Catalytic and peroxidase-like activity of carbon based-AuPd bimetallic nanocomposite produced using carbon dots as the reductant

In situ formation of fluorescence species for the detection of alkaline phosphatase and organophosphorus pesticide via the ascorbate oxidase mimetic activity of AgPd bimetallic nanoflowers

Sensitive detection strategies for enzymes and their inhibitors not only have critical significance in clinical diagnosis but can be extended to food and environment analysis. Here, bimetallic AgPd alloy nanoflowers were synthesized using carbon dots as the reductant via a two-step reduction method. The AgPd bimetallic nanoflowers exhibit ascorbate oxidase mimetic activity, which can rapidly catalyze the oxidization of ascorbic acid to dehydroascorbic acid (DHA). The DHA can then react with o-phenylenediamine (OPD) to produce 3-(1, 2-dihydroxyethyl)furo[3,4-b] quinoxalin-1(3H)-one (DFQ), accompanying with the characteristic fluorescence peak at 440 nm for DFQ. Alkaline phosphatase catalyzes l-ascorbyl-2-phosphate to generate AA, while organic phosphorus pesticides (OPPs) such as chlorpyrifos can inhibit the activity of alkaline phosphatase. By utilizing the enzyme-nanozyme tandem catalytic reaction, the fluorescence of the system varies in the presence of different concentrations of ALP or OPPs, which can be used to detect ALP in serum and OPPs in vegetables and fruits.

Self-Supported Ag/Pt/Pd Alloy Aerogels as High-Performance Bifunctional and Durable Electrocatalysts for Methanol and Ethanol Oxidation Reactions

Assembly of nanoparticles (NPs) into functional macrostructures is imperative for the development of NP-based devices. However, existing methods employ insulating organic ligands, polymers, and biomolecules as mediators for the NP assembly, which are detrimental for charge transport and interparticle coupling that impede the efficient integration of low-dimensional properties. Herein, we report a methodology for the direct self-supported assembly of Ag/Pt/Pd alloy NPs into high surface area (119.1 ± 3.9 to 140.1 ± 5.7 m2/g), mesoporous (19.7 ± 6.2 to 23.0 ± 1.6 nm), and conducting nanostructures (aerogels) that show superior electrocatalytic activity and stability in methanol (MOR) and ethanol (EOR) oxidation reactions. Ultrasmall (3.9 ± 1.3 nm) and quasi-spherical Ag/Pt/Pd alloy NPs were synthesized via stepwise galvanic replacement reaction (GRR) of glutathione (GSH)-coated Ag NPs. As-synthesized NPs were transformed into free-standing alloy hydrogels via chemical oxidation of the GSH ligands. The composition of alloy aerogels was tuned by varying the oxidant/thiolate molar ratio of the precursor NP sol that prompts Ag dealloying with in situ generated HNO3, selectively enriching the Pt and Pd catalytic sites on the aerogel surface. The highest-performing alloy aerogel (Ag0.449Pt0.480Pd0.071) demonstrates excellent mass activity for methanol (3179.5 mA/mg) and ethanol (2444.5 mA/mg) electro-oxidation reactions, which are ∼4-5 times higher than those of commercial Pt/C and Pd/C electrocatalysts. The aerogel also maintained high alcohol oxidation activity for 17 h at a constant potential of -0.3 V in an alkaline medium. The synergistic effects of noble metal alloying, high surface area and mesoporosity, and the pristine active surface of aerogels provide efficient interaction of analytes with the nanostructure surface, facilitating both MOR and EOR activity and improving tolerance for poisonous byproducts, enabling the Ag/Pt/Pd alloy aerogel a promising (electro)catalyst for a number of new technologies.

Multi-signal aptasensor for thrombin detection based on catalytically active gold nanoparticles and fluorescent silicon quantum dots

