Peroxidase-like Catalytic Activity Research Articles

Spectrophotometric detection of uric acid with enzyme-like reaction mediated 3,3′,5,5′-tetramethylbenzidine oxidation

ABSTRACT. WO3 nanosheets (NSs) were prepared and characterized by X-ray photoelectron spectrometer (XPS), X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The obtained WO3 NSs exhibited peroxidase-like catalytic activity, which can catalyze H2O2 to oxidize 3,3 ',5,5 '-tetramethylbenzidine (TMB) to generate oxidized TMB (oxTMB) with an absorption peak centered at 652 nm. Based on this, a facile method for the spectrophotometric determination of H2O2 was established. Under the selected conditions, the increase in absorbance of oxTMB enabled the detection of H2O2 ranging from 2.0 to 180 μM. Considering the fact that H2O2 is one of the products of urate oxidase (UAO)-catalyzed uric acid (UA) oxidation, a convenient method for the selective determination of UA was further developed with the help of UV–vis spectrophotometer. The increase of absorbance at 652 nm showed a linear response to UA concentration over the range of 2.0–180 μM. The limit of detection for UA was as low as 1.25 μM. More importantly, the proposed method was applied to the determination of UA in serum samples with satisfactory results.
 
 KEY WORDS: Spectrophotometric, WO3 nanosheets, Uric acid, Determination
 
 Bull. Chem. Soc. Ethiop. 2023, 37(1), 11-21. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i1.2

Plasmon resonance-based study of the peroxidaselike catalytic effect of gold nanoparticles

In this paper, the peroxidaselike catalytic effect of gold nanoparticles (AuNPs) was explored in dye wastewater treatment by visible light excitation. Using hydrogen peroxide as a substrate, the peroxidaselike reaction was evaluated with AuNPs catalyzing the substrate oxidative degradation of the organic dye rhodamine B (RhB). The synthesized AuNPs were characterized by transmission electron microscopy. The degradation of RhB was observed by a UV-visible spectrophotometer. The results showed that under visible light irradiation, the AuNPs exhibited good peroxidaselike catalytic activity for the oxidative degradation of RhB by hydrogen peroxide. By studying the light wavelength and light intensity-dependent reaction rates, radical trapping, and hole acceptor incorporation, it was found that AuNPs can absorb photon energy and generate hot electrons through a localized surface plasmon resonance effect under light irradiation. Subsequently, hot electrons flow into the molecular orbitals of H2O2 based on energy matching, activating the molecule and transforming it into the transition state, which is proceeded by breakdown to release hydroxyl radicals (⋅OH) for oxidative destruction of RhB.

Fe-Doped MoS2 Nanozyme for Antibacterial Activity and Detoxification of Mustard Gas Simulant.

The peroxidase-like catalytic activity of various nanozymes was extensively applied in various fields. In this study, we have demonstrated the preparation of Fe-doped MoS2 (Fe@MoS2) nanomaterials with enhanced peroxidase-like activity of MoS2 in a co-catalytic pathway. In view of Fenton reaction, the peroxidase-like Fe@MoS2 nanozyme prompted the decomposition of hydrogen peroxide (H2O2) to a reactive hydroxyl radical (·OH). The efficient decomposition of H2O2 in the presence of Fe@MoS2 has been employed toward the antibacterial activity and detoxification of mustard gas simulant. The combined effect of Fe@MoS2 and H2O2 showed remarkable antibacterial activity against the drug-resistant bacterial strain methicillin-resistant Staphylococcus aureus and Escherichia coli with the use of minimal concentration of H2O2. Fe@MoS2 was further applied for the detoxification of the chemical warfare agent sulfur mustard simulant, 2-chloroethyl ethyl sulfide, by selective conversion to the nontoxic sulfoxide. This work demonstrates the development of a hybrid nanozyme and its environmental remediation from harmful chemicals to microbes.

Pd@Pt Nanodendrites as Peroxidase Nanomimics for Enhanced Colorimetric ELISA of Cytokines with Femtomolar Sensitivity.

