Fabrication of a Tubular CuO/NiO Biomimetic Nanozyme with Synergistically Promoted Peroxidase-like Performance for Isoniazid Sensing

Isoniazid is an antibiotic primarily used in clinical treatment of tuberculosis, but excessive usage can lead to serious consequences such as hepatotoxicity, neurotoxicity, and even coma and death. Therefore, it is critical to exploit a quick, facile, and acute way for isoniazid analysis. In this work, we have demonstrated an efficient electrospinning-carbonation-wet chemistry reaction-calcination process to fabricate CuO/NiO nanotubes (NTs) as a promising nanozyme for peroxidase (POD) mimicking. In virtue of the distinct tubular structure and synergy between CuO and NiO from the mechanisms of both electron transfer and hydroxyl radical generation, a remarkably improved catalytic activity is realized for the CuO/NiO NTs compared with bare CuO and NiO samples. According to the admirable POD-like property, a rapid colorimetric detection for isoniazid is accomplished with a detection limit of 0.4 μM (S/N = 3) and favorable selectivity. In addition, the sensing capability of isoniazid in a real sample is also investigated with satisfactory results. This work offers a novel tactic to fabricate high-performance nanozymes with efficient isoniazid sensing capabilities to address challenges in disease treatment efficacy and public safety monitoring.

Hierarchical microtubes constructed using Fe-doped MoS2 nanosheets for biosensing applications

The structural design of multiple functional components could enhance the synergistic catalytic performance of MoS₂-based composites in enzyme-like catalysis. Herein, one-dimensional (1D) Fe-MoS₂ microtubes were designed to prepare tubular Fe-doped MoS₂ composites with MoO₃ microrods as self-sacrificing precursors. Remarkably, the results indicated that the generated ammonia released from the sulfidation process led to the dissolution of MoO₃ cores and the generation of a tubular structure. The Fe-MoS₂ composites integrated the synergistic effects of Fe-doped MoS₂ nanosheets (NSs) and the 1D tubular structure. Thus, a higher catalytic activity was observed in peroxidase-like catalysis than in other components, such as MoO₃@FeOOH, FeOOH and MoS₂ NSs. The peroxidase-like mechanism originated from the generation of the ˙OH radical. The Fe-MoS₂ microtube-based colorimetric assay was used to detect H₂O₂ with a detection limit (LOD) of 0.51 μM in a linear range from 1.25 to 50 μM. The colorimetric method was simple, selective, and sensitive for glutathione (GSH) detection in the range of 0.25-125 μM with a detection limit (LOD) of 0.12 μM. Thus, we provide a facile synthetic strategy for simultaneously integrating electronic modulation and structural design to develop an efficient MoS₂-based functional catalyst.

Graphene-Based Surface-Enhanced Raman Scattering (SERS) Sensing: Bibliometrics Based Analysis and Review

Surface-enhanced Raman scattering (SERS) has received increasing attention from researchers since it was first discovered on rough silver electrode surfaces in 1974 and has promising applications in life sciences, food safety, and environmental monitoring. The discovery of graphene has stirred considerable waves in the scientific community, attracting widespread attention in theoretical research and applications. Graphene exhibits the properties of a semi-metallic material and has also been found to have Raman enhancement effects such as in metals. At the same time, it quenches the fluorescence background and improves the ratio of a Raman signal to a fluorescence signal. However, graphene single-component substrates exhibit only limited SERS effects and are difficult to use for trace detection applications. The common SERS substrates based on noble metals such as Au and Ag can produce strong electromagnetic enhancement, which results in strong SERS signals from molecules adsorbed on the surface. However, these substrates are less stable and face the challenge of long-term use. The combination of noble metals and graphene to obtain composite structures was an effective solution to the problem of poor stability and sensitivity of SERS substrates. Therefore, graphene-based SERS has been a popular topic within the last decade. This review presents a statistically based analysis of graphene-based SERS using bibliometrics. Journal and category analysis were used to understand the historical progress of the topic. Geographical distribution was used to understand the contribution of different countries and institutions to the topic. In addition, this review describes the different directions under this topic based on keyword analysis and keyword co-occurrence. The studies on this topic do not show a significant divergence. The researchers’ attention has gradually shifted from investigating materials science and chemistry to practical sensing applications. At the end of the review, we summarize the main contents of this topic. In addition, several perspectives are presented based on bibliometric analysis.

