Amorphous MoO3-x nanosheets prepared by the reduction of crystalline MoO3 by Mo metal for LSPR and photothermal conversion

MoOx-Based Colorimetric Sensor for Ultraviolet Visualization

Due to the depletion of the global ozone layer and the presence of ozone holes, humans are increasingly exposed to threats from solar ultraviolet radiation. Therefore, researching and developing a highly selective, sensitive, simple, and fast ultraviolet sensor is of significant importance for personal protection. In recent years, new nanomaterials have shown good application prospects in the research of ultraviolet sensors. MoOx nanostructures were prepared by a hydrothermal method. The experimental results show that, compared to traditional photochromic compounds, the new MoOx nanostructures exhibit high uniqueness, high selectivity, and excellent stability, and can perform rapid and accurate detection under full-band light. The beam sensor can not only detect through traditional electrical signal output, but also amplify, display, and analyze the beam through visualization and visual analysis, further improving the reliability and practicality of its application.

Light-Triggered Reversible Change in the Electronic Structure of MoO3 Nanosheets via an Excited-State Proton Transfer Mechanism

Light is an attractive source of energy for regulating stimulus-responsive chemical systems. Here, we use light as a gating source to control the redox state, the localized surface plasmonic resonance (LSPR) peak, and the structure of molybdenum oxide (MoO3) nanosheets, which are important for various applications. However, the light excitation is not that of the MoO3 nanosheets but rather that of pyranine (HPTS) photoacids, which in turn undergo an excited-state proton transfer (ESPT) process. We show that the ESPT process from HPTS to the nanosheets and the intercalation of protons within the MoO3 nanosheets trigger the reduction of the nanosheets and the broadening of the LSPR peak, a process that is reversible, meaning that in the absence of light, the LSPR peak diminishes and the nanosheets return to their oxidized form. We further show that this reversible process is accompanied by a change in the nanosheet size and morphology.

Redox-Activatable Magnetic Nanoarchitectonics for Self-Enhanced Tumor Imaging and Synergistic Photothermal-Chemodynamic Therapy

Oral squamous cell carcinoma (OSCC) is a prevalent malignancy of the head and neck region associated with high recurrence rates and poor prognosis under current diagnostic and treatment methods. The development of nanomaterials that can improve diagnostic accuracy and therapeutic efficacy is of great importance for OSCC. In this study, a redox-activatable nanoarchitectonics is designed via the construction of dual-valence cobalt oxide (DV-CO) nanospheres, which can serve as a contrast agent for magnetic resonance (MR) imaging, and exhibit enhanced transverse and longitudinal relaxivities through the release and redox of Co3+ /Co2+ in an acidic condition with glutathione (GSH), resulting in self-enhanced T1 /T2 -weighted MR contrast. Moreover, DV-CO demonstrates properties of intracellular GSH-depletion and hydroxyl radicals (•OH) generation through a Fenton-like reaction, enabling strengthened chemodynamic (CD) effect. Additionally, DV-CO displays efficient near-infrared laser-induced photothermal (PT) effect, thereby exhibiting synergistic PT-CD therapy for suppressing OSCC tumor cells. It further investigates the tumor-specific self-enhanced MR imaging of DV-CO both in subcutaneous and orthotopic OSCC mouse models, and demonstrate the therapeutic effects of DV-CO in orthotopic OSCC mouse models. Overall, the in vitro and in vivo findings highlight the excellent theranositc potentials of DV-CO for OSCC and offer new prospects for future advancement of nanomaterials.

Oxygen-Deficient Bioceramics: Combination of Diagnosis, Therapy, and Regeneration

The journey of ceramics in medicine has been synchronized with an evolution from the first generation-alumina, zirconia, etc.-to the third -3D scaffolds. There is an up-and-coming member called oxygen-deficient or colored bioceramics, which have recently found their way through biomedical applications. The oxygen vacancy steers the light absorption toward visible and near infrared regions, making the colored bioceramics multifunctional-therapeutic, diagnostic, and regenerative. Oxygen-deficient bioceramics are capable of turning light into heat and reactive oxygen species for photothermal and photodynamic therapies, respectively, and concomitantly yield infrared and photoacoustic images. Different types of oxygen-deficient bioceramics have been recently developed through various synthesis routes. Some of them like TiO2- x , MoO3- x , and WOx have been more investigated for biomedical applications, whereas the rest have yet to be scrutinized. The most prominent advantage of these bioceramics over the other biomaterials is their multifunctionality endowed with a change in the microstructure. There are some challenges ahead of this category discussed at the end of the present review. By shedding light on this recently born bioceramics subcategory, it is believed that the field will undergo a big step further as these platforms are naturally multifunctional.