A multi-signal aptasensor for thrombin determination is proposed based on catalytically active gold nanoparticles (AuNPs) and fluorescent silicon quantum dots (SiQDs). Yellow 4-Nitrophenol (4-NP) could be converted to colorless 4-Aminophenol (4-AP) by catalytically active aptamer-modified AuNPs (S1-AuNPs). The SiQDs emitted strong blue fluorescence at 455 nm at the excitation wavelength of 367 nm. When thrombin was absent, S1-AuNPs could catalytically reduce yellow 4-NP to colorless 4-AP. When thrombin was added, the aptamer could be transformed into a G-quadruplex structure, which masked the surface-active catalytic sites of AuNPs and restrained the reduction of 4-NP. Thus, the fluorescence of SiQDs was greatly quenched by 4-NP through the inner filter effect (IFE), and the solution color remained yellow. As the concentration of thrombin increased, the catalytic activity of S1-AuNPs decreased. The concentration of 4-NP that was converted to 4-AP declined and the unconverted 4-NP increased. In this process, the absorption peak of 4-NP at 400 nm increased while the fluorescence emission of SiQDs at 455 nm decreased. The linear ranges of the fluorometric and colorimetric aptasensor were 0.5-30 nM and 0.3-30 nM, respectively. The limits of detection (LOD) for the two modes were 0.15 nM and 0.13 nM. Furthermore, a portable sensing platform was constructed by combining the smartphone-based device with the software ImageJ for the determination of thrombin. With the advantages of cost-effectiveness, simplicity of operation and broad applicability, this aptasensor provided a new perspective for on-site determination of thrombin in the clinical field.

Smartphone-assisted colorimetric detection of Salmonella typhimurium based on the catalytic reduction of 4-nitrophenol by β-cyclodextrin-capped gold nanoparticles

Salmonella typhimurium (S. typhimurium) is one of the most common pathogens in the environment, such as in drinking water and soil. Herein, an on-site detection method was developed by combining silver-coated magnetic nanoparticles (Fe₃O₄@Ag NPs) with the β-cyclodextrin-capped gold nanoparticles (β-CD-Au NPs) to achieve sensitive detection of S. typhimurium. After they formed a sandwich structure in the presence of S. typhimurium, the 4-nitrophenol was reduced to 4-aminophenol based on the nitro-reductase activity of β-CD-Au NPs. The naked eyes were able to observe the color change from yellow to colorless. Under optimal conditions, the detection range of S. typhimurium was 10-10⁷ CFU mL^-1, and the limit of detection (LOD) was 10 CFU mL^-1. The total detection time was 90 min, showing satisfactory performance in real samples. We combined a smartphone app with the colorimetric method, making it possible to semi-quantitatively detect S. typhimurium by analyzing the grey value. In conclusion, this assay detects S. typhimurium in environmental samples, offering an accurate and sensitive detection method without sophisticated equipment.

Recent advances in biomedical applications of 2D nanomaterials with peroxidase-like properties

Significant progress has been made in developing two-dimensional (2D) nanomaterials owing to their ultra-thin structure, high specific surface area, and many other advantages. Recently, 2D nanomaterials with enzyme-like properties, especially peroxidase (POD)-like activity, are highly desirable for many biomedical applications. In this review, we first classify the types of 2D POD-like nanomaterials and then summarize various strategies for endowing 2D nanomaterials with POD-like properties. Representative examples of biomedical applications are reviewed, emphasizing in antibacterial, biosensing, and cancer therapy. Last, the future challenges and prospects of 2D POD-like nanomaterials are discussed. This review is expected to provide an in-depth understanding of 2D POD-like materials for biomedical applications.

Heparin-enhanced peroxidase-like activity of iron-cobalt oxide nanosheets for sensitive colorimetric detection of trypsin

Iron-cobalt oxide nanosheets (FeCo-ONSs) were proved to have intrinsic peroxidase-like activity. Additionally, the peroxidase-like activity of FeCo-ONSs toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) was dramatically enhanced after heparin addition due to the stronger affinity toward TMB. Protamine combines with heparin, so the promotion of peroxidase-like activity of FeCo-ONSs with heparin was suppressed. With the addition of trypsin, protamine was hydrolyzed and the enhancement effect of catalytic activity of FeCo-ONSs was recovered. Based on above process, a sensitive colorimetric platform for trypsin activity determination was constructed through measuring the absorbance of produced oxTMB at 652 nm, providing a linear detection range of 5 to 500 ng/mL and a low detection limit of 2.8 ng/mL. The method was applied to trypsin determination in real samples (human urine sample and multienzyme tablet sample) with satisfactory results, illustrating the potential application of this biosensor.

Fluorimetric and ratiometric colorimetric dual-mode detection of organophosphorus pesticides based on carbon dots/DTNB

Carbon dots/DTNB as fluorimetric and ratiometric colorimetric dual-mode probes for the detection of chlorpyrifos.

