Search

As a potent detection method for cancer biomarkers in physiological fluid, a colorimetric and electrochemical dual-mode sensing platform for breast cancer biomarker thioredoxin 1 (TRX1) was developed based on the excellent peroxidase-mimicking and electrocatalytic property of Prussian blue nanoparticles (PBNPs). PBNPs were hydrothermally synthesized using K3[Fe(CN)6] as a precursor and polyvinylpyrrolidone (PVP) as a capping agent. The synthesized spherical PBNPs showed a significant peroxidase-like activity, having approximately 20 and 60% lower Km values for 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2, respectively, compared to those of horseradish peroxidase (HRP). The PBNPs also enhanced the electron transfer on the electrode surface. Based on the beneficial features, PBNPs were used to detect target TRX1 via sandwich-type immunoassay procedures. Using the strategies, TRX1 was selectively and sensitively detected, yielding limit of detection (LOD) values as low as 9.0 and 6.5 ng mL−1 via colorimetric and electrochemical approaches, respectively, with a linear range of 10–50 ng mL−1 in both strategies. The PBNP-based TRX1 immunoassays also exhibited a high degree of precision when applied to real human serum samples, demonstrating significant potentials to replace conventional HRP-based immunoassay systems into rapid, robust, reliable, and convenient dual-mode assay systems which can be widely utilized for the identification of important target molecules including cancer biomarkers. [ABSTRACT FROM AUTHOR]

The proteolytic enzyme ficin exhibits peroxidase-like activity but it is low and insufficient for real applications. Herein, we developed ficin-copper hybrid nanoflowers and demonstrated that they have significantly enhanced peroxidase-like activity of over 6-fold higher than that of free ficin, with one of the lowest Km and highest kcat values among all reported ficin-based peroxidase-like nanozymes. This was most likely caused by the synergistic catalysis of co-existing ficin and crystalline copper phosphate within nanoflower matrices having a large surface area. The nanoflowers were easily prepared by incubating ficin and copper sulfate at ambient temperature, causing coordination interactions between ficin's amine/amide moieties and copper ions, followed by concomitant anisotropic growth of petals composed of copper phosphate crystals with ficin. When compared to free ficin and natural horseradish peroxidase, the resulting nanoflowers' affinity toward H2O2 was greatly increased, yielding Km values of half and one-tenth, respectively, as well as noticeably improved stability. The nanoflowers were then applied to colorimetric determination of biological thiols (biothiols), such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), based on their inhibition of nanoflowers' peroxidase-like activity, producing reduced color intensities as the concentration of biothiols increased. This strategy achieved highly sensitive colorimetric determinations of Cys, GSH, and Hcy after only 25-min incubation. Additionally, using this technique, biothiols in human serum were successfully determined with excellent precision, suggesting the potential application of this technology in clinical settings, particularly in point-of-care testing environments. [ABSTRACT FROM AUTHOR]

The accurate and simultaneous detection of neurotransmitters, such as dopamine (DA) and epinephrine (EP), is of paramount importance in clinical diagnostic fields. Herein, we developed cerium–molybdenum disulfide nanoflowers (Ce-MoS2 NFs) using a simple one-pot hydrothermal method and demonstrated that they are highly conductive and exhibit significant peroxidase-mimicking activity, which was applied for the simultaneous electrochemical detection of DA and EP. Ce-MoS2 NFs showed a unique structure, comprising MoS2 NFs with divalent Ce ions. This structural design imparted a significantly enlarged surface area of 220.5 m2 g−1 with abundant active sites as well as enhanced redox properties, facilitating electron transfer and peroxidase-like catalytic action compared with bare MoS2 NFs without Ce incorporation. Based on these beneficial features, Ce-MoS2 NFs were incorporated onto a screen-printed electrode (Ce-MoS2 NFs/SPE), enabling the electrochemical detection of H2O2 based on their peroxidase-like activity. Ce-MoS2 NFs/SPE biosensors also showed distinct electrocatalytic oxidation characteristics for DA and EP, consequently yielding the highly selective, sensitive, and simultaneous detection of target DA and EP. Dynamic linear ranges for both DA and EP were determined to be 0.05~100 μM, with detection limits (S/N = 3) of 28 nM and 44 nM, respectively. This study shows the potential of hierarchically structured Ce-incorporated MoS2 NFs to enhance the detection performances of electrochemical biosensors, thus enabling extensive applications in healthcare, diagnostics, and environmental monitoring. [ABSTRACT FROM AUTHOR]

