Search

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]

The pervasive spread of infectious diseases and pandemics, such as the 2019 coronavirus disease (COVID-19), are becoming increasingly serious and urgent threats to human health. Preventing the spread of such diseases prioritizes the development of sensing devices that can rapidly, selectively, and reliably detect pathogens at minimal cost. Paper-based analytical devices (PADs) are promising tools that satisfy those criteria. Numerous paper-based biosensors have been established that rival conventional pathogen detection methods. Among them, colorimetric strategies are promising since results can be interpreted by eye, and are simple to operate, which is advantageous for point-of-care testing (POCT). Particularly, the application of nanomaterials on paper-based biosensors has become important as these materials are capable of converting signals from pathogens through unique mechanisms to yield an amplified colorimetric readout. To highlight the research progress on using nanomaterials in colorimetric paper-based biosensor for pathogen detection, we discuss the sensing mechanisms of how they work, structural and analytical characteristics of the devices, and representative recent applications. Current challenges and future directions of using PADs and nanomaterial-mediated strategies are also discussed. Image 1 • Recent developments in paper-based analytical devices for colorimetric detection of pathogens are reviewed in detail. • Three main types of point-of-care paper-based devices are exploited for robust performance in pathogen detection. • Colorimetric strategies are sensitive and offer fast response and convenience to end-users. • Diverse nanomaterials are deployed for both signal transduction and amplification to enhance sensitivity. • Sensing mechanisms fundamental to colorimetric pathogen detection are discussed. [ABSTRACT FROM AUTHOR]

A reagent-free colorimetric method for galactose quantification using a composite of cerium oxide nanoparticles (nanoceria) and galactose oxidase (Gal Ox) entrapped in an agarose gel was developed. In the presence of galactose, the Gal Ox entrapped within the agarose gel catalyzed the oxidation of galactose to generate H2O2, which induced a color change from white to intense yellow. This reaction occurred without any chromogenic substrate. This color transition is presumed to be due to the H2O2-mediated alteration of the oxidation state of cerium ions present on the surface of the nanoceria. The intensity of color change was quantified by acquiring an image with a conventional smartphone, converting the image to cyan-magenta-yellow-black (CMYK) mode, and subsequently analyzing the image using the ImageJ software. Using this strategy, galactose concentration was specifically determined with excellent sensitivity of as low as 0.05 mM. The analytical utility of the assay was successfully verified by correctly determining diverse levels of galactose in human serum, which is enough to diagnose galactosemia, a genetic disorder characterized by the malfunctioning of enzymes responsible for galactose metabolism. The assay employing a hydrogel composite with entrapped nanoceria and Gal Ox, is a simple, cost-effective, and rapid colorimetric assay for galactose quantification, without using any chromogenic reagent. This cost-effective method has great potential for the diagnosis of galactosemia and is highly promising in comparison to the laborious instrumentation-based methods currently in use. [ABSTRACT FROM AUTHOR]

Over the past decade, the catalytic activity of nanozymes has been greatly enhanced, but their selectivity is still low and considered a critical issue to overcome. Herein, Fe–N4 single site embedded graphene (Fe–N‐rGO), which resembles the heme cofactor present in natural horseradish peroxidase, shows a marked enhancement in peroxidase‐like catalytic efficiency of up to ≈700‐fold higher than that of undoped rGO as well as excellent selectivity toward target H2O2 without any oxidizing activity. Importantly, when Fe or N is doped alone or when Fe is replaced with another transition metal in the Fe–N4 site, the activity is negligibly enhanced, showing that mimicking the essential cofactor structure of natural enzyme might be essential to design the catalytic features of nanozymes. Density functional theory results for the change in Gibbs free energy during the peroxide decomposition reaction explain the high catalytic activity of Fe–N‐rGO. Based on the high and selective peroxidase‐like activity of Fe–N‐rGO, trace amounts of H2O2 produced from the enzymatic reactions from acetylcholine and cancerous cells are successfully quantified with high sensitivity and selectivity. This work is expected to encourage studies on the rational design of nanozymes pursuing the active site structure of natural enzymes. [ABSTRACT FROM AUTHOR]

An effective novel strategy to detect bacteria is promising because it may improve human health by allowing early diagnosis and timely treatment of bacterial infections. Here, we report a simple, reliable, and economical colorimetric assay using the peroxidase-like activity of chitosan-coated iron oxide magnetic nanoparticles (CS-MNPs). When CS-MNPs are incubated with a sample containing bacterial cells such as the gram-negative Escherichia coli or the gram-positive Staphylococcus aureus, the negatively-charged bacterial membrane interacts with positively-charged chitosan on the surface of CS-MNPs, thus resulting in significant reduction of their peroxidase-like activity presumably by a hindrance in the accessibility of the negatively charged substrate, 2-2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) to the positively-charged CS-MNPs. This simple colorimetric strategy allowed the rapid detection of bacterial cells down to 104 CFU mL−1 by the naked eye and 102 CFU mL−1 by spectrophotometry within 10 min. Based on the results, we anticipate that the CS-MNPs-based assay has great potential for the on-site diagnosis of bacterial infections in facility-limited or point-of-care testing (POCT) environments. [ABSTRACT FROM AUTHOR]

