dynamics (CFD) are used to calculate the permeability under laminar flow conditions. The results reveal that the scaffolds with optimized structures possess lower permeability due to the rougher inner surface. In summary, the proposed method is effective to tailor both the mechanical properties and permeability, and thus offers a means for the selection and design of porous scaffolds in biomedical fields.

Nanozyme-strip for rapid and ultrasensitive nucleic acid detection of SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic has created a huge demand for sensitive and rapid detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current gold standard for SARS-CoV-2 detection is reverse transcription-polymerase chain reaction (RT-PCR)-based nucleic acid amplification. However, RT-PCR is time consuming and requires specialists and large instruments that are unattainable for point-of-care testing (POCT). To develop POCT for SARS-CoV-2, we combined recombinase polymerase amplification (RPA) and FeS2 nanozyme strips to achieve facile nucleic acid amplification and subsequent colorimetric signal enhancement based on the high peroxidase-like activity of the FeS2 nanozymes. This method showed a nucleic acid limit of detection (LOD) for SARS-CoV-2 of 200 copies/mL, close to that of RT-PCR. The unique catalytic properties of the FeS2 nanozymes enabled the nanozyme-strip to amplify colorimetric signals via the nontoxic 3,3',5,5'-tetramethylbenzidine (TMB) substrate. Importantly, the detection of clinical samples of human papilloma virus type 16 (HPV-16) showed 100% agreement with previous RT-PCR results, highlighting the versatility and reliability of this method. Our findings suggest that nanozyme-based nucleic acid detection has great potential in the development of POCT diagnosis for COVID-19 and other viral infections.

A Bispidine-Based Chiral Amine Catalyst for Asymmetric Mannich Reaction of Ketones with Isatin Ketimines.

A unique chiral amine organocatalyst with a bispidine structure was found to be efficient for the diastereo- and enantioselective Mannich reaction of isatin ketimines with ketones. A series of 3-substituted 3-amino-2-oxindoles bearing vicinal tertiary and quaternary chiral stereogenic centers were obtained in excellent yields with excellent dr and ee values. The gram-scale synthesis and transformation of the product showed the practicability of this methodology. In addition, a possible transition state model was proposed to explain the origin of the stereoselectivity.

Redrawing the Iceland-Scotland Overflow Water pathways in the North Atlantic.

Iceland-Scotland Overflow Water (ISOW) is a primary deep water mass exported from the Norwegian Sea into the North Atlantic as part of the global Meridional Overturning Circulation. ISOW has historically been depicted as flowing counter-clockwise in a deep boundary current around the subpolar North Atlantic, but this single-boundary-following pathway is being challenged by new Lagrangian observations and model simulations. We show here that ISOW leaves the boundary and spreads into the interior towards the central Labrador and Irminger basins after flowing through the Charlie-Gibbs Fracture Zone. We also describe a newly observed southward pathway of ISOW along the western flank of the Mid-Atlantic Ridge. The partitioning of these pathways is shown to be influenced by deep-reaching eddies and meanders of the North Atlantic Current. Our results, in tandem with previous studies, call for a revision in the historical depiction of ISOW pathways throughout the North Atlantic.

Chiral Zinc(II)-Catalyzed Enantioselective Tandem α-Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines.

A new catalytic asymmetric tandem α-alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N'-dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α-alkenyl addition of silyl enol ether to the ketimine. A wide range of ß-amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama-Mannich reaction and tandem α-alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained ß-amino silyl enol ethers were easily transformed into ß-fluoroamines containing two vicinal tetrasubstituted carbon centers.

Catalytic Asymmetric Inverse-Electron-Demand Hetero-Diels-Alder Reaction of Dioxopyrrolidines with Hetero-Substituted Alkenes.

A highly efficient enantioselective inverse-electron-demand hetero-Diels-Alder reaction of dioxopyrrolidines with heterosubstituted alkenes has been realized by using a N, N'-dioxide/Ni(II) complex as the catalyst. A series of chiral bicyclic dihydropyranes were generated in excellent yields, good dr, and excellent ee values. Besides, a catalytic cycle with a possible transition state was proposed.

Catalytic asymmetric Meerwein-Ponndorf-Verley reduction of glyoxylates induced by a chiral N,N'-dioxide/Y(OTf)3 complex.

An asymmetric Meerwein-Ponndorf-Verley (MPV) reduction of glyoxylates was for the first time accomplished via an N,N'-dioxide/Y(OTf)3 complex with aluminium alkoxide and molecular sieves (MSs) as crucial additives. A variety of optically active α-hydroxyesters were obtained with excellent results. A possible reaction mechanism was proposed based on the experiments.