We report a fluorescent assay for the determination of vitamin B12 (VB12) based on the inner filter effect (IFE) of 1,3-propanedithiol-functionalized silver nanoparticles (PDT-AgNPs). PDT was simply functionalized on the surface of AgNPs through Ag–thiol interaction, which leads to significantly enhanced fluorescence, with excitation and emission at 360 and 410 nm, respectively, via their thiol-mediated aggregation. Since target VB12 has strong absorption centered at 360 nm, which is almost completely overlapping with the excitation spectra of PDT-AgNPs, the VB12 induced strong quenching of the fluorescence of PDT-AgNPs via IFE. The IFE-based mechanism for the fluorescence quenching of PDT-AgNPs in the presence of VB12 was confirmed by the analyses of Stern–Volmer plots at different temperatures and fluorescence decay curves. The fluorescence-quenching efficiency of PDT-AgNPs was linearly proportional to the concentration of VB12 in a wide range of 1 to 50 μM, with a lower detection limit of 0.5 μM, while preserving excellent selectivity toward target VB12 among possible interfering molecules. Furthermore, the PDT-AgNPs-mediated assay succeeded in quantitatively detecting VB12 in drug tablets, indicating that PDT-AgNPs can serve as an IFE-based fluorescent probe in pharmaceutical preparations by taking advantages of its ease of use, rapidity, and affordability. [ABSTRACT FROM AUTHOR]

Developing a convenient detection method for dopamine holds a significant incentive due to its high clinical significance. Herein, we synthesize crystalline MnOOH nanowires (MNWs) via a simple solvothermal treatment of KMnO4 and demonstrate that they possess excellent oxidase-like activity owing to the presence of pure Mn3+ sites on the MNWs. Particularly, MNWs catalyze the rapid oxidation of dopamine into aminochromes, which show a vivid brown color. The dopamine oxidase-like activity of MNWs follows the typical Michaelis–Mentenkinetics with excellent storage stability. Based on the affirmative catalytic features, a paper dipstick incorporating MNWs in the detection zone is constructed for the one-step colorimetric detection of target dopamine. By immersing the dipstick into the sample solution for 30 min, the sample spontaneously moves to the detection zone due to capillary force, yielding a brown color proportional to the amount of dopamine, which is quantified from an image acquired using a smartphone. With the MNW-containing solution-based assay and MNW-incorporated paper dipstick, dopamine is successfully determined with high selectivity, sensitivity, and detection precision when using spiked human serum and pharmaceutical dopamine injection samples, respectively. Successful analytical values such as the dynamic linear ranges of 3–60 μM and 0.05–7 mM are achieved with the solution-based assay and paper dipstick, respectively, along with excellent detection accuracy (95–99%) and precision (1.0–3.1%). Hence, we developed a simple and efficient nanozyme-based paper dipstick biosensor for dopamine that can be used in point-of-care testing environments. [ABSTRACT FROM AUTHOR]

Microcystin-LR (MC-LR) is a hepatotoxin generated by the excessive proliferation of cyanobacteria, which is a threat to humans and wildlife. Therefore, rapid detection of MC-LR is an important challenge. This study describes a rapid electrochemical biosensor comprising nanozymes and aptamers. Alternating current electrothermal flow (ACEF) significantly reduced the MC-LR detection period to 10 min. We also used MnO2/MC-LR aptamer conjugates to improve the sensitivity to MC-LR detection. Here, MnO2 amplified the electrochemical signal and the aptamer showed high selectivity for MC-LR. Under the optimal conditions, the limit of detection (LOD) and selectivity in freshwater were detected using cyclic voltammetry and differential pulse voltammetry. As a result, an LOD of 3.36 pg mL−1 was observed in the linear concentration range of 10 pg mL−1 to 1 μg mL−1. This study quickly and sensitively detected MC-LR in a situation where it causes serious damage worldwide. In addition, the ACEF technology introduction is the first example of MC-LR detection, suggesting a wide range of possibilities for MC-LR biosensors. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid nanoflowers (HNFs) have generated widespread research interest owing to their properties to efficiently entrap organic components like protein or enzyme within their nanostructured matrices, yielding high activity, stability, and recyclability. Recently, much effort has been devoted to developing advanced HNFs composed of diversified components, such as multiple proteins, nanoparticles, polymers, and nucleic acids, to achieve different functionalities enabling extended applications. Compared to the conventional HNFs primarily serving as immobilization supports for enzyme, diversified component incorporated HNFs can have unique multiple functionalities, essentially for developing novel biosensing and biomedical strategies. Herein, an overview for the recent advances on diversified components incorporated HNFs is presented with an emphasis on the potential biotechnological applications. Synthetic strategies, structural characteristics, and unique properties of diverse HNFs are discussed with representative studies, demonstrating the versatility of the HNFs. Current challenges and future opportunities of the HNFs are also discussed. [ABSTRACT FROM AUTHOR]

