Peroxidase Catalysis Research Articles

Rapid detection of nitrite and Listeria monocytogenes in food based on multiple simulated enzyme activities of Fe3O4-ZnO-MnO2 nanocomposites

Food safety has emerged as a paramount concern in global health, prompting innovative approaches to ensure the safety of people's sustenance. In this study, a novel strategy was devised to fabricate Fe3O4-ZnO-MnO2 hybrid nanobiocatalysts, which exhibited remarkable enzymatic activity surpassing that of Horseradish peroxidase (HRP) catalysis. It demonstrated exceptional proficiency in decomposing 3,3′,5,5′-tetramethylbenzidine (TMB) without the need for harsh reaction conditions or the aid of H2O2. We established colorimetric detection systems based on Fe3O4-ZnO-MnO2-TMB both for nitrite (NO2−) and Listeria monocytogenes (LM) in food. Impressively, the detection limit of nitrite reached an astonishingly low level of 0.022 mg L−1, and the detection limit for LM was determined to be 3.5 cfu mL−1. These compelling results unequivocally validate the potential of these hybrid nanobiocatalysts to fortify food safety measures. Moreover, they serve as a valuable reference for the colorimetric detection of diverse analytes and the simultaneous detection of multiple targets.

Distance-based analytical device integrated with carbon nanomaterials for sarcosine quantification in human samples.

Astraightforward distance-based paper analytical device (dPAD) was developedfor monitoring sarcosine levels in human samples for the rapid diagnosis and prognosis of prostate cancer and related symptoms. This assay eliminates the need for the expensive horseradish peroxidase (HRP) enzyme by utilizing carbon nanodots (CDs) as a peroxidase-like nanozyme. The proposed dPAD sensor consists of a sample zone pre-deposited with sarcosine oxidase (SOx) and CDs, and a detection zone containing 3,3',5,5'-tetramethylbenzidine (TMB). When a solution containing sarcosine is added to the sample zone, hydroxyl radicals (•OH) are produced through SOx oxidation and subsequent peroxidase catalysis by the CDs. The formed •OH radicals immediately flow to the detection zone via capillary force, where they oxidize TMB, resulting in a visible colour change from colourless to blue. Sarcosine quantification is effortlessly accomplished by measuring the distance of the blue colour in the detection zone. The developed dPAD offers a linear working range between 12.5 and 35.0nmol L-1 (R2 = 0.9959) and a detection limit (LOD) of 10.0nmol L-1. This covers the clinical range for urinary sarcosine determination, thereby suggesting no additional sample preparation or dilution is needed. The sensor shows high precision with the highest relative standard deviation (RSD) of 4.58% and demonstrates excellent selectivity with no observed interferences. Furthermore, recovery studies in human control urine samples ranged from 98.67 to 101.50%, with the highest RSD of 2.03%. Correspondingly, our dPAD method showed a great match with the performance of a commercial ELISA method for detecting sarcosine in human control serum. The sensor is more cost-effective, user-friendly, and accessible than previous methods. Overall, the proposed method represents a promising analytical tool for sarcosine quantification. The concept is also applicable for broader analytical applications in detecting other biomolecules.

Unveiling Generally-ignored Co-substrate Effect of Catalase-inherent Peroxidase Mimic for Self-verifiable Detection of High-concentration Hydrogen Peroxide.

One nanoparticle possessing both peroxidase (POD) and catalase (CAT) activities is a prevalent co-substrate nanozyme system, distinct from the extensively researched cascade nanozyme system. During the sensing of hydrogen peroxide by POD, the impact of CAT is actually ignored in most studies. In this study, the CAT effect on hydrogen peroxide detection is thoroughly investigated based on POD catalysis by finely tuning the relative activity of POD and CAT. It is discovered that the CAT effect can be changed by delaying the injection of chromogenic substrate after adding hydrogen peroxide and that the linear range grows with the delayed time. Then, a theoretical mechanism showed that the time-delay mediated CAT effect magnification does not change the Vmax, but it causes Km to linearly increase with delayed time, consistent with the experiment results. Furthermore, the detection of high concentrations of hydrogen peroxide is successfully realized in contact lens care solutions by utilizing time-delay-mediated POD/CAT nanozyme. On the other hand, its linear range-tunable characteristic is used to produce multiple standard curves, then enabled self-verifying hydrogen peroxide detection. Overall, this work investigates the role of CAT in CAT-inherent POD nanozymes both theoretically and experimentally, and confirms POD/CAT nanozyme's priority in developing high-performance sensors.