Progress in the Application of Carbon Dots-Based Nanozymes

As functional nanomaterials with simulating enzyme-like properties, nanozymes can not only overcome the inherent limitations of natural enzymes in terms of stability and preparation cost but also possess design, versatility, maneuverability, and applicability of nanomaterials. Therefore, they can be combined with other materials to form composite nanomaterials with superior performance, which has garnered considerable attention. Carbon dots (CDs) are an ideal choice for these composite materials due to their unique physical and chemical properties, such as excellent water dispersion, stable chemical inertness, high photobleaching resistance, and superior surface engineering. With the continuous emergence of various CDs-based nanozymes, it is vital to thoroughly understand their working principle, performance evaluation, and application scope. This review comprehensively discusses the recent advantages and disadvantages of CDs-based nanozymes in biomedicine, catalysis, sensing, detection aspects. It is expected to provide valuable insights into developing novel CDs-based nanozymes.

Furfural and organic acid targeted carbon dot sensor array for the accurate identification of Chinese baijiu

Baijiu quality control has always been a major challenge for researchers. In this paper, taking furfural which is closely related to baijiu brewing process and organic acids related to baijiu fermentation process and microorganism types as the main discriminating factors, a carbon dot (CDs) sensor array targeting furfural and organic acids was constructed to identify 41 kinds of baijiu. Through the fluorescence response investigation of CDs synthesized by isomers of benzenediol, aminophenol, and phenylenediamine to different baijiu, two CDs synthesized by meta-benzene substitutions containing -NH₂ were selected to build a fluorescence sensor array. Due to the aggregation-induced enhancement effect between furfural and the CDs, and the protonation of organic acid and the CDs, different fluorescence changes were observed, the sensor array combined with partial least squares regression could quantitatively analyze furfural and organic acids. What is more, semi-quantitative analysis of furfural and lactic acid in baijiu was performed. Owing to the interaction of the two CDs with furfural and organic acids in baijiu, the sensor array could accurately identify different baijiu through linear discriminant analysis. This sensor array has potential applications in the quantitative analysis of flavor substances in other alcoholic beverages, moreover, this method could provide a quick response and practical tool for real-time quality control monitoring in the baijiu industry.

Detection of enrofloxacin by flow injection chemiluminescence immunoassay based on cobalt hydroxide nanozyme

The emergence and development of low-cost and high-efficiency nanozymes are promising to replace natural enzymes promoting the application of chemiluminescence immunoassays. Herein, a rapid and highly sensitive flow injection chemiluminescence immunoassay based on cobalt hydroxide (Co(OH)₂) nanozyme was established to detect enrofloxacin (ENR) residues in food. In this system, Co(OH)₂ nanosheets act as nanozymes to catalyze and amplify the chemiluminescence signal of the luminol-PIP-H₂O₂ system, as well as a carrier for immobilizing antibodies to form stable immunoprobes. In addition, carboxyl resin beads with good stability and biocompatibility were used as the base of the immunosensor to carry more coating antigens, based on the principle of competitive immunity and to achieve the rapid detection of ENR. Under optimal conditions, the linear working range is 0.0001 ~ 1000 ng/mL, and the limit of detection (LOD) is 0.041 pg/mL (S/N = 3). The method has been successfully applied to the analysis of aquatic products and poultry food. A non-enzyme immunosensor using Co(OH)₂ nanosheets as antibody-conjugated carriers and peroxidase mimics for catalytic amplification of the chemiluminescence signal of luminol and using carboxyl resin beads as platform was designed to detect ENR residues in food.

Superior reducing carbon dots from proanthocyanidin for free-radical scavenging and for cell imaging

The presence of excessive ROS can cause much harm to the human body and can even cause diseases. Therefore, it is important to detect and remove ROS, but there is no ideal method available for this at present. In this research, using procyanidins, a type of plant extract with strong reducibility, as raw materials, fluorescent carbon dots (CDs) were prepared by a hydrothermal method. The proanthocyanidin-based carbon dots (PCDs) emit a light-green colored light under UV irradiation. The PCDs retain the strong reducibility of procyanidins and are highly water-soluble compared with procyanidins. The PCDs, in addition to having good biocompatibility, also have the superior properties of radical scavenging activity and cell imaging. In in vitro experiments, 1,1-diphenyl-2-picrylhydrazyl (DPPH; 100 μM) was reduced by 30% when PCDs were added up to a concentration of 87.5 μg mL^-1. At the same time, the fluorescence quenching correlates with the concentration of hypochlorite and hydrogen peroxide and has a good linearity in the range of 250-2250 nM and 60-180 μM with a detection limit of 3.676 nM and 0.602 μM, respectively. Based on the previously described advantages, PCDs have potential as a biomedicine.