Nucleic acid aptamer-based research has focused on achieving the highest performance for bioassays. However, there are limitations in evaluating the affinity for the target analytes in these nucleic acid aptamer-based bioassays. In this study, we mainly propose graphene oxide (GO)-based electrical and optical analyses to efficiently evaluate the affinity between an aptamer and its target. We found that an aptamer-coupled GO-based chip with an electrical resistance induced by a field-effect transistor, with aptamers as low as 100 pM, can detect the target, thrombin, at yields as low as 250 pM within five minutes. In the optical approach, the fluorescent dye-linked aptamer, as low as 100 nM, was efficiently used with GO, enabling the sensitive detection of thrombin at yields as low as 5 nM. The cantilever type of mechanical analysis also demonstrated the intuitive aptamer–thrombin reaction in the signal using dBm units. Finally, a comparison of electrical and optical sensors' characteristics was introduced in the attachment and detachment of aptamer to propose an efficient analysis that can be utilized for various aptamer-based research fields. [ABSTRACT FROM AUTHOR]

Background: Laccase-based biosensors are efficient for detecting phenolic compounds. However, the instability and high cost of laccases have hindered their practical utilization. Results: In this study, we developed hierarchical manganese dioxide–copper phosphate hybrid nanoflowers (H–Mn–Cu NFs) as excellent laccase-mimicking nanozymes. To synthesize the H–Mn–Cu NFs, manganese dioxide nanoflowers (MnO2 NFs) were first synthesized by rapidly reducing potassium permanganate using citric acid. The MnO2 NFs were then functionalized with amine groups, followed by incubation with copper sulfate for three days at room temperature to drive the coordination interaction between the amine moieties and copper ions and to induce anisotropic growth of the petals composed of copper phosphate crystals, consequently yielding H–Mn–Cu NFs. Compared with those of free laccase, at the same mass concentration, H–Mn–Cu NFs exhibited lower Km (~ 85%) and considerably higher Vmax (~ 400%), as well as significantly enhanced stability in the ranges of pH, temperature, ionic strength, and incubation periods evaluated. H–Mn–Cu NFs also catalyzed the decolorization of diverse dyes considerably faster than the free laccase. Based on these advantageous features, a paper microfluidic device incorporating H–Mn–Cu NFs was constructed for the convenient visual detection of phenolic neurotransmitters, including dopamine and epinephrine. The device enabled rapid and sensitive quantification of target neurotransmitters using an image acquired using a smartphone. Conclusions: These results clearly show that H–Mn–Cu NFs could be potential candidates to replace natural laccases for a wide range of applications in biosensing, environmental protection, and biotechnology. [ABSTRACT FROM AUTHOR]

Peroxidase‐mimicking nanozymes have been extensively studied, however, their application is limited by the requirement for an acidic pH. Herein, the development of Co‐doped mesoporous cerium oxide (Co‐m‐ceria) is reported, which operates optimally at a near‐neutral pH and exhibits a peroxidase‐like catalytic efficiency that is 600‐times higher than that of pristine m‐ceria. Density functional theory (DFT) calculations for the application of pristine and various metal‐doped m‐ceria in peroxidase‐like reactions under different pH environments are conducted to select Co as the appropriate dopant. The high peroxidase‐like activity of Co‐m‐ceria under neutral conditions and its mesoporous nature enable its application in a one‐pot cascade reaction system, wherein biomarkers of oxidative enzymes can be detected without altering the pH. Five different oxidative enzymes are immobilized in the pores of Co‐m‐ceria at high loadings, followed by incorporation of the enzyme‐containing Co‐m‐ceria in paper microfluidic devices for the convenient and simultaneous detection of multiple biomarkers. The Co‐m‐ceria‐incorporated paper microfluidic device enables the selective and sensitive determination of multiple biomarkers using a smartphone‐acquired image. This study demonstrates the potential of the rational design of nanozymes and their application in paper microfluidic devices, laying the groundwork for future applications of nanozymes in point‐of‐care testing environments. [ABSTRACT FROM AUTHOR]

During the recent several decades, lateral flow immunoassay (LFIA) constructed with gold nanoparticle (AuNP) has been widely utilized to conveniently detect target analyte. However, AuNP-based LFIA has limitations, such as limited detection sensitivity and quantification capability. Herein, to overcome these constraints, we have developed cerium oxide nanoparticle (nanoceria)-based LFIA for C-reactive protein (CRP) detection in human serum samples. It was fabricated with nanoceria, a notable nanozyme that shows an oxidase activity to quickly oxidize organic substrate, such as 3,3′,5,5′-tetramethylbenzidine (TMB), to produce colored product without any oxidizing agent (e.g., hydrogen peroxide), which is advantageous for realizing point-of-care testing (POCT) applications. By employing human blood serum spiked with CRP, the nanoceria-based LFIA showed two blue-colored lines on the test and control region within 3 min via TMB oxidation, by the captured nanoceria through antigen–antibody interaction. The produced blue-colored lines were distinguished by naked eyes and quantitated with real images acquired by a conventional smartphone with the ImageJ software. With this strategy, target CRP was specifically determined down to 117 ng mL−1 with high detection precisions yielding coefficient of variation of 9.8–11.3% and recovery of 90.7–103.2% using human blood serum samples. This investigation demonstrates the potential of oxidase-like nanoceria for developing LFIA, which is particularly useful in instrumentation-free POCT environments. [ABSTRACT FROM AUTHOR]