Colorimetric enzyme-linked immunosorbent assay (ELISA) has been widely applied as the gold-standard method for cytokine detection over decades. However, it has become a critical challenge to further improve the detection sensitivity of ELISA as limited by the catalytic activity of enzymes. Herein, we report an enhanced colorimetric ELISA for ultrasensitive detection of interleukin-6 (IL-6, as a model cytokine for demonstration) using core@shell nanodendrites ( NDs) as peroxidase nanomimics (named " ND ELISA"), pushing the sensitivity up to femtomolar level. Specifically, the NDs are rationally engineered by depositing Pt atoms on Pd nanocubes (NCs) to generate rough dendrite-like Pt skins on the Pd surfaces via Volmer-Weber growth mode. They can be produced on a large scale with highly uniform size, shape, composition, and structure. They exhibit significantly enhanced peroxidase-like catalytic activity with catalytic constants () more than 2000-fold higher than those of horseradish peroxidase (HRP, an enzyme commonly used in ELISA). Using NDs as the signal labels, the ND ELISA presents strong colorimetric signals for the quantitative determination of IL-6 with a wide dynamic range of 0.05-100 pg mL-1 and an ultralow detection limit of 0.044 pg mL-1 (1.7 fM). This detection limit is 21-fold lower than that of conventional HRP-based ELISA. The reproducibility and specificity of the ND ELISA are excellent. More significantly, the ND ELISA was validated for analyzing IL-6 in human serum samples with high accuracy and reliability through recovery tests. Our results demonstrate that the colorimetric ND ELISA is a promising biosensing tool for ultrasensitive determination of cytokines and thus is expected to be applied in a variety of clinical diagnoses and fundamental biomedical studies.

Valence-switchable and biocatalytic vanadium-based MXene nanoplatform with photothermal-enhanced dual enzyme-like activities for anti-infective therapy

Nanocatalytic technology is a promising approach for anti-infective therapy based on artificial nanoscale enzyme mimics (nanozymes). Nevertheless, the complex infective microenvironment and single catalytic mechanism restrict the catalytic activity of nanozyme, making it difficult to achieve the desired therapeutic effect. Herein, we developed vanadium nitride MXene (V2N) by a modified chemical exfoliation approach. Benefiting from the valence-switchable state and large specific surface area of V2N, which possesses superior intrinsic dual enzyme-like (oxidase-like and peroxidase-like) catalytic activities in weak acidic conditions (mimic biofilm microenvironment). Typically, V2N exhibited desirable photothermal conversion efficiency (PCE) in the second near-infrared (NIR-II) window, which can remarkably enhance the dual enzyme-like catalytic activities and avoid local hyperthermia to damage surrounding normal tissue. These integrated merits enable the V2N to generate abundant reactive oxygen species (ROS) to effectively eradicate bacteria in vitro and promote the healing of subcutaneous abscesses with negligible toxicity in vivo. Overall, this work proposed a promising strategy based on photothermal-enhanced dual enzyme-like catalytic activities for effective anti-infective therapy.

A dual-channel probe based on copper ion-mediated metal organic framework composite for colorimetric and ratiometric fluorescence monitoring ofglyphosate degradation in soil and water.

A dual-channel probe was developed, based on a novel composite metal organic frameworks (ZnMOF-74@Al-MOF) for glyphosate determination through ratio fluorescence and colorimetric methods. The prepared probe can not only recognize and combine glyphosate by introducing copper ion into the MOF, but also possess peroxidase-like catalytic activity. The recognition of target glyphosate brought about changes relative to its concentration on fluorescence intensity and ultraviolet absorption. And, the high specific surface area and porosity of porphyrin MOF provides the developed probe with more response opportunities to afford a better detection performance for glyphosate. Under optimum conditions, the copper ion-mediated method exhibited good detection performance for glyphosate with low detection limits (0.070 and 0.092μgmL-1 for fluorescence and colorimetric techniques, respectively). Furthermore, the possible mechanisms of the fluorescence quenching and the peroxidase-like catalytic of the probe were also explored. This dual-channel method was applied to monitor glyphosate degradation in environmental samples and satisfactory results were obtained.