Responsive-released strategy based on lead ions-dependent DNAzyme functionalized UIO-66-NH2 for tumor marker

Signal labeling on electrode interface is an important step during the construction of immunosensor and most signal substances are directly affixed on the immunoprobe or substrate so that some problems such as flimsy labeling method and interference of insulating proteins on electrode surface have been existed to affect their readout. In order to solve above problems in electrochemical immunoassay, a lead ions-decodable autocephalous signal integrator based on UIO-66-NH₂ was proposed for the detection of prostate specific antigen (PSA). Briefly, a lead ions-dependent DNAzyme functionalized UIO-66-NH₂, in which methylene blue was encapsulated, was independently dispersed in solution phase to be closely associated with the lead sulfide labeled sandwich bioconjugates, and internal methylene blue molecules can be sustained released once a cationic exchange reaction was occurred between lead sulfide label and adscititious silver ions. Based on this designing, immunoassay for PSA was effectively connected with the dynamic behavior of methylene blue molecules through the cleavage of DNAzyme on MOFs surface and performed a wide linear range from 1 pg mL^-1 to 10 ng mL^-1 and a satisfactory detection limit with 0.34 pg mL^-1. The proposed strategy was expected to offer more valuable information for the application of MOFs in early and accurate cancer diagnosis.

Acid-activated ROS generator with folic acid targeting for bacterial biofilm elimination

Many medical and chemical applications require the precise supply of antimicrobial components in a controlled manner at the location of mature biofilm deposits. This work reports a facile strategy to fabricate nanoscale metal-organic frameworks (NMOFs) coencapsulating the antibacterial ligand (lysine carbon dots, Lys-CDs) and targeted drug (folic acid, FA) in one pot to improve antibiofilm efficiency against established biofilms. The resulting products are characterized by transmission electron microscopy, field-emission scanning electron microscopy, powder x-ray diffraction, and ultraviolet-visible spectroscopy. The results show that Lys-CDs could coordinate with Zn²⁺ and the adding of FA inhibits the coordination of Lys-CDs with central ions of Zn. The Lys-CDs and FA are successfully exposed with the NMOFs disintegrating in the acid environment of bacterial metabolites. We are surprised to find a sharp increase of reactive oxygen species (ROS) inside the bacterial cells by FA functionalizing NMOFs, which undoubtedly enhance the antibacterial and antibiofilm activity. The as-synthesized ZIF-8-based nanocomposites also show the peroxidase-like activity in an acid environment, and produce extremely active hydroxyl radicals resulting in the improved antibacterial and antibiofilm activity. The possible mechanisms of antibacterial activities indicate that the presence of FA is significant in the sense of targeting bacteria. This study shows a novel approach to construct acid stimulation supply system which may be helpful for the research of antibiofilms.

Enhanced Supercapacitor Performance and Electromagnetic Interference Shielding Effectiveness of CuS Quantum Dots Grown on Reduced Graphene Oxide Sheets

This study is focused on the preparation of the CuS/RGO nanocomposite via the hydrothermal method using GO and Cu-DTO complex as precursors. X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopy study revealed the formation of the CuS/RGO nanocomposite with improved crystallinity, defective nanostructure, and the presence of the residual functional group in the RGO sheet. The morphological study displayed the transformation of CuS from nanowire to quantum dots with the incorporation of RGO. The galvanostatic charge/discharge curve showed that the CuS/RGO nanocomposite (12 wt % Cu-DTO complex) has tremendous and outperforming specific capacitance of 3058 F g-1 at 1 A g-1 current density with moderate cycling stability (∼60.3% after 1000 cycles at 10 A g-1). The as-prepared nanocomposite revealed excellent improvement in specific capacitance, cycling stability, Warburg impedance, and interfacial charge transfer resistance compared to neat CuS. The fabricated nanocomposites were also investigated for their bulk DC electrical conductivity and EMI shielding ability. It was observed that the CuS/RGO nanocomposite (9 wt % Cu-DTO) exhibited a total electromagnetic shielding efficiency of 64 dB at 2.3 GHz following absorption as a dominant shielding mechanism. Such a performance is ascribed to the presence of interconnected networks and synergistic effects.

