Titania-coated gold nanorods with expanded photocatalytic response. Enzyme-like glucose oxidation under near-infrared illumination

Single-Molecule Spectroscopy Reveals the Plasmon-Assisted Nanozyme Catalysis on AuNR@TiO2

Gold nanoparticles are frequently employed as nanozyme materials due to their capacity to catalyze various enzymatic reactions. Given their plasmonic nature, gold nanoparticles have also found extensive utility in chemical and photochemical catalysis owing to their ability to generate excitons upon exposure to light. However, their potential for plasmon-assisted catalytic enhancement as nanozymes has remained largely unexplored due to the inherent challenge of rapid charge recombination. In this study, we have developed a strategy involving the encapsulation of gold nanorods (AuNRs) within a titanium dioxide (TiO2) shell to facilitate the efficient separation of hot electron/hole pairs, thereby enhancing nanozyme reactivity. Our investigations have revealed a remarkable 10-fold enhancement in reactivity when subjected to 530 nm light excitation following the introduction of a TiO2 shell. Leveraging single-molecule kinetic analyses, we discovered that the presence of the TiO2 shell not only amplifies catalytic reactivity by prolonging charge relaxation times but also engenders additional reactive sites within the nanozyme's intricate structure. We anticipate that further enhancements in nanozyme performance can be achieved by optimizing interfacial interactions between plasmonic metals and semiconductors.

Copper Immobilized over 2D Hexagonal SBA-15 for Electrochemical and Colorimetric Sulfite Sensing

Sulfite (SO₃^2-) is considered a highly toxic anion for living organisms. Herein, we report the synthesis of copper immobilized over a 2D hexagonally ordered mesoporous silica material CuMS as an electrochemical and colorimetric dual-technique-based sensing platform for sulfite detection. The immobilization of copper on silica was achieved through the bis[3-(triethoxysilyl)propyl]tetrasulfide (TEPTS) ligand. Morphological and physical properties of the material were confirmed by several characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N₂ sorption, and X-ray photoelectron spectroscopy. The CuMS material retained mesoporosity with a narrow pore size distribution (D ≈ 5.4 nm) and a high Brunauer-Emmett-Teller surface area of 682 m² g^-1 after the immobilization of copper. The prepared catalyst shows promising electrocatalytic activity toward sulfite oxidation. A linear variation in the peak current was obtained for SO₃^2- oxidation in the 0.2-15 mM range with a high sensitivity of 62.08 μA cm^-2, under optimum experimental conditions. The limit of detection (LOD) was found to be 1.14 nM. CuMS also shows excellent activity toward colorimetric detection of sulfite anions with an LOD of 0.4 nM. The proposed sensor shows high selectivity toward the sulfite anion, even in the presence of common interferents. The detection of sulfite in white wine with excellent recovery demonstrates the practical applicability of this sensor.

Gold-Platinum Nanoparticles with Core-Shell Configuration as Efficient Oxidase-like Nanosensors for Glutathione Detection

Nanozymes, defined as nanomaterials that can mimic the catalytic activity of natural enzymes, have been widely used to develop analytical tools for biosensing. In this regard, the monitoring of glutathione (GSH), a key antioxidant biomolecule intervening in the regulation of the oxidative stress level of cells or related with Parkinson’s or mitochondrial diseases can be of great interest from the biomedical point of view. In this work, we have synthetized a gold-platinum Au@Pt nanoparticle with core-shell configuration exhibiting a remarkable oxidase-like mimicking activity towards the substrates 3,3′,5,5′-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD). The presence of a thiol group (-SH) in the chemical structure of GSH can bind to the Au@Pt nanozyme surface to hamper the activation of O₂ and reducing its oxidase-like activity as a function of the concentration of GSH. Herein, we exploit the loss of activity to develop an analytical methodology able to detect and quantify GSH up to µM levels. The system composed by Au@Pt and TMB demonstrates a good linear range between 0.1–1.0 µM to detect GSH levels with a limit of detection (LoD) of 34 nM.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Plasma Cu-decorated TiO2-x/CoP particle-level hierarchical heterojunctions with enhanced photocatalytic-photothermal performance