The valine-based N-doped carbon dots with high peroxidase-like activity.

Developing artificial nanoparticles with peroxidase-like activity have attracted great interests because their catalytic activity is not easy to lose under harsh conditions compared with natural enzymes. In this work, the N-doped carbon dots (CDs) were prepared; it was found that the N-doped CDs showed high peroxidase-like catalytic activity towards the reaction system of hydrogen peroxide:3,3',5,5'-tetramethylbenzidine (TMB). The catalytic mechanism of the N-doped CDs was explored using electron spin resonance spectra, cyclic voltammetry methods and simulation of density functional theory calculations. This work can offer a new feasible method for synthesizing N-doped carbon quantum dots used as artificial peroxidases in biological and environment applications.

Peroxidase-like activity of bimetal Cu-Zn oxide mesoporous nanospheres for the determination of o-aminophenol.

To enhance the peroxidase-like performance and its application in detection of toxic o-aminophenol (o-AP), a kind of bimetal Cu-Zn oxide-based mesoporous nanosphere (Cu2/3Zn1/3O PNPs) was constructed under microwave-radiation conditions. Its mesoporous microstructure and peroxidase-like catalytic activity were investigated in detail. The results showed that Cu2/3Zn1/3O PNPs possessed a high specific surface area of 34.89 m2g-1 and a well-distributed mesoporous size of approximate 6.07nm, which endowed the superior peroxidase-like performance. The materialcatalyzes the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with Km/Vmax of 0.104mM/3.79 × 10-8M·s-1 in the presence of H2O2. Especially o-AP could exclusively deteriorate the characteristic UV-Vis absorbance intensity at 653nm (A653) of the Cu2/3Zn1/3O PNPs-TMB-H2O2 system with obvious color change from blue to colorless. Under the optimal conditions, the effect of some interfering substances was low and the limit of detection (LOD) for o-AP was 1.65 × 10-8mol/L (S/N = 3). When applied to thecolorimetric detection of o-AP in practice, the recovery was between 96.1 and 107.2% with R.S.D. less than 2.04%. The mechanism of synergic-enhancement peroxidase-mimic activity of Cu2/3Zn1/3O PNPs and its exclusive colorimetric response to o-AP were proposed as well.

Photothermal Regulated Nanozyme of CuFeS2 Nanoparticles for Efficiently Promoting Wound Healing Infected by Multidrug Resistant Bacteria.

Peroxidase-mediated chemokinetic therapy (CDT) can effectively resist bacteria; however, factors such as the high dosage of drugs seriously limit the antibacterial effect. Herein, CuFeS2 nanoparticles (NPs) nanozyme antibacterial system with the photothermal effect and peroxidase-like catalytic activity are proposed as a combined antibacterial agent with biosafety, high-efficiency, and broad-spectrum antibacterial ability. In addition, the as-obtained CuFeS2 NPs with a low doses of Cu+ and Fe3+ can change the permeability of bacterial cell membranes and break the antioxidant balance by consuming intracellular glutathione (GSH), which results in more conducive ROS production. Meanwhile, the photothermal heating can regulate the CuFeS2 NPs close to their optimal reaction temperature (60 °C) to release more hydroxyl radical in low concentrations of H2O2 (100 µM). The proposed CuFeS2 NPs-based antibacterial system achieve more than 99% inactivation efficiency of methicillin-resistant Staphylococcus aureus (106 CFU mL−1 MRSA), hyperspectral bacteria β-Escherichia coli (106 CFU mL−1 ESBL) and Pseudomonas aeruginosa (106 CFU mL−1 PA), even at low concentration (2 μg mL−1), which is superior to those of the conventional CuO NPs at 4 mg mL−1 reported in the literature. In vivo experiments further confirm that CuFeS2 NPs can effectively treat wounds infected by MRSA and promote the wound healing. This study demonstrates that excellent antibacterial ability and good biocompatibility make CuFeS2 NPs a potential anti-infection nanozyme with broad application prospects.

