Palladium-Based Nanomaterials: A Platform to Produce Reactive Oxygen Species for Catalyzing Oxidation Reactions

Modifying Parallel Excitations into One Framework for C(sp3)─H Bond Activation with Energy Combined More Than Two Photons

Natural photosynthesis enzymes utilize energies of several photons for challenging oxidation of water, whereas artificial photo-catalysis typically involves only single-photon excitation. Herein, a multiphoton excitation strategy is reported that combines parallel photo-excitations with a photoinduced electron transfer process for the activation of C(sp3)─H bonds, including methane. The metal-organic framework Fe3-MOF is designed to consolidate 4,4',4″-nitrilotrisbenzoic units for the photoactivation of dioxygen and trinuclear iron clusters as the HAT precursor for photoactivating alkanes. Under visible light irradiation, the dyes and iron clusters absorbed parallel photons simultaneously to reach their excited states, respectively, generating 1O2 via energy transfer and chlorine radical via ligand-to-metal charge transfer. The further excitation of organic dyes leads to the reduction of 1O2 into O2 •- through a photoinduced electron transfer, guaranteeing an extra multiphoton oxygen activation manner. The chlorine radical abstracts a hydrogen atom from alkanes, generating the carbon radical for further oxidation transformation. Accordingly, the total oxidation conversion of alkane utilizing three photoexcitation processes combines the energies of more than two photons. This new platform synergistically combines a consecutive excited photoredox organic dye and a HAT catalyst to combine the energies of more than two photons, providing a promising multiphoton catalysis strategy under energy saving, and high efficiency.

Metal-Free Activation of Molecular Oxygen by 9-Fluorenone-Based Porous Organic Polymers for Selective Aerobic Oxidation

Oxygen activation is a critical step in heterogeneous oxidative processes, particularly in catalytic, electrolytic, and pharmaceutical applications. Among the various catalysts available for photocatalytic O2 activation, homogeneous aryl ketones are at the forefront. To avoid the degradation and deactivation of aryl ketones, 9-fluorenone-based porous organic polymers were designed and regulated by doping them with co-monomers. The obtained heterogeneous photocatalyst showed good performance in O2 activation, and its performance was better than that of homogeneous 9-fluorenone. The obtained heterogeneous photocatalyst showed good reusability. We believe that the presented method and findings represent an important step toward designing catalysts tailored for specific tasks.

A nanoparticle-based sonodynamic therapy reduces Helicobacter pylori infection in mouse without disrupting gut microbiota

Infection by Helicobacter pylori, a prevalent global pathogen, currently requires antibiotic-based treatments, which often lead to antimicrobial resistance and gut microbiota dysbiosis. Here, we develop a non-antibiotic approach using sonodynamic therapy mediated by a lecithin bilayer-coated poly(lactic-co-glycolic) nanoparticle preloaded with verteporfin, Ver-PLGA@Lecithin, in conjunction with localized ultrasound exposure of a dosage permissible for ultrasound medical devices. This study reveals dual functionality of Ver-PLGA@Lecithin. It effectively neutralizes vacuolating cytotoxin A, a key virulence factor secreted by H. pylori, even in the absence of ultrasound. When coupled with ultrasound exposure, it inactivates H. pylori by generating reactive oxygen species, offering a potential solution to overcome antimicrobial resistance. In female mouse models bearing H. pylori infection, this sonodynamic therapy performs comparably to the standard triple therapy in reducing gastric infection. Significantly, unlike the antibiotic treatments, the sonodynamic therapy does not negatively disrupt gut microbiota, with the only major impact being upregulation of Lactobacillus, which is a bacterium widely used in yogurt products and probiotics. This study presents a promising alternative to the current antibiotic-based therapies for H. pylori infection, offering a reduced risk of antimicrobial resistance and minimal disturbance to the gut microbiota.

Complexed Photosensitizer of Hypericin with G-Quadruplex: Structure-Dependent Behavior

Despite the increased interest of visible-light-absorbing compound Hypericin (Hyp) in photodiagnosis, photocatalysis, and photodynamic therapy (PDT) applications, a major obstacle still exists; i.e., the photoactivity is diminished due to the facile aggregation of Hyp in aqueous environment that induces excited-state quenching. Herein, we explore the excited-state property of Hyp bound to the DNA G-quadruplex by combining multiple steady-state and time-resolved spectroscopy. We find that the aggregation-induced quenching effect can be successfully prevented by appropriate G-quadruplex binders that disperse Hyp into monomer. The binding of Hyp/G-quadruplex is selective, however, exhibiting a preferential binding toward parallel G-quadruplexes (c-kit2, C14B1, STAT3, S50, and PS2.M), over antiparallel or hybrid G-quadruplex (Tel22, TBA). The excited-state property of Hyp is highly related to the binding behavior, showing a consistent trend that the better the Hyp/G-quadruplex binding, the longer the triplet 3Hyp* lifetime and the higher the efficiency to produce 1O2. For Hyp/c-kit2, the major binding mode is 5'-end stacking, which offers protection from collisional quenching reactions and ensures a stable photocycle of 3Hyp*-O2 energy transfer forming 1O2, leading to the highest 1O2 quantum yield (0.67) with superior photostability. These findings open possibilities of developing Hyp/G-quadruplex complex as a biocompatible photosensitizer for PDT applications, etc.