Cordyceps militaris is a medicinal mushroom used to treat immune-related diseases in East Asia. We investigated the anti-inflammatory effect of the extract of C. militaris grown on germinated Rhynchosia nulubilis (GRC) fermented with Pediococcus pentosaceus ON89A isolated from onion (GRC-ON89A) in vivo as well as in vitro. The anti-inflammatory effect of GRC-ON89A was investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. The total polyphenol content (TPC) and total flavonoid content (TFC) in the GRC-ON89A ethanol extract were significantly increased compared to that in GRC. GRC-ON89A hexane fraction (GRC-ON89A-Hex) inhibited the release of nitric oxide (NO) compared to that of the LPS-treated control without cytotoxicity in LPS-stimulated RAW 264.7 macrophages. GRC-ON89A-Hex decreased the inducible NO synthase (iNOS), cyclooxygenase 2 (COX2), and tumor necrosis factor (TNF)-α mRNA expression in LPS-stimulated RAW 264.7 macrophages. In addition, pre-treatment with GRC-ON89A-Hex significantly inhibited LPS-stimulated phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-κB. To induce allergic contact dermatitis (ACD), 1-fluoro-2, 4-dinitrofluorobenzene (DNFB) was applied to the surface of the right ears of C57BL/6N mice. GRC-ON89A reduced the ear swelling and thickness in DNFB-induced ACD mice. This study demonstrates the potential usefulness of GRC-ON89A as an anti-inflammatory dietary supplement or drug. [ABSTRACT FROM AUTHOR]

To understand the protein functions within a cell, where proteins exist in an extremely crowded and confined state, various modeling and experimental methods have been proposed. Here, we propose a new experimental approach to modulate the macromolecular crowding and/or confinement effects by using mesoporous silicas with two different pore structures. SBA-15 and MSU-F with linear and mesocellular pore structures, respectively, were used to adsorb a model enzyme, glucose oxidase (GOx), in various concentrations ranging from 3 to 430 mg ml−1. The concentration of adsorbed GOx in the mesopores, representing the degree of crowding, showed a good correlation with thermal enzyme stability. Interestingly, the increase of thermal stability as a function of macromolecular crowding showed different correlations depending on the pore structure of mesoporous silicas. It represents that combination of crowding and confinement effects can promote different microenvironments for enzyme molecules, while mesoporous silicas can impose controlled crowding and confinement effects on enzymes due to their uniform and tunable pore structures. It is anticipated that this new and simple approach can provide a tool to elucidate crowding and confinement effects on the protein functions, including its stability in vivo , because the mesopore environments could mimic the real macromolecular cell system under crowding. [ABSTRACT FROM AUTHOR]

Abstract We herein developed a simple and ultrafast electrochemical DNA detection method by utilizing the oxidase-mimicking activity of cerium oxide nanoparticles (CeO 2). In the sensor, the presence of DNA, which electrostatically interacts with CeO 2 and 3,3′,5,5′-tetramethylbenzidine (TMB) substrate, limits the formation of CeO 2 -TMB complex that is required for the oxidase-like reaction. As a result, the oxidase-mimicking activity of CeO 2 is not effectively exerted, leading to the significantly diminished electrochemical current signal. With this novel strategy, we successfully determined DNA amplicon derived from Escherichia coli (E. coli) with the total assay time less than 6 min even without the post-purification of DNA amplicon. Graphical abstract Unlabelled Image Highlights • A simple and ultrafast electrochemical DNA detection method is devised. • It is the first report to use oxidase-mimicking activity of cerium oxide nanoparticles for electrochemical target DNA detection. • This method contains advantageous features such as simplicity, rapidity, and cost-effectiveness. • This method could be employed to detect a broad range of targets including proteins, small molecules, and inorganic ions. [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]