Plasma Cu-decorated TiO_2-x/CoP particle-level hierarchical heterojunction photocatalysts with surface engineering were fabricated through solvothermal and solid phase reduction strategies. The CoP nanoparticles not only serve as a cost-effective cocatalyst but also provide abundant surface active sites, which facilitate rapid transfer of photogenerated carriers. The Ti³⁺ and oxygen vacancy defects extend photoresponse from UV to visible light region, and enhance the separation efficiency of photogenerated carriers efficiently. Because of surface plasma resonance (SPR) of Cu, Cu/TiO_2-x/CoP with average particle size of 100-200 nm has significant photothermal effect, in which the temperature of Cu/TiO_2-x/CoP is increased by 76 °C with irradiation for 30 s, ~ 8 times higher than that of the original TiO₂. Cu/TiO_2-x/CoP exhibits a high photocatalytic degradation rates for highly toxic 2,4-dichlorophenol (99.2%) and 2,4,6-trichlorophenol (98.5%), which higher 7.6 and 8.9 times than the initial TiO₂, respectively. Thanks to the particle-level hierarchical heterojunction, the efficient surface engineering and SPR effect favoring the spatial charge separation, Cu/TiO_2-x/CoP shows excellent photocatalytic-photothermal Performance. This particle-level hierarchical heterojunction architectural design provides a new insight for synthesizing particulate photocatalysts with high-efficiency.

Near-Infrared-Driven Photocatalysts: Design, Construction, and Applications

Photocatalysts, which utilize solar energy to catalyze the oxidation or reduction half reactions, have attracted tremendous interest due to their great potential in addressing increasingly severe global energy and environmental issues. Solar energy utilization plays an important role in determining photocatalytic efficiencies. In the past few decades, many studies have been done to promote photocatalytic efficiencies via extending the absorption of solar energy into near-infrared (NIR) light. This Review comprehensively summarizes the recent progress in NIR-driven photocatalysts, including the strategies to harvest NIR photons and corresponding photocatalytic applications such as the degradation of organic pollutants, water disinfection, water splitting for H₂ and O₂ evolution, CO₂ reduction, etc. The application of NIR-active photocatalysts employed as electrocatalysts is also presented. The subject matter of this Review is designed to present the relationship between material structure and material optical properties as well as the advantage of material modification in photocatalytic reactions. It paves the way for future material design in solar energy-related fields and other energy conversion and storage fields.

Recent Advances in the Design and Photocatalytic Enhanced Performance of Gold Plasmonic Nanostructures Decorated with Non-Titania Based Semiconductor Hetero-Nanoarchitectures

Plasmonic photocatalysts combining metallic nanoparticles and semiconductors have been aimed as versatile alternatives to drive light-assisted catalytic chemical reactions beyond the ultraviolet (UV) regions, and overcome one of the major drawbacks of the most exploited photocatalysts (TiO2 or ZnO). The strong size and morphology dependence of metallic nanostructures to tune their visible to near-infrared (vis-NIR) light harvesting capabilities has been combined with the design of a wide variety of architectures for the semiconductor supports to promote the selective activity of specific crystallographic facets. The search for efficient heterojunctions has been subjected to numerous studies, especially those involving gold nanostructures and titania semiconductors. In the present review, we paid special attention to the most recent advances in the design of gold-semiconductor hetero-nanostructures including emerging metal oxides such as cerium oxide or copper oxide (CeO2 or Cu2O) or metal chalcogenides such as copper sulfide or cadmium sulfides (CuS or CdS). These alternative hybrid materials were thoroughly built in past years to target research fields of strong impact, such as solar energy conversion, water splitting, environmental chemistry, or nanomedicine. Herein, we evaluate the influence of tuning the morphologies of the plasmonic gold nanostructures or the semiconductor interacting structures, and how these variations in geometry, either individual or combined, have a significant influence on the final photocatalytic performance.