The peroxidase-like catalytic activity of in situ prepared cobalt carbonate and its applications in colorimetric detection of hydrogen peroxide, glucose and ascorbic acid

In this study, the cobalt carbonate (CoCO3) was in situ prepared using cobalt (Ⅱ) and carbonate at room temperature, and the intrinsic peroxidase-like activity of CoCO3 was demonstrated for the first time through the oxidation of chromogenic substrate 3, 3', 5, 5' - tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). The effects of pH, reaction temperature, and incubation time on the catalytic activity of CoCO3 were studied. Under the optimal reaction conditions, the Michaelis constant (Km) of CoCO3 to H2O2 is 0.443 mM, which is lower than that of natural horseradish peroxidase and the previously reported peroxidase mimics. Furthermore, the mechanism exploration experiments confirm that the catalytic activity of CoCO3 is mainly attributed to the hydroxyl radical (•OH). Finally, based on the outstanding peroxidase-like activity of CoCO3, a colorimetric sensor for the detection of H2O2, glucose, and ascorbic acid (AA) was developed, which shows satisfactory selectivity and recovery. In addition, the total antioxidant capacity of three types of tea, dried lemon, three kinds of fresh fruit juice, and vitamin C tablet were determined. In short, this study reports a novel in situ generated CoCO3, which can be prepared rapidly at room temperature, eliminating the harsh, cumbersome, and time-consuming synthesis and purification process. The developed sensor based on the newly found excellent peroxidase-like activity of in situ prepared CoCO3 for the determination of H2O2, glucose, and AA is fast, simple, low cost, and high sensitivity.

Investigation on the Peroxidase-like Activity of Vitamin B6 and Its Applications in Colorimetric Detection of Hydrogen Peroxide and Total Antioxidant Capacity Evaluation.

The peroxidase-like activity of vitamin B6 (VB6) was firstly demonstrated by catalyzing the peroxidase chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) at the existence of H2O2. The influence of different factors on the catalytic property of VB6, including pH, temperature, VB6 concentration, and incubation time, were investigated. The steady-state kinetic study results indicate that VB6 possesses higher affinity to H2O2 than natural horseradish peroxidase and some other peroxidase mimics. Besides, the radical quenching experiment results confirm that hydroxyl radical (•OH) accounts for the catalytic process. Based on the excellent peroxidase-like catalytic activity of VB6, the colorimetric methods for H2O2 and gallic acid (GA) detection were developed by measuring the absorbance variance of the catalytic system. Under the optimal conditions, the linear ranges of the methods for H2O2 and GA determination with good selectivity are 50.0–600.0 μM and 10.0–50.0 μM, respectively. In addition, the developed method was applied in the detection of H2O2 in milk samples and evaluation of total antioxidant capacity of different tea infusions. This study may broaden the application prospect of VB6 in environmental and biomedical analysis fields, contribute to profound insight of the physiological functions of VB6, as well as lay foundation for further excavation of small-molecule peroxidase mimics.

Cobalt-Based Metal-Organic Framework Nanoparticles with Peroxidase-like Catalytic Activity for Sensitive Colorimetric Detection of Phosphate