Ascorbate peroxidase catalyses synthesis of protocatechualdehyde from p-hydroxybenzaldehyde in Lycoris aurea

Protocatechualdehyde is a plant natural phenolic aldehyde and an active ingredient with important bioactivities in traditional Chinese medicine. Protocatechualdehyde is also a key intermediate in the synthesis of Amaryllidaceae alkaloids for supplying the C6-C1 skeleton. However, the biosynthesis of protocatechualdehyde in plants remains obscure. In this study, we measured the protocatechualdehyde contents in the root, bulb, scape and flower of the Amaryllidaceae plant Lycoris aurea (L’Hér.) Herb., and performed the correlation analysis between the protocatechualdehyde contents and the transcriptional levels of the phenolic oxidization candidate protein encoding genes. We found that a novel ascorbate peroxidase encoded by the contig_24999 in the L. aurea transcriptome database had potential role in the biosynthesis of protocatechualdehyde. The LauAPX_24999 gene was then cloned from the cDNA of the scape of L. aurea. The transient expression of LauAPX_24999 protein in Arabidopsis protoplasts demonstrated that LauAPX_24999 protein was localized in the cytoplasm, thus belonging to Class II L-ascorbate peroxidase. Subsequently, LauAPX_24999 protein was heterogenously expressed in Escherichia coli, and identified that LauAPX_24999 biosynthesized protocatechualdehyde from p-hydroxybenzaldehyde using L-ascorbic acid as the electron donor. The protein structure modelling and molecular docking indicated that p-hydroxybenzaldehyde could access to the active pocket of LauAPX_24999 protein, and reside at the δ-edge of the heme group while L-ascorbic acid binds at the γ-heme edge. To our knowledge, LauAPX_24999 is the first enzyme discovered in plants able to biosynthesize protocatechualdehyde from p-hydroxybenzaldehyde, and offers a competent enzyme resource for the biosynthesis of Amaryllidaceae alkaloids via synthetic biology.

An injectable hydrogel of Enteromorpha polysaccharide/gelatin–derivatives inspired by siderophores and biocatalysis for addressing all phases of chronic diabetic wound healing

Given that chronic diabetic wounds are difficult to cure because of disruptions in the four healing phases (hemostasis, immune regulation, cell proliferation, and tissue regeneration), wound dressings promoting all of these phases and thus accelerating diabetic wound healing are highly desirable. To address this need, inspired by siderophore-Fe3+ chelation and horseradish peroxidase (HRP) catalysis, we synthesized a tyramine-modified Enteromorpha prolifera polysaccharide and dopamine-modified gelatin and used them to fabricate an injectable hydrogel (PG-Fe) featuring interpenetrating polymer networks facilitated by catecholate/carboxylate-Fe3+ coordination bonding and HRP-mediated covalent bonding between phenolic groups. PG-Fe exhibited good injectability, rapid gelation (11.5 s), suitable mechanical properties, enhanced tissue adhesiveness (50.5 kPa), and rapid self-healing (60 s) because of its intrinsic moieties and introduced modifications. Furthermore, it exhibited enhanced antioxidant, anti-inflammatory, cell adhesion, and migration effects. Consequently, PG-Fe simultaneously addressed all four wound healing phases, thereby shortening the closure time of normal and chronic diabetic wounds to 21 days. Following application, PG-Fe could be decomposed using a desferrioxamine solution and easily removed. Taken together, our study provides a novel strategy for fabricating injectable hydrogels that exhibit desirable physicochemical properties and enhanced biological functions to accelerate all phases of chronic diabetic wound healing.

PH-dependent and whole-cell catalytic decolorization of dyes using recombinant dye-decolorizing peroxidase from Rhodococcus jostii.

