Water-Splitting Based and Related Therapeutic Effects: Evolving Concepts, Progress, and Perspectives

Two-Dimensional SnS Mediates NiFe-LDH-Layered Electrocatalyst toward Boosting OER Activity for Water Splitting

NiFe-layered double hydroxides (NiFe-LDHs), as promising electrocatalysts, have received significant research attention for hydrogen and oxygen generation through water splitting. However, the slow oxidation kinetics of NiFe-LDH, due to the limited number of active sites and the low conductivity, hinders the improvement of the water-splitting efficiency. Therefore, to overcome the obstacles, two-dimensional (2D) SnS was first explored to tailor the prepared NiFe-LDH via the hydrothermal method. A NiFe-LDH/SnS heterojunction is built, which is observed from the microstructural investigations. SnS incorporation could greatly improve the conductivity of the NiFe-LDH sheets, which was reflected by the reduced charge transfer resistance. Moreover, SnS layers modulated the electronic environment around the active sites, favoring the adsorption of intermediates during the oxygen evolution reaction (OER) process, which was verified by density functional theory calculations. A synergistic effect induced by the NiFe-LDH/SnS heterostructure promoted the OER activities in electrical, electronic, and energetic aspects. Consequently, the as-prepared NiFe-LDH/SnS electrocatalyst greatly improved the electrocatalytic performance, exhibiting 20% and 27% reductions in the overpotential and Tafel slope compared with those of pristine NiFe-LDH, respectively. The results provide a strategy for regulating NiFe-based electrocatalysts by using emerging 2D materials to enhance water-splitting efficiency.

Near-infrared-driven upconversion nanoparticles with photocatalysts through water-splitting towards cancer treatment

Water splitting is promising, especially for energy and environmental applications; however, there are limited studies on the link between water splitting and cancer treatment. Upconversion nanoparticles (UCNPs) can be used to convert near-infrared (NIR) light to ultraviolet (UV) or visible (Vis) light and have great potential for biomedical applications because of their profound penetration ability, theranostic approaches, low self-fluorescence background, reduced damage to biological tissue, and low toxicity. UCNPs with photocatalytic materials can enhance the photocatalytic activities that generate a shorter wavelength to increase the tissue penetration depth in the biological microenvironment under NIR light irradiation. Moreover, UCNPs with a photosensitizer can absorb NIR light and convert it into UV/vis light and emit upconverted photons, which excite the photoinitiator to create H2, O2, and/or OH˙ via water splitting processes when exposed to NIR irradiation. Therefore, combining UCNPs with intensified photocatalytic and photoinitiator materials may be a promising therapeutic approach for cancer treatment. This review provides a novel strategy for explaining the principles and mechanisms of UCNPs and NIR-driven UCNPs with photocatalytic materials through water splitting to achieve therapeutic outcomes for clinical applications. Moreover, the challenges and future perspectives of UCNP-based photocatalytic materials for water splitting for cancer treatment are discussed in this review.

Flexocatalytic Reduction of Tumor Interstitial Fluid/Solid Pressure for Efficient Nanodrug Penetration

The practical efficacy of nanomedicines for treating solid tumors is frequently low, predominantly due to the elevated interstitial pressure within such tumors that obstructs the penetration of nanomedicines. This increased interstitial pressure originates from both liquid and solid stresses related to an undeveloped vascular network and excessive fibroblast proliferation. To specifically resolve the penetration issues of nanomedicines for tumor treatment, this study introduces a holistic "dual-faceted" approach. A treatment platform predicated on the WS2/Pt Schottky heterojunction was adopted, and flexocatalysis technology was used to disintegrate tumor interstitial fluids, thus producing oxygen and reactive oxygen species and effectively mitigating the interstitial fluid pressure. The chemotherapeutic agent curcumin was incorporated to further suppress the activity of cancer-associated fibroblasts, minimize collagen deposition in the extracellular matrix, and alleviate solid stress. Nanomedicines achieve homologous targeting by enveloping the tumor cell membrane. It was found that this multidimensional strategy not only alleviated the high-pressure milieu of the tumor interstitium─which enhanced the efficiency of nanomedicine delivery─but also triggered tumor cell apoptosis via the generated reactive oxygen species and modulated the tumor microenvironment. This, in turn, amplified immune responses, substantially optimizing the therapeutic impacts of nanomedicines.

