Silver Nanoflower Decorated Graphene Oxide Sponges for Highly Sensitive Variable Stiffness Stress Sensors

Soft conductive materials should enable large deformation while keeping high electrical conductivity and elasticity. The graphene oxide (GO)‐based sponge is a potential candidate to endow large deformation. However, it typically exhibits low conductivity and elasticity. Here, the highly conductive and elastic sponge composed of GO, flower‐shaped silver nanoparticles (AgNFs), and polyimide (GO‐AgNF‐PI sponge) are demonstrated. The average pore size and porosity are 114 µm and 94.7%, respectively. Ag NFs have thin petals (8–20 nm) protruding out of the surface of a spherical bud (300–350 nm) significantly enhancing the specific surface area (2.83 m² g^?1). The electrical conductivity (0.306 S m^?1 at 0% strain) of the GO‐AgNF‐PI sponge is increased by more than an order of magnitude with the addition of Ag NFs. A nearly perfect elasticity is obtained over a wide compressive strain range (0–90%). The strain‐dependent, nonlinear variation of Young's modulus of the sponge provides a unique opportunity as a variable stiffness stress sensor that operates over a wide stress range (0–10 kPa) with a high maximum sensitivity (0.572 kPa^?1). It allows grasping of a soft rose and a hard bottle, with the minimal object deformation, when attached on the finger of a robot gripper.     

Hydrophilic bismuth sulfur nanoflower superstructures with an improved photothermal efficiency for ablation of cancer cells

Nanomaterials with intense near-infrared (NIR) absorption exhibit effective photon-to-thermal energy transfer capabilities and can generate heat to ablate cancer cells, thus playing a pivotal role in photothermal cancer therapeutics. Herein, hydrophilic flower-like bismuth sulfur (Bi₂S₃) superstructures with uniform size and improved NIR absorption were controllably synthesized via a facile solvothermal procedure assisted by polyvinylpyrrolidone (PVP), which could adjust the product morphology. Induced by an 808-nm laser, the as-prepared Bi₂S₃ nanoflowers exhibited much higher photothermal conversion efficiency (64.3%) than that of Bi₂S₃ nanobelts (36.5%) prepared in the absence of PVP. This can be attributed not only to the Bi₂S₃ nanoflower superstructures assembled by 3-dimensional crumpled-paper-like nanosheets serving as many laser-cavity mirrors with improved reflectivity and absorption of NIR light but also to the amorphous structures with a lower band gap. Thus, to achieve the same temperature increase, the concentration or laser power density could be greatly reduced when using Bi₂S₃ nanoflowers compared to when using Bi₂S₃ nanobelts, which makes them more favorable for use in therapy due to decreased toxicity. Furthermore, these Bi₂S₃ nanoflowers effectively achieved photothermal ablation of cancer cells in vitro and in vivo. These results not only supported the Bi₂S₃ nanoflowers as a promising photothermal agent for cancer therapy but also paved an approach to exploit new agents with improved photothermal efficiency.

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Facile synthesis of porous Pd nanoflowers with excellent catalytic activity towards CO oxidation☆

Microorganism-mediated, hexadecyltrimethylammonium chloride (CTAC)-directed (MCD) method was employed in this work to synthesize Pd nanoflowers (PdNFs). Proper Pichia pastoris cel s (PPCs) dosage, ascorbic acid (AA), Pd(NO3)2 and CTAC concentrations were essential for the growth of the PdNFs. The size of the as-synthesized PdNFs could be tuned by adjusting the amount of Pd(NO3)2 solution and dosage of PPCs used. Char-acterization techniques such as X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to verify the nature of the PdNFs. Finally the PdNF/PPC nanocomposites were immobilized onto TiO2 supports to obtain bio-PdNF/TiO2 catalysts which showed excellent catalytic activity for CO oxidation, obtaining 100%conversion at 100 °C and remaining stable over a period of 52 h of reaction time.     

Ti3C2 MXene coupled with CdS nanoflowers as 2D/3D heterostructures for enhanced photocatalytic hydrogen production activity

As a novel co-catalyst, Ti₃C₂ MXene has an excellent prospect in the field of photocatalysis. Herein, the 2D/3D Ti₃C₂ MXene@CdS nanoflower (Ti₃C₂@CdS) composite was successfully synthesized by a hydrothermal method. The combination of 2D Ti₃C₂ MXene and 3D CdS nanoflowers can promote carrier transfer and separation, which can improve the performance of CdS. Compared to pure CdS nanoflowers, Ti₃C₂@CdS composite presents lower photoluminescence intensity, longer fluorescence lifetime, higher photocurrent density and smaller electrochemical impedance. The Ti₃C₂@CdS composite with 15 wt% Ti₃C₂ adding amount presents high photocatalytic hydrogen evolution activity (88.162 μmol g^?1 h^?1), 91.57 times of pure CdS. The improved photocatalytic activity of Ti₃C₂@CdS composite is ascribed to the addition of lamellar Ti₃C₂ MXene, which improves the electrical conductivity of the photocatalytic system and effectively accelerates the excited electrons transfer from CdS to Ti₃C₂ MXene.     