Appropriate addition of phosphate salt in food can improve the food quality and taste. However, extensive intake of phosphate salt may lead to some human diseases such as hyperphosphatemia and renal insufficiency. Thus, it is essential to establish a cost-effective, convenient, sensitive, and selective method for monitoring phosphate ion (Pi) to ensure food quality control. In this work, a Co-based metal-organic frameworks (Co-MOF) nanomaterial with dual functions (peroxidase-like activity and specific recognition) was designed for acting as a catalytic chromogenic platform for sensitive detection of Pi. The Co2+ nodes not only provide high enzyme-like activity to catalyze the 3,3′,5,5′--tetramethylbenzidine (TMB) substrate to blue oxTMB (652 nm) but also act as selective sites for Pi recognition. The use of cationic organic ligands (2-methylimidazole) and cationic metal ions (Co2+) endows the Co-MOF with a strong positive surface charge, which is beneficial to the capture of negative-charged Pi and the dramatically suppressed TMB oxidation. When Pi exists, it specifically adsorbs onto the Co-MOF through the Co-O-P bond and the strong electrostatic interaction, leading to the change of surface charge on Co-MOF. The peroxidase-like catalytic activity of Co-MOF is thus restrained, causing a different catalytic effect on TMB oxidation from that without Pi. Based on this principle, a colorimetric assay was established for rapid and sensitive detection of Pi. A good linear relationship was obtained between Pi concentration and the absorbance at 652 nm, with a linear range of 0.009–0.144 mg/L and a detection limit of 5.4 μg/L. The proposed assay was applied to the determination of Pi in actual food samples with recoveries of 92.2–108% and relative standard deviations (RSDs) of 2.7–7.3%, illustrating the promising practicality for actual samples analysis.

Vanadium Disulfide Nanosheet Boosts Optical Signal Brightness as a Superior Enzyme Label to Improve the Sensitivity of Lateral Flow Immunoassay.

The color-enzyme lateral flow immunoassay (LFIA) has attracted widespread attention to expand the detection range and improve sensitivity via amplifying the color signal after catalyzing the substrate. As a kind of layered transition-metal dichalcogenide (TMD), the vanadium disulfide nanosheet (VS2NS) possesses superior peroxidase-like catalytic activity. Here, a VS2NS was applied as an enzyme label in the LFIA to detect 17β-estradiol (E2). Compared to natural horseradish peroxidase, the VS2NS expresses a more prominent enzyme catalytic performance, stability, and adsorption ability. Under optimal conditions, the calculated limit of detection (cLOD) of the VS2NS-based LFIA is 0.065 ng mL-1 for E2, which is sixfold lower than that of the optimized colloidal nanoparticle-based LFIA (cLOD = 0.406 ng mL-1). Besides, the detection linear range of the VS2NS-based LFIA can be widened by 1.5 times after the catalytic reaction. Moreover, the VS2NS-based LFIA exhibits excellent practicability in real sample detection. Simultaneously, this study helps open up the application of the VS2NS in the trace analysis of LFIAs, which can broaden TMDs' scope of application and better show their properties of color enzymes.

Metallic deep eutectic solvents-assisted synthesis of Cu, Cl-doped carbon dots as oxidase-like and peroxidase-like nanozyme for colorimetric assay of hydroquinone and H2O2

As an emerging carbon nanomaterial, carbon dots (CDs) have drawn significant attention in the catalytic field owing to their low toxicity, high stability and superior biocompatibility. Herein, for the first time, Cu and Cl co-doped CDs (Cu, Cl-CDs) were synthesized via hydrothermal method utilizing citric acid as carbon source and metallic deep eutectic solvents (MDESs) as green solvent and passivation agent. It was proved that the prepared Cu, Cl-CDs exhibited oxidase-like (OD-like) and peroxidase-like (POD-like) catalytic activities. The catalytic performance, mechanism and steady-state kinetics of Cu, Cl-CDs were systematically investigated. Accordingly, bifunctional colorimetric platforms based on the OD-like and POD-like activities of Cu, Cl-CDs using 3,3′,5,5′-Tetramethylbenzidine (TMB) as substrate were established for determining hydroquinone (HQ) and H2O2, respectively, both of which showed high accuracy and sensitivity. HQ, as a reducing agent, could be detected by this method with a linear range of 0.1–120 µM and limit of detection (LOD) of 0.08 µM. And the degree of discoloration varied linearly with H2O2 in the range of 1–600 µM with LOD of 0.35 µM. Thus, Cu, Cl-CDs have broad prospects in catalysis and environmental chemistry, and provide rational guidance for green synthesis of carbon-based nanozymes with multi-enzyme catalytic performance.