Gold-Based Nanoparticles on Amino-Functionalized Mesoporous Silica Supports as Nanozymes for Glucose Oxidation

The transformation of glucose represents a topic of great interest at different levels. In the first place, glucose is currently conceived as a green feedstock for the sustainable production of chemicals. Secondly, the depletion of glucose at the cellular level is currently envisioned as a promising strategy to treat and alter the erratic metabolism of tumoral cells. The use of natural enzymes offers multiple advantages in terms of specificity towards the glucose substrate but may lack sufficient robustness and recyclability beyond the optimal operating conditions of these natural systems. In the present work, we have evaluated the potential use of an inorganic based nanohybrid containing gold nanoparticles supported onto ordered mesoporous supports. We have performed different assays that corroborate the enzyme-mimicking response of these inorganic surrogates towards the selective conversion of glucose into gluconic acid and hydrogen peroxide. Moreover, we conclude that these enzyme-like mimicking surrogates can operate at different pH ranges and under mild reaction conditions, can be recycled multiple times and maintain excellent catalytic response in comparison with other gold-based catalysts.

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.

A H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods for highly sensitive sensing of matrix metalloproteinase 2

We construct for the first time a H₂O₂-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods in neutral substrate solutions for highly sensitive detection of matrix metalloproteinase 2.

Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine

BACKGROUND

Gold nanoparticles (AuNPs) with unique physicochemical properties have received a great deal of interest in the field of biological, chemical and biomedical implementations. Despite the widespread use of AuNPs in chemical and biological sensing, catalysis, imaging and diagnosis, and more recently in therapy, no comprehensive summary has been provided to explain how AuNPs could aid in developing improved sensing and catalysts systems as well as medical settings.

SCOPE OF REVIEW

The chemistry of Au-based nanosystems was followed by reviewing different applications of Au nanomaterials in biological and chemical sensing, catalysis, imaging and diagnosis by a number of approaches, and finally synergistic combination therapy of different cancers. Afterwards, the clinical impacts of AuNPs, future application of AuNPs, and opportunities and challenges of AuNPs application were also discussed.

MAJOR CONCLUSIONS

AuNPs show exclusive colloidal stability and are considered as ideal candidates for colorimetric detection, catalysis, imaging, and photothermal transducers, because their physicochemical properties can be tuned by adjusting their structural dimensions achieved by the different manufacturing methods.

GENERAL SIGNIFICANCE

This review provides some details about using AuNPs in sensing and catalysis applications as well as promising theranostic nanoplatforms for cancer imaging and diagnosis, and sensitive, non-invasive, and synergistic methods for cancer treatment in an almost comprehensive manner.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Photocatalytic oxidation of glucose in water to value-added chemicals by zinc oxide-supported cobalt thioporphyrazine

Efficient photocatalytic oxidation of glucose into value-added chemicals was achieved by ZnO/CoPzS₈ composite in water, the presence of CoPzS₈ changed the glucose reaction pathway and glucaric acid was obtained in this photocatalytic system.

Synergistic Nanozymetic Activity of Hybrid Gold Bipyramid-Molybdenum Disulfide Core@Shell Nanostructures for Two-Photon Imaging and Anticancer Therapy

In recent years, the concept of combined therapy using gold hybrid nanomaterials has been broadly adopted to pioneer new anticancer treatments. However, their synergistic anticancer effects have yet to be thoroughly investigated. Herein,a hybrid gold nanobipyramid nanostructure coated with molybdenum disulfide (MoS₂) semiconductor (AuNBPs@MoS₂) was proposed as a smart nanozyme for anticancer therapy and two-photon bioimaging. The hybrid material showed dramatically enhanced localized surface plasmon resonance property under excitation owing to its anisotropic nature, coupled with the rich electron density in MoS_2, resulting in the superior in situ photogeneration of reactive oxidative species (ROS - ¹O₂, ^•OH). We demonstrated that the synergistic effect of enhanced photothermal conversion and generation of ROS could increase the anticancer effect of AuNBPs@MoS₂. Two-photon luminescence imaging confirmed that AuNBPs@MoS₂ was successfully internalized in cancer cells and that simultaneous anticancer treatments based on catalytic and photothermal therapy could be achieved. This study highlighted, for the first time, a novel approach of plasmon-mediated powerful anticancer therapy and imaging via the unprecedented combination of anisotropic AuNBPs and two-dimensional MoS₂ material.