Prussian blue analog with separated active sites to catalyze water driven enhanced catalytic treatments

Chemodynamic therapy (CDT) uses the Fenton or Fenton-like reaction to yield toxic ‧OH following H2O2 → ‧OH for tumoral therapy. Unfortunately, H2O2 is often taken from the limited endogenous supply of H2O2 in cancer cells. A water oxidation CoFe Prussian blue (CFPB) nanoframes is presented to provide sustained, external energy-free self-supply of ‧OH from H2O to process CDT and/or photothermal therapy (PTT). Unexpectedly, the as-prepared CFPB nanocubes with no near-infrared (NIR) absorption is transformed into CFPB nanoframes with NIR absorption due to the increased Fe3+-N ≡ C-Fe2+ composition through the proposed proton-induced metal replacement reactions. Surprisingly, both the CFPB nanocubes and nanoframes provide for the self-supply of O2, H2O2, and ‧OH from H2O, with the nanoframe outperforming in the production of ‧OH. Simulation analysis indicates separated active sites in catalyzation of water oxidation, oxygen reduction, and Fenton-like reactions from CFPB. The liposome-covered CFPB nanoframes prepared for controllable water-driven CDT for male tumoral mice treatments.

Innovative strategies for photodynamic therapy against hypoxic tumor

Photodynamic therapy (PDT) is applied as a robust therapeutic option for tumor, which exhibits some advantages of unique selectivity and irreversible damage to tumor cells. Among which, photosensitizer (PS), appropriate laser irradiation and oxygen (O₂) are three essential components for PDT, but the hypoxic tumor microenvironment (TME) restricts the O₂ supply in tumor tissues. Even worse, tumor metastasis and drug resistance frequently happen under hypoxic condition, which further deteriorate the antitumor effect of PDT. To enhance the PDT efficiency, critical attention has been received by relieving tumor hypoxia, and innovative strategies on this topic continue to emerge. Traditionally, the O₂ supplement strategy is considered as a direct and effective strategy to relieve TME, whereas it is confronted with great challenges for continuous O₂ supply. Recently, O₂-independent PDT provides a brand new strategy to enhance the antitumor efficiency, which can avoid the influence of TME. In addition, PDT can synergize with other antitumor strategies, such as chemotherapy, immunotherapy, photothermal therapy (PTT) and starvation therapy, to remedy the inadequate PDT effect under hypoxia conditions. In this paper, we summarized the latest progresses in the development of innovative strategies to improve PDT efficacy against hypoxic tumor, which were classified into O₂-dependent PDT, O₂-independent PDT and synergistic therapy. Furthermore, the advantages and deficiencies of various strategies were also discussed to envisage the prospects and challenges in future study.

Robust route to H2O2 and H2 via intermediate water splitting enabled by capitalizing on minimum vanadium-doped piezocatalysts

H₂O₂ is an environmentally friendly chemical for a wide range of water treatments. The industrial production of H₂O₂ is an anthraquinone oxidation process, which, however, consumes extensive energy and produces pollution. Here we report a green and sustainable piezocatalytic intermediate water splitting process to simultaneously obtain H₂O₂ and H₂ using single crystal vanadium (V)-doped NaNbO₃ (V-NaNbO₃) nanocubes as catalysts. The introduction of V improves the specific surface area and active sites of NaNbO₃. Notably, V-NaNbO₃ piezocatalysts of 10 mg exhibit 3.1-fold higher piezocatalytic efficiency than the same catalysts of 50 mg, as more piezocatalysts lead to higher probability of aggregation. The aggregation causes reducing active sites and decreased built-in electric field due to the neutralization between different nano-catalysts. Remarkably, piezocatalytic H₂O₂ and H₂ production rates of V-NaNbO₃ (10 mol%) nanocubes (102.6 and 346.2 µmol·g^-1·h^-1, respectively) are increased by 2.2 and 4.6 times compared to the as-prepared pristine NaNbO₃ counterparts, respectively. This improved catalytic efficiency is attributed to the promoted piezo-response and more active sites of NaNbO₃ catalysts after V doping, as uncovered by piezo-response force microscopy (PFM) and density functional theory (DFT) simulation. More importantly, our DFT results illustrate that inducing V could reduce the dynamic barrier of water dissociation over NaNbO₃, thus enhancing the yield of H₂O₂ and H₂. This facile yet robust piezocatalytic route using minimal amounts of catalysts to obtain H₂O₂ and H₂ may stand out as a promising candidate for environmental applications and water splitting.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (typical Raman spectra of NaNbO₃ and V-NaNbO₃ with various doping concentrations (Fig. S1). XPS spectra of Na 1s (Fig. S2). PL spectra of solution obtained from the piezocatalytic system using NaNbO₃ and V-NaNbO₃ (10 mol%) as the catalysts after 1 h (Fig. S3). The length of NaNbO₃ and V-NaNbO₃ nanocubes calculated from XRD data of their (101) planes (Table S1)) is available in the online version of this article at 10.1007/s12274-022-4506-0.