Highlights: Enzyme-mimicking activities of different nanomaterials (nanozymes) and the recent progress in the construction of nanozyme-based biosensors with various examples are discussed in this review. Physicochemical properties of nanomaterials (size, composition, pH, temperature, surface chemistry) play crucial role in the nanozyme activities. The emerging nanozyme-based biosensors promise great potential for point-of-care diagnostic applications following the ASSURED criteria defined by WHO.Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal–organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications. [ABSTRACT FROM AUTHOR]

Hybrid nanoflowers consisting of graphitic carbon nitride (GCN) and copper were successfully constructed without the involvement of any biomolecule, by simply mixing them at room temperature to induce proper self-assembly to achieve a flower-like morphology. The resulting biomolecule-free GCN-copper hybrid nanoflowers (GCN-Cu NFs) exhibited an apparent peroxidase-mimicking activity, possibly owing to the synergistic effect from the coordination of GCN and copper, as well as their large surface area, which increased the number of catalytic reaction sites. The peroxidase-mimicking GCN-Cu NFs were then employed in the colorimetric determination of selected phenolic compounds hydroquinone (HQ), methylhydroquinone (MHQ), and catechol (CC). For samples without phenolic compounds, GCN-Cu NFs catalyzed the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, producing an intense blue color signal. Conversely, in the presence of phenolic compounds, the oxidation of TMB was inhibited, resulting in a significant reduction of the color signal. Using this strategy, HQ, MHQ, and CC were selectively and sensitively determined in a linear range up to 100 μM with detection limits down to 0.82, 0.27, and 0.36 μM, respectively. The practical utility of this assay system was also validated by using it to detect phenolic compounds spiked in tap water, yielding a good recovery of 97.1–108.9% and coefficient of variation below 3.0%, demonstrating the excellent reliability and reproducibility of this strategy. [ABSTRACT FROM AUTHOR]

Exposure to toxins through contaminated food is a serious concern. For the detection of toxins in complex matrices, there are many analytical instrumentation-based methods; however, these approaches are generally expensive, laborious to perform, and require skilled technicians. Thus, they can only be utilized in centralized laboratories. To efficiently prevent the contamination by toxins and improve food safety, the use of on-site toxin detection methods enabling simple, rapid, sensitive, specific, reliable, and affordable identification of toxins is required. A colorimetric toxin detection strategy providing a naked-eye readout platform suits these requirements. Notably, the implementation of nanomaterials in the colorimetric strategy has proven to rapidly generate a higher capacity for detectable color responses owing to their unique physicochemical and catalytic properties. In this review, recent research on colorimetric toxin detection utilizing diverse nanostructures including noble metal nanoparticles and enzyme-like catalytic nanomaterials (nanozymes) is reviewed and discussed. Current challenges and future prospects for the utilization of nanomaterials in colorimetric toxin detection are also discussed. [ABSTRACT FROM AUTHOR]

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H2O2 over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 μM with a dynamic linear concentration range of 5.0 to 275.0 μM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. [ABSTRACT FROM AUTHOR]

Epoxy composites are widely used in commercial products. For industrial purposes, storage stability is one of their most important characteristics. To enable this feature, alternative promoters that are stable at a low-energy state, where they do not react, are needed. Zeolitic imidazolate frameworks (ZIFs) are organic–inorganic complexes, and they contain imidazolate linkers, which are one of the promoters in the epoxy–amine reaction. In this study, the stability of a one-pot epoxy–amine composite was improved by using ZIFs as promoters. ZIFs were synthesized using the solvothermal method, and their structure were confirmed using X-ray diffraction analysis and field-emission scanning electron microscopy. The activation energy of the ZIFs was measured using the non-isothermal method of differential scanning calorimetry, and it was calculated using the Kissinger equation. Furthermore, the storage stability of the one-pot epoxy–amine system was measured considering the viscosity change with time at constant temperature. The viscoelastic behavior of the cured sample was demonstrated using dynamic mechanical analysis. [ABSTRACT FROM AUTHOR]