Spectrofluorimetric determination of Cr(VI) and Cr(III) by quenching effect of Cr(III) based on the Cu-CDs with peroxidase-mimicking activity

The study presents a spectrofluorimetric method for the determination of Cr(III) based on 2,3-diaminophenazine (DAP) as fluorescent nano sensor. With the peroxidase-mimicking activity of copper-doped carbon dots (Cu-CDs), colorless o-phenylenediamine (OPD) was oxidized to fluorescent DAP in the presence of H₂O₂ via generation of hydroxyl radicals. The Cr(III) was found to decrease the fluorescent intensity of the Cu-CDs-mediated OPD oxidation system. Cr(VI) species were reduced to Cr(III) by employing 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the reductant, and a novel spectrofluorimetric method for the highly sensitive detection of speciation Cr(VI) and Cr(III) was developed. The Cu-CDs nanozyme was prepared from ethylenediaminetetraacetic acid copper disodium salt (Na₂[Cu (EDTA)]) by one-step pyrolysis method. Under optimal conditions, the fluorescence intensity of DAP is linearly proportional to the Cr(III) ion concentration in the range of 5 × 10^-6 to 1.5 × 10^-4 mol L^-1 and the detection limit is 1.2 × 10^-7 mol L^-1. The method has a good anti-interference performance against some metal ions, such as, Hg²⁺, Co²⁺, Cu²⁺, Mg²⁺, Ba²⁺, K⁺, Mn²⁺, Ni²⁺, Al³⁺, and Fe³⁺. The proposed method was successfully applied in the determination of Cr(VI) and Cr(III) in water samples.

Triggered peroxidase-like activity of Au decorated carbon dots for colorimetric monitoring of Hg2+ enrichment in Chlorella vulgaris

Developing a rapid, low-cost, and multimode detection method for heavy metal ions remains a compelling goal for many applications, including food safety, environmental and biological analysis. This study investigated the influence of Hg²⁺ on the peroxidase-like activity of gold nanoparticles (GNPs) decorated on carbon dots (CDs) from lysine (denoted as GNP@CDs). A new type of Hg²⁺-triggered peroxidase-like activity of GNP@CDs was discovered, which could catalyze the oxidation of the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMB. Based on the regulation of the catalytically triggered activity, a sensitive colorimetric method for the detection of Hg²⁺ was developed, with a linear range of 7-150 nM, providing a limit of detection as low as 3.7 nM. The sensor is simple and rapid, and was successfully applied to the detection of Hg²⁺ enrichment in chlorella, suggesting a promising application in biological analysis.

Novel mulberry silkworm cocoon-derived carbon dots and their anti-inflammatory properties

Mulberry silkworm cocoon (MSC) carbonisata has been used for the treatment of inflammatory diseases for hundreds of years; however, after years of research efforts, little information is available on its anti-inflammatory components and underlying mechanism. We developed novel carbon dots (CDs) derived from MSC carbonisata (MSC-CDs), for the first time, with an average diameter of 2.26-9.35 nm and a quantum yield (QY) of 6.32%. The MSC-CDs were prepared using a modified pyrolysis method, and no further modification and external surface passivation agent was required. With abundant surface groups, MSC-CDs showed distinct solubility and bioactivity. In this study, we innovatively used three classical experimental models of inflammation to evaluate the anti-inflammatory bioactivity of MSC-CDs. The results indicated that MSC-CDs exhibited marked anti-inflammatory bioactivity which was likely mediated by inhibition of the expression of interleukin-6 and tumour necrosis factor-α. These results suggest that MSC-CDs possess a remarkable anti-inflammatory property, which provides evidence to support further investigation of the considerable potential and effective material basis of this traditional Chinese medicine.