The Advancement of Gas-Generating Nanoplatforms in Biomedical Fields: Current Frontiers and Future Perspectives

Diverse gases (NO, CO, H₂ S, H₂ , etc.) have been widely applied in the medical intervention of various diseases, including cancer, cardiovascular disease, ischemia-reperfusion injury, bacterial infection, etc., attributing to their inherent biomedical activities. Although many gases have many biomedical activities, their clinical use is still limited due to the rapid and free diffusion behavior of these gases molecules, which may cause potential side effects and/or ineffective treatment. Gas-generating nanoplatforms (GGNs) are effective strategies to address the aforementioned challenges of gas therapy by preventing gas production or release at nonspecific sites, enhancing GGNs accumulation at targeted sites, and controlling gas release in response to exogenous (UV, NIR, US, etc.) or endogenous (H₂ O₂ , GSH, pH, etc.) stimuli at the lesion site, further maintaining gas concentration within the effective range and achieving the purpose of disease treatment. This review comprehensively summarizes the advancements of "state-of-the-art" GGNs in the recent three years, with emphasis on the composition, structure, preparation process, and gas release mechanism of the nanocarriers. Furthermore, the therapeutic effects and limitations of GGNs in preclinical studies using cell/animal models are discussed. Overall, this review enlightens the further development of this field and promotes the clinical transformation of gas therapy.

Recent advances in ZnO-based photosensitizers: Synthesis, modification, and applications in photodynamic cancer therapy

Zinc oxide nanoparticles (ZnO NPs) are important semiconductor materials with interesting photo-responsive properties. During the past, ZnO-based NPs have received considerable attention for photodynamic therapy (PDT) due to their biocompatibility and excellent potential of generating tumor-killing reactive oxygen species (ROS) through gentle photodynamic activation. This article provides a comprehensive review of the recent developments and improvements in optical properties of ZnO NPs as photosensitizers for PDT. The optical properties of ZnO-based photosensitizers are significantly dependent on their charge separation, absorption potential, band gap engineering, and surface area, which can be adjusted/tuned by doping, compositing, and morphology control. Here, we first summarize the recent progress in the charge separation capability, absorption potential, band gap engineering, and surface area of nanosized ZnO-based photosensitizers. Then, morphology control that is closely related to their synthesis method is discussed. Following on, the state-of-art for the ZnO-based NPs in the treatment of hypoxic tumors is comprehensively reviewed. Finally, we provide some outlooks on common targeted therapy methods for more effective tumor killing, including the attachment of small molecules, antibodies, ligands molecules, and receptors to NPs which further improve their selective distribution and targeting, hence improving the therapeutic effectiveness. The current review may provide useful guidance for the researchers who are interested in this promising dynamic cancer treatment technology.

Artificial photoactive chlorophyll conjugated vanadium carbide nanostructure for synergistic photothermal/photodynamic therapy of cancer

Optically active nanostructures consisting of organic compounds and metallic support have shown great promise in phototherapy due to their increased light absorption capacity and high energy conversion. Herein, we conjugated chlorophyll (Chl) to vanadium carbide (V2C) nanosheets for combined photodynamic/photothermal therapy (PDT/PTT), which reserves the advantages of each modality while minimizing the side effects to achieve an improved therapeutic effect. In this system, the Chl from Leptolyngbya JSC-1 extracts acted as an efficient light-harvest antenna in a wide NIR range and photosensitizers (PSs) for oxygen self-generation hypoxia-relief PDT. The available large surface of two-dimensional (2D) V2C showed high Chl loading efficiency, and the interaction between organic Chl and metallic V2C led to energy conversion efficiency high to 78%. Thus, the Chl/ V2C nanostructure showed advanced performance in vitro cell line killing and completely ablated tumors in vivo with 100% survival rate under a single NIR irradiation. Our results suggest that the artificial optical Chl/V2C nanostructure will benefit photocatalytic tumor eradication clinic application.