Dyes in wastewater have adverse effects on the environment and human health. Dye-decolorizing peroxidase (DyP) is a promising biocatalyst to dyes degradation, but the decolorization rates varied greatly which influencing factors and mechanisms remain to be fully disclosed. To explore an effective decolorizing approach, we have studied a DyP from Rhodococcus jostii (RhDyPB) which was overexpressed in Escherichia coli to decolorize four kinds of dyes, Reactive blue 19, Eosin Y, Indigo carmine, and Malachite green. We found the decolorization rates of the dyes by purified RhDyPB were all pH-dependent and the highest one was 94.4% of Malachite green at pH 6.0. ESI-MS analysis of intermediates in the decolorization process of Reactive blue 19 proved the degradation was due to peroxidase catalysis. Molecular docking predicated the interaction of RhDyPB with dyes, and a radical transfer reaction. In addition, we performed decolorization of dyes with whole E. coli cell with and without expressing RhDyPB. It was found that decolorization of dyes by E. coli cell wasdue to both cell absorption and degradation, and RhDyPB expression improved the degradation rates towards Reactive blue 19, Indigo carmine and Malachite green. The effective decolorization of Malachite green and the successful application of whole DyP-overexpressed cells in dye decolorization is conducive to the bioremediation of dye-containing wastewaters by DyPs.

Deep eutectic solvent-assisted synthesis of La-Ce hybrid nanorods for the colorimetric determination of tetracycline in foods.

Tetracycline (TC) as a broad-spectrum antibiotic, is widely used in the prevention and treatment of various bacterial diseases. However, its abuse in the livestock industry may lead to interference in human microecology, thereby causing various side effects. In this study, deep eutectic solvents (DESs) were synthesized using L-(-)-threonine (L-(-)-Thr) and cerium nitrate hexahydrate (Ce(NO3)3·6H2O), and later lanthanum nitrate hexahydrate (La(NO3)3·6H2O) was doped to synthesize La-Ce hybrid nanorods. These nanorods can be used for the determination of TC with high sensitivity and selectivity by the colorimetric method. This approach has a linear response to TC between 0.05 μM and 10 μM, with a detection limit of 0.016 μM. In this system, good dispersion provides the substance with a distinct peroxidase activity, which is used to create a colorimetric sensor for detecting TC. Mechanism studies show that the superoxide radical generated by the La-Ce nanomembrane plays a key role in peroxidase catalysis. Finally, the practicality of the method was verified by the determination of TC in food products (milk, pork and honey), which demonstrated that a good recovery rate can be obtained (91.4-102%).

A Co-Immobilized Enzyme-Mediator System for Facilitating Manganese Peroxidase Catalysis in Solution Free of Divalent Manganese Ions

Manganese peroxidase (MnP) offers significant potential in various environmental and industrial applications; however, its reliance on Mn2+ ions for electron shuttling limits its use in Mn2+-deficient systems. Herein, a novel approach is presented to address this limitation by co-immobilizing MnP and Mn2+ in silica gels. These gels were synthesized following the standard sol–gel method and found to effectively immobilize Mn2+ ions, primarily through electrostatic interactions. The MnP co-immobilized with Mn2+ ions in the silica gel exhibited 4–5 times higher activity than the MnP immobilized alone in activity assays, and generated Mn3+ within the gel, indicating the immobilized Mn2+ ions remain capable of shuttling electrons to the co-immobilized MnP. In decolorization tests with two organic dyes, the co-immobilized system also outperformed the MnP immobilized without Mn2+ ions, resulting in 2–4 times higher dye removals. This study will enable a broader application of MnP enzymes in sustainable environmental remediation and industrial catalysis.

Glucose-responsive enzymatic biomimetic nanodots for H2O2 self-supplied catalytic photothermal/chemodynamic anticancer therapy

