Haiwon Lee

Thalappil Pradeep, Kaoru Tamada, Haiwon Lee and Dong-Hwan Kim introduce the Nanoscale themed collection on the changing canvas of nano.

Owing to their large surface‐area‐to‐volume ratios, 2D titanium carbides and nitrides (MXenes) have emerged as promising materials for energy storage devices. However, poor interlayer and interparticle conductivity of MXenes (due to its anisotropic nature) is a bottleneck for widening their applications. Additionally, the stacked structure of MXene sheets limits the exposed surface area and renders a complex electrolyte diffusion. To address these issues, a unique composite comprising of homogeneously grown multiwall carbon nanotubes (MWCNTs) on carbon cloth (CC)‐supported MXene sheets (denoted as MWCNTs‐MXene@CC) is proposed. The MWCNTs‐MXene@CC reveal the synergistic combination of exfoliated large surface area and excellent conductivity. Consequently, the fabricated electrode exhibits a specific capacitance of 114.58 mF cm⁻² at a discharge current of 1 mA cm⁻², while maintaining high retention after 1.6 × 10⁴ cycles at 10 mA cm⁻². Such high performance of the composite structure is attributed to the superb interlayer and interparticle conductivity imparted by the grown MWCNTs. Furthermore, the grown MWCNTs also serve as the interlayer pillar in MXene sheets, thus preventing the spontaneous collapse of the latter. The approach can be extended to other electrocatalyst systems in which ion transport and electrolyte diffusion need to be addressed simultaneously.

A 3D nanoweb-like zeolite imidazole framework (ZIF-8) as an efficient heterogeneous catalyst was structured inside a microfluidic channel for Knoevenagel condensation reaction by growing the ZIF on 3D carbon nanotube (CNT) networks bridging the built-in micropillars.

Accurate detection and sensing of bacteria are becoming increasingly important not only in microbiology but in a variety of fields including medicine, food, public health, and environmental science. However, even new rapid methods are not convenient enough. Here, we describe a simple and efficient label-free bacterial detection system using the polydiacetylene (PDA) liposomes immobilized on the 3D polydimethylsiloxane (PDMS) micropillars. Our system utilizes the colorimetric response of amine functionalized PDA vesicles to surfactin, a bacterial cyclic lipopeptide commonly released by Gram-positive Bacillus species as an antibiotic. To improve the sensitivity of PDA vesicles to surfactin by increasing the number and surface area of immobilized vesicles, the PDA vesicles were immobilized on the micropillar structure to give a hierarchical 3D PDA vesicle structure. For the fabrication of the 3D micropillar structure, polydimethylsiloxane (PDMS) was used to overcome the limitations imposed by silicon-based fabrication. In contrast to the 2D-PDA-PDMS system, which could only hardly detect the presence of 500 μM surfactin, the 3D-PDA-PDMS system could efficiently detect the presence of 5 μM surfactin and the initial presence of 4 × 10¹ cells/ml of Bacillus subtilis NCIB3610, which actively produces surfactin. Furthermore, bacterial strains that are known to produce no surfactin, such as Staphylococcus aureus Newman, Escherichia coli DH5α, and Pseudomonas aeruginosa PA14 were not detected by our system suggesting that the 3D-PDA-PDMS system is highly specific to surfactin but not to other chemicals produced by bacteria. Taken together, our results suggest that the 3D-PDA-PDMS system can sensitively and selectively be used for the high throughput detection and screening of biotechnologically important surfactin-producing bacterial strains.

We herein report a simple chemical route to prepare Au–Ag and Ag–Au core–shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)–Au(s) core–shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)–Ag(s) core–shell structures show formation of merely nanocubes. Although UV–visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)–Au(s) and Au(c)–Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy–high-angle annular dark field elemental mapping in the case of Au(c)–Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2–93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.

Dialyzed natural polymer, fibroin, from Bombyx mori was used to synthesize biocompatible silver and gold nanoparticles in-situ in dispersion form. The films of pure fibroin (PF), fibroin-silver nanocomposite (FSNC) and fibroin-gold nanocomposite (FGNC) were fabricated by drop casting method. The characterization of the resultant dispersion and films was performed by visual color change, UV-Vis spectroscopy and atomic force microscopy. The dispersions of PF, FSNC and FGNC were tested for antibacterial activity against E. coli NCIM 2065, S. aureus NCIM 5021, K. pneumoniae NCIM 2957, P. aeruginosa ATCC 9027 and antifungal activity against A. fumigatus NCIM 902. FSNC dispersion exhibited an effective antimicrobial action against all the tested microbes as compared to FGNC dispersion. The mechanism of action for FSNC and FGNC against these microorganisms is proposed. Additionally, the larvicidal activity of the films was investigated against the larvae of Aedes aegypti. The films of FSNC exhibited 100% mortality while the films of FGNC revealed 86–98% mortality against all the larval instars and pupae of A. aegypti. The phytotoxicity study of the nanocomposite films was also carried out to confirm the reusability of water. This is first noble metal nanocomposite based report on larvicidal activity of zika virus vector.

Herein, we report the synthesis of metallic molybdenum microspheres and hierarchical MoS2 nanostructures by facile template-free solvothermal and hydrothermal approach, respectively. The morphological transition of the Mo microspheres to hierarchical MoS2 nanoflower architectures is observed to be accomplished with change in solvent from ethylenediamine to water. The resultant marigold flower-like MoS2 nanostructures are few layers thick with poor crystallinity while spherical ball-like molybdenum microspheres exhibit better crystalline nature. This is the first report pertaining to the synthesis of Mo microspheres and MoS2 nanoflowers without using any surfactant, template or substrate in hydro/solvothermal regime. It is opined that such nanoarchitectures of MoS2 are useful candidates for energy related applications such as hydrogen evolution reaction, Li ion battery and pseudocapacitors. Inquisitively, metallic Mo can potentially act as catalyst as well as fairly economical Surface Enhanced Raman Spectroscopy (SERS) substrate in biosensor applications.

The dual-suspended architectures, consisting of CNT networks penetrating through cuprous oxides with (quasi-)octahedron structures, are constructed between Si pillars, which show excellent photocatalytic abilities towards MB dye decomposition.

A three-dimensional network of carbon nanotubes (3DNC) coaxially coated with manganese oxides (MnO_x) is used as an electrode for supercapacitors. 3DNC serves as a stable and conductive framework for controlled electrochemical deposition (ECD), and provides sufficient voids for fast ionic transport and diffusion. The coated thin layer MnO_x reduces ion diffusion and electron transport distance, enabling fast reversible faradic reactions.