Water Flow-Driven Coupling Process of Anodic Oxygen Evolution and Cathodic Oxygen Activation for Water Decontamination and Prevention of Chlorinated Byproducts

Electrochemical advanced oxidation process (EAOP) is a promising technology for decentralized water decontamination but is subject to parasitic anodic oxygen evolution and formation of toxic chlorinated byproducts in the presence of Cl-. To address this issue, we developed a novel electrolytic process by water flow-driven coupling of anodic oxygen evolution reaction (OER) and cathodic molecular oxygen activation (MOA). When water flows from anode to cathode, O2 produced from OER is carried by water through convection, followed by being activated by atomic hydrogen (H*) on Pd cathode to produce •OH. The water flow-driven OER/MOA process enables the anode to be polarized at low potential (1.7 V vs SHE) that is lower than that of conventional EAOP whose •OH is produced from direct water oxidation (>2.3 V vs SHE). At a flow rate of 30 mL min-1, the process could achieve 94.8% removal of 2,4-dichlorophenol (2,4-DCP) and 71.5% removal of chemical oxygen demand (COD) within 45 min at an anode potential of 1.7 V vs SHE and cathode potential of -0.5 V vs SHE. To achieve the comparable 2,4-DCP removal performance, 4.3-fold higher energy consumption was needed for the conventional EAOP with titanium suboxide anode (anode potential of 2.9 V vs SHE), but current efficiency declined by 3.5 folds. Unlike conventional EAOP, chlorate and perchlorate were not detected in the OER/MOA process, because low anode potential <2.0 V vs SHE was thermodynamically unfavorable for the formation of chlorinated byproducts by anodic oxidation, indicated by theoretical calculations and experimental data. This study provides a proof-in-concept demonstration of water flow-driven OER/MOA process, representing a paradigm shift of electrochemical technology for water decontamination and prevention of chlorinated byproducts, making electrochemical water decontamination more efficient, more economic, and more sustainable.

Integrating Dual-Single-Atom Moieties with N, S Co-Coordination Configurations for Oxidative Cascaded Catalysis

Oxidation reaction is of critical importance in chemical industry, in which the primary O2 activation step still calls for high-performance catalysts. Here, a newly developed precise locating carbonization strategy for the fabrication of 21 kinds of dual-metal single-atom catalysts with N, S co-coordinated configurations is reported. As is exemplified by CoN3 S1 /CuN4 @NC, systematical characterizations and in situ observations imply the atomic CoN3 S1 and CuN4 sites immobilized on N-doped carbon, over which the remarkable electron redistribution originating from their unsymmetrical coordination configurations. Impressively, the obtained CoN3 S1 /CuN4 @NC exhibits unprecedented capability in O2 activation and enables a spontaneous process through its dynamic configuration, significantly outperforming the CoN4 /CuN4 @NC and CoN3 S1 @NC counterparts. Hence, the CoN3 S1 /CuN4 @NC shows attractive performance in domino synthesis of natural flavone and 19 kinds of derivatives from benzyl alcohol, 2'-hydroxyacetophenone, and corresponding substituted substrates via aerobic oxidative coupling-dehydrogenation. Detailed reaction mechanisms and molecule behaviors over CoN3 S1 /CuN4 @NC are also investigated through in situ experiments and simulations.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Recent advances in stimuli-responsive nano-heterojunctions for tumor therapy

Stimuli-responsive catalytic therapy based on nano-catalysts has attracted much attention in the field of biomedicine for tumor therapy, due to its excellent and unique properties. However, the complex tumor microenvironment conditions and the rapid charge recombination in the catalyst limit catalytic therapy's effectiveness and further development. Effective heterojunction nanomaterials are constructed to address these problems to improve catalytic performance. Specifically, on the one hand, the band gap of the material is adjusted through the heterojunction structure to promote the charge separation efficiency under exogenous stimulation and further improve the catalytic capacity. On the other hand, the construction of a heterojunction structure can not only preserve the function of the original catalyst but also achieve significantly enhanced synergistic therapy ability. This review summarized the construction and functions of stimuli-responsive heterojunction nanomaterials under the excitation of X-rays, visible-near infrared light, and ultrasound in recent years, and further introduces their application in cancer therapy. Hopefully, the summary of stimuli-responsive heterojunction nanomaterials' applications will help researchers promote the development of nanomaterials in cancer therapy.

All-or-None Selectivity in Probing Polarity-Determined Trinucleotide Repeat Foldings with a Parity Resolution by a Beyond-Size-Matching Ligand

Abnormal amplification of trinucleotide repeats (TNRs) is associated with neurodegenerative diseases by forming a particular hairpin bulge. It is well known that the polarity and parity of TNRs can regulate the formed hairpin structures. Therefore, there is a great challenge to efficiently discriminate the hairpin structures of TNRs with substantial selectivity. Herein, we developed a fluorescent ligand of pseudohypericin (Pse) with a beyond-size-matching (BSM) geometry to selectively sense hairpin structures of GTC and CTG TNRs. The GTC hairpin structures can bind with Pse dominantly at extreme T-T mismatches by the virtue of their most extrahelical conformations, while there is no binding event to occur with the polarity-inverted counterpart CTG hairpin structures because of the limited space provided by their intrahelical T-T mismatches. In addition, this all-or-none response with the polarity-dependent folding (PoDF) is independent of the length of these TNRs. Interestingly, the parity-dependent folding (PaDF) of GTC hairpin structures can also be resolved. Besides pure TNRs, the competency of this BSM ligand to sense the PoDF and PaDF effects was also generalized to DNAs with TNRs occurring at loop and stem end regions. To our knowledge, this is the first experimental observation with the state-of-the-art performance over the fluorescence measurement of PoDF and PaDF in TNRs. Our work provides an expedient way to elucidate the TNR folding by designing ligands having BSM features.