Flower-shaped organic-inorganic hybrid nanostructures, termed nanoflowers, have received considerable recent attention as they possess greatly enhanced activity, stability, durability, and even selectivity of entrapped organic biomolecules, which are much better than those from the conventional methods. They can be synthesized simply via co-incubation of organic and inorganic components in aqueous buffer at room temperature and yield hierarchical nanostructures with large surface-to-volume ratios, allowing for low-cost production by easy scale-up, as well as the high loading capacity of biomolecules without severe mass transfer limitations. Since a pioneering study reported on hybrid nanoflowers prepared with protein and copper sulfate, many other organic and inorganic components, which endow nanoflowers with diverse functionalities, have been employed. Thanks to these features, they have been applied in a diverse range of areas, including biosensors and biocatalysis. To highlight the progress of research on organic-inorganic hybrid nanoflowers, this review discusses their synthetic methods and mechanisms, structural and biological characteristics, as well as recent representative applications. Current challenges and future directions toward the design and development of multi-functional nanoflowers for their widespread utilization in biotechnology are also discussed. [ABSTRACT FROM AUTHOR]

Nanomaterials that exhibit enzyme-like characteristics, which are called nanozymes, have recently attracted significant attention due to their potential to overcome the intrinsic limitations of natural enzymes, such as low stability and relatively high cost for preparation and purification. In this study, we report a highly efficient colorimetric allergy detection system based on an immunoassay utilizing the peroxidase-mimicking activity of hierarchically structured platinum nanoparticles (H-Pt NPs). The H-Pt NPs had a diameter of 30 nm, and were synthesized by a seed-mediated growth method, which led to a significant amount of peroxidase-like activity. This activity mainly occurs because of the high catalytic power of the Pt element, and the fact that the H-Pt NPs have a large surface area available for catalytic events. The H-Pt NPs were conjugated to an antibody for the detection of immunoglobulin E (IgE) in the analytes; IgE is a representative marker for the diagnosis of allergies. They were then successfully integrated into a conventionally used allergy diagnostic test, the ImmunoCAP diagnostic test, as a replacement for natural signaling enzymes. Using this strategy, total and specific IgE levels were detected within 5 min at room temperature, with high specificity and sensitivity. The practical utility of the immunoassay was also successfully verified by correctly determining the levels of both total and specific IgE in real human serum samples with high precision and reproducibility. The present H-Pt NP-based immunoassay system would serve as a platform for rapid, robust, and convenient analysis of IgE, and can be extended to the construction of diagnostic systems for a variety of clinically important target molecules. [ABSTRACT FROM AUTHOR]

In this study, we describe a novel peroxidase-like activity of Co-aminoclay [CoAC] present at pH ~5.0 and its application to fluorescent biosensor for the determination of H2O2 and glucose. It is synthesized with aminoclays (ACs) entrapping cationic metals such as Fe, Cu, Al, Co., Ce, Ni, Mn, and Zn to find enzyme mimicking ACs by sol–gel ambient conditions. Through the screening of catalytic activities by the typical colorimetric reaction employing 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt (ABTS) as a substrate with or without H2O2, Fe, Cu, and CoACs are found to exhibit peroxidase-like activity, as well as oxidase-like activity was observed from Ce and MnACs. Among them, CoAC shows exceptionally high peroxidase-like activity, presumably due to its ability to induce electron transfer between substrates and H2O2. CoAC is then used to catalyze the oxidation of Amplex® UltraRed (AUR) into a fluorescent end product, which enables a sensitive fluorescent detection of H2O2. Moreover, a highly sensitive and selective glucose biosensing strategy is developed, based on enzyme cascade reaction between glucose oxidase (GOx) and CoAC. Using this strategy, a highly linear fluorescence enhancement is verified when the concentration of glucose is increased in a wide range from 10 μM to 1 mM with a lower detection limit of 5 μM. The practical diagnostic capability of the assay system is also verified by its use to detect glucose in human blood serum. Based on these results, it is anticipated that CoAC can serve as potent peroxidase mimetics for the detection of clinically important target molecules. [ABSTRACT FROM AUTHOR]

A simple and eco-friendly method has been developed for the one-pot synthesis of DNA–copper nanoflowers that exhibit high loading efficiencies, low cytotoxicities, and strong resistance against nucleases. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework ZIF-23 was prepared and used as catalyst for the solventless synthesis of cyclic carbonate from CO and propylene oxide with or without TBAB co-catalyst. ZIF-23 catalysts were prepared by a solvothermal or microwave method and they were characterized by various physicochemical techniques such as XRD, FT-IR, BET, TGA, and FE-SEM. The effects of reaction parameters such as temperature, reaction time, CO pressure, and co-catalyst on the reactivity of catalyst were investigated. ZIF-23 was recyclable up to four times without any considerable loss of its initial activity. Reaction mechanism containing the role of ZIF-23 with TBAB co-catalyst was also proposed. [ABSTRACT FROM AUTHOR]