Recent advances in in situ oxygen-generating and oxygen-replenishing strategies for hypoxic-enhanced photodynamic therapy

Cancer is a leading cause of death worldwide, accounting for an estimated 10 million deaths by 2020. Over the decades, various strategies for tumor therapy have been developed and evaluated. Photodynamic therapy (PDT) has attracted increasing attention due to its unique characteristics, including low systemic toxicity and minimally invasive nature. Despite the excellent clinical promise of PDT, hypoxia is still the Achilles' heel associated with its oxygen-dependent nature related to increased tumor proliferation, angiogenesis, and distant metastases. Moreover, PDT-mediated oxygen consumption further exacerbates the hypoxia condition, which will eventually lead to the poor effect of drug treatment and resistance and irreversible tumor metastasis, even limiting its effective application in the treatment of hypoxic tumors. Hypoxia, with increased oxygen consumption, may occur in acute and chronic hypoxia conditions in developing tumors. Tumor cells farther away from the capillaries have much lower oxygen levels than cells in adjacent areas. However, it is difficult to change the tumor's deep hypoxia state through different ways to reduce the tumor tissue's oxygen consumption. Therefore, it will become more difficult to cure malignant tumors completely. In recent years, numerous investigations have focused on improving PDT therapy's efficacy by providing molecular oxygen directly or indirectly to tumor tissues. In this review, different molecular oxygen supplementation methods are summarized to alleviate tumor hypoxia from the innovative perspective of using supplemental oxygen. Besides, the existing problems, future prospects and potential challenges of this strategy are also discussed.

Conquering the Hypoxia Limitation for Photodynamic Therapy

Photodynamic therapy (PDT) has aroused great research interest in recent years owing to its high spatiotemporal selectivity, minimal invasiveness, and low systemic toxicity. However, due to the hypoxic nature characteristic of many solid tumors, PDT is frequently limited in therapeutic effect. Moreover, the consumption of O₂ during PDT may further aggravate the tumor hypoxic condition, which promotes tumor proliferation, metastasis, and invasion resulting in poor prognosis of treatment. Therefore, numerous efforts have been made to increase the O₂ content in tumor with the goal of enhancing PDT efficacy. Herein, these strategies developed in past decade are comprehensively reviewed to alleviate tumor hypoxia, including 1) delivering exogenous O₂ to tumor directly, 2) generating O₂ in situ, 3) reducing tumor cellular O₂ consumption by inhibiting respiration, 4) regulating the TME, (e.g., normalizing tumor vasculature or disrupting tumor extracellular matrix), and 5) inhibiting the hypoxia-inducible factor 1 (HIF-1) signaling pathway to relieve tumor hypoxia. Additionally, the O₂ -independent Type-I PDT is also discussed as an alternative strategy. By reviewing recent progress, it is hoped that this review will provide innovative perspectives in new nanomaterials designed to combat hypoxia and avoid the associated limitation of PDT.

Peroxidase Mimetic Nanozymes in Cancer Phototherapy: Progress and Perspectives

Nanomaterial-mediated cancer therapeutics is a fast developing field and has been utilized in potential clinical applications. However, most effective therapies, such as photodynamic therapy (PDT) and radio therapy (RT), are strongly oxygen-dependent, which hinders their practical applications. Later on, several strategies were developed to overcome tumor hypoxia, such as oxygen carrier nanomaterials and oxygen generated nanomaterials. Among these, oxygen species generation on nanozymes, especially catalase (CAT) mimetic nanozymes, convert endogenous hydrogen peroxide (H2O2) to oxygen (O2) and peroxidase (POD) mimetic nanozymes converts endogenous H2O2 to water (H2O) and reactive oxygen species (ROS) in a hypoxic tumor microenvironment is a fascinating approach. The present review provides a detailed examination of past, present and future perspectives of POD mimetic nanozymes for effective oxygen-dependent cancer phototherapeutics.