Photothermal therapy (PTT) combined with chemodynamic therapy (CDT) presents an appealing complementary anti-tumor strategy, wherein PTT accelerates the production of reactive oxygen species (ROS) in CDT and CDT eliminates residual tumor tissues that survive from PTT treatment. However, nanomaterials utilized in PTT/CDT are limited by non-specific damage to the entire organism. Herein, a glucose-responsive enzymatic Fe@HRP-ABTS/GOx nanodot is judiciously designed for tumor-specific PTT/CDT via a simple and clean protein-templated biomimetic mineralization synthesis. By oxidizing glucose in tumor cells, glucose oxidase (GOx) activates glucose-responsive tumor therapy and increases the concentration of H2O2 at the tumor site. More importantly, the self-supplied peroxide hydrogen (H2O2) can convert ABTS (2,2′-Hydrazine-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamine salt) into oxidized ABTS (oxABTS) through horseradish peroxidase (HRP) catalysis for PTT and photoacoustic (PA) imaging. Furthermore, the Fe2+ arising from the reduction of Fe3+ by overexpressed GSH reacts with H2O2 to generate intensely reactive •OH through the Fenton reaction, concurrently depleting GSH and inducing efficient tumor CDT. The in vitro and in vivo experiments demonstrate superior cancer cell killing and tumor eradication effect of Fe@HRP-ABTS/GOx nanodot under near-infrared (NIR) laser irradiation. Collectively, the nanodots provide mutually reinforcing catalytic PTT/CDT anti-tumor strategies for treating liver cancer and potentially other malignancies. Statement of significanceCombinatorial antitumor therapy with nanomedicines presents great prospects for development. However, the limitation of non-specific damage to normal tissues hinders its further clinical application. In this work, we fabricated tumor-selective biomimetic Fe@HRP-ABTS/GOx nanodots for H2O2 self-supplied catalytic photothermal/chemodynamic therapy of tumors. The biomimetic synthesis strategy provides the nanodots with enzymatic activity in response to glucose to produce H2O2. The self-supplied H2O2 initiates photothermal therapy with oxidized ABTS and enhances chemodynamic therapy through simultaneous •OH generation and GSH depletion. Our work provides a new paradigm for developing tumor-selective catalytic nanomedicines and will guide further clinical translation of the enzymatic biomimetic synthesis strategy.

Molecularly imprinted polymers enhanced peroxidase-like activity of AuNPs for determination of glutathione.

An elaborate composite of molecularly imprinted polymer (MIP)-modified gold nanoparticles (AuNPs)@silica dioxide (SiO2) was designed and prepared for real-time colorimetric determination of glutathione (GSH) in serum. Firstly, the MIPs were synthesized on the surface of SiO2 utilizing GSH as template molecules. Then, AuNPs were synthesized on the surface of MIPs@SiO2 to produce a composite of MIPs modified by AuNPs@SiO2. Compared with plain AuNPs, the composite possessed better peroxidase catalysis activity due to stabilization and protection from hydrophilic SiO2, which can catalyze H2O2 to·OH oxidizing 3,3,5,5-tetramethylbenzidine (TMB) to the colored product. In addition, its selectivity was enhanced by MIP modification with special recognition cavities. With the composite as the sensor, GSH was precisely and sensitively detected in the range 5 ~ 40μM with a limit of determination of 1.16μM according to the principle of inhibitive peroxidase catalysis activity by GSH. The proposed colorimetric detection was successfully utilized for selective, convenient, and rapid determination of GSH in serum. It provided a new strategy for drug real-time monitoring and has high potential in clinical drug analysis.

Horseradish peroxidase catalyzed grafting of chitosan oligosaccharide with different flavonols: structures, antioxidant activity and edible coating application.

Enzymatic catalyzed grafting of oligosaccharides with polyphenols is a safe and environmentally friendly approach to simultaneously enhance the bioactivity of oligosaccharides and the solubility of polyphenols. In this study, chitosan oligosaccharide (COS) was grafted with three different flavonols including myricetin (MYR), quercetin (QUE) and kaempferol (KAE) by horseradish peroxidase (HRP) catalysis. The structures, antioxidant activity and edible coating application of COS-flavonol conjugates were investigated. The total phenol content of COS-MYR, COS-QUE and COS-KAE conjugates was 59.89, 68.37 and 53.77 mg gallic acid equivalents g-1 , respectively. Thin layer chromatography showed the conjugates did not contain ungrafted flavonols. COS-flavonol conjugates showed ultraviolet absorption peak at about 294 nm, corresponding to the A-ring of flavonols. Fourier-transform infrared spectra of conjugates confirmed the formation of Schiff-base and Michael-addition products. The proton-nuclear magnetic resonance spectrum of COS-KAE conjugate exhibited phenyl proton signals of KAE. X-ray diffraction patterns of conjugates showed some diffraction peaks of flavonols. COS-flavonol conjugates presented rough and porous morphologies with sheet-like and/or blocky structures. The conjugates showed higher water solubility, free radical scavenging activity and reducing power than flavonols. Moreover, fish gelatin/COS-flavonol conjugate coatings effectively prolonged the shelf life of refrigerated largemouth bass (Micropterus salmoides) fillets from 5 days to 7-8 days. COS-flavonol conjugates prepared by HRP catalysis have great potentials as novel antioxidant agents. © 2022 Society of Chemical Industry.