Production of gold/silver doped carbon nanocomposites for effective photothermal therapy of colon cancer

Surgery followed by adjuvant chemotherapy is a reliable therapy for colon cancer, but is associated with side effects and risks. Recent advancements in nanobioengineering in the form of targeted nanoparticles, cubosomes, liposomes, nanosheets, nanorods, quantum dots have generated substantial advancements in theranostics of colon cancer decreasing the cytotoxic drugs' side effects. We describe a facile mechanism of preparation of hybrid nanocomposite encompassing Au and Ag. Preparation of hybrid nanocomposite is one step process which may be easily escalated. The nanocomposite was characterized using transmission eleactron microscopy, energy dispersive X-Ray spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infra-red spectroscopy, UV-Vis spectroscopy, photoluminescence and cytotoxic studies. In-vivo studies were carried out in Balb/c mice. Photothermal heating experiments in HeLa cells were promising and the characterization studies clearly indicated the formation of hybrid nanocomposite. In-vivo experiments confirmed the efficacy of treatment, along with involvement of epigenetic regulation, which may be helpful in translation from research to clinical applications.

Carbon dot-based composites for catalytic applications

We summarize the construction methods and influencing factors of CDs-based composites and discuss their catalytic applications, including photocatalysis, chemical catalysis, peroxidase-like catalysis, Fenton-like catalysis and electrocatalysis.

A sensitive electrochemical sensor for bisphenol A on the basis of the AuPd incorporated carboxylic multi-walled carbon nanotubes

A sensitive electrochemical sensor for BPA based on the AuPd incorporated carboxylic multi-walled carbon nanotubes (MWCNT) with synergetic amplified current signal was developed, where MWCNT was used as supporter to improve electron transport and poly (diallyldimethylammonium chloride) (PDDA) was used as dispersant for MWCNT and overcome the intrinsic van der Waals interactions between MWCNT and further increase metal NPs loading. The prepared MWCNT-PDDA-AuPd showed enhanced electrocatalytic performance toward BPA, which is better than those of homologous monometallic counterparts and MWCNT-PDDA though the content of AuPd is really low. The peak currents of BPA increased with BPA concentration in linear range of 0.18-18 μM and the detection limit of 60 nM. The sensor showed high sensitivity, good stability, repeatability and can be used to detect BPA in milk and water samples with good performance, which demonstrate that MWCNTs-PDDA-AuPd nanocomposite may be an attractive material in applications of environmental and food analysis.

Metal–oxygen clusters as peroxidase mimics for their multifarious applications in colorimetric sensors

Metal–oxygen cluster (Fe₂₈) was certified to own inherent peroxidase-like performance, which displayed multi-functional applications in H₂O₂, glucose and dopamine detection.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Colorimetric determination of glucose in solution and via the use of a paper strip by exploiting the peroxidase and oxidase mimicking activity of bimetallic Cu-Pd nanoparticles deposited on reduced graphene oxide, graphitic carbon nitride, or MoS2 nanosheets

This work describes the preparation of bimetallic Cu-Pd nanoparticles (NPs) on supports like reduced graphene oxide (rGO), graphitic carbon nitride (g-C₃N₄) and MoS₂ sheets with a size of <10 nm. rGO is found to be the best support for synthesizing Cu-Pd NPs with controlled shape, size and oxidation state. The Cu-Pd/rGO nanocomposite also demonstrated the best peroxidase and oxidase mimicking activity compared to Cu-Pd/g-C₃N₄ and Cu-Pd/MoS₂ nanocomposites. The peroxidase mimicking activity of Cu-Pd/rGO was investigated in more detail, and a glucose oxidase (GOx) based glucose sensor was constructed that is based on the enzymatic formation of H₂O₂ and the Cu-Pd NPs-assisted oxidation of tetramethylbenzidine by H₂O₂ to give a blue-green coloration with absorption maxima at 652 nm. The assay has a 0.29 μM detection limit and a detection range that extends from 0.2 to 50 μM. The method was applied to the determination of glucose in diluted serum samples, and results compared well to those acquired with a clinical analyzer. The method also was applied in a colorimetric paper-based test stripe that can detect glucose within 10 min. Graphical abstract Schematic representation of a sensitive colorimetric glucose assay based on bimetallic Cu-Pd nanoparticles supported on 2D nanosheets, and construction of a paper based device for rapid glucose detection.