Novel Microbial Palladium Nanoparticles with a High Photothermal Effect for Antibacterial Applications

Novel biocompatible palladium nanoparticles (Pd-NPs) have been prepared by microorganisms via Bacillus megaterium Y-4. It was demonstrated that ultrasonication treatment of biologically reduced Pd-NPs impart a much higher absorption in NIR regions and a better photothermal conversion efficiency to the material. The as-prepared material showed excellent biocompatibility and antibacterial activity under NIR irradiation. In less than 10 min, the disinfection efficiency for a low dosage of Pd-NPs (20 mg/L) was 99.99% toward both Staphylococcus aureus and Escherichia coli. The exclusive and even dispersed microbial Pd-NPs display a high efficiency of photothermal conversion under the irradiation of NIR, which endows them with excellent antibacterial activity in a low dosage.

SDS coated Fe3O4@MoS2 with NIR-enhanced photothermal-photodynamic therapy and antibiotic resistance gene dissemination inhibition functions

Infection caused by antibiotic-resistant bacteria is serious threat for public health, and calls for novel antibacterial agents with versatile functions. In particular, nanomaterial is one of promising candidates to fight the increasing antibiotic resistance crisis. Here, we synthesized distinct Fe₃O₄@MoS₂@SDS nanocomposites by ultrasonication assisted SDS coating on the Fe₃O₄@MoS₂. Photothermal investigation indicated that the Fe₃O₄@MoS₂@SDS showed excellent and stable photothermal performance and could be a NIR-induced photothermal reagent. It also displayed superior disinfection ability of Escherichia coli (E. coli), Methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa (P. aeruginosa) and in vivo wound healing ability with the help of NIR irradiation. According to the results of electron paramagnetic resonance (EPR) and radical capture tests, plenty of superoxide, hydroxyl radicals, singlet oxygen and living cell reactive oxygen species can be observed under NIR irradiation. Besides, the synergistic effect Fe₃O₄@MoS₂@SDS and NIR irradiation eradicated almost all the biofilms of MRSA, so this kind of function enhanced the disinfection ability of Fe₃O₄@MoS₂@SDS under NIR irradiation. Furthermore, its inhibition effect on antibiotic resistance gene dissemination was also investigated. As expected, the Fe₃O₄@MoS₂@SDS could efficiently and broadly block the horizontal transfer of antibiotic resistance genes which mediated by conjugative plasmids, and its blocking effect was better than that we have reported Fe₃O₄@MoS₂. Overall, our findings revealed that the Fe₃O₄@MoS₂@SDS could be a potential candidate for photothermal-photodynamic therapy and antibiotic resistance gene dissemination inhibition.

How to Make Personal Protective Equipment Spontaneously and Continuously Antimicrobial (Incorporating Oxidase-like Catalysts)

The inability of commercial personal protective equipment (PPE) to inactivate microbes in the droplets/aerosols they intercept makes used PPE a potential source of cross-contamination. To make PPE spontaneously and continuously antimicrobial, we incorporate PPE with oxidase-like catalysts, which efficiently convert O₂ into reactive oxygen species (ROS) without requiring any externally applied stimulus. Using a single-atom catalyst (SAC) nanoparticle containing atomically dispersed copper atoms as the reactive centers (Cu-SAC) and a silver-palladium bimetallic alloy nanoparticle (AgPd_0.38) as models for oxidase-like catalysts, we show that the incorporation of oxidase-like catalysts enables PPE to inactivate bacteria in the droplets/aerosols they intercept without requiring any externally applied stimulus. Notably, this approach works both for PPE that are fibrous and woven such as a commercial KN95 facial respirator and for those made of solid plastics such as an apron. This work suggests a feasible and global approach for preventing PPE from spreading infectious diseases.

Preparation of Two-Dimensional Pd@Ir Nanosheets and Application in Bacterial Infection Treatment by the Generation of Reactive Oxygen Species

Noble metal nanozymes have shown great promise in biomedicine; however, developing novel and high-performance noble metal nanozymes is still highly pressing and challenging. Herein, we, for the first time, prepared two-dimensional (2D) Pd@Ir bimetal nanosheets (NSs) with well-defined size and composition by a facile seed-mediated growth strategy. Enzyme-mimicked investigations find that the Pd@Ir NSs possess oxidase (OXD)-, peroxidase (POD)-, and catalase (CAT)-like multienzyme-mimetic activities. Especially, they exhibited much higher OXD- and POD-like activities than individual Pd NSs and Ir nanoparticles (NPs). The density functional theory (DFT) calculations reveal that the adsorption energy of O2 on Pd@Ir NSs is lower than that on the pure Pd NSs, which is more favorable for the conversion of O2 molecules from the triplet state (3O2) into the singlet state (1O2). Finally, based on the outstanding nanozyme activities to yield highly active singlet oxygen (1O2) and hydroxyl radicals (•OH) as well as excellent biosafety, the as-prepared Pd@Ir NSs were applied to treat bacteria-infected wounds, and satisfactory therapeutic outcomes were achieved. We believe that the highly efficient 2D Pd@Ir nanozyme will be an effective therapeutic reagent for various biomedical applications.

Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn-Co Catalyst

Activation of molecular oxygen plays a crucial role in natural organisms and the modern chemical industry. Herein, we report a Mn-Co dual-single-atom catalyst that exerts a specific synergy in boosting O₂ activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O₂ is demonstrated through transforming O₂ into a reactive superoxide anion radical (O₂^•-) on Co-N₄ sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn-N_xO_y). EXAFS analysis results show a longer average Mn-O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn-O bonds easier to cycle. Control experiments support that such Mn-O bonding conditions could facilitate H-elimination of C-H in HMF. The co-existence of two types of ROS effectively matches the oxidation of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diatomic catalyst for activating O₂ by two types of activation pathways.

