Oxidase-like Activity Research Articles

The fabrication of phosphotungstate@UIO-Au/reduced graphene oxidation for electrochemical ultrasensitive detection of alpha-fetoprotein.

As an early multi-purpose tumor marker of hepatocellular carcinoma, alpha-fetoprotein (AFP) plays a vital role in early diagnosis and treatment. To achieve the early and accurate determination of AFP, the POMOF was fabricated by embedding H3PW12O40 (PW12) into UIO-66-NH2, further immobilized on reduced GO (rGO) and fabricated an innovative POMOF nanocomposite (PW@UIO-Au/rGO) as an electrochemical immunosensor (ECI-sensor). The PW@UIO-Au/rGO achieved 17-fold signal enhancement owing to their synergistic effect, enabling PW@UIO-Au/rGO exhibit high oxidase-like catalytic activity, facilitating their sensing performance. Under optimal experimental conditions, the proposed PW@UIO-Au/rGO ECI-sensor presented excellent sensing performance over a wide range from 0.01 ng mL-1 to 500 ng mL-1 with ultra-low detection of 4.0 pg mL-1. Notably, sensing results in real serum samples were verified by the clinical enzyme-linked immunosorbent assay (ELISA) and electrochemiluminescence immunoassay (ECL) methods with excellent accuracy and consistency, indicating the excellent environmental tolerance of the proposed ECI-sensor. This work provided a promising strategy for designing feasible ultra-sensitive probe for sensing AFP in clinical test.

Selenium Hydride-Induced Oxidase-like Activity Inhibition of Amorphous/Crystalline Manganese Dioxide: Colorimetric Assay for Selenium Detection.

Hydride generation-based optical sensors have achieved on-site visual selenium (Se) determination with high anti-interference capability, yet they rely on the change of single-color intensity with a narrow linear dynamic range. Herein, we combined selenium hydride (H2Se)-induced activity inhibition of a manganese dioxide (MnO2) nanozyme with different degrees of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to realize sensitive multicolor visual detection of Se(IV). Due to its high oxidase-like (OXD-like) activity and sensitive response to H2Se, amorphous/crystalline manganese dioxide (ac-MnO2) was selected to form the headspace single droplet for microextraction and recognition. Via headspace redox reaction with H2Se, ac-MnO2 was reduced into low valence accompanied by in situ generation of Se nanoparticles, leading to the formation of a Se-MnOx aggregate. The experimental results and theoretical calculation indicated that, compared with MnO2, Se-MnOx had decreased active sites for adsorbing O2 to generate •O2-, resulting in the nanozyme activity inhibition that was totally dependent on Se(IV) concentration. The implementation of this strategy enabled accurate Se(IV) detection with a linear range from 10 to 600 μg L-1 and a limit of detection of 1.8 μg L-1. The portable smartphone-based detection for real sample analysis further demonstrated that this assay can be an easy, convenient, and intelligent tool for on-site selenium determination.

Nanowire-like phosphorus modulated carbon-based iron nanozyme with oxidase-like activity for sensitive detection of choline and dye degradation

Choline is mainly supplemented through food intake, lack of choline would result in diseases like liver cirrhosis, hardening of the arteries, or neurodegenerative disorders. The accurate detection of choline is important for human health. Herein, a novel nanowire-like phosphorus/nitrogen co-doped carbon-based iron nanozyme (Fe-NPC) with outstanding oxidase-like activity was synthesized, and the influence of phosphorus doping on oxidase-like activity was explored. Proper phosphorus doping was found to enhance the oxidase-like activity of Fe-NPC by increasing surface defects, promoting iron loading, and modulating chemical environment of central site. The oxidase-like activity of Fe-NPC was successfully applied to colorimetric-fluorescent dual mode detection of choline, and good linear relationship in the ranges of 3–200 μM were achieved with LODs of 1.95 and 1.50 μM, respectively. The fluorescent detection was constructed based on the fluorescence quenching of silicon quantum dots (Si QDs) by quinone-imine. The quenching mechanism was attributed to FRET due to the large spectra overlap, reduced fluorescence lifetime and proper donor−acceptor distance. The successful application to the detection of choline in milk proved the practicability of the proposed sensing method. The oxidase-like properties of Fe-NPC was further used in the degradation of cationic dye methyl blue, high degradation efficiency of 74 % was achieved within 5 min under optimal conditions, proving the enormous potential of Fe-NPC for application in environment protection.

Engineering Strain-Defects to Enhance Enzymatic Therapy and Induce Ferroptosis.

The effect of mimetic enzyme catalysis is often limited by insufficient activity and a single therapy is not sufficient to meet the application requirements. In this study, a multifunctional nanozyme, MMSR-pS-PEG, is designed and fabricated by modifying poly (ethylene glycol) grafted phosphorylated serine (pS-PEG) on mesoporous hollow MnMoOx spheres, followed by loading sorafenib (SRF) into the pores. Strain engineering-induced oxygen defects endow the nanozyme with enhanced dual-enzymatic activity to mimic catalase and oxidase-like activities, which catalyze the conversion of endogenous H2O2 into oxygen and subsequently into superoxide ions in the acidic tumor microenvironment. Moreover, as an n-type semiconductor, MnMoOx generates reactive oxygen species by separating electrons and holes upon ultrasonic irradiation and simultaneously deplete glutathione by holes, thereby further augmenting its catalytic effect. As a ferroptosis inducer, SRF restrains the system xc - and indirectly inhibits glutathione synthesis, synergistically interacting with the nanozyme to stimulate ferroptosis by promoting lipid peroxidation and accumulation and the downregulation of glutathione peroxidase 4. These results provide valuable insights into the design of enzymatic therapy with high performance and highlight a promising approach for the synergism of ferroptosis and enzymatic tumor therapy.