The use of protein-inorganic hybrid nanoflowers for the immobilization of enzymes has received a significant degree of attention owing to their capability to retain high enzymatic activity and stability. However, the relative lack of reusability due to the weakness of the flower-like structure has limited their practical applications. Herein, we have developed a simple but efficient method to synthesize highly robust enzyme-inorganic hybrid nanoflowers, which relies on further crosslinking of the enzyme molecules entrapped in the hybrid nanoflowers by treatment with glutaraldehyde (GA). By employing lipase from Candida rugosa as a model enzyme with copper phosphate during 3 days incubation followed by the additional GA treatment for only 1 h, we could successfully synthesize GA-treated lipase nanoflowers having similar flower-like morphology and hydrolytic activity ( ca. 95% compared with the free lipase) as conventionally synthesized lipase nanoflowers without GA treatment. Importantly, the conventional lipase nanoflowers seemed not to be reusable because they lost most of their activity (∼90%) after recycling 4 times, whereas GA-treated lipase nanoflowers exhibited higher retention of their initial activity (over 70%) after 4 reuses, which was also accompanied by an efficient maintenance of their flower-like morphology. Based on our results, we expect that this simple GA-mediated strategy to synthesize enzyme-inorganic hybrid nanoflowers can be readily extended to other enzymes for various biotechnological applications. [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]

Mercury (Hg) emissions are increasing annually owing to rapid global industrialization. Hg poisoning can severely affect the human body owing to its persistence and bioaccumulation. In this study, hybrid nanoflowers (NFs) were synthesized by promoting the formation of primary copper-phosphate crystals coordinated with polydopamine (PDA) and Fe 3 O 4 magnetic nanoparticles (MNPs), followed by coating with silver nanoparticles on the surface of the NFs (Ag-MNP-PDA-Cu NFs). The results suggest that the hierarchical structure of the NFs enabled a large surface area with nanosized pores, which were exploited for Hg adsorption. The adsorbed Hg ions could be further eliminated from the solution based on the magnetic characteristics of the NFs. Additionally, hybrid NFs functionalized with Hg2+-binding aptamers (Apt-Ag-MNP-PDA-Cu NFs) were prepared based on the silver–sulfur interactions between the Ag-MNP-PDA-Cu NFs and thiol-modified aptamers. The performance of both adsorbents demonstrated that the immobilization of Hg2+-binding aptamers significantly improved the elimination of Hg from solution. The Hg2+ adsorption isotherm of the Apt-Ag-MNP-PDA-Cu NFs followed the Dubinin–Radushkevich model, with a maximum adsorption capacity of 1073.19 mg/g. The Apt-Ag-MNP-PDA-Cu NFs adsorbed greater amounts of Hg2+ than the non-functionalized NFs at the same concentrations, which confirmed that the functionalization of Hg2+-binding aptamers on the NFs improved the Hg2+ removal performance. The results suggest that Apt-Ag-MNP-PDA-Cu NFs could serve as an efficient Hg-removing adsorbent, possibly by providing binding sites for the formation of T-Hg2+-T complexes. [Display omitted] • The aptamer hybrid nanoflower particles were synthesized to remove mercury ions. • Thymine-rich Hg2+-binding aptamers were functionalized to nanoflower particles. • The aptamer hybrid nanoflower particles improved the performance of mercury ions adsorption. • The maximum Hg2+ adsorption capacity of aptamer hybrid nanoflower was 1073.19 mg/g. • The adsorption isotherm of aptamer hybrid nanoflower on Hg2+ followed the Dubinin–Radushkevich model. [ABSTRACT FROM AUTHOR]

Carbon-based nanozymes possessing peroxidase-like activity have attracted significant interest because of their potential to replace native peroxidases in biotechnology. Although various carbon-based nanozymes have been developed, their relatively low catalytic efficiency needs to be overcome to realize their practical utilization. Here, inspired by the elemental uniqueness of Cu and the doped elements N and S, as well as the active site structure of Cu-centered oxidoreductases, we developed a new carbon-based peroxidase-mimicking nanozyme, single-atom Cu-centered N- and S-codoped reduced graphene oxide (Cu-NS-rGO), which preserved many Cu–N 4 and Cu–N 4 S active sites and showed dramatically high peroxidase-like activity without any oxidase-like activity, yielding up to 2500-fold higher catalytic efficiency (k cat /K m) than that of pristine rGO. The high catalytic activity of Cu-NS-rGO might be attributed to the acceleration of electron transfer from Cu single atom as well as synergistic effects from both Cu–N 4 and Cu–N 4 S active sites, which was theoretically confirmed by Gibbs free energy calculations using density functional theory. The prepared Cu-NS-rGO was then used to construct an electrochemical bioassay system for detecting choline and acetylcholine by coupling with the corresponding oxidases. Using this system, both target molecules were selectively determined with high sensitivity that was sufficient to clinically determine their levels in physiological fluids. Overall, this study will facilitate the development of nanocarbon-based nanozymes and their electrochemical biosensing applications, which can be extended to the development of miniaturized devices in point-of-care testing environments. [Display omitted] [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]