An energy efficient and economically viable bimetallic heterogeneous catalyst system composed of Co and Zn as active centers and 2-methylimidazole as a linker has been synthesized in water at room temperature. The synthesized material (CZ-ZIF) possesses a sodalite topology, similar to the parent materials, ZIF-8 and ZIF-67, with a high surface area of ＞1400 m2 g−1. The Zn and Co metal ions were shown to occupy equivalent sites throughout the framework in similar proportions, as confirmed by inductively coupled plasma atomic emission spectroscopy and energy dispersive X-ray spectroscopy techniques. CZ-ZIF rendered a high catalytic conversion of epoxides to five-membered cyclic carbonates using CO2 as the C1 source under solvent- and co-catalyst-free conditions with excellent selectivity and manifested better catalytic abilities than ZIF-67 and enhanced framework stability compared to ZIF-8. Furthermore, CZ-ZIF exhibited catalytic activity even at room temperature in the presence of a co-catalyst, and was reusable over a minimum of five cycles with no noticeable decrease in activity. A plausible mechanism for CZ-ZIF catalyzed solvent- and co-catalyst-free epoxide–CO2 cycloaddition has been proposed. [ABSTRACT FROM AUTHOR]

The catalytic oxidation of hydrogen sulfide (HS) to elemental sulfur was studied over CeO-TiO catalysts. The synthesized catalysts were characterized by various techniques such as X-ray diffraction, BET, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia, and scanning electron microscopy (SEM). Catalytic performance studies of the CeO-TiO catalysts showed that HS was successfully converted to elemental sulfur without considerable emission of sulfur dioxide. CeO-TiO catalysts with Ce/Ti=1/5 and 1/3 exhibited the highest HS conversion, possibly due to the uniform dispersion of metal oxides, high surface area, and high amount of acid sites. [ABSTRACT FROM AUTHOR]

Recently, nanomaterial-based enzyme mimetics (nanozymes) have attracted enormous interest. They exhibit unique advantages such as excellent robustness, stability, and low-cost production with easy scale-up, which are critically needed as an alternative to natural enzymes. These nanozymes exhibit natural enzyme-like activity and have been applied to various kinds of detection and treatment methods for biomolecules such as DNA, proteins, cells, and small molecules including glucose. To highlight progress in the field of nanozymes, this review discusses recent nanozyme-based research results and their applications for the development of novel biosensor, immunoassay, cancer diagnostics, therapeutics, and environmental engineering technologies. Current challenges and future prospects of nanozymes for widespread use in biotechnology are also discussed. [ABSTRACT FROM AUTHOR]

Microbial cell arrays have attracted consistent attention for their ability to provide unique global data on target analytes at low cost, their capacity for readily detectable and robust cell growth in diverse environments, their high degree of convenience, and their capacity for multiplexing via incorporation of molecularly tailored reporter cells. To highlight recent progress in the field of microbial cell arrays, this review discusses research on genetic engineering of reporter cells, technologies for patterning live cells on solid surfaces, cellular immobilization in different polymers, and studies on their application in environmental monitoring, disease diagnostics, and other related fields. On the basis of these results, we discuss current challenges and future prospects for novel microbial cell arrays, which show promise for use as potent tools for unraveling complex biological processes. [ABSTRACT FROM AUTHOR]

The catalytic oxidation of hydrogen sulfide (HS) in the presence of ammonia was studied over niobium pentoxide supported on Fe-pillared clay catalysts (Nb/Fe-PILCs). The synthesized catalysts were characterized by various techniques such as X-ray diffraction, BET method, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed desorption of ammonia, and transmission electron microscopy. Catalytic performance studies of the Nb/Fe-PILC catalysts showed that HS was successfully converted to elemental sulfur and ammonium thiosulfate without any considerable emission of sulfur dioxide. The results show that 3 wt% Nb/Fe-PILC exhibited the highest HS conversion, which might be due to the uniform dispersion of niobium-oxide species on the Fe-PILC support. Niobium on the fresh Nb/Fe-PILC catalyst was in the +5 oxidation state and it was partially reduced to a lower oxidation state after the reaction. [ABSTRACT FROM AUTHOR]

The synthesis of glycerol carbonate by glycerolysis of urea was investigated under mild conditions, using immobilized metal-containing ionic liquid catalysts. Three different catalysts were prepared, with the following supports: (1) polystyrene (PS), (2) commercial silica (CS), and (3) chitosan (CH). The glycerolysis of urea was considered to include two main reactions: carbamoylation of glycerol and carbonylation of glycerol carbamate. The approximate rate constant for PS-(Im)ZnBr was higher than those of CH-(Im)ZnBr and CS-(Im)ZnBr probably due to its wellbalanced acid-base properties. The activation energies for PS-, CH-, and CS-(Im)ZnBr were 142.9, 163.0, and 166.7 kJ mol, respectively. PS-(Im)ZnBr exhibited better reuse properties than CH-(Im)ZnBr and CS-(Im)ZnBr catalysts. [ABSTRACT FROM AUTHOR]