Magneto‐Thermal Metrics Can Mirror the Long‐Term Intracellular Fate of Magneto‐Plasmonic Nanohybrids and Reveal the Remarkable Shielding Effect of Gold

Multifunctional nanoparticles such as magneto‐plasmonic nanohybrids are rising theranostic agents. However, little is yet known of their fate within the cellular environment. In order to reach an understanding of their biotransformations, reliable metrics for tracking and quantification of such materials properties during their intracellular journey are needed. In this study, their long‐term (one month) intracellular fate is followed within stem‐cell spheroids used as tissue replicas. A set of magnetic (magnetization) and thermal (magnetic hyperthermia, photothermia) metrics is implemented to provide reliable insightsinto the intracellular status. It shows that biodegradation is modulated by the morphology and thickness of the gold shell. First a massive dissolution of the iron oxide core (nanoflower‐like) is observed, starting with dissociation of the multigrain structure. Second, it is demonstrated that an uninterrupted gold shell can preserve the magnetic core and properties (particularly magnetic hyperthermia). In addition to the magnetic and thermal metrics, intracellular high‐resolution chemical nanocartography evidences the gradual degradation of the magnetic cores. It also shows different transformation scenarios, from the release of small gold seeds when the magnetic core is dissolved (interesting for long‐term elimination) to the protection of the magnetic core (interesting for long‐term therapeutic applicability).     

A noble silver nanoflower on nitrogen doped carbon nanotube for enhanced oxygen reduction reaction

An electrodeposition-approach for the synthesis of silver nanoflowers (AgNFs) on nitrogen doped carbon nanotubes (NCNTs) for the oxygen reduction reaction (ORR) in alkaline media has been developed. The as prepared material (NCNTs-AgNFs) has been characterized by various instrumental methods. The morphological analysis shows the unique rose-like AgNFs are placed onto the NCNTs with better dispersion. The higher population of AgNFs has also been observed onto NCNTs coated glassy carbon (GC) rather than bare GC plate. The X-ray photoelectron spectroscopy shows chemical reduction and N-doping has done successfully with the restoring sp² domain in carbon network. The electrocatalytic activities have been verified using cyclic voltammetry (CV) and hydrodynamic voltammetry techniques in 0.1 M KOH electrolyte. The resulting catalyst system, NCNT-AgNFs, surpasses the performance of Pt/C, in terms of a kinetic current density, better fuel selectivity and durability. It is also noteworthy that the NCNT-AgNFs exhibits a four-electron reduction pathway for ORR with lowering H₂O₂ yield. The admirable performance of NCNT-AgNFs catalyst along with higher durability holds great potential for application in various fuel cells as cathode catalyst.     

Engineered Metal-Loaded Biohybrids to Promote the Attachment and Electron-Shuttling between Enzymes and Carbon Electrodes

The inorganic content and the catalytic performance pose metal-loaded enzyme nanoflowers as promising candidates for developing bioelectrodes capable of functioning without the external addition of a redox mediator. However, these protein-inorganic hybrids have yet to be successfully applied in combination with electrode materials. Herein, the synthesis procedure of these bionanomaterials is reproposed to precisely control the morphology, composition, and performance of this particular protein-mineral hybrid, formed by glucose oxidase and cobalt phosphate. This approach aims to enhance the adherence and electron mobility between the enzyme and a carbon electrode. The strategy relies on dressing the protein in a tailored thin nanogel with multivalent chemical motifs. The functional groups of the polymer facilitate the fast protein sequence-independent biomineralization. Furthermore, the engineered enzymes enable the fabrication of robust cobalt-loaded enzyme inorganic hybrids with exceptional protein loads, exceeding 90% immobilization yields. Notably, these engineered biohybrids can be readily deposited onto flat electrode surfaces without requiring chemical pre-treatment. The resulting bioelectrodes are robust and exhibit electrochemical responses even without the addition of a redox mediator, suggesting that cobalt complexes promote electron wiring between the active site of the enzyme and the electrode.     

High Surface‐Enhanced Raman Scattering Performance of Individual Gold Nanoflowers and Their Application in Live Cell Imaging

Molecular imaging techniques based on surface‐enhanced Raman scattering (SERS) face a lack of reproducibility and reliability, thus hampering its practical application. Flower‐like gold nanoparticles have strong SERS enhancement performance due to having plenty of hot‐spots on their surfaces, and this enhancement is not dependent on the aggregation of the particles. These features make this kind of particle an ideal SERS substrate to improve the reproducibility in SERS imaging. Here, the SERS properties of individual flower‐like gold nanoparticles are systematically investigated. The measurements reveal that the enhancement of a single gold nanoparticle is independent of the polarization of the excitation laser with an enhancement factor as high as 10⁸. After capping with Raman signal molecules and folic acid, the gold nanoflowers show strong Raman signal in the living cells, excellent targeting properties, and a high signal‐to‐noise ratio for SERS imaging.     

Enhanced band-edge photoluminescence from ZnO-passivated ZnO nanoflowers by atomic layer deposition

The ZnO nanoflowers were synthesized by reactive vapor deposition. A secondary nucleation in the stalk/leaves interface was suggested. The photoluminescence revealed that there were many oxygen vacancies in the nanoflowers. To tune the optical properties of ZnO nanoflowers, ZnO thin films with varying thicknesses were coated on the nanoflowers by atomic layer deposition, which can distinctly improve the band-edge photoluminescence properties.