Abstract: In this study, tetraoctyl ammonium chloride (TOAC) ionic liquid supported on K+-montmorillonite clay (K10) was prepared by the adsorption of the ionic liquid onto the clay. The TOAC-K10 was characterized by elemental analysis (EA), BET, 13C NMR, 27Al NMR, SEM, TEM, and FT-IR. The surface area and average pore diameter of the TOAC-K10 decreased with the immobilization of TOAC onto K10. The TOAC-K10 showed good catalytic activity for the synthesis of cyclic carbonate from allyl glycidyl ether (AGE) and carbon dioxide. The effects of reaction parameters such as reaction temperature, reaction time, and CO2 pressure on the reactivity of TOAC-K10 in a conventional heating batch reactor are discussed. Microwave irradiation was also applied for the reaction, and good conversions of AGE were obtained within <1h. The catalytic performance was highly dependant on the weight of catalyst, microwave power, and CO2 pressure. The catalyst in the microwave system could be reused for up to 4 consecutive runs without significant loss of its initial activity. [Copyright &y& Elsevier]

Abstract: This study focuses on the selective catalytic oxidation of hydrogen sulfide (H2S) over vanadia supported on TiO2-pillared clay catalysts (V/Ti-PILCs) in the presence of ammonia and water. The synthesized V/Ti-PILC catalysts were characterized by chemical analysis, surface area/pore volume measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–vis-diffuse reflectance spectroscopy (UV–vis-DRS), temperature-programmed reduction by H2 (H2-TPR), and thermogravimetric (TG) analysis. The results of a catalytic performance study showed that in the presence of the V/Ti-PILC catalysts, H2S was successfully converted into elemental sulfur and ammonium thiosulfate (ATS) without any notable sulfur dioxide emission. This superior performance of the V/Ti-PILC catalysts was probably related to the uniform dispersion of the vanadia species on the Ti-PILC support. [Copyright &y& Elsevier]

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]

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]

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]

Inspired by the active site structure of natural horseradish peroxidase having iron as a pivotal element with coordinated histidine residues, we have developed histidine coated magnetic nanoparticles (His@MNPs) with relatively uniform and small sizes (less than 10 nm) through one-pot heat treatment. In comparison to pristine MNPs and other amino acid coated MNPs, His@MNPs exhibited a considerably enhanced peroxidase-imitating activity, approaching 10-fold higher in catalytic reactions. With the high activity, His@MNPs then were exploited to detect the important neurotransmitter acetylcholine. By coupling choline oxidase and acetylcholine esterase with His@MNPs as peroxidase mimics, target choline and acetylcholine were successfully detected via fluorescent mode with high specificity and sensitivity with the limits of detection down to 200 and 100 nM, respectively. The diagnostic capability of the method is demonstrated by analyzing acetylcholine in human blood serum. This study thus demonstrates the potential of utilizing His@MNPs as peroxidase-mimicking nanozymes for detecting important biological and clinical targets with high sensitivity and reliability. [ABSTRACT FROM AUTHOR]

Hydrolase-mimicking nanozymes have received increasing attention in recent years, but the effective rational design and development of these materials has not been realized, as they are not at present considered a critical research target. Herein, we report that Zn-doped mesoporous ceria (Zn-m-ceria) engineered to have an abundance of two different active sites with different functions—one that allows both co-adsorption binding of organophosphate (OP) and water and another that serves as a general base—has significant organophosphorus hydrolase (OPH)-like catalytic activity. Specifically, Zn-m-ceria exhibits a catalytic efficiency over 75- and 25-fold higher than those of m-ceria and natural OPH, respectively. First-principles calculations reveal the importance of Zn for the OPH-mimicking activity of the material, promoting substrate adsorption and proton-binding. The OPH-like Zn-m-ceria catalyst is successfully applied to detect a model OP, methyl paraoxon, in spiked tap water samples with excellent sensitivity, stability, and detection precision. We expect that these findings will promote research based on the rational engineering of the active site of nanozymes and efficient strategies for obtaining a diverse range of catalysts that mimic natural enzymes, and hence the utilization in real-world applications of enzyme-mimicking catalysts with properties superior to their natural analogs should follow. [Display omitted] [ABSTRACT FROM AUTHOR]