Bi-directional feedback controlled transience in Cucurbituril based tandem nanozyme

Life is fueled by multi-enzymatic tandem processes that display unmatched catalytic efficiencies owing to certain features of the biological reactors such as compartmentalization, nano-confinement, and out-of-equilibrium dynamics. With an attempt to match such natural catalytic systems, herein, we present a chemoenzymatic pH clock mediated transient assembly of a vesicular nanozyme. Distinct confinement of two catalytically discrete units, Histidine groups on the periphery and hemin in the lipid bilayer, results in an efficient hydrolase-peroxidase tandem catalysis in a temporally controlled fashion. The pH clock, constituted by alkaline TRIS (Tris(hydroxymethyl)aminomethane hydrochloride) buffer (promoter) and glucose oxidase (GOx) catalyzed oxidation of glucose, steers the transience in an asymmetric fashion. Alkaline TRIS buffer enhances the pH of the system and triggers the formation of imine linked Supramolecular Peptide Amphiphiles (SPAs) that further assemble into vesicles. On the other hand, oxidation of glucose produces gluconolactone and H2O2. Gluconolactone hydrolyzes to gluconic acid (deactivator) which dissipates the nanozyme while H2O2 is used in the peroxidase catalysis. Thus, the bi-directional feedback from the fuel not only regulates the existence of the transient state but also controls the activity of the assembly. The transiently assembled nanozyme protected the activity of the catalytic units, displayed substrate specificity and catalytic reproducibility over multiple fueling cycles.

Zettomole electrochemical HIV DNA detection using 2D DNA-Au nanowire structure, hemin/G-quadruplex and polymerase chain reaction multi-signal synergistic amplification

Multi-signal synergistically amplified electrochemical sensing of HIV DNA was proposed based on two-dimensional (2D) DNA-Au nanowire structure coupled with hemin/G-quadruplex and polymerase chain reaction (PCR). In the design, by using target HIV DNA as the template, PCR generated numbers of double-stranded DNA (dsDNA) with free single-stranded DNA (ssDNA) tails on one side and free G-quadruplex sequences on the other side. Then, the ssDNA tails of the PCR products were hybridized with the capture probe (CP) to introduce the hemin/G-quadruplex to the electrode surface as a redox-active reporter and to amplify the electrochemical signal as mimic peroxidase catalysis in the presence of H2O2. Meanwhile, (+)AuNPs were electrostatically adsorbed onto dsDNA surface for the formation of 2D DNA-Au nanowire structure, amplifying the electrochemical signal further as another mimic peroxidase and electric conductor together. By effectively combining these signal amplification processes, ultrasensitive HIV DNA detection was achieved with a detection limit of 1.3 aM, indicating that it has potential application in clinical diagnosis.

Exploration of Lignocellulolytic Microbes in Oil Palm Rhizosphere on Peat Soils and Their Respiration Activities

Microbial respiration in peatlands plays a role in contributing CO2 emissions. Studies of microbial exploration and respiration on peat soils in oil palm plantations have not been widely reported. This study aims to explore lignocellulolytic microbes found in peat soils in compared with mineral soils planted with 12-year-old oil palm. Exploration is done by growing the samples on the specific medium of each group of microbial functions. In the next stage, the culture obtained was analysed the respiration activity based on the oxidation of peroxidase catalysis using a chromogen substrate (tetramethylbenzidine) and measured using spectrophotometry at a wavelength of 450 nm. The results showed that both in mineral and peat planted with oil palm in a depths of 0-20 cm were found lignolytic fungi with a population of 17 x 102. Similar results were also found in peat with fern vegetation but at a depth of 20-40 cm. Lignolytic bacteria (methylene blue degradation) can be found on peat soils planted with oil palm at a depth of 0-60 cm and the population increases with increasing depth. This bacterium is also found on peat soils with fern vegetation and mineral soils planted with palm. At a depth of 0-20 cm the population of lignolytic bacteria in non-oil palm peat is highest. Cellulolytic bacteria were isolated at a depth of 0-60 cm. Cellulolytic bacterial populations were highest in oil palm peat at all depths compared to other samples. Respiration analysis of several dominant isolates showed fairly high variation between microbial function groups and within the same function group. The lignolytic microbial group degrading methylene blue showed high respiration activity and  varies greatly (0.19-1.85 MER). While the respiration activity of cellulolytic bacteria ranged from 0.45 to 0.62 MER.