This study outlines an algorithm that can be used for individual tree detection and crown delineation; it was applied to coniferous forest using aerial imagery. This article explains the assumptions and processes involved in the algorithm, presents the results of the applications, and discusses possible limitations. The algorithm, which adopts contextual analysis that excludes the need to specify window size, was applied to detect and delineate individual trees based on morphological and reflective characteristics. The preprocessing steps included suppression of the non-coniferous area (i.e. non-forest and leaf-off deciduous forest) and the creation of appropriately smoothed imagery using an optimal smoothing level based on accuracy index (AI); thereafter, unconstrained directional peak- and edge-finding algorithms were processed separately. To assess the tree detection and crown delineation processes, the results of the algorithms were evaluated carefully against visually interpreted crowns in six square plots using several statistical measures based on tree top correspondence, positional difference of tree top, directional crown width, and crown area assessment. The average tree top correspondence had an AI of 88.83%. The positional difference between detected and visually interpreted tree tops was measured and its average was 0.6 m. For our 0.5 m/pixel aerial imagery, the average root mean square error (RMSE) of crown width in six sample plots was found to be 2.8 m, and crown area estimation resulted in RMSE of approximately 9.23 m2(23.25%). In general, this study highlights the potentiality of the proposed algorithm to efficiently and automatically acquire forest information such as tree numbers, crown width, and crown area. [ABSTRACT FROM PUBLISHER]

An effective strategy to detect biological thiols (biothiols), including glutathione (GSH), cysteine (Cys), and homocysteine (Hcy), holds significant incentive since they play vital roles in many cellular processes and are closely related to many diseases. Here, we demonstrated that hybrid nanoflowers composed of crystalline copper phosphate and horseradish peroxidase (HRP) served as a functional unit exhibiting dual catalytic activities of biothiol oxidase and HRP, yielding a cascade reaction system for a sensitive one-pot fluorescent detection of biothiols. The nanoflowers were synthesized through the anisotropic growth of copper phosphate petals coordinated with the amine/amide moieties of HRP, by simply incubating HRP and copper(II) sulfate for three days at room temperature. Copper phosphates within the nanoflowers oxidized target biothiols to generate H2O2, which activated the entrapped HRP to oxidize the employed Amplex UltraRed substrate to produce intense fluorescence. Using this strategy, biothiols were selectively and sensitively detected by monitoring the respective fluorescence intensity. This nanoflower-based strategy was also successfully employed for reliable quantification of biothiols present in human serum, demonstrating its great potential for clinical diagnostics. [ABSTRACT FROM AUTHOR]

In this study, a series of imidazolium-based ionic liquids (ILs) having carboxylic acid moieties were synthesized and used as new homogeneous catalysts to synthesize cyclic carbonates from CO and epoxides. Even in the absence of any co-catalyst and organic solvent, carboxylic-acid-functionalized ILs showed better catalytic activity in the coupling reaction of CO and styrene oxide for the production of styrene carbonate than did hydroxyl-functionalized ILs and conventional ILs without any functional moieties. A detailed investigation was carried out on a variety of factors that affected the reactivity, such as the alkyl chain length and the molecular composition of IL molecules including the halide ions. The effect of various reaction parameters such as reaction time, temperature, CO pressure and catalyst amount was also investigated in detail. The mechanism underlying the enhanced rate of the cycloaddition reaction in the presence of carboxylic-acid-functionalized ILs was proposed. [ABSTRACT FROM AUTHOR]

A series of vanadia-doped iron-oxide-pillared clays (V/Fe-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H2S was investigated. V/Fe-PILCs were characterized using X-ray diffraction (XRD), surface area- and pore volume measurements, chemical analysis, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H2(H2-TPR). V/Fe-PILCs showed better catalytic performance than Fe-PILC without any significant SO2emissions. The H2S conversion over V/Fe-PILCs increased with increasing vanadia content up to 7 wt.%. However, it decreased at higher vanadia loading due to the decrease in surface area and the formation of the crystalline V2O5phase. The presence of water vapor in the reactant mixture resulted in a decrease of H2S conversion. [ABSTRACT FROM AUTHOR]

Perovskite LaCoO3 and perovskite-like LaSrCoO4 mixed oxides were prepared by polyglycol gel method, and their catalytic performance was compared for the selective oxidation of hydrogen sulfide in a stream containing excess amount of ammonia and water for the first time. These samples were investigated by using XRD, BET, O2-TPD and XPS. The catalytic activity and the selectivity to solid products (ammonium thiosulfate and elemental sulfur) of LaCoO3 were better than those of LaSrCoO4, and this is explained in terms surface contents of oxygen and cobalt, oxidation state of cobalt, and BET surface area. [ABSTRACT FROM AUTHOR]