Folic acid conjugated chitosan encapsulated palladium nanoclusters for NIR triggered photothermal breast cancer treatment

This study developed folic acid (FA) conjugated chitosan (CS) encapsulated rutin (R) synthesized palladium nanoclusters (Pd NCs) for NIR triggered and folate receptor (FR) targeted triple-negative breast cancer (MDA-MB 231 cells) treatment. R-Pd NCs exhibited flower-shaped particles with an average size of <100 nm. FA-CS encapsulation concealed the flower shape of R-Pd NCs with a positive charge. The XRD spectrum confirmed the cubic crystalline structure of Pd. The FA conjugation on CS improved the cellular uptake of R-Pd NCs in MDA-MB 231 cells was confirmed by TEM. FA-CS-R-Pd NCs (+NIR) treatment was considerably inhibited the MDA-MB 231 cells proliferation evidenced by cell viability, fluorescent staining, and flow cytometry analysis. Further, in vitro hemolysis assay and in Ovo model confirmed the non-toxic nature of FA-CS-R-Pd-NCs with or without NIR radiation. Hence, this study concluded that FA-CS-R-Pd NCs can be applied for the treatment of drug-resistant breast cancer.

The synergy of adsorption and photosensitization of platinum-doped graphitic carbon nitride for improved removal of rhodamine B

Graphitic carbon nitride (g-C₃N₄) has attracted growing attention recently for photodegradation of pollutants. However, the photosensitization performance of g-C₃N₄ was limited by insufficient generation efficiency of reactive oxygen species (ROS) and weak light absorption. In this study, platinum (Pt)-doped g-C₃N₄ photocatalyst was synthesized by thermal polycondensation using dicyandiamide and chloroplatinic acid. The structure and composition of Pt-doped g-C₃N₄ were tested by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS), which indicated that the Pt-doped g-C₃N₄ was successfully prepared. Compared with bare g-C₃N₄, Pt²⁺-doped g-C₃N₄ has wider light absorption range, lower band gap, and higher photon-generated carrier migration efficiency, which significantly improved the light absorption range and photosensitization efficiency of Pt²⁺-doped g-C₃N₄, while photodegradation efficiency for Rhodamine B (RhB) increased from 50 to 90%. The effecting factors of adsorption and photocatalytic degradation performance of Pt²⁺-doped g-C₃N₄ for RhB were investigated in detail. The adsorption is a monolayer adsorption process that fits the Langmuir model, as well as being a spontaneous endothermic process. Using a white LED as an excitation source, electrons and holes in Pt²⁺-doped g-C₃N₄ were generated. The electrons reacting with dissolved oxygen produce active oxygen species such as •OH and ¹O₂, which can degrade RhB on the surface of Pt²⁺-doped g-C₃N₄. The photocatalytic method has the advantages of simple operation, low cost, and high efficiency, and has the potential to directly remove dyes in wastewater utilizing sunlight.

Near-Infrared Light-Excited Reactive Oxygen Species Generation by Thulium Oxide Nanoparticles

Exploring materials that can absorb near-infrared (NIR) light to produce reactive oxygen species (ROS) is necessary for many fields. Herein we show that thulium oxide nanoparticles are viable for NIR-stimulated ROS generation. This property may be related to the unique energy levels, large absorption cross section, low fluorescence emission, and ∼10-3 s lifetime of the 3H4 state of Tm ions. We further demonstrate the impact of these nanoparticles on photodynamic therapy (PDT), in which impressive tumor inhibition was recorded after exposure to either a broadband halogen lamp or an 808 nm laser. Our results may provide insight into the areas of photocatalysis, pollution treatment, and fine chemical synthesis.

Efficient Magnetic Nanocatalyst-Induced Chemo- and Ferroptosis Synergistic Cancer Therapy in Combination with T1-T2 Dual-Mode Magnetic Resonance Imaging Through Doxorubicin Delivery

Excessive iron ions in cancer cells can catalyze H₂O₂ into highly toxic ^•OH and then promote the generation of reactive oxygen species (ROS), inducing cancer ferroptosis. However, the efficacy of the ferroptosis catalyst is still insufficient because of low Fe(II) release, which severely limited its application in clinic. Herein, we developed a novel magnetic nanocatalyst for MRI-guided chemo- and ferroptosis synergistic cancer therapies through iRGD-PEG-ss-PEG-modified gadolinium engineering magnetic iron oxide-loaded Dox (ipGdIO-Dox). The introduction of the gadolinium compound disturbed the structure of ipGdIO-Dox, making the magnetic nanocatalyst be more sensitive to weak acid. When ipGdIO-Dox entered into cancer cells, abundant Fe(II) ions were released and then catalyzed H₂O₂ into highly toxic OH^•, which would elevate cellular oxidative stress to damage mitochondria and cell membranes and induce cancer ferroptosis. In addition, the iRGD-PEG-ss-PEG chain coated onto the nanoplatform was also broken by high expression of GSH, and then, the Dox was released. This process not only effectively inhibited DNA replication but also further activated cellular ROS, making the nanoplatform achieve stronger anticancer ability. Besides, the systemic delivery of ipGdIO-Dox significantly enhanced the T₁- and T₂-weighted MRI signal of the tumor, endowing accurate diagnostic capability for tumor recognition. Therefore, ipGdIO-Dox might be a promising candidate for developing an MRI-guided chemo- and ferroptosis synergistic theranostic system.

Activating the Neutral pH Photozymatic Activity of g-C3N4 Nanosheet through Post-Synthetic Incorporation of Pt

The catalytic activity of photozyme can be regulated through light irradiation time and intensity, but it still suffers from low activity in physiological neutral pH (typically, pH < 5). Herein,...