Bacterial contamination causes various problems ranging from bacterial infection to biofouling. As an effective and non-toxic agent for bacterial de-contamination, glucose oxidase (GOx)-copper hybrid nanoflowers embedded with amine-functionalized magnetic nanoparticles (NH 2 -MNPs), called 'MNP-GOx NFs', are developed. Positively-charged NH 2 -MNPs and negatively-charged GOx molecules are first interacted via electrostatic attraction which can be controlled by changing the buffer pH, and the follow-up addition of copper(II) sulfate leads to blooming of nanoflowers (MNP-GOx NFs) after incubation at room temperature for 3 days. MNP-GOx NFs show effective antibacterial activity by generating H 2 O 2 from GOx-catalyzed glucose oxidation. For example, 99.9% killings of Staphylococcus aureus and Escherichia coli are achieved after 3 h treatment of 106/mL cells with 0.2 and 3.0 mg/mL MNP-GOx NFs, respectively, revealing that Gram-positive S. aureus with mono-layer membrane system is more vulnerable to the treatment of MNP-GOx NFs than Gram-negative E. coli with two-layer membrane system. MNP-GOx NFs can maintain 97% of bactericidal activity even after recycled uses by magnetic separation for eight times iterative bacterial killings. Finally, MNP-GOx NFs are employed for the fabrication of antibacterial gauzes. MNP-GOx NFs have also opened up a great potential for their applications in biosensors, biofuel cells and bioconversion as well as bacterial de-contamination. • Magnetic nanoparticles and glucose oxidase are complexed via charge interaction. • Follow-up addition of CuSO 4 leads to the blooming of hybrid nanoflowers (MNP-GOx NFs). • MNP-GOx NFs show antibacterial activity against S. aureus and E. coli. • MNP-GOx NFs maintain 97% of bactericidal activity after recycled uses eight times. • MNP-GOx NFs are employed to develop antibacterial gauzes. [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]

We herein describe novel amine-grafted metal–organic frameworks (MOFs) as a promising alternative to natural peroxidase enzyme and their applications for a fluorescent assay of choline (Cho) and acetylcholine (ACh). Among diverse amine-functionalized MOFs, N , N , N ′, N ′-tetramethyl-1,4-butanediamine (TMBDA)-functionalized MIL-100(Fe) (TMBDA-MIL-100(Fe)) exhibited the highest peroxidase activity by developing intense fluorescence from Amplex UltraRed (AUR) in the presence of H 2 O 2 , which was presumably due to the synergetic effect of the enhanced negative potential and precisely controlled molecular size of the grafted diamine. Based on the excellent peroxidase-like activity of TMBDA-MIL-100(Fe), choline and ACh were reliably determined down to 0.027 and 0.036 µM, respectively. Furthermore, practical applicability of this strategy was successfully demonstrated by detecting choline and ACh in spiked samples of milk and serum, respectively. This work highlights the advantages of amine-grafted MOFs for the preparation of biomimetic catalysts, extending their scope to biosensor applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A single Fe-site-containing hydrogel nanozyme was synthesized via an ionic gelation. • Fe-N sites function as active sites, yielding a significant peroxidase-like activity. • Foldable paper microfluidic device integrating two pH systems was developed. • Foldable device showed excellent analytical performances for detecting glucose. Peroxidase-mimicking nanozymes have been extensively studied, but their real utilization is limited by their working conditions limited to acidic pH, which makes it difficult to couple with oxidative enzymes operating at near-neutral pH. Here, we have developed a foldable paper microfluidic device that enables a highly convenient cascade reaction between peroxidase-mimicking nanozymes and oxidative enzymes to visually identify the target molecules. A single-atom iron-site-containing poly-γ-glutamic acid/chitosan hydrogel nanoparticle (PGA-Fe/CS NP) was developed, as a model peroxidase-like nanozyme, via rapid ionic gelation. Glucose oxidase (GOx) was used as a model oxidative enzyme. The paper device was constructed by simple wax-printing, including two parts with a foldable configuration: the first is for glucose oxidation under neutral pH and the second is for H 2 O 2 reduction to produce a colorimetric signal under acidic pH. By dropping the sample solution in the first part, the device allowed efficient glucose oxidation by the immobilized GOx at neutral pH. On merely folding the device, the produced H 2 O 2 from the glucose oxidation easily transfers to the second part of the device where PGA-Fe/CS NP was immobilized, inducing the peroxidase-like catalytic reaction at acidic pH. Using the foldable paper microfluidic device, the target glucose was successfully determined with excellent selectivity, sensitivity, stability, and reliability, using an image acquired by a smartphone. Since any oxidative enzymes could be incorporated into the device with the peroxidase-like PGA-Fe/CS NP, we expect that the foldable paper microfluidic device, which conveniently allows the cascade reaction under different pH environments, would be highly beneficial for the detection of various clinically important target molecules, thus laying the groundwork for future biosensing applications of nanozymes in point-of-care testing environments. [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]

