Nitrogen dioxide (NO2) is a gas species that plays an important role in certain industrial, farming, and healthcare sectors. However, there are still significant challenges for NO2 sensing at low detection limits, especially in the presence of other interfering gases. The NO2 selectivity of current gas-sensing technologies is significantly traded-off with their sensitivity and reversibility as well as fabrication and operating costs. In this work, we present an important progress for selective and reversible NO2 sensing by demonstrating an economical sensing platform based on the charge transfer between physisorbed NO2 gas molecules and two-dimensional (2D) tin disulfide (SnS2) flakes at low operating temperatures. The device shows high sensitivity and superior selectivity to NO2 at operating temperatures of less than 160 °C, which are well below those of chemisorptive and ion conductive NO2 sensors with much poorer selectivity. At the same time, excellent reversibility of the sensor is demonstrated, which has rarely been observed in other 2D material counterparts. Such impressive features originate from the planar morphology of 2D SnS2 as well as unique physical affinity and favorable electronic band positions of this material that facilitate the NO2 physisorption and charge transfer at parts per billion levels. The 2D SnS2-based sensor provides a real solution for low-cost and selective NO2 gas sensing.

Nanoparticles (NPs) have demonstrated great potential for the oral delivery of protein drugs that have very limited oral bioavailability. Orally administered NPs could be absorbed by the epithelial tissue only if they successfully permeate through the mucus that covers the epithelium. However, efficient epithelial absorption and mucus permeation require very different surface properties of a nanocarrier. We herein report self-assembled NPs for efficient oral delivery of insulin by facilitating both of these two processes. The NPs possess a nanocomplex core composed of insulin and cell penetrating peptide (CPP), and a dissociable hydrophilic coating of N-(2-hydroxypropyl) methacrylamide copolymer (pHPMA) derivatives. After systematic screening using mucus-secreting epithelial cells, NPs exhibit excellent permeation in mucus due to the "mucus-inert" pHPMA coating, as well as high epithelial absorption mediated by CPP. The investigation of NP behavior shows that the pHPMA molecules gradually dissociate from the NP surface as it permeates through mucus, and the CPP-rich core is revealed in time for subsequent transepithelial transport through the secretory endoplasmic reticulum/Golgi pathway and endocytic recycling pathway. The NPs exhibit 20-fold higher absorption than free insulin on mucus-secreting epithelium cells, and orally administered NPs generate a prominent hypoglycemic response and an increase of the serum insulin concentration in diabetic rats. Our study provides the evidence of using pHPMA as dissociable "mucus-inert" agent to enhance mucus permeation of NPs, and validates a strategy to overcome the multiple absorption barriers using NP platform with dissociable hydrophilic coating and drug-loaded CPP-rich core.

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Mesostructured silica MCM-41 has been one of the most extensively studied mesostructured materials since its first synthesis by Mobil scientists in 1992.[1] Many important applications [2] of mesostructured silica MCM-41 in catalysis, separation, and nanoengineering are closely correlated to its ordered two-dimensional (2D) hexagonal mesostructure/ mesopore. Besides the usual straight 2D hexagonal mesostructure, [3] various curved mesostructures of MCM-41 have also been reported by several research groups in the last decade, [4] which has aroused great academic interest in their enigmatic morphogenesis. Recently our research group has investigated the topological transformation of a series of vesicular MCM-41 compounds with different mesostructures in an alkaline synthesis system [5] that was initialy developed by Rathouský and co-workers.[6] The self-assembly of sodium silicate (SS) and cetyltrimethylammonium bromide (CTAB) into a hexagonal mesostructure in such a method is driven by the hydrolysis of ethyl acetate (EA). Herein we report that chiral mesostructured silica nanofibers of MCM-41 can be fabricated in this SS/CTAB/EA/H 2 O system by simply lowering the SS and CTAB concentrations below 0.5 mol per 1000 mol H 2 O. It is remarkable that two types of chiral mesostructures with different symmetries were synthesized from the usual achiral materials in this study. Moreover, a relationship between the chiral and ordinary achiral mesostructures of MCM-41 was revealed through a systematic investigation of the synthesis system.The first type of chiral nanofibers of MCM-41 (Figure 1 a, b) has a single twist axis. The XRD pattern of such a single-axis nanofiber (Figure 1 c) reveals a highly ordered 2D hexagonal mesostructure with a lattice constant of 4.5 nm. The N 2 sorption isotherms of the calcined product show a steep capillary condensation at a P/P 0 ratio of 0.2:1-0.3:1, which corresponds to a BJH pore size of 2.4 nm (Figure 1 d). The BET surface area and mesopore volume of the single-axis nanofiber are 960 m 2 g À1 and 0.63 cm 3 g À1 , respectively. Analysis of the chiral mesostructure of the single-axis nanofibers by electron microscopy showed: 1) The twisted crystal facets could be distinguished from their field-emission SEM images (see Supporting Information); 2) periodic fringes along the axis of the nanofiber in the TEM image (Figure 1 b); and 3) the observed fringes moved along the axis when the