A Novel Pd-P Nano-Alloy Supported on Functionalized Silica for Catalytic Aerobic Oxidation of Benzyl Alcohol

Catalytic aerobic oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) over supported noble metal catalysts has grabbed the attention of researchers due to the critical role of PhCHO in numerous industrial syntheses. In the present study, a novel catalyst, Pd-P alloy supported on aminopropyl-functionalized mesoporous silica (NH2-SiO2), was prepared through in situ reduction and characterized by BET-BJH analysis, SEM, TEM, XRD, FTIR, TG-DTA, and XPS. Chemical properties and catalytic performance of Pd-P/NH2-SiO2 were compared with those of Pd° nanoparticles (NPs) deposited on the same support. Over Pd-P/NH2-SiO2, the BnOH conversion to PhCHO was much higher than over Pd°/NH2-SiO2, and significantly influenced by the nature of solvent, reaching 57% in toluene at 111 °C, with 63% selectivity. Using pure oxygen as an oxidant in the same conditions, the BnOH conversion increased up to 78%, with 66% selectivity. The role of phosphorous in improving the activity may consist of the strong interaction with Pd that favours metal dispersion and lowers Pd electron density.

Selective Heavy Atom Effect Forming Photosensitizing Hot Spots in Double-Stranded DNA Matrix

Triplet exciton formation is essential for photosensitization-based photochemistry and photobiology. The heavy atom effect (HAE), in the form of either external or internal mode, is a basic mechanism for increasing the triplet exciton yield of photosensitizers. Herein, we report a new HAE mode by noncovalent cohosting of heavy atoms and photosensitizers in a double-stranded DNA (dsDNA) matrix. With dsDNA bearing several thymine (T) or cytosine (C) mismatches, heavy atoms (e.g., Hg²⁺ or Ag⁺) and dsDNA-staining dyes (photosensitizers) were spatially adjoined in close proximity, thus resulting in enhanced phosphorescence and ¹O₂ generation from the photosensitizers. The dsDNA-hosted HAE provides highly selective recognition for the heavy atoms, which is not applicable in either the external or the internal mode. Considering the simpleness and efficiency of the spatially adjoined HAE, as well as the functionality of DNA, the proposed HAE mode is appealing for various singlet oxygen- and phosphorescence-related applications.

Promoting reactive oxygen species generation: a key strategy in nanosensitizer-mediated radiotherapy

The radiotherapy enhancement effect of numerous nanosensitizers is based on the excessive production of reactive oxygen species (ROS), and only a few systematic reviews have focused on the key strategy in nanosensitizer-mediated radiotherapy. To clarify the mechanism underlying this effect, it is necessary to understand the role of ROS in radiosensitization before clinical application. Thus, the source of ROS and their principle of tumor inhibition are first introduced. Then, nanomaterial-mediated ROS generation in radiotherapy is reviewed. The double-edged sword effect of ROS and the potential dangers they may pose to cancer patients are subsequently addressed. Finally, future perspectives regarding ROS-regulated nanosensitizer applications and development are discussed.

Surface-bound reactive oxygen species generating nanozymes for selective antibacterial action

Acting by producing reactive oxygen species (ROS) in situ, nanozymes are promising as antimicrobials. ROS' intrinsic inability to distinguish bacteria from mammalian cells, however, deprives nanozymes of the selectivity necessary for an ideal antimicrobial. Here we report that nanozymes that generate surface-bound ROS selectively kill bacteria over mammalian cells. This result is robust across three distinct nanozymes that universally generate surface-bound ROS, with an oxidase-like silver-palladium bimetallic alloy nanocage, AgPd0.38, being the lead model. The selectivity is attributable to both the surface-bound nature of ROS these nanozymes generate and an unexpected antidote role of endocytosis. Though surface-bound, the ROS on AgPd0.38 efficiently eliminated antibiotic-resistant bacteria and effectively delayed the onset of bacterial resistance emergence. When used as coating additives, AgPd0.38 enabled an inert substrate to inhibit biofilm formation and suppress infection-related immune responses in mouse models. This work opens an avenue toward biocompatible nanozymes and may have implication in our fight against antimicrobial resistance.

Self-Driven Reactive Oxygen Species Generation via Interfacial Oxygen Vacancies on Carbon-Coated TiO2-x with Versatile Applications

The effective activation and utilization of O₂ have always been the focus of scientists because of its wide applications in catalysis, organic synthesis, life and medical science. Here, a novel method for activating O₂ spontaneously via interfacial oxygen vacancies on carbon-coated TiO_2-x to generate reactive oxygen species (ROS) with versatile applications is reported. The interfacial oxygen vacancies can be stabilized by the carbon layer and hold its intrinsic properties for spontaneous oxygen activation without light irradiation, while common surface oxygen vacancies on TiO_2-x are always consumed by the capture of H₂O to form the surface hydroxyls. Thus, O₂ absorbed at the interface of carbon and TiO_2-x can be directly activated into singlet oxygen (¹O₂) or superoxide radicals (·O₂^-), confirmed both experimentally and theoretically. These reactive oxygen species exhibit excellent performance in oxidation reactions and inhibition of MCF-7 cancer cells, providing new insight into the effective utilization of O₂ via oxygen vacancies on metal oxides.

Nanozymes for Environmental Pollutant Monitoring and Remediation

Nanozymes are advanced nanomaterials which mimic natural enzymes by exhibiting enzyme-like properties. As nanozymes offer better structural stability over their respective natural enzymes, they are ideal candidates for real-time and/or remote environmental pollutant monitoring and remediation. In this review, we classify nanozymes into four types depending on their enzyme-mimicking behaviour (active metal centre mimic, functional mimic, nanocomposite or 3D structural mimic) and offer mechanistic insights into the nature of their catalytic activity. Following this, we discuss the current environmental translation of nanozymes into a powerful sensing or remediation tool through inventive nano-architectural design of nanozymes and their transduction methodologies. Here, we focus on recent developments in nanozymes for the detection of heavy metal ions, pesticides and other organic pollutants, emphasising optical methods and a few electrochemical techniques. Strategies to remediate persistent organic pollutants such as pesticides, phenols, antibiotics and textile dyes are included. We conclude with a discussion on the practical deployment of these nanozymes in terms of their effectiveness, reusability, real-time in-field application, commercial production and regulatory considerations.