Prompting peroxidase-like activity of gold nanorod composites by localized surface plasmon resonance for fast colorimetric detection of prostate specific antigen

The interaction between incident light and surface electrons in conductive nanoparticles produces localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, and dielectric environment. Hybrid heterostructure materials combining two or more materials in one structure represent a powerful way to achieve unique properties and multifunctionality compared to those of the individual nanoparticle components. Hybrid gold nanorods and gold nanoclusters (GNR/AuNCs) heterostructures prepared by intimate integration of GNRs with AuNCs exhibit both localized surface plasmon resonance (LSPR) property and peroxidase-like activity. It is found that the catalytic activity of the AuNC/GNR heterostructure could be remarkably enhanced by LSPR induced by photon-plasmon coupling in the visible to near-infrared (NIR) region. Meanwhile, the catalytic activity of enzyme-like AuNC/GNRs may be regulated by immunoreactions to realize specific recognition of a target analyte. Accordingly, a fast colorimetric assay within 5 min for the detection of prostate specific antigen (PSA) was developed based on a AuNC/GNRs heterostructure mask regulated by the target molecule under photon-plasmon coupling. The color intensity is inversely proportional to the PSA concentration, and quantitative analysis may be achieved in a range of 10 and 200 pg mL-1. This sensor was practically applied to detect PSA levels in prostate cancer serum samples and the determined values agreed well with those measured by the hospital using standard methods. This indicates that the AuNC/GNRs heterostructure-based assay has high accuracy for the analysis of practical samples. Moreover, the new method has the advantages of very fast determination and low sample volume requirements.

A glucose/O2 fuel cell-based self-powered biosensor for probing a drug delivery model with self-diagnosis and self-evaluation

Extending the application of self-powered biosensors (SPB) into the drug delivery field is highly desirable. Herein, a robust glucose/O2 fuel cell-based biosensor is successfully integrated with a targeted drug delivery system to create a self-sustained and highly compact drug delivery model with self-diagnosis and self-evaluation (DDM-SDSE). The glucose/O2 fuel cell-based biosensor firstly performs its diagnostic function by detecting the biomarkers of cancer. The drug delivery system attached on the anode of the glucose/O2 fuel cell can be released during the diagnostic operation to guarantee the occurrence of a therapy process. Accompanied by the therapy process, the glucose/O2 fuel cell-based biosensor can also act as an evaluation component to dynamically monitor the therapy efficacy by analyzing drug-induced apoptotic cells. In addition, the use of an abiotic catalyst largely improves the stability of the glucose/O2 fuel cell without sacrificing the output performance, further ensuring long-time dynamic evaluation as well as highly sensitive diagnosis and evaluation in this DDM-SDSE. Therefore, the present study not only expands the application of SPBs but also offers a promising in vitro "diagnosis-therapy-evaluation" platform to acquire valuable information for clinical cancer therapy.

In-Situ Deposition of Plasmonic Gold Nanotriangles and Nanoprisms onto Layered Hydroxides for Full-Range Photocatalytic Response towards the Selective Reduction of p-Nitrophenol

In this work, we present photocatalysis as a greener alternative to conventional catalysis where harsh reaction conditions, temperature and/or pressure are needed. Photodegradation of organic pollutants is a cost-effective, eco-friendly solution for the decontamination of water and air, and is a field that has been continuously growing over the last decade. Plasmonic metal nanoparticles absorb light irradiation that is transferred to the chemical reaction in a different fashion. Furthermore, plasmonic nanostructures can be combined with other materials, such as semiconductors or a basic support, to create hybrid systems capable of overcoming certain challenges that photocatalysis is facing nowadays and to expand the photocatalytic response towards the whole visible-near infrared (Vis-NIR) ranges. The main objective of this work has been to in-situ synthesize plasmonic anisotropic gold nanoparticles onto hydrotalcite (HT) and calcined hydrotalcite (CHT) supports by way of a sequential deposition-reduction (DR) process and to evaluate their efficiency as heterogeneous catalysts towards the selective oxidation of p-nitrophenol (hereafter 4-NP), a well-known model contaminant, either in the absence or the presence of full-range light irradiation sources (LEDs) spanning the whole UV-Vis-NIR range. Special attention has been paid to the optimization of the catalyst preparation parameters, including the pH and the concentration of reducing and stabilizing agents. Interestingly, the use of thermally modified hydrotalcites has enabled a strong metal-support interaction to induce the preferential formation of triangular-shaped Au nanoparticles with ca. 0.8 wt.% loading while increasing the colloidal stability and surface area of the catalyst with respect to the commercial untreated HT supports.