Pyroelectric Catalysis-Based "Nano-Lymphatic" Reduces Tumor Interstitial Pressure for Enhanced Penetration and Hydrodynamic Therapy

Because of the deficiency of lymphatic reflux in the tumor, the retention of tumor interstitial fluid causes aggravation of the tumor interstitial pressure (TIP), which leads to unsatisfactory tumor penetration of nanomedicine. It is the main inducement of tumor recurrence and metastasis. Herein, we design a pyroelectric catalysis-based "Nano-lymphatic" to decrease the TIP for enhanced tumor penetration and treatments. It realizes photothermal therapy and decomposition of tumor interstitial fluid under NIR-II laser irradiation after reaching the tumor, which reduces the TIP for enhanced tumor penetration. Simultaneously, reactive oxygen species generated during the pyroelectric catalysis can further damage deep tumor stem cells. The results indicate that the "Nano-lymphatic" relieves 52% of TIP, leading to enhanced tumor penetration, which effectively inhibits the tumor proliferation (93.75%) and recurrence. Our finding presents a rational strategy to reduce TIP by pyroelectric catalysis for enhanced tumor penetration and improved treatments, which is of great significance for drug delivery.

Mitochondria Targeted O2 Economizer to Alleviate Tumor Hypoxia for Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) often suffers from the exacerbated tumor hypoxia and the heterogeneous distribution of photosensitizers, leading to an inefficient ROS productivity and availability. In this work, a mitochondria targeted O₂ economizer (designated as Mito-OxE) is developed to improve PDT efficiency by alleviating tumor hypoxia and enhancing the subcellular localization of photosensitizers. Specifically, the photosensitizer of protoporphyrin IX (PpIX) is modified with the hydrophilic polyethylene glycol and the lipophilic cation of triphenylphosphine (TPP) to fabricate the biocompatible mitochondria targeted photosensitizers (designated as Mito-PSs). And Mito-OxE is prepared by using Mito-PSs to load the mitochondrial oxidative phosphorylation inhibitors of atovaquone (ATO). Benefiting from the targeting capability of TPP, Mito-OxE can selectively accumulate in mitochondria after cellular uptake. Subsequently, the mitochondrial respiration would be suppressed to with the participation of ATO, resulting in a local hypoxia mitigation for enhanced PDT. Compared with Mito-PSs, Mito-OxE maximizes the therapeutic effect against hypoxic tumors under light irradiation. This design of mitochondria targeted O₂ economizer would advance the development of targeted drug delivery system for effective PDT regardless of hypoxic microenvironment.

Strategies of Alleviating Tumor Hypoxia and Enhancing Tumor Therapeutic Effect by Macromolecular Nanomaterials

Hypoxia as one of the most prominent features in tumors, has presented negative effects on tumor therapies including photodynamic therapy, radiotherapy, and chemotherapies, leading to the tumor regeneration and metastasis. Recently, nanomedicines have been proposed to handle the hypoxia dilemma. Some nanomedicines alleviated hypoxia to enhance the therapeutic effect, others used hypoxia-sensitive substances to treat tumor. Among them, macromolecular nanomaterials-based nanomedicine has attracted increased research interest. However, the complicated tumor microenvironment disturbs the practical application of macromolecular nanomaterials to deal with hypoxia. This review highlights the influence of hypoxia on tumor therapy and some new strategies of using macromolecular nanomaterials to overcome hypoxia for effective tumor therapy.

V2C Nanosheets as Dual-Functional Antibacterial Agents

Antibiotic-resistant bacterial strains have been continuously increasing and becoming a supreme threat to public health globally. The nanoparticle-based photothermal treatment has emerged as a powerful tool to combat toxic bacteria. Photothermal agents (PTAs) with cost-effective and high photothermal conversion efficiency are highly desirable. Herein, we unite the green process for delamination of V2AlC to produce a high yield mass of two-dimensional (2D) V2C nanosheets (NSs) by using algae extracts and demonstrate their high antibacterial efficiency. The resultant V2C NSs present decent structural reliability and intrinsic antibacterial ability. Powerful near-infrared (NIR) absorption and extraordinary photothermal conversion proficiency make it a good PTA for the photothermal treatment of bacteria. The antibacterial efficiency evaluation indicated that V2C NSs could effectively kill both Gram-positive S. aureus and Gram-negative E. coli. About 99.5% of both types of bacteria could be killed with low-dose of V2C NSs suspension (40 μg/mL) with 5 min NIR irradiation due to the intrinsic antibacterial ability and photothermal effect of V2C NSs, which is much higher than previous reports on Ta4C3, Ti3C2, MoSe2, and Nb2C. This work expands the application of MXene V2C NSs for rapid bacteria-killing and would gain promising attention for applications in the sterilization industry.