Copper-Zinc Bimetallic Single-Atom Catalysts with Localized Surface Plasmon Resonance-Enhanced Photothermal Effect and Catalytic Activity for Melanoma Treatment and Wound-Healing

Nanomaterials with photothermal combined chemodynamic therapy (PTT-CDT) have attracted the attention of researchers owing to their excellent synergistic therapeutic effects on tumors. Thus, the preparation of multifunctional materials with higher photothermal conversion efficiency and catalytic activity can achieve better synergistic therapeutic effects for melanoma. In this study, a Cu-Zn bimetallic single-atom (Cu/PMCS) is constructed with augmented photothermal effect and catalytic activity due to the localized surface plasmon resonance (LSPR) effect. Density functional theory calculations confirmed that the enhanced photothermal effect of Cu/PMCS is due to the appearance of a new d-orbital transition with strong spin-orbit coupling and the induced LSPR. Additionally, Cu/PMCS exhibited increased catalytic activity in the Fenton-like reaction and glutathione depletion capacity, further enhanced by increased temperature and LSPR. Consequently, Cu/PMCS induced better synergistic anti-melanoma effects via PTT-CDT than PMCS in vitro and in vivo. Furthermore, compared with PMCS, Cu/PMCS killed bacteria more quickly and effectively, thus facilitating wound healing owing to the enhanced photothermal effect and slow release of Cu2+ . Cu/PMCS promoted cell migration and angiogenesis and upregulated the expression of related genes to accelerate wound healing. Cu/PMCS has potential applications in treating melanoma and repairing wounds with its antitumor, antibacterial, and wound-healing properties.

Progress on two-dimensional binary oxide materials

Two-dimensional van der Waals (2D vdW) materials have attracted much attention because of their unique electronic and optical properties. Since the successful isolation of graphene in 2004, many interesting 2D materials have emerged, including elemental olefins (silicene, germanene, etc.), transition metal chalcogenides, transition metal carbides (nitrides), hexagonal boron, etc. On the other hand, 2D binary oxide materials are an important group in the 2D family owing to their high structural diversity, low cost, high stability, and strong adjustability. This review systematically summarizes the research progress on 2D binary oxide materials. We discuss their composition and structure in terms of vdW and non-vdW categories in detail, followed by a discussion of their synthesis methods. In particular, we focus on strategies to tailor the properties of 2D oxides and their emerging applications in different fields. Finally, the challenges and future developments of 2D binary oxides are provided.

Recent advances in the fabrication of 2D metal oxides

Atomically thin two-dimensional (2D) metal oxides exhibit unique optical, electrical, magnetic, and chemical properties, rendering them a bright application prospect in high-performance smart devices. Given the large variety of both layered and non-layered 2D metal oxides, the controllable synthesis is the critical prerequisite for enabling the exploration of their great potentials. In this review, recent progress in the synthesis of 2D metal oxides is summarized and categorized. Particularly, a brief overview of categories and crystal structures of 2D metal oxides is firstly introduced, followed by a critical discussion of various synthesis methods regarding the growth mechanisms, advantages, and limitations. Finally, the existing challenges are presented to provide possible future research directions regarding the synthesis of 2D metal oxides. This work can provide useful guidance on developing innovative approaches for producing both 2D layered and non-layered nanostructures and assist with the acceleration of the research of 2D metal oxides.