Metal-organic frameworks (MOFs) derived carbon-coated NiS nanoparticles anchored on graphene layers for high-performance Li-S cathode material

Due to its high capacity (1675 mAh g^-1), Li-S batteries have been considered as one of the ideal energy storage systems. The grand challenges of lithium-sulfur batteries are sulfur immobilization and improving electrical conductivity of cathode composite. The carbon-sulfur (C-S) composites and the polar materials (Ni(OH)₂, TiO₂, MnO₂, TiS₂, Co₉S₈, etc) integration have been proven to be two of the most effective routes to achieving good Li-S battery performance. However, each strategy has drawbacks: the C-S composites have low volume density and the polar materials are often lack of electrical conductivity. Therefore, the hybridization of carbon and polar materials shall provide synergistic effects achieving ideal sulfur cathode. Herein, a hybrid material with carbon-coated NiS nanoparticles grown on graphene sheets was synthesized through a hydrothermal reaction followed by two steps of annealing. The obtained composite has a well-balanced ratio between graphene and NiS. An optimized energy density was demonstrated in lithium-sulfur cells.

Oxygen Vacancy Defect-Induced Activity Enhancement of Gd Doping Magnetic Nanocluster for Oxygen Supplying Cancer Theranostics

This work finds that Fe₃O₄ nanoclusters can rearrange by Gd doping and then self-assemble to a hollow magnetic nanocluster (HMNC), providing larger magnetic moments to obtain an excellent MRI capability and increasing the number of oxygen vacancies in HMNC. The hollow structure makes platinum(IV) prodrugs effectively load into HMNC. Second, plenty of oxygen vacancy defects can capture oxygen molecules, enhance the catalytic activity of HMNC, and then promote intracellular ROS generation. On the basis of this, a targeting iRGD-labeled HMNC nanosystem (iHMNCPt-O₂) is developed through loading oxygen molecules and platinum(IV) prodrugs for chemo- and chemodynamic therapy of cancer. This nanosystem shows an excellent response ability to weak acid and GSH, which can cause a series of cascade reactions in a cell. These cascade reactions are dramatically enhanced at the intracellular ROS level, cause mitochondria and DNA damage, and then induce cancer cell death. Besides, systemic delivery of iHMNCPt-O₂ significantly enhanced the MRI contrast signal of tumors and improved the quality of MR images, accurately diagnosing tumors. Therefore, this work provides a novel method for accelerating the Fenton-like reaction and enhancing the MRI capability and fabricates a promising "all-in-one" system to overwhelm the problems of cancer theranostic.

2D AuPd alloy nanosheets: one-step synthesis as imaging-guided photonic nano-antibiotics

The complicated synthesis and undesirable biocompatibility of nanomaterials hinder the synergistic photothermal/photodynamic therapy for bacterial infections. Herein, we develop a one-step preparation method of 2D AuPd alloy nanosheets as imaging-guided photonic nano-antibiotics. 2D AuPd alloy nanosheets with an extremely small thickness (∼1.5 nm) exhibit prominent photothermal effects (η = 76.6%), excellent ROS generation, strong photoacoustic signals and desirable biocompatibility. AuPd nanosheets can eliminate 100% of representative Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) when irradiated using an 808 nm laser at 1 W cm^-2 for 5 minutes. After being modified with a bacterial targeting peptide, under the guidance of photoacoustic imaging, AuPd nanosheets achieve promising synergistic photothermal/photodynamic therapeutic efficacy in treating Staphylococcus aureus infected mice. This work expands the biomedical application of 2D noble metal nanomaterials to the field of photonic nano-antibiotics.

Manipulation of Neighboring Palladium and Mercury Atoms for Efficient *OH Transformation in Anodic Alcohol Oxidation and Cathodic Oxygen Reduction Reactions

The synergetic effect of neighboring heterogeneous atoms is capable of enabling unexpected catalytic performance, and the design of a well-ordered atomic structure and elaborating the underlying interactions are crucial for the development of superior electrocatalysts in fuel cells. We demonstrate here that an ordered Pd-Hg intermetallic alloy with dimensions of several nanometers can be subtly manipulated using a mild wet-chemical reduction approach. On the basis of combined results of XPS and HAADF-STEM analysis, the adjacent regions of metallic atoms were found to be evenly occupied by heterogeneous elements from the distribution features of the surface structure. Due to charge transfer from Hg to neighboring Pd, the down-shift of the d-band center in PdHg alloys was theoretically beneficial for desorption of crucial intermediates (*OH), both in anodic ethanol oxidation reaction (EOR) and in cathodic oxygen reduction reaction (ORR). In the presence of Hg atoms with lower *OH desorption energy, the rapid dissociation of *OH from Pd facilitated the final H₂O formation, with superior ORR efficiency comparable to Pt/C catalysts. Remarkably, the rapid combination of *OH on Hg atoms with CH₃CO* on neighboring Pd atoms unambiguously favored generation of acetate ions (rate-determining) in the catalytic EOR process, resulting in a high mass activity (7.68 A per mgPd). This well-ordered atomic structure also shows excellent long-term stability in ethylene glycol oxidation reaction and ORR.