4-Thiouridine-Enhanced Peroxidase-Generated Biotinylation of RNA.

Peroxidase-generated proximity labeling is in widespread use to study subcellular proteomes and the protein interaction networks in living cells, but the development of subcellular RNA labeling is limited. APEX-seq has emerged as a new method to study subcellular RNA in living cells, but the labeling of RNA still has room to improve. In this work, we describe 4-thiouridine (s4 U)-enhanced peroxidase-generated biotinylation of RNA with high efficiency. The incorporation of s4 U could introduce additional sites for RNA labeling, enhanced biotinylation was observed on monomer, model oligo RNA and total RNA. Through the s4 U metabolic approach, the in vivo RNA biotinylation efficiency by peroxidase catalysis was also dramatically increased, which will benefit RNA isolation and study for the spatial transcriptome.

A sandwich electrochemiluminescent assay for determination of concanavalin A with triple signal amplification based on MoS2NF@MWCNTs modified electrode and Zn-MOF encapsulated luminol.

An ultrasensitive sandwich electrochemiluminescence (ECL) biosensor was designed for determination of concanavalin A (ConA) through the specific carbohydrate-ConA interactions. Three-dimensional porous metal-organic framework (Zn-MOF) was synthesized, which loaded a large amount of luminescent reagents as luminol by encapsulating into its pores to form Zn-MOF@luminol complex. Interestingly, Zn-MOF also acted as the coreactant accelerator in the luminol-H2O2 ECL system. This Zn-MOF@luminol complex was used as the signal probe to achieve a super strong and stable ECL signal. In addition, three-dimensional hierarchical molybdenum disulfide nanoflower and multiwalled carbon nanotubes complex (MoS2NF@MWCNTs) with peroxidase-mimicking enzyme property were used as a substrate to modify the glassy carbon electrode to further enhance the ECL signal of luminol by promoting decomposition of H2O2 into reactive oxygen species (ROSs). In addition to the horseradish peroxidase (HRP) catalysis effect on the luminol ECL signal, a triple amplified ConA sandwich ECL sensor with high sensitivity sensor was constructed. The linear range for ConA detection was from 0.5pg/mL to 100ng/mL with a detection limit of 0.3pg/mL (S/N = 3). The recovery test for ConA in human serum samples was performed with satisfactory results. Graphical abstract.

Magnetothermally responsive composite submicron particles for recyclable catalytic applications

To improve the recycling efficiency of magnetic recycling system, magnetothermally responsive composite submicron particles (CFMNs@PEG CSPs) were designed and prepared for recyclable catalytic applications, in which poly(ethylene glycol) gel was used as the shell and clusters of cobalt ferrite magnetic nanoparticles as the core. A novel strategy for recycling both loadings and carriers was proposed based on loadings immobilized CFMNs@PEG CSPs via magnetic separation at first and then magnetothermally responsive release. The morphology and core–shell structure were observed by transmission electron microscope. The physicochemical characteristics were investigated by Fourier transform infrared, 1H NMR, Magnetic property measurement system, thermogravimetric analysis and X-ray photoelectron spectroscopy. The size of CFMNs@PEG CSPs was 285.1 ± 7.6 nm (the core was 160.0 ± 13.2 nm and PEG gel shell was 62.6 nm). The shell thickness of CFMNs@PEG CSPs shrunk from 62.6 nm to 35.5 nm when the temperature changed from 25 °C to 50 °C, and more than 95% of the loadings were released in 30 min by magnetothermally responsive release. Combing magnetic separation and magnetothermally responsive release, CFMNs@PEG CSPs were recycled over 42 times for horseradish peroxidase catalysis (horseradish peroxidase was re-immobilized for six times and reused seven times for each re-immobilization) and 25 times for gold nanoparticles catalysis (reactivated gold nanoparticles were re-immobilized for five times and reused five times for each re-immobilization) without significant catalytic activity loss, indicating their extensive potential in recyclable catalytic applications and other applications.

Immunoassay-type biosensor based on magnetic nanoparticle capture and the fluorescence signal formed by horseradish peroxidase catalysis for tumor-related exosome determination.