We investigated the selective oxidation of hydrogen sulfide to elemental sulfur and ammonium thiosulfate by using Bi4V2-xSbxO11- y catalysts. The catalysts were prepared by the calcination of a homogeneous mixture of Bi2O3, V2O5, and Sb2O3 obtained by ball-milling adequate amounts of the three oxides. The main phases detected by XRD analysis were Bi4V2O11, Bi1.33V2O6, BiSbO4 and BiVO4. They showed good H2S conversion with less than 2% of SO2 selectivity with a feed composition of H2S/O2/NH3/H2O/He=5/2.5/5/60/27.5 and GHSV=12,000 h-1 in the temperature ranges of 220–260 ‡C. The highest H2S conversion was obtained for x=0.2 in Bi4V2-xSbxO11- y catalyst. TPR/TPO results showed that this catalyst had the highest amount of oxygen consumption. XPS analysis before and after reaction confirmed the least reduction of vanadium oxide phase for this catalyst during the reaction. It means that the catalyst with x=0.2 had the highest reoxidation capacity among the Bi4V2-xSbxO11- y catalysts. [ABSTRACT FROM AUTHOR]

PRK1, a receptor-like kinase that is expressed in pollen, pollen tubes, and ovaries, has been shown to play important roles in pollen development and embryo sac development in Petunia inflata. We have used the kinase domain of PRK1 as a bait in the yeast two-hybrid system to identify PRK1-interacting proteins. The screening resulted in isolation of a cDNA encoding a protein highly homologous to the human and yeast beta-subunit of translation initiation factor 2B (e1F2B-beta), which was designated NeIF2B beta. e1F2B is a guanine nucleotide exchange protein that functions in the regulation of translation in eukaryotic cells. Deletion mutants of NeIF2B beta were analyzed for their interaction with PRK1, and the results suggested that the N-terminal half of NeIF2B beta, especially the region between residue 103 and 235, is important for the interaction. This protein association was confirmed by in vitro binding assay of the recombinant NeIF2B beta and PRK1 proteins. Despite high sequence homology between NeIF2B beta and its yeast counterpart, the NeIF2B beta cDNA could not rescue the phenotype of the yeast mutant strain lacking the GCD7 gene encoding e1F2B-beta, when transferred into the mutant strain. [ABSTRACT FROM AUTHOR]

The appearance and evolution of biofuel cells can be categorized into three groups: microbial biofuel cells (MBFCs), enzymatic biofuel cells (EBFCs), and enzyme-like nanomaterial (nanozyme)-based biofuel cells (NBFCs). MBFCs can produce electricity from waste; however, they have significantly low power output as well as difficulty in controlling electron transfer and microbial growth. EBFCs are more productive in generating electricity with the assistance of natural enzymes, but their vulnerability under diverse environmental conditions has critically hindered practical applications. In contrast, because of the intrinsic advantages of nanozymes, such as high stability and robustness even in harsh conditions, low synthesis cost through facile scale-up, and tunable catalytic activity, NBFCs have attracted attention, particularly for developing wearable and implantable devices to generate electricity from glucose in the physiological fluids of plants, animals, and humans. In this review, recent studies on NBFCs, including the synthetic strategies and catalytic activities of metal and metal oxide-based nanozymes, the mechanism of electricity generation from glucose, and representative studies are reviewed and discussed. Current challenges and prospects for the utilization of nanozymes in glucose biofuel cells are also discussed. [ABSTRACT FROM AUTHOR]

Light-activated nanozymes possess several advantages, such as light-mediated activity regulation, utilization of molecular oxygen as a green oxidant, and highly enhanced activity; however, the types of light-activated nanozymes are still limited. In this study, we found that Mg aminoclay-based Fe3O4/TiO2 hybrids (MgAC-Fe3O4/TiO2) exhibited peroxidase-like catalytic activity to catalyze the oxidation of the peroxidase substrate 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) in the presence of H2O2, which was significantly enhanced under ultraviolet (UV)-light irradiation. Compared with MgAC-Fe3O4 and MgAC-TiO2, MgAC-Fe3O4/TiO2 showed around three-fold enhancement in the absorption intensity corresponding to the oxidized ABTS under UV-light irradiation, presumably due to the synergistic effect between Fe3O4 and TiO2, thereby facilitating photocatalytic electron transfer during the catalytic action. In addition, the MgAC-Fe3O4/TiO2 showed vivid stability enhancement in wide range of pH and temperature values compared with natural peroxidase. The UV-light-driven MgAC-Fe3O4/TiO2-based system was successfully applied for the colorimetric detection of phenolic compounds, including pyrocatechol and resorcinol, in a dynamic linear range of 0.15–1.30 mg/mL with a limit of detection as low as 0.1 mg/mL. Further, the system could successfully determine the phenolic compounds in spiked tap water, and thus, it can be used for practical applications. We believe that the UV-light-driven enhancement in the peroxidase-like catalytic performances highlights the potential of MgAC-Fe3O4/TiO2 for detecting phenolic compounds as well as other clinically and environmentally important substances. [ABSTRACT FROM AUTHOR]