Photoelectrochemical aptasensor for thrombin based on Au-rGO-CuS as signal amplification elements

A photoelectrochemical platform for thrombin determination was developed based on Au-rGO-CuS as multiple signal amplification elements. CuInS₂ QDs was used to sensitize burr-shape TiO₂ (b-TiO₂) to obtain a strong photocurrent. Under the specific recognition between aptamer and thrombin, a sandwichlike structure was formed and the Au-rGO-CuS-labeled aptamer (S2@Au-rGO-CuS) was immobilized on the electrode surface. This induced a sharp decrease in photocurrent. The phenomenon is mainly due to the fact that CuS NPs can competitively consume the light energy and electron donor with CuInS₂/b-TiO₂. The rGO can increase the amount of CuS NPs and the Au NPs can accelerate charge transferring which depress the recombination of photogenerated electrons and holes in CuS to further enhance the competitive capacity of CuS. The sandwichlike structure has a steric hindrance effect. Therefore, the S2@Au-rGO-CuS has a multiple signal amplification function for thrombin determination. Under optimal conditions, the PEC aptasensor exhibited a wide linear concentration range from 0.1 pM to 10 nM with a low detection limit of 30 fM (S/N = 3) for thrombin. Besides, the designed aptasensor performed well in the assay of human serum sample, indicating good potential for the determination of thrombin in real samples. Graphical abstract.

Intrinsic Oxidase-like Nanoenzyme Co4S3/Co(OH)2 Hybrid Nanotubes with Broad-Spectrum Antibacterial Activity

Improving the antibacterial activity of nanomaterials and avoiding the use of H₂O₂ are vital for biosecurity and public health. In this work, novel Co₄S₃/Co(OH)₂ hybrid nanotubes (HNTs) for the first time were successfully synthesized through the control of Na₂S treatment of Co(CO₃)_0.35Cl_0.20(OH)_1.10 precursor. On the basis of Kirkendall effect, acicular precursor was vulcanized to form Co₄S₃/Co(OH)₂ HNTs that possess great properties including favorable storage ability and ideal stability. By tailoring the composition and structure, Co₄S₃/Co(OH)₂ HNTs were found to have profound oxidase-like catalytic activities. When pH = 3 precursor was treated with 900 mg of Na₂S, Co₄S₃/Co(OH)₂ HNTs exhibit superior performance. Owing to the outstanding oxidase-like activity, Co₄S₃/Co(OH)₂ HNTs can eliminate Escherichia coli, Pseudomonas aeruginosa, Staphylococcus sciuri, and Bacillus without the help of H₂O₂. It turned out that the sterilization ability came from the superoxide anion radical generated by Co₄S₃/Co(OH)₂ HNTs. With Co₄S₃/Co(OH)₂ HNTs, the intracellular reactive oxygen species level can be enhanced and the toxicity of H₂O₂ can be absolutely avoided. Overall, the synthesis of antibacterial nanomaterials is unparalleled and the results of this work would facilitate the utilization in medical science, new energy, and environmental catalysis.

A gold nanoparticle-intercalated mesoporous silica-based nanozyme for the selective colorimetric detection of dopamine

Highly dispersed aggregation-free gold nanoparticles intercalated into the walls of mesoporous silica (AuMS) were synthesized using thioether-functionalized silica as a nanozyme, which exhibited an excellent peroxidase mimic activity. The AuMS material was characterized via XRD, N₂ adsorption-desorption, FESEM, SEM-EDS particle mapping, TEM, and XPS. The peroxidase-like activity of the AuMS material was studied thoroughly, and the effect of pH and temperature was evaluated. The reproducibility of the peroxidase mimic activity and long-term stability of the AuMS catalyst were also studied. Furthermore, the AuMS catalyst was successfully utilized for the detection and quantification of dopamine, an important neurotransmitter, colorimetrically with a linear range of 10-80 μM and a limit of detection (LOD) value of 1.28 nM. The determination of dopamine concentration in commercially available dopamine hydrochloride injection showed high accuracy, good reproducibility, and high selectivity in the presence of uric acid, ascorbic acid, glucose, tryptophan, phenylalanine, and tyrosine.

Continuous phase regulation of MoSe2 from 2H to 1T for the optimization of peroxidase-like catalysis

Simultaneous and synergistic modulation of the crystal phase and disorder in MoSe₂ to dramatically enhance their peroxidase-like activity.

Facile preparation of peroxidase-like core-shell nanorods and application as platform for colorimetric determination of glucose, insulin and glucose/insulin ratio