Luminescent mesoporous nanorods as photocatalytic enzyme-like peroxidase surrogates

One-step synthesis of luminescent mesoporous rods with enhanced photocatalytic response as novel metal-free peroxidase-like nanozymes.

Herein we report on a novel inorganic peroxidase-mimicking nanocatalyst activated under blue LED photoirradiation. A novel flash-pyrolysis method has been developed for the generation of strong blue photoluminescence (PL) centers attributed to silicon and carbon-based sites within a mesoporous SBA-15 silica nanorod platform. The type of centers and their PL response can be controlled by varying the flash thermal treatment conditions. By tailoring the operating conditions the system can be driven towards the preferential generation of carbon-based luminescent centers, with or without the simultaneous generation of silicon-based centers. The properties and the nature of these luminescent centers within the mesoporous nanorods have been thoroughly corroborated by a battery of characterization techniques including fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) at the local level of the structures combined with scanning transmission electron microscopy (STEM) imaging. In addition, these luminescent mesoporous nanorods have been successfully tested as robust photocatalysts able to display peroxidase-like activity and indirect glucose sensing in a wider range of pH conditions compared to the natural enzyme, especially when carbogenic dots and oxygen-deficient silica centers are simultaneously present in the structure.

A full-spectrum photocatalyst with strong near-infrared photoactivity derived from synergy of nano-heterostructured Er3+-doped multi-phase oxides

The development of full-spectrum photocatalysts active in the near-infrared (NIR) region has gained increasing attention in the photodegradation of organic pollutants. Herein, we designed a full-spectrum photocatalyst with strong NIR photoactivity based on the synergy of Er³⁺-doped ZnO-CuO-ZnAl₂O₄ multi-phase oxides (Er³⁺-doped Zn/Cu/Al-MPO) via the formation of n-p-n double heterojunctions. The photocatalyst was prepared by synthesizing nanosheets of a Zn/Cu/Al/Er hydrotalcite-like compound (Zn/Cu/Al/Er-HLC) with a co-precipitation method followed by calcination of the nanosheets at 800 °C. The as-prepared Er³⁺-doped Zn/Cu/Al-MPO inherits the nanosheet morphology of Zn/Cu/Al/Er-HLC, and displays over-doubled photoactivity in the entire ultraviolet (UV), visible and NIR regions compared to undoped Zn/Cu/Al-MPO. The excellent photocatalytic activity of Er³⁺-doped Zn/Cu/Al-MPO, especially its strong NIR photoactivity, is ascribed to its Er³⁺-doped CuO-involved multi-crystalline phase heterostructure, i.e., n-p-n double heterojunctions, which does not only offer an enhanced NIR absorption but also promotes the separation of photogenerated charge carriers. Importantly, the synergy of all the parts of the n-p-n double heterojuctions plays an important role in interface band structure regulation for the enhancement of the photocatalytic properties of Er³⁺-doped Zn/Cu/Al-MPO. This work has demonstrated the feasibility of utilizing hydrotalcite-like precursors in the design of full-spectrum photocatalysts active in the NIR region.

Mimicking horseradish peroxidase and oxidase using ruthenium nanomaterials

Ru NPs could catalyze the oxidation of 3,3,5,5-tetramethylbenzidine, o-phenylenediamine and dopamine hydrochloride in the presence of H₂O₂, and also catalyze the oxidization of 3,3,5,5-tetramethylbenzidine and sodium l-ascorbate by dissolved oxygen.