Modulating the electrocatalytic activity of N-doped carbon frameworks via coupling with dual metals for Zn-air batteries.

N-Doped carbon electrocatalysts are a promising alternative to precious metal catalysts to promote oxygen reduction reaction (ORR). However, it remains a challenge to design the desired active sites on carbon skeletons in a controllable manner for ORR. Herein, we developed a facile approach based on oxygen-mediated solvothermal radical reaction (OSRR) for preparation of N-doped carbon electrocatalysts with a pre-designed active site and modulated catalytic activity for ORR. In the OSRR, 2-methylimidazole reacted with Co and Mn salts to form an active site precursor (MnCo-MIm) in N-methyl-2-pyrrolidone (NMP) at room temperature. Then, the reaction temperature increased to 140 °C under an oxygen atmosphere to generate NMP radicals, followed by their polymerization with the pre-formed MnCo-MIm to produce Mn-coupled Co nanoparticle-embedded N-doped carbon framework (MnCo-NCF). The MnCo-NCF showed uniform dispersion of nitrogen atoms and Mn-doped Co nanoparticles on the carbon skeleton with micropores and mesopores. The MnCo-NCF exhibited higher electrocatalytic activity for ORR than did a Co nanoparticle only-incorporated carbon framework due to the improved charge transfer from the Mn-doped Co nanoparticles to the carbon skeleton. In addition, the Zn-air battery assembled with MnCo-NCF had superior performance and durability to the battery using commercial Pt/C. This facile approach can be extended for designing carbon electrocatalysts with desired active sites to promote specific reactions.

Multivalent Nanosheet Antibody Mimics for Selective Microbial Recognition and Inactivation.

Antibodies are widely used as recognition elements in sensing and therapy, but they suffer from poor stability, long discovery time, and high cost. Herein, a facile approach to create antibody mimics with flexible recognition phases and luminescent rigid scaffolds for the selective recognition, detection, and inactivation of pathogenic bacteria is reported. Tripeptides with a nitriloacetate-Cu group are spontaneously assembled on transition metal dichalcogenide (TMD) nanosheets via coordination bonding, providing a diversity of TMD-tripeptide assembly (TPA) antibody mimics. TMD-TPA antibody mimics can selectively recognize various pathogenic bacteria with nanomolar affinities. The bacterial binding sites for TMD-TPA are identified by experiments and molecular dynamics simulations, revealing that the dynamic and multivalent interactions of artificial antibodies play a crucial role for their recognition selectivity and affinity. The artificial antibodies allow the rapid and selective detection of pathogenic bacteria at single copy in human serum and urine, and their effective inactivation for therapy of infected mice. This work demonstrates the potential of TMD-TPA antibody mimics as an alternative to natural antibodies for sensing and therapy.

Sustainable Nanosheet Antioxidants for Sepsis Therapy via Scavenging Intracellular Reactive Oxygen and Nitrogen Species.

Sepsis is an aberrant systemic inflammatory response mediated by excessive production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Developing an efficient antioxidant therapy for sepsis via scavenging ROS and RNS remains a big challenge owing to the insufficient activity and sustainability of conventional antioxidants. Herein, biocompatible transition-metal dichalcogenide antioxidants with excellent scavenging activity and sustainability for H2O2, O2•-, OH•, and nitric oxide are developed for effective sepsis treatment. WS2, MoSe2, and WSe2 nanosheets exfoliated and functionalized with a biocompatible polymer effectively scavenge mitochondrial and intracellular ROS and RNS in inflammatory cells. Among the nanosheets, WS2 most efficiently suppresses the excessive secretion of inflammatory cytokines along with scavenging ROS and RNS without affecting the expression levels of the anti-inflammatory cytokine and ROS-producing enzymes. The WS2 nanosheets significantly improve the survival rate up to 90% for severely septic mice by reducing systemic inflammation. The pharmacokinetics suggests that the WS2 nanosheets can be excreted from mice 3 days after intravenous injection. This work demonstrates the potential of therapeutic nanosheet antioxidants for effective treatment of ROS and RNS-related diseases.

Modulation of oligonucleotide-binding dynamics on WS2 nanosheet interfaces for detection of Alzheimer's disease biomarkers.

Non-covalent adsorption and desorption of oligonucleotides on two-dimensional nanosheets are widely employed to design nanobiosensors for the rapid optical detection of targets. A precise control over the weak interactions between nanosheet interfaces and oligonucleotides is crucial for a high-sensing performance. Herein, the interface of ultrathin WS2 nanosheets used as a fluorescence quencher was engineered by four different dextran polymers in an aqueous solution to control the adsorption kinetics and thermodynamics of the DNA probe. The WS2 nanosheets, functionalized by the carboxyl group-bearing dextran (CM-dex-WS2) or the trimethylammonium-modified dextran (TMA-dex-WS2), exhibited 3.6-fold faster adsorption rates of the fluorescein-labeled DNA probe (FAM-DNA), which led to the effective fluorescence quenching of FAM, compared to the nanosheets functionalized with pristine dextran (dex-WS2) or the hydrophobic phenoxy groups-bearing dextran (PhO-dex-WS2). Isothermal titration calorimetry measurements showed that the adsorption strength of FAM-DNA for CM-dex-WS2 was one order of magnitude greater than its hybridization energy for a target microRNA (miR-29a) that is well-known as an Alzheimer's disease (AD) biomarker, leading to the unfavorable desorption of the DNA probe from the surface. In contrast, TMA-dex-WS2 exhibited the proper adsorption strength of FAM-DNA, which was lower than its hybridization energy for miR-29a, leading to its favorable desorption from the nanosheet surface along with the noticeable restoration of the quenched fluorescence after its hybridization with miR-29a. Finally, the interface modulation of WS2 nanosheets allowed the selective and sensitive recognition of miR-29a against non-complementary RNA and single base-mismatched RNA in human serum via increases in target-specific fluorescence.