A nanozyme-based colorimetric sensor array as electronic tongue for thiols discrimination and disease identification

Thiol analysis is of vital significance due to the essential roles in disease diagnosis, while the highly similar structures of thiols are a major challenge in practical determination. Herein, a nanozyme-based colorimetric sensor array has been proposed as electronic tongue for excellent discrimination and sensitive quantitation of thiols. The sensing units are fabricated by integrating the terephthalic acid modified graphene quantum dots (TPA@GQDs) with three transition metal ions (Fe2+, Cu2+ and Zn2+) via coordination, respectively, which not only provide sufficient substrate binding sites but also form the metal ion-regulated catalytic active centers. In this way, disparate promotion degrees on the peroxidase-like catalytic activity have been achieved in different metal ion-TPA@GQD ensembles. Based on the strong binding affinity between metal ions and thiols, the catalytic active centers are removed from TPA@GQDs, which inhibits the catalytic activity of sensing unit to diverse degrees. Accordingly, using 3, 3′, 5, 5′-tetramethylbenzidine (TMB) as chromogenic substrate in the presence of hydrogen peroxide (H2O2), each sensing unit can generate differential colorimetric signals (fingerprints) for six thiol analytes, which can be accurately discriminated through linear discriminant analysis (LDA) with a detection limit of 50 nM. In addition, the discrimination of the same thiol with different concentrations and thiol mixtures have also been achieved. Furthermore, inspired by the distinct levels of thiols in practical samples, the proposed sensor array enables the identification of thiol-associated diseases by means of machine learning algorithm, which makes a positive contribution to medical diagnosis.

Comparative study of Pd@Pt nanozyme improved colorimetric N-ELISA for the paper-output portable detection of Staphylococcus aureus

Staphylococcus aureus is a frequent pathogenic bacterium that has a significant detrimental influence on the health of the human body. Therefore, developing a practical and portable detection platform is critical to ensuring food safety. Nanozymes are a kind of engineered nanomaterials with superior enzyme-like activities, providing infinite possibilities for the development of highly sensitive analytical assays. In this study, mesoporous core−shell palladium@platinum (Pd@Pt) nanozymes were synthesized and then applied as a signal amplifier in Staphylococcus aureus colorimetric immunoassay. At the same time, a careful comparative study of the catalytic performance with natural horseradish peroxidase (HRP), Pd@Pt nanozymes and their complexes Pd@Pt-HRP (HRP coupling with Pd@Pt nanozymes) were firstly performed, as well as clever using a colorimeter to achieve portable signal output. Pd@Pt-HRP bioprobes enable remarkable peroxidase-like catalytic activity, resulting in the highest sensitivity with a limit of detection (LOD) improved from 1 × 105 to 1 × 103 CFU/mL. In all, this work conducted a valuable comparative study and presented an improved strategy for the portable detection of pathogenic bacteria, which was expected to be used in a wide range of applications in food safety regulation and biomedicals arenas.

Nitrogen plasma-mediated deposition of silver onto MoS2 towards robust nanozyme with enhanced catalysis for colorimetric assay of hydrogen sulfide in aquaculture water

Ultra-thin MoS2 nanosheets were treated by nitrogen (N2) plasma to mediate the photo-reduction deposition of silver forming N/Ag@MoS2 nanozymes for the catalysis-based colorimetric assay of hydrogen sulfide (H2S) in aquaculture water. It was found that the as-produced N/Ag@MoS2 could display a greatly enhanced peroxidase-like catalytic activity than that of MoS2 nanosheets (about three times higher). Also, in the presence of H2S, a strong Ag-S interaction could occur to form non-conductive Ag2S onto N/Ag@MoS2 nanocomposites towards the rationally reduced catalysis depending on H2S concentrations. Herein, on the one hand, the plasma treatment-aided doping of N elements into MoS2 nanosheets might facilitate the robust deposition of silver onto MoS2 nanosheets through the strong Ag-N chelation, and the enhanced internal electron transferring of N/Ag@MoS2 nanozymes. On the other hand, the so deposited silver could not only enhance the catalytic properties of nanozymes, but also act as a specific probe for recognizing H2S to trigger the decreased catalysis of nanozymes. Importantly, such a N2 plasma treatment pathway that mediates the deposition of silver onto two-dimensional structures like MoS2 nanosheets may pave the way toward the design of various nanozymes for the analysis of different targets in the biomedical, food, and environmental monitoring fields.