Interlaced Pd-Ag nanowires rich in grain boundary defects for boosting oxygen reduction electrocatalysis

Given the high cost and poisoning issues of Pt, developing Pd-based catalysts as substitutes is highly essential. Although substantial progress has been made, the synthesis of Pd-based electrocatalysts with both high activity and stability in the oxygen reduction reaction (ORR) remains a challenge. In this work, we prepared Pd-Ag nanowires with up to micro-sized length and a diameter of ∼17 nm via a facile modified polyol method. The obtained Pd-Ag nanowires (NWs) exhibit interlaced features and are rich in grain boundary defects. Due to the continuous grain boundaries in the one-dimensional (1D) structure and the optimized composition, the synthesized Pd1Ag1 NWs show half-wave potential of 0.897 V and mass activity of 0.103 A mg-1 in alkaline media toward ORR, higher than those of both state-of-the-art Pt/C and other Pd-Ag counterparts. Significantly, after stability tests over 5000 cycles, Pd1Ag1 NWs shows a 2 mV positive shift, much better than that of Pt/C, exhibiting striking stability for ORR. This work may provide an avenue to construct advanced catalysts by surface defect engineering.

Light-activated nanozymes: catalytic mechanisms and applications

Recently, nanozymes have attracted enormous interest for their high stability, low cost and various enzyme-like activities. In nature, many biochemical reactions require light. Recently, introducing light to nanozymes has also been reported, especially for photosensitized oxygen activation. Compared to normal nanozymes, light-activated nanozymes possess several advantages including light-regulated activity, using molecular oxygen as a green oxidant, and often higher activity can be achieved. Herein, we summarize light-activated nanozymes, starting from their photophysical processes and identification of reactive oxygen species (ROS). Although the types of light-activated nanozymes are still quite limited and cannot yet mimic the same reactions as natural photo-related enzymes, they have widened the range of nanozymes. A few specific applications are highlighted, including sensing, chemical synthesis, degradation of organic pollutants, and cleavage and repair of DNA. Finally, a few future research opportunities are discussed.

Highly efficient Cu(ii)-pyrazoledicarboxylate heterogeneous catalysts for a base-free aerobic oxidation of benzylic alcohol to benzaldehyde with hydrogen peroxide as the oxidant

A Cu(ii)-pyrazoledicarboxylate MOF displayed high activity and selectivity in the base-free oxidation of benzyl alcohol to benzaldehyde combined with H₂O₂.

Highly efficient oxygen photosensitization of carbon dots: the role of nitrogen doping

The role of nitrogen doping in the highly efficient oxygen photosensitization of carbon dots is underlined.

Engineering Two-Dimensional Pd Nanoplates with Exposed Highly Active {100} Facets Toward Colorimetric Acid Phosphatase Detection

Enzyme-like activity and efficiency of nanomaterials are strongly controlled by their size, composition, and structure, and hence the structural parameters need to be optimized. Here, we report that two-dimensional Pd nanoplates enclosed by {100}-facets [{100}PdSP@rGO] exhibit substantially enhanced intrinsic oxidase-like activities relative to the {111}-facets ones and Pd nanocubes in catalyzing the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine. By taking ascorbic acid 2-phosphate as the substrate, which transforms to ascorbic acid in the presence of acid phosphatase (ACP), the {100}PdSP@rGO could be used as an efficient nanozyme for colorimetric ACP detection without resorting to destructive H₂O₂. A good linear relationship from 0.01 to 6.0 mU/mL with a detection limit of 8.3 μU/mL is obtained, which is better than most previously reported ACP assays. Importantly, the excellent assay performance could be successfully applied to ACP determination in serum samples with high accuracy. This study demonstrates that the enzyme-like activity of nanomaterials could be finely tuned simultaneously by controlling their exposed crystal facets and high specific surface area.

From bimetallic PdCu nanowires to ternary PdCu-SnO2 nanowires: Interface control for efficient ethanol electrooxidation

At present, although a large number of palladium-based nanowire electrocatalysts have been prepared, there are few reports on nanowires containing rich metal oxides. Herein, porous PdCu alloy nanowires and PdCu-SnO₂ nanowires were prepared by using a galvanic displacement synthesis method. Due to their one-dimensional structure, rough surfaces with non-homogeneous edges, electronic effect, and the advanced PdCu/SnO₂ interface of the as-synthesized PdCu-SnO₂ nanowire catalysts, they exhibited a mass activity of 7770.0 mA mg^-1 towards ethanol oxidation, which was 7.6-fold higher than that of Pd/C catalysts (1025.0 mA mg^-1). In addition, they behaved strong durability upon chronoamperometry and continuous cyclic voltammetry tests. The electrochemical measurements demonstrated that SnO₂ was introduced into the PdCu/SnO₂ interface, which promoted the oxidation of ethanol at a lower potential and accelerated the oxidation of Pd-CO_ads via SnO₂-OH_ads to regenerate the active sites. This research highlights the significance of introducing metal oxides into the nanostructure interface, and the performance of Pd-containing catalysts towards ethanol oxidation reaction was greatly improved.

Radiosensitizing Effect of Gadolinium Oxide Nanocrystals in NSCLC Cells Under Carbon Ion Irradiation

Gadolinium-based nanomaterials can not only serve as contrast agents but also contribute to sensitization in the radiotherapy of cancers. Among radiotherapies, carbon ion irradiation is considered one of the superior approaches with unique physical and biological advantages. However, only a few metallic nanoparticles have been used to improve carbon ion irradiation. In this study, gadolinium oxide nanocrystals (GONs) were synthesized using a polyol method to decipher the radiosensitizing mechanisms in non-small cell lung cancer (NSCLC) cell lines irradiated by carbon ions. The sensitizer enhancement ratio at the 10% survival level was correlated with the concentration of Gd in NSCLC cells. GONs elicited an increase in hydroxyl radical production in a concentration-dependent manner, and the yield of reactive oxygen species increased obviously in irradiated cells, which led to DNA damage and cell cycle arrest. Apoptosis and cytostatic autophagy were also significantly induced by GONs under carbon ion irradiation. The GONs may serve as an effective theranostic material in carbon ion radiotherapy for NSCLC.