In this study, silver nanoparticle-coated polydopamine-copper phosphate hybrid nanoflowers (Ag-PDA-Cu 3 (PO 4) 2 NFs) were synthesized and demonstrated to serve as efficient surface-enhanced Raman spectroscopy (SERS) probes for detecting thiol-containing molecules such as benzenethiol and thiocholine. Ag-PDA-Cu 3 (PO 4) 2 NFs were fabricated by forming PDA-Cu 3 (PO 4) 2 NFs through the nucleation of Cu 3 (PO 4) 2 on the PDA surface via interaction between Cu2+ and the free amine groups of dopamine, followed by the anisotropic growth of Cu 3 (PO 4) 2 crystals into flower-like microparticles. The NFs were then incubated with silver nitrate for in situ reduction to form Ag nanoparticles (NPs) on the surface of the NFs. The resulting hybrid NFs were demonstrated to act as SERS probes, sensitively detecting thiol-containing molecules, based on the successful interaction between Ag NPs and the thiol group (S-H) of the target molecules. The SERS intensities of benzenethiol and thiocholine at various concentrations were analyzed and found to yield superior limits of detection of 800 and 60 pM, respectively. Therefore, Ag-PDA-Cu 3 (PO 4) 2 NFs could be excellent SERS probes for detecting various thiol-containing molecules, particularly to determine the status of patients exposed to thiol-containing pesticides. • Silver nanoparticle-coated polydopamine-copper phosphate hybrid nanoflowers (Ag-PDA-Cu 3 (PO 4) 2 NFs) were successfully synthesized. • Demonstration of Ag-PDA-Cu 3 (PO 4) 2 NFs as surface-enhanced Raman spectroscopy (SERS) probes. • Sensitive detection of thiol-containing molecules based on interaction between Ag NPs and thiol group. • Superior limit of detection of 800 and 60 pM for detection of benzenethiol and thiocholine. [ABSTRACT FROM AUTHOR]

In this study, zeolitic imidazolate framework (ZIF-90) was synthesized from Zn(NO 3 ) 2 ·4H 2 O and imidazolate-2-carboxyaldehyde (ICA), then it was post-functionalized to form F-ZIF-90 using hydrazine followed by quaternization. The ZIFs were characterized by elemental analysis (EA), BET, XRD, 13 C NMR, FT-IR, and SEM. The surface area and pore volume of F-ZIF-90 were smaller than those of ZIF-90 due to functionalization inside the pores. The F-ZIF-90 showed excellent catalytic activity for the synthesis of the cyclic carbonate from allyl glycidyl ether (AGE) and carbon dioxide. The effects of the reaction parameters such as catalyst amount, reaction time, CO 2 pressure, and reaction temperature on the reactivity of F-ZIF-90 were also studied, and reaction mechanism including the role of F-ZIF-90 catalyst was proposed. The F-ZIF-90 catalyst, however, partially lost its crystalline structure and superior catalytic performance when it was reused. [ABSTRACT FROM AUTHOR]

Polystyrene-supported quaternized ammonium salt catalysts (PS-alkyl-AX) were synthesized and characterized by various physicochemical analytic methods such as EA, FT-IR, XPS, and SEM. The reactivity of the catalysts was investigated for the synthesis of allyl glycidyl carbonate from CO 2 and allyl glycidyl ether under mild reaction conditions. The PS-alkyl-AX catalysts showed good catalytic activity without using any solvent due to the synergistic effect of NH functional group and quaternary ammonium salt structure. Theoretical studies using density functional theory (DFT) was applied to investigate the reaction mechanism. The PS-hexyl-MeI catalyst was readily recoverable and reusable in subsequent reaction cycles without a significant loss in its activity. [ABSTRACT FROM AUTHOR]

For large-scale energy storage, aqueous rechargeable zinc-ion batteries are one of the most promising battery systems to replace lithium-ion batteries. In this study, a facile and scalable hydrothermal method is used to prepare VO 2 nanorods, which are ball-milled with carbon black to prepare VO 2 @C nanoparticles. Characterizations using several advanced techniques confirm the successful synthesis of pure VO 2 nanorods. Prior to electrochemical measurements, the VO 2 @C nanostructured cathode materials are transformed into V 2 O 5 · nH 2 O via an in situ electrochemical oxidation technique. The VO 2 @C/Zn aqueous zinc-ion full cell exhibits a reversible capacity of 300 mA h g−1 and a retention capacity of 85% after 1000 cycles at a current density of 5 A g−1 with a 2 M ZnSO 4 electrolyte. The full cell also retains a remarkable capacity of 159 mA h g−1, even after 4000 galvanostatic charge–discharge cycles at 5 A g−1. The cell also shows excellent rate capabilities at a wide range of current densities from 0.1 to 20 A g−1, with a reversible discharge capacity and Coulombic efficiency of 100 mA h g−1 and 99%, respectively, at 20 A g−1. The remarkable performance is attributed to the nanoscale size of the prepared nanorods and the in situ electrochemical transformation. [Display omitted] • Inexpensive aqueous Zn-ion battery is developed with ZnSO 4 electrolyte and VO 2. • VO 2 nanorods are transformed into V 2 O 5 . nH 2 O via in situ electrochemical reaction. • VO 2 @C/Zn full cell retains a capacity of 159 mAh g−1 after 4000 cycles at 5 A g−1. • Zn-ion full cell shows a capacity of 100 mAh g−1 after 10 000 cycles at 20 A g−1. [ABSTRACT FROM AUTHOR]