N- and B-doped fullerene as peroxidase- and catalase-like metal-free nanozymes with pH-switchable catalytic activity: A first-principles approach

Metal-free nanozymes are designed to function as peroxidase or catalase, controllable by pH conditions. Using first-principles density functional theory (DFT) calculations, we propose that heteroatomic doping of N and B to fullerene is promising to form active sites for catalyzing oxygenate intermediates for H2O2 decomposition. In neutral pH with bare surfaces, both N- and B-doped fullerenes show peroxidase-like catalytic activity rather than a catalase-like one. The presence of water, at neutral pH, drives peroxidase-like catalysis on the B-doped fullerene with marginal energy, in which the B atom functions as a strong electrophile that firmly adsorbs OH* and promotes O-O chemical bond dissociation. Interestingly, acidic, and basic environments tune their selectivity toward peroxidase- and catalase-like catalytic activity, respectively, mediated by pre-adsorbed H* and OH*. The DFT calculations demonstrate the applicability of N- and B-doped fullerenes by showing significantly decreased dissociation energy barriers of H2O2 into 2OH during the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). We believe that the results can provide a useful guide for designing highly active and selective carbon-based nanozymes toward H2O2 decomposition.

Rhodium nanocatalyst-based lateral flow immunoassay for sensitive detection of staphylococcal enterotoxin B

Compared with traditional laboratory-based tests, lateral flow immunoassay (LFA) has been developed as one of the emergent and popularly used rapid detection technology. Due to unique physical and chemical properties, novel nanomaterials have been widely used as the signal label in LFA for the detection of analytes, but these assays merit further development to improve sensitivity. Here, we developed a rhodium (Rh) nanozyme-labeled LFA with high sensitivity for paper-based detection of staphylococcal enterotoxin B (SEB), one of the super-antigens that may cause illness. The synthesis and optimization of Rh nanozymes were illustrated, which show excellent peroxidase-like catalytic activity. Harnessing the catalytic amplification of Rh nanozymes enabled naked-eye detection of SEB as low as 1.2 pg·mL-1 in the whole milk sample, which increases 250 folds compared with the commercial ELISA tests. Additionally, the recoveries rate for spiking dairy samples was determined to be 94.3–124.8% for SEB, which indicated the good accuracy and precision of Rh-based LFA. We believe this Rh based LFA for detecting toxins may open new possibilities for similar immunochromatographic testing methods.

Enzyme-free sandwich-type electrochemical immunosensor based on high catalytic binary PdCu mesoporous metal nanoparticles and conductive black phosphorous nanosheets for ultrasensitive detection of pro-SFTPB in non-small cell lung cancer

Pro-surfactant protein B (pro-SFTPB) has been proven to be a powerful biomarker for the early diagnosis of non-small-cell lung cancer (NSCLC). In this study, a novel enzyme-free electrochemical immunosensor is developed for the ultrasensitive detection of pro-SFTPB using binary PdCu mesoporous metal nanoparticles (MMNs) and few-layer black phosphorous (BP nanosheets). Concretely, PdCu MMNs, as novel essential signal labels, were successfully synthesized, offering excellent outstanding peroxidase-like catalytic activity toward hydrogen peroxide (H2O2). Meanwhile, the combination of BP nanosheets with biocompatible gold nanoparticles (AuNPs) served as the substrate on the electrode. With the aid of binary PdCu MMNs nanozymes and BP nanosheets, the enzyme-free electrochemical immunosensor revealed ultrasensitivity detection of pro-SFTPB ranging from 10 pg/mL to 100 ng/mL with an ultralow limit of detection of 5.3 pg/mL. In addition, the immunosensor enables accurate detection of pro-SFTPB in serum samples. Altogether, the developed electrochemical immunosensor provides an enzyme-free platform for pro-SFTPB detection, providing a new method for the early diagnosis of NSCLC.