Defect Engineering of Palladium-Tin Nanowires Enables Efficient Electrocatalysts for Fuel Cell Reactions

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd-Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd₄Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd₄Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd⁰ sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd₄Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

Simultaneously Broadened Visible Light Absorption and Boosted Intersystem Crossing in Platinum-Doped Graphite Carbon Nitride for Enhanced Photosensitization

Herein, taking graphite carbon nitride ( g-C₃N₄) as the example, we demonstrated that the two limiting factors that determine the photosensitization performance, namely, light absorption and intersystem crossing (ISC), could be simultaneously enhanced through Pt²⁺ doping. Specifically, as a π-conjugated two-dimensional semiconductor, g-C₃N₄ is capable of absorbing light shorter than 460 nm (2.7 eV). Upon Pt²⁺ doping that allows metal-to-ligand charge transfer (MLCT) from Pt²⁺ to the substrate g-C₃N₄, the light absorption of g-C₃N₄ was greatly expanded up to 1000 nm. Meanwhile, the large atomic number of Pt²⁺ ensures promotion of ISC to activate the triplet state of g-C₃N₄ via heavy atom effect (HAE), which was confirmed via both photosensitization performance and photophysical characterizations. Further, the enhanced light absorption and photosensitization of Pt²⁺-doped g-C₃N₄ were harvested for antibiotics removal, a type of environment contaminants that gained global attention because of their worldwide abuse. Compared with its undoped counterpart, Pt²⁺-doped g-C₃N₄ featured significantly improved antibiotics removal in the presence of low-power white LED irradiation, which is promising for photosensitized environmental remediation.

Enhanced Generation of Non-Oxygen Dependent Free Radicals by Schottky-type Heterostructures of Au-Bi2S3 Nanoparticles via X-ray-Induced Catalytic Reaction for Radiosensitization

Despite the development of nanomaterials with high-Z elements for radiosensitizers, most of them suffer from their oxygen-dependent behavior in hypoxic tumor, nonideal selectivity to tumor, or inevasible damages to normal tissue, greatly limiting their further applications. Herein, we develop a Schottky-type heterostructure of Au-Bi₂S₃ with promising ability of reactive free radicals generation under X-ray irradiation for selectively enhancing radiotherapeutic efficacy by catalyzing intracellular H₂O₂ in tumor. On the one hand, like many other nanomaterials with rich high-Z elements, Au-Bi₂S₃ can deposit higher radiation dose within tumors in the form of high energy electrons. On the other hand, Au-Bi₂S₃ can remarkably improve the utilization of a large number of X-ray-induced low energy electrons during radiotherapy for nonoxygen dependent free radicals generation even in hypoxic condition. This feature of Schottky-type heterostructures Au-Bi₂S₃ attributes to the generated Schottky barrier between metal Au and semiconductor Bi₂S₃, which can trap the X-ray-generated electrons and transfer them to Au, resulting in efficient separation of the electron-hole pairs. Then, because of the matched potential between the conduction band of Bi₂S₃ and overexpressed H₂O₂ within tumor, the Au-Bi₂S₃ HNSCs can decompose the intracellular H₂O₂ into highly toxic ^•OH for selective radiosensitization in tumor. As a consequence, this kind of nanoparticle provides an idea to develop rational designed Schottky-type heterostructures as efficient radiosensitizers for enhanced radiotherapy of cancer.

Catalytic Mechanisms of Nanozymes and Their Applications in Biomedicine

The research on nanozymes has increased dramatically in recent years and a new interdiscipline, nanozymology, has emerged. A variety of nanomaterials have been designed to mimic the characteristics of natural enzymes, which connects an important bridge between nanotechnology and biological science. Unlike natural enzymes, the nanoscale properties of nanozymes endow them with the potential to regulate their enzymatic-like activity from different perspectives. The mechanisms behind those methods are intriguing. In this Review, we introduce these mechanisms from the aspects of surface chemistry, surface modification, molecular imprinting, and hybridization and then focus attention on some specific catalytic mechanisms of several representative nanozymes. The applications of nanozymes ranging from bioassay, imaging, to disease therapy are also discussed in detail to prove the fact that the inherent physicochemical properties of nanomaterials not only make nanozymes the analogues of biological enzymes, but also endow them with incomparable advantages and broad prospects in biomedical fields. Finally, four characteristics and some challenges of nanozymes are summarized.

Theoretical insight into the electrocatalytic reduction of CO2 with different metal ratios and reaction mechanisms on palladium-copper alloys

Environmental impacts of continued CO2 production have led to an increased need for new methods of CO2 removal and energy development. Electrochemical reduction of CO2 has been shown to be a good method through recent studies. Alloys are of special interest for these applications, because of their unique chemical and physical properties that allow for highly active surfaces. Here, PdnCum (m + n = 15 and n > m) bimetallic electrocatalysts were used for systematic studies to understand the effect of the composition of Pd and Cu on the electrochemical reduction of CO2 to CO. In particular, the Pd-Cu alloy with the Pd/Cu = 2/1 atomic ratio (i.e., Pd10Cu5) has the best catalytic effect, particularly true at the step of the hydrogenation of CO2 to COOH, and the Pd10Cu5 catalyst is better than most known electrodes. With the energetic analysis of the proposed reaction pathways over the Pd10Cu5 catalyst, the limiting voltages for CO2 reduction to CH3OH, CH4, and CH3CH2O have been compared. Most importantly, the kinetic model analysis showed that the rate constant values indicate that the probability of generating C2H5OH on the Pd10Cu5 catalyst is greater than that of CH3OH or CH4. The findings revealed in this study may shed some light on the design of cost-effective and efficient electrocatalysts for CO2 conversion to CO or to other useful hydrocarbons.