A sandwich-type fluorescent biosensor for the determination of tumor-related exosome was designed. Itis based on magnetic nanoparticle (MNP) capture and horseradish peroxidase (HRP) catalysis. MNPs were used as the substrate to capture exosomes by modifying the CD63 antibody on MNPs surface. After that, the biotinylated epithelial cell adhesion molecule (EpCAM) antibody was used to capture the tumor-related exosomes, which specifically expressEpCAM. A novel method for the fluorescence measurement of tumor-associated exosome was achieved, with a detection limit as low as 200 (± 9) particles mL-1. The analytical range of this method is from 576 (± 15) particles mL-1 to 5.76 × 107 (± 5.1 × 105) particles mL-1. For the fluorescence measurement, the excitation wavelength was set to 320nm. Fluorescent spectra were collected at emission wavelength in the range370 to 550nm; the data shown in the calibration plot were studied by using the fluorescence intensity at 406nm. This sensor was also able to successfullydetect the exosomes from the plasma of patients with hepatocellular carcinoma (HCC) and healthy humans. Graphical abstract Schematic representation of the sensing process of immunoassay-type biosensor based on magnetic nanoparticle capture and the fluorescence signal formed by the horseradish peroxidase (HRP) catalysis for tumor-related exosome determination.

Simultaneous quantification of peroxidase and ascorbic acid in biosamples with an automatic system based on a Fe(iii)/methylthymol blue-carbon dot simulative enzyme.

Peroxidase (POD) and ascorbic acid (AsA) usually coexist in organisms to synergistically protect them from reactive oxygen damage, and their contents undergo dynamic changes under different physiological conditions. What's more, the response of POD-catalytic activity in spectrophotometry has to be corrected using the content of concomitant AsA because we found that there is an extinction reaction between AsA and chromogenic products obtained from POD catalysis. With these implications, by skilfully using the chromogenic and the extinction phenomena in the guaiacol/POD/H2O2 reaction, an automatic analysis system for simultaneous quantification of POD (73-440 U L-1) and AsA (4-60 mg L-1) was successfully established based on flow injection analysis (FIA). Furthermore, under acidic conditions (0.5 mol L-1 of HCl), hydrothermal synthesis (250 °C for 1 h) was used for synthesizing new carbon dots (sPOD-CDs) of methylthymol blue (0.08 g L-1)/FeCl3 (0.8 g L-1), which is a simulative enzyme for POD, and it was first used for catalyzing the guaiacol/H2O2 reaction within the FIA system to replace natural HRP in the extinction reaction. This sPOD-CD solution has no background absorption and its concentration shows excellent correlation with simulative POD-activity. Finally, after optimization, this FIA system was utilized to testify that the reducibility of AsA is due to ascorbate ions and to determine POD and AsA in some plant samples. The standard addition recovery experiment showed that there was no interference from the matrix in real samples (recoveries: 95%-105%), and the obtained POD and AsA results were also consistent with the reference experiments (relative deviation ≤ 2.80%, t-test ≥ 0.07). The proposed FIA system is characterized by high sample-throughput (40 samples per h), better repeatability (relative standard deviation ≤ 1.4%), etc.

An effective toluene removal from waste‐air by a simple process based on absorption in silicone oil (PDMS) and cross‐linked Brassica rapa peroxidase (BRP‐CLEAs) catalysis in organic medium: Optimization with RSM

AbstractIn the present study, absorption in an organic solvent followed by enzymatic biodegradation by cross‐linked peroxidase from Brassica rapa (BRP‐CLEAs) was successfully applied as a solution for toluene removal from waste‐air in batch experiments. Silicone oil (PDMS 47V20) showed a high capacity for toluene absorption, regarding its air‐PDMS partition coefficient (2.08 Pa m3 mol−1) when compared to air‐water (666 Pa m3 mol−1). Box–Behnken restricted duplicate design was employed for the optimization of the enzymatic degradation of toluene in PDMS. Effects of four independent variables, namely, BRP‐CLEAs activity, toluene and hydrogen peroxide concentrations and sonication, were studied by choosing two responses: conversion yield and initial rate of reaction. Analysis of the results showed that both hydrogen peroxide and toluene concentrations presented the largest effect on the process while sonication had no effect. On the other hand, the coefficient of determination R2 and the adjusted R2 were 0.828 and 0.770 for conversion and 0.919 and 0.911 for initial rate, respectively. The optimum conversion determined was 60% of toluene removal.