Laccases are important multicopper oxidases that are involved in many biotechnological processes; however, they suffer from poor stability as well as high cost for production/purification. Herein, we found that DNA-copper hybrid nanoflowers, prepared via simple self-assembly of DNA and copper ions, exhibit an intrinsic laccase-mimicking activity, which is significantly higher than that of control materials formed in the absence of DNA. Upon testing all four nucleobases, we found that hybrid nanoflowers composed of guanine-rich ssDNA and copper phosphate (GNFs) showed the highest catalytic activity, presumably due to the affirmative coordination between guanine and copper ions. At the same mass concentration, GNFs had similar K m but 3.5-fold higher V max compared with those of free laccase, and furthermore, they exhibited significantly-enhanced stability in ranges of pH, temperature, ionic strength, and incubation period of time. Based on these advantageous features, GNFs were applied to paper microfluidic devices for colorimetric detection of diverse phenolic compounds such as dopamine, catechol, and hydroquinone. In the presence of phenolic compounds, GNFs catalyzed their oxidation to react with 4-aminoantipyrine for producing a colored adduct, which was conveniently quantified from an image acquired using a conventional smartphone with ImageJ software. Besides, GNFs successfully catalyzed the decolorization of neutral red dye much faster than free laccase. This work will facilitate the development of nanoflower-type nanozymes for a wide range of applications in biosensors and bioremediation. • DNA-copper hybrid nanoflowers exhibited an intrinsic laccase-like activity. • Hybrid nanoflowers composed of guanine-rich ssDNA and copper phosphates (GNFs) showed enhanced activity and stability. • GNFs-based paper microfluidic device showed excellent performances for detecting phenolic compounds. • GNFs successfully catalyzed the decolorization of neutral red dye. [ABSTRACT FROM AUTHOR]

• Effective ECH/IPA recovery process is required to reduce the cost of epoxy resin manufacture. • Distillation/PV hybrid process was investigated to recover ECH/IPA from byproducts of the epoxy. • PV membranes were prepared by coating α-Al 2 O 3 /SiO 2 -ZrO 2 intermediate and SiO 2 separation layer. • PV process selectively removed water from the 1st distillate, and the loss of IPA and ECH was a little. Epoxy is a widely used thermosetting resin that exhibits good mechanical strength, chemical resistance, and dimensional stability. In order to manufacture this resin, isopropyl alcohol (IPA) and excess epichlorohydrin (ECH) are used as a solvent and an indispensable raw material, respectively. However, ECH and IPA form a ternary azeotropic mixture in the presence of water, rendering it difficult to separate the materials with high purity via distillation. Therefore, a hybrid of pervaporation (PV)-coupled distillation was attempted to improve the epoxy manufacturing process. Silica-zirconia composite membranes were prepared by coating the α-Al 2 O 3 /SiO 2 -ZrO 2 intermediate layer and the SiO 2 separation layer, i.e., dip-coating was performed on the α-Al 2 O 3 support and subsequently applied to the hybrid process. When the pervaporation process of distillate get from the epoxy by-product was applied, H 2 O selectivity for IPA/ECH was 15–30 and for H 2 O/aqueous impurities was 8–54, indicating that H 2 O for H 2 O/aqueous impurities permeated relatively faster than IPA/ECH. Therefore, pervaporation coupled distillation using an inorganic composite membrane was feasible for the selective removal of H 2 O/aqueous impurities in epoxy by-product mixture obtained from epoxy manufacturing. [ABSTRACT FROM AUTHOR]

• Hybrid nanoflowers are in situ grown on activated carbon fibers. • The hybrid structure is more active and stable than enzymes adsorbed physically. • Power retention of cells prepared from the hybrid structures is 80% after one month. Hybrid nanoflowers (HnFs) are novel structures that comprise enzymes (laccase, glucose oxidase, or catalase) and Cu 3 (PO 4) 2 -based crystals, which can directly in situ grow on activated carbon fibers (ACFs) for the preparation of electrodes (HnF/ACF) used in glucose biofuel cells. The HnF/ACF structures perform higher enzymatic activities (~4 times) and stability (~2 times) than the enzymes physically adsorbed on ACFs in distinct analyses such as epinephrine oxidation, H 2 O 2 decomposition, and glucose oxidation. The power density of an HnF/ACF-based cell (50 µW cm−2 for a glucose concentration of 50 mM) is 3–5 times higher than that of a cell prepared from conventional enzyme immobilization routes, which can be sustained at up to 80% after one month of operation. [ABSTRACT FROM AUTHOR]