To obtain sensitive analytical detection methods, many unique materials have been developed and made them promising candidates for biosensing. In this study, a type of core-shell gold nanorods, GNR@Au₂S/AuAgS/CuS, possessing peroxidase-like activity was prepared in a simple, facile manner. A colorimetric strategy for detection of blood glucose, insulin and differentiating type 1 and type 2 diabetes was developed based on the unique GNR@Au₂S/AuAgS/CuS. The sensitive colorimetric approach for detection of glucose in the dynamic range of 2.5-200 μM was first established based on the catalytic performance of GNR@Au₂S/AuAgS/CuS. Meanwhile, the catalytic activity of the peroxidase-like GNR@Au₂S/AuAgS/CuS can be regulated by introducing the high affinity and specific reaction between DNA aptamer and insulin on the surface of GNR@Au₂S/AuAgS/CuS, which allows the colorimetric assay to be extended to the detection of insulin, and a quantitative analysis of insulin based on the specific recognition can be implemented at the range from 0.014 to 1.08 μU/mL. Furthermore, colorimetric approach coupling peroxidase-like performance and specific recognition on the surface of GNR@Au₂S/AuAgS/CuS nanoparticles was developed to measure glucose/insulin ratio and directly differentiate type 1 and type 2 diabetes mellitus. Practical human serum samples were tested and only the glucose/insulin ratio greater than 2.2 (μU/mL) may lead to the appearance of color change. The coupling of this different bioassay on the same nanoparticles reflects the versatility and integration characteristics of the colorimetric assay and is highly promising for improving diabetes management.

Photoelectrochemical biosensor for CEA detection based on SnS2-GR with multiple quenching effects of Au@CuS-GR

A novel signal on-off type photoelectrochemical (PEC) biosensing system was designed for sensitive detection of carcinoembryonic antigen (CEA) based on tin disulfide nanosheets loaded on reduced graphene cxide (SnS₂-GR) as the photoactive material and gold nanoparticles coated on reduced graphene oxide-functionalized copper sulfide (Au@CuS-GR) for signal amplification. It's the first time for SnS₂-GR was exploited as a sensing matrix. Here, the photocurrent signals of SnS₂ were amplified attributed to the sensitization effect of graphene. As signal amplifier, Au@CuS-GR could quench the photocurrents of SnS₂-GR not only through the p-n type semiconductor quenching effect as well as the steric hindrance effect, but also as peroxidase mimetics to catalyze the oxidation of 4-Chloro-1-naphthol (4-CN) to produce insoluble product on the electrode surface. Based on the multiple signal amplification ability of Au@CuS-GR, CEA was detected sensitively with a linear range from 0.1 pg mL^-1 to 10 ng mL^-1 and limit of detection down to 59.9 fg mL^-1 (S/N = 3). Meanwhile, the PEC biosensor displayed excellent performance in the assay of human serum sample, showing good application prospects for various target analysis.

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.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

FeCo nanoparticles-embedded carbon nanofibers as robust peroxidase mimics for sensitive colorimetric detection of l-cysteine

A simple and low cost detection of l-cysteine is essential in the fields of biosensors and medical diagnosis. In this study, we have developed a simple electrospinning, followed by calcination process to prepare FeCo nanoparticles embedded in carbon nanofibers (FeCo-CNFs) as an efficient peroxidase-like mimic for the detection of l-cysteine. FeCo nanoparticles are uniformly dispersed within CNFs, and their diameters are highly influenced by the calcination temperature. The calcination temperature also influences the peroxidase-like catalytic activity, and the maximum activity is achieved at a calcination temperature of 550 °C. Owing to the high catalytic activity of the as-prepared FeCo-CNFs, a colorimetric technique for the rapid and accurate determination of l-cysteine has been developed. The detection limit is about 0.15 μM with a wide linear range from 1 to 20 μM. In addition, a high selectivity for the detection of l-cysteine over other amino acids, glucose and common ions is achieved. This study provides a simple, rapid and sensitive sensing platform for the detection of l-cysteine, which is a promising candidate for potential applications in biosensing, medicine, environmental monitoring.

Controllable Synthesis of SERS-Active Magnetic Metal-Organic Framework-Based Nanocatalysts and Their Application in Photoinduced Enhanced Catalytic Oxidation

Fabrication of multifunctional nanocatalysts with surface-enhanced Raman scattering (SERS) activity is of vital importance for monitoring catalytic courses in situ and studying the reaction mechanisms. Herein, SERS-active magnetic metal-organic framework (MOF)-based nanocatalysts were successfully prepared via a three-step method, including a solvothermal reaction, an Au seed-induced growth process, and a low-temperature cycling self-assembly technique. The as-synthesized magnetic MOF-based nanocatalysts not only exhibit outstanding peroxidase-like activity, but can also be applied as a SERS substrate. Owing to these features, they can be used for monitoring in situ catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ via a SERS technique, and the concentration of H₂O₂ was determined. Owing to the intrinsic character of the Fe-based MOF material (MIL-100(Fe)), a novel photoinduced enhanced catalytic oxidation effect was demonstrated, in which the catalytic oxidation of TMB and o-phenylenediamine was accelerated. This study provides a versatile approach for the fabrication of functional MOF-based nanocomposites as a promising SERS substrate with a unique photoinduced enhanced peroxidase-like activity for potential applications in ultrasensitive monitoring, biomedical treatment, and environmental evaluation.