Colorimetric aptasensor for Campylobacter jejuni cells by exploiting the peroxidase like activity of Au@Pd nanoparticles

The authors describe a method for colorimetric determination of Campylobacter jejuni (C. jejuni) in milk samples. It is based on the interaction of a specific DNA aptamer with surface protein in the cell membranes of C. jejuni. Specific binding of the aptamer with the cell membrane leads to an uptake of aptamer from solution. As a result, the concentration of aptamer floating in the solution is reduced. In the presence of large quantities of aptamer, the surface of added Au@Pd nanoparticles (NPs) is covered with aptamer via electrostatic interactions. Hence, they cannot act as a peroxidase mimic and oxidize the substrate 3,3^',5,5^'-tetramethylbenzidine (TMB) to give a blue product. However, when the aptamer is bound by the target cells, the surface of the NPs is not blocked by aptamer and the NPs exert a strong peroxidase -like activity. Under defined experimental conditions, the intensity of the blue color increases with the concentration of C. jejuni, and as little as 100 CFU·mL^-1 can bedetected in milk. Graphical abstract A colorimetric aptasensor for assay Campylobacter jejuni whole cell in food samples was investigated. This assay was designed based on interaction of specific DNA aptamer with surface protein in c. jejuni cell membrane without any modification of aptamer.

Synthesis of hierarchical Co3O4@NiO core-shell nanotubes with a synergistic catalytic activity for peroxidase mimicking and colorimetric detection of dopamine

Fabrication of core-shell nanostructured catalyst is a promising way for tuning its catalytic performance due to the highly active interface and rich redox properties. In this work, hierarchical Co₃O₄@NiO core-shell nanotubes are fabricated by the deposition of NiO shells via a chemical bath treatment using electrospun Co-C composite nanofibers as templates, followed by a calcination process in air. The as-prepared Co₃O₄@NiO core-shell nanotubes exhibit a uniform and novel hollow structure with Co₃O₄ nanoparticles attached to the inner wall of NiO nanotubes and excellent catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. Due to the synergistic effect, the peroxidase-like activity of the Co₃O₄@NiO core-shell nanotubes is much higher than that of individual Co₃O₄ and NiO components. Owing to the superior peroxidase-like activity, a simple and rapid colorimetric approach for the detection of dopamine with a detection limit of 1.21µM and excellent selectivity has been developed. It is anticipated that the prepared Co₃O₄@NiO core-shell nanotubes are promising materials applied for biomedical analysis and environmental monitoring.

Facile synthesis of gold/gadolinium-doped carbon quantum dot nanocomposites for magnetic resonance imaging and photothermal ablation therapy

Composites of gold nanomaterials and imaging agents show promise in cancer therapy.

Surface-Engineered Polydopamine Particles as an Efficient Support for Catalytic Applications

Mussel-inspired polydopamine (PDA) particles with the size of ∼270 nm are used as a support of palladium (Pd) nanoparticles (NPs) for catalyst preparation. The surface morphology of the PDA particle has been modified via corrosion of CF₃COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of a carboxylic acid-terminated alkanethiol monolayer. The obtained self-assembled monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H₂PdCl₄ solution to a suspension of SAM-PDA particles at room temperature. Transmission electron microscopy, energy-dispersive X-ray mapping, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis, and Fourier transform infrared are used to characterize the catalyst and to investigate the process. Uniform Pd NPs (2-3 nm) have been well-dispersed on the SAM-PDA particles via controllable surface engineering. Surface charges and interactions with a metal ion are regulated by the monolayer of carboxylic acids. The surface chemistry of PDA particles has been finely engineered for efficient loading of noble metal NPs. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H₂. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir-Hinshelwood (L-H) model, and the calculated apparent activation energy of this process is 40.77 kJ mol^-1.

Carbon Nanodots as Peroxidase Nanozymes for Biosensing

'Nanozymes', a term coined by Scrimin, Pasquato, and co-workers to describe nanomaterials with enzyme-like characteristics, represent an exciting and emerging research area in the field of artificial enzymes. Indubitably, the last decade has witnessed substantial advancements in the design of a variety of functional nanoscale materials, including metal oxides and carbon-based nanomaterials, which mimic the structures and functions of naturally occurring enzymes. Among these, carbon nanodots (C-dots) or carbon quantum dots (CQDs) offer huge potential due to their unique properties as compared to natural enzymes and/or classical artificial enzymes. In this mini review, we discuss the peroxidase-like catalytic activities of C-dots and their applications in biosensing. The scope intends to cover not only the C-dots but also graphene quantum dots (GQDs), doped C-dots/GQDs, carbon nitride dots, and C-dots/GQDs nanocomposites. Nevertheless, this mini review is designed to be illustrative, not comprehensive.

Synthesis of a hollow CeO2/Au/C hierarchical nanostructure for high catalytic activity and recyclability

We report uniform hollow CeO₂/Au/C nanocatalysts with hierarchical structures fabricated successfully via an etching process.