Plasmonic Oxygen Defects in MO3- x (M = W or Mo) Nanomaterials: Synthesis, Modifications, and Biomedical Applications

Nanomedicine is a promising technology with many advantages and provides exciting opportunities for cancer diagnosis and therapy. During recent years, the newly developed oxygen-deficiency transition metal oxides MO_{3- x} (M = W or Mo) have received significant attention due to the unique optical properties, such as strong localized surface plasmon resonance (LSPR) , tunable and broad near-IR absorption, high photothermal conversion efficiency, and large X-ray attenuation coefficient. This review presents an overview of recent advances in the development of MO_{3- x} nanomaterials for biomedical applications. First, the fundamentals of the LSPR effect are introduced. Then, the preparation and modification methods of MO_{3- x} nanomaterials are summarized. In addition, the biological effects of MO_{3- x} nanomaterials are highlighted and their applications in the biomedical field are outlined. This includes imaging modalities, cancer treatment, and antibacterial capability. Finally, the prospects and challenges of MO_{3- x} and MO_{3- x} -based nanomaterial for fundamental studies and clinical applications are also discussed.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Two-Dimensional MoO2 Nanosheet Composite Hydrogels with High Transmittance and Excellent Photothermal Property for Near-Infrared Responsive Actuators and Microvalves

Stimulus-responsive intelligent hydrogel actuators have highly promising applications in the fields of soft robotics, smart manipulators, and flexible devices. Near-infrared (NIR) light is considered an ideal method to trigger the response behavior remotely and precisely. In order to realize the excellent optical transmittance and photothermal property of NIR-responsive hydrogels at the same time, two-dimensional nonlayered MoO₂ nanosheets (2D-MoO₂) with excellent photothermal efficiency (62% under an NIR light irradiation of 808 nm), splendid chemistry stability, and low preparation cost are used as photothermal agents and incorporated into the poly(N-isopropylacrylamide) (PNIPAM) hydrogel network, forming the 2D-MoO₂/Laponite/PNIPAM ternary nanocomposite hydrogel (TN hydrogel). It is remarkable that compared with the GO and MXene hydrogels with the same agent content (1.0 mg mL^-1) and thickness (1 mm) whose transmittance values are only ∼5% at 600 nm, the TN hydrogel shows a similar NIR-responsive temperature, but much higher optical transmittance (∼53%). Besides, of the three hydrogels with similar transmittance, the TN hydrogel shows a much higher NIR-responsive temperature. The TN hydrogel with a low loading of 2D-MoO₂ (1.5 mg mL^-1) can produce a significant temperature increase of ∼30 °C after the application of 0.8 W cm^-2 NIR light irradiation for 15 s. Impressively, the TN hydrogel exhibits excellent anti-fatigue property, keeping a fast response and temperature rise behavior even after 50 times of heating-cooling cycles. The flexibly controllable and reversible deformation is realized by a well-designed bilayer structure even in harsh environments. The transparent and asymmetric bilayer hydrogel is further used as a soft manipulator to capture objects visually and accurately. The NIR light-controlled microvalve based on this composite hydrogel is also demonstrated. This work provides a novel kind of transparent hybrid NIR response hydrogel for the further development of smart, programmable, reversible hydrogel-based actuators and soft robotics.

CO2-Assisted Synthesis of 2D Amorphous MoO3-x Nanosheets: From Top-Down to Bottom-Up

Supercritical CO₂ has shown great potential in the top-down fabrication of two-dimensional (2D) amorphous nanomaterials. However, a few works focus on the SC CO₂-assisted synthesis of 2D amorphous nanomaterials by a bottom-up approach. Here we report the facile bottom-up synthesis of 2D amorphous MoO_3-x nanosheets, using SC CO₂ as a surface confining agent. Moreover, the morphology of the MoO_3-x can be tailored by simply adjusting the pressure of the SC CO₂. The as-prepared 2D amorphous MoO_3-x nanosheets exhibit enhanced surface plasma resonance in the visible and near-infrared regions, showing outstanding photothermal conversion performance. This work constructs a new approach for the preparation of 2D amorphous nanosheets, throwing light on the amorphization mechanism of 2D materials.

Supercritical CO2-assisted amorphization of WO2.72 and its high-efficiency photothermal conversion

Amorphization of WO_2.72 was successfully achieved with the assistance of supercritical carbon dioxide (SC CO₂). Amorphous SC CO₂-treated sample has strong optical absorbance and excellent photothermal conversion efficiency of 52.5% indicates they can be a promising photothermal agent.