• Ultrarapid, size-controlled, and high-crystalline synthetic protocol for ceria nanoparticles were developed. • Plasma-mediated ceria nanoparticles exhibited an efficient color-changing activity toward H 2 O 2. • The ceria nanoparticles-embedded paper strip showed high selectivity, sensitivity, reusability, and stability for glucose detection. • Diverse glucose levels in human blood were successfully determined with excellent reproducibility and reliability. We describe an ultrarapid (within several minutes), size-controlled (<100 nm in diameter), and high-crystalline plasma-mediated synthesis of ceria nanoparticles and their application in reagent-free colorimetric test strips. Glucose oxidase (GOx) incorporated onto the paper matrix generates H 2 O 2 with glucose, subsequently inducing color changes of the embedded ceria nanoparticles from white/yellow to yellow/orange without any involvement of colorimetric substrate or dye. The optimized protocol yielded ∼2-fold higher color intensity compared to that of commercially available ceria nanoparticles, presumably due to its much larger surface area and higher Ce3+ content, facilitating the oxidation from Ce3+ to Ce4+ and formation of peroxide complexes at the nanoparticle surfaces. Using the colorimetric test strip, glucose was specifically detected over a wide linear range (0.1−10 mM), with excellent reusability, storage stability, precision, and reproducibility. The innovative plasma-mediated ultrarapid synthesis of size-controlled and high-crystalline ceria nanoparticles and their utilization on reagent-free colorimetric test strip allow for a straightforward sensing platform for the point-of-care detection of glucose and can be expanded to other oxidative enzymes for facile colorimetric detection of various clinically important target molecules. [ABSTRACT FROM AUTHOR]

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 K 3 [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 K m values for 3,3',5,5'-tetramethylbenzidine (TMB) and H 2 O 2 , 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.

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-MoS 2 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-MoS 2 NFs showed a unique structure, comprising MoS 2 NFs with divalent Ce ions. This structural design imparted a significantly enlarged surface area of 220.5 m 2 g -1 with abundant active sites as well as enhanced redox properties, facilitating electron transfer and peroxidase-like catalytic action compared with bare MoS 2 NFs without Ce incorporation. Based on these beneficial features, Ce-MoS 2 NFs were incorporated onto a screen-printed electrode (Ce-MoS 2 NFs/SPE), enabling the electrochemical detection of H 2 O 2 based on their peroxidase-like activity. Ce-MoS 2 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 MoS 2 NFs to enhance the detection performances of electrochemical biosensors, thus enabling extensive applications in healthcare, diagnostics, and environmental monitoring.

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 K m and highest k cat 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 H 2 O 2 was greatly increased, yielding K m 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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

We report a fluorescent assay for the determination of vitamin B 12 (VB 12 ) 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 VB 12 has strong absorption centered at 360 nm, which is almost completely overlapping with the excitation spectra of PDT-AgNPs, the VB 12 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 VB 12 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 VB 12 in a wide range of 1 to 50 μM, with a lower detection limit of 0.5 μM, while preserving excellent selectivity toward target VB 12 among possible interfering molecules. Furthermore, the PDT-AgNPs-mediated assay succeeded in quantitatively detecting VB 12 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.

Surface engineering of nanozymes has been recognized as a potent strategy to improve their catalytic activity and specificity. We synthesized polydopamine-coated Co 3 O 4 nanoparticles (PDA@Co 3 O 4 NPs) through simple dopamine-induced self-assembly and demonstrated that these NPs exhibit catalase-like activity by decomposing H 2 O 2 into oxygen and water. The activity of PDA@Co 3 O 4 NPs was approximately fourfold higher than that of Co 3 O 4 NPs without PDA, possibly due to the additional radical scavenging activity of the PDA shell. In addition, PDA@Co 3 O 4 NPs were more stable than natural catalase under a wide range of pH, temperature, and storage time conditions. Upon the addition of a sample containing sulfide ion, the activity of PDA@Co 3 O 4 NPs was significantly inhibited, possibly because of increased mass transfer limitations via the absorption of the sulfide ion on the PDA@Co 3 O 4 NP surface, along with NP aggregation which reduced their surface area. The reduced catalase-like activity was used to determine the levels of sulfide ion by measuring the increased fluorescence of the oxidized terephthalic acid, generated from the added H 2 O 2 . Using this strategy, the target sulfide ion was sensitively determined to a lower limit of 4.3 µM and dynamic linear range of up to 200 µM. The fluorescence-based sulfide ion assay based on PDA@Co 3 O 4 NPs was highly precise when applied to real tap water samples, validating its potential for conveniently monitoring toxic elements in the environment.

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.

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 H 2 O 2 , 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.

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.