Multifunctional nanozymes: enzyme-like catalytic activity combined with magnetism and surface plasmon resonance

Over decades, as alternatives to natural enzymes, highly-stable and low-cost artificial enzymes have been widely explored for various applications. In the field of artificial enzymes, functional nanomaterials with enzyme-like characteristics, termed as nanozymes, are currently attracting immense attention. Significant progress has been made in nanozyme research due to the exquisite control and impressive development of nanomaterials. Since nanozymes are endowed with unique properties from nanomaterials, an interesting investigation is multifunctionality, which opens up new potential applications for biomedical sensing and sustainable chemistry due to the combination of two or more distinct functions of high-performance nanozymes. To highlight the progress, in this review, we discuss two representative types of multifunctional nanozymes, including iron oxide nanomaterials with magnetic properties and metal nanomaterials with surface plasmon resonance. The applications are also covered to show the great promise of such multifunctional nanozymes. Future challenges and prospects are discussed at the end of this review.

Plasmonic Cu/CuCl/Cu2S/Ag and Cu/CuCl/Cu2S/Au Supports with Peroxidase-Like Activity: Insights from Surface Enhanced Raman Spectroscopy

In the present study, we present nanostructured bimetallic Cu/CuCl/Cu2S/Au(Ag) supports that exhibit plasmonic electromagnetic field enhancement and peroxidase-like catalytic activity. The Cu2S component acts as the peroxidase-like catalyst, while the Au or Ag component provides the necessary light enhancement for surface enhanced Raman spectroscopic (SERS) studies of surface bound molecular reactants. As a test reaction the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 was investigated. The comparison of product evolution in solution measured by UV-Vis spectroscopy and on the surface measured via SERS is able to give more insight into the different steps involved in the overall catalysis.

Surface-enhanced Raman spectroscopic detection of molecular chemo- and plasmo-catalysis on noble metal nanoparticles

The in situ detection of reactions catalyzed by metal NPs is challenging because the underlying chemical transformations occur at interfaces. Surface-enhanced Raman scattering (SERS), a surface-selective, sensitive and label-free vibrational spectroscopic technique, is ideally suited for monitoring of heterogeneous catalysis with high chemical specificity. A major limitation in the past, however, was that small, catalytically active metal NPs do not exhibit the high plasmonic activity required for SERS. This feature article focuses on the design, synthesis and use of bifunctional NPs with both catalytic and plasmonic activity for in situ SERS detection of reactions catalyzed by metal NPs. We focus on model reactions induced by chemical reducing agents such as hydride or molecular hydrogen as well as on plasmon-induced photo-catalysis including both photo-oxidation and photo-reduction. Finally, we highlight the concept of photo-recycling on halide-containing silver surfaces for unprecedented multi-electron reduction chemistry.

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.

Recent progress on graphene-based substrates for surface-enhanced Raman scattering applications

Graphene-based SERS substrates are classified and introduced, and their applications in biosensing-related fields are reviewed.

Fabrication of Ag-Cu2O/Reduced Graphene Oxide Nanocomposites as Surface-Enhanced Raman Scattering Substrates for in Situ Monitoring of Peroxidase-Like Catalytic Reaction and Biosensing

Highly sensitive biosensors are essential in medical diagnostics, especially for monitoring the state of an individual's disease. An ideal way to achieve this objective is to analyze human sweat secretions by noninvasive monitoring. Due to low concentrations of target analytes in human secretions, fabrication of ultrasensitive detection devices is a great challenge. In this work, Ag-Cu₂O/reduced graphene oxide (rGO) nanocomposites were prepared by a facile two-step in situ reduction procedure at room temperature. Ag-Cu₂O/rGO nanocomposites possess intrinsic peroxidase-like activity and rapidly catalyze oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. On the basis of the excellent SERS properties and high peroxidase-like activity of the Ag-Cu₂O/rGO nanocomposites, the catalytic oxidation of TMB can be monitored by SERS. This approach can detect H₂O₂ and glucose with high sensitivity and distinguish between diabetic and normal individuals using glucose levels in fingerprints. Our work provides direction for designing other SERS substrates with high catalytic activity and the potential for application in biosensing, forensic investigation, and medical diagnostics.

Carbon dots/Fe3O4 hybrid nanofibers as efficient peroxidase mimics for sensitive detection of H2O2 and ascorbic acid

Carbon dots/Fe₃O₄ hybrid nanofibers as efficient peroxidase mimics for sensitive detection of H₂O₂ and ascorbic acid have been developed.