Near-Infrared Light-Responsive Cu2MoS4@GelMA Hydrogel with Photothermal Therapy, Antibacterial Effect and Bone Immunomodulation for Accelerating Infection Elimination and Fracture Healing.

Managing fracture infections is a significant challenge in trauma orthopedics, given the limited self-healing capacity of fractures and the difficulty in eradicating infections. In this study, Cu2MoS4 nanoparticles (CMSs) with are prepared enzyme-like activity and both pH and near-infrared (NIR) light responsiveness. These CMSs are combined with methacrylated gelatin (GelMA) to synthesize CMSs hydrogels (CMSs@Gel) with antimicrobial and bone tissue repair-promoting capabilities. In vitro and in vivo experiments, the CMSs@Gel demonstrated good biocompatibility; peroxidase-like (POD), oxidase-like (OXD), and catalase-like (CAT) activities; excellent photothermal conversion efficiency; and immunomodulatory capacity. Furthermore, the CMSs@Gel exhibited slow degradation, enabling it to exert different pH-responsive enzyme activities and modulate the production of reactive oxygen species (ROS) and the polarization of macrophages throughout the treatment process. Notably, these effects are significantly enhanced under near-infrared (NIR) light. Additionally, under NIR irradiation, the CMSs@Gel maintained the fracture environment at a mild temperature (40-42°C), promoting osteogenesis and angiogenesis. In summary, the CMSs@Gel enhances bactericidal activity during fracture infection and effectively promotes fracture healing after infection control, providing long-term therapeutic effects. This study offers a robust theoretical basis for the staged and long-term treatment of fracture infections in the future.

Tunable Multi-Enzyme Activities of Platinum Nanoclusters for Enhanced Specificity and Sensitivity in Biosensing

Nanozymes have gained prominence for their utility in biosensing and disease diagnostics. However, challenges arise from complex sample matrices and nonspecific enzyme activities that contribute to false signals. This study introduces multifunctional platinum nanoclusters (Pt NCs) exhibiting peroxidase-like (POD-like), oxidase-like (OXD-like), and laccase-like activities tailored for enhanced biosensing capabilities. By adjusting pH, we optimized the conditions to achieve distinct POD-like and OXD-like responses, thereby reducing background signals and improving detection accuracy. The addition of ATP further amplified the POD-like activity while minimizing interference from OXD-like activity. This combined strategy substantially enhanced biomarker detection selectivity, demonstrated through glucose detection in human serum samples. Moreover, thiol inhibition of laccase-like activity in Pt NCs was leveraged for thiol-based antioxidant assessment, revealing their application in quantifying total antioxidant capacity (TAC) in human liver cancer cells, accounting for 44% of TAC. The Pt NCs demonstrated robust sensitivity and reusability, offering a novel multi-enzyme nanomaterial with potential for precise and interference-free biosensing applications. These findings contribute to the development of advanced nanozyme-based biosensors, addressing specificity regulation challenges and expanding their practical application in biosensing and disease diagnostics.

Synergistic Antimicrobial Packaging Film with Photothermal-Controlled Biocatalytic Capability for Tangerine Preservation

The nanomaterials-functionalized composite packaging film with antimicrobial performance has attracted more and more research interests. However, designing the multi-mode synergistic composite film for efficient and intelligent antibacterial is still a challenge. In this work, a Fe-MoOx functionalized chitosan composite film (CS/FM) was designed by doping the Fe-MoOx into chitosan film. CS/FM film inherited excellent photothermal performance and photothermal-enhanced oxidase-like activity of Fe-MoOx, which endow CS/FM film with superior antimicrobial ability. The optimal composite film (CS/FM0.2) able to killed ≥98.87% of S. aureus and ≥98.26% of E. coli, and could significantly inhibit the growth of P. expansum and P. italicum. Besides, CS/FM0.2 film also showed good water vapor permeability (0.71 × 10−10 g m−1 s−1 Pa−1) and tensile strength (58.16 MPa). Low hemolysis rate (≤ 4.91%), high cell viability (≥ 90.32%), and the normal body organs after being treated with Fe-MoOx verified the biosafety of CS/FM film. The tangerine preservation results indicated that CS/FM0.2 film could extend the shelf life of tangerine by at least 9 days and prevent the loss of tangerine nutrients. Our work boosted the development of designing composite packaging film with multi-mode synergistic antimicrobial effect via nanomaterials functionalized for food preservation.

Paper-based triple-readout nanosensor for point-of-care detection of glucose in urine

Glucose detection is critical for diabetes diagnosis and management. This study aimed to develop an enzyme-free, cascade-based, triple-readout paper sensor utilizing bismuth (Bi)-based metal-organic frameworks/gold nanoparticles (Bi-BDC-NH2@Au) for detecting urine glucose. Herein, Bi-BDC-NH2@Au exhibited glucose oxidase-like activity and oxidized glucose to generate H2O2, which then quenched the blue fluorescence of FP@Bi-BDC-NH2@Au through an inner filter effect. Additionally, owing to its pronounced peroxidase-like activity, Bi-BDC-NH2@Au catalyzed H2O2 to produce ·OH, which oxidized colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB), thereby increasing the system temperature owing to the excellent photothermal conversion properties of oxTMB. These mechanisms enabled the triple-readout of glucose levels. Quantification in the fluorescence and colorimetric modes was achieved through a Python-based image recognition algorithm that accurately read B/(R+G+B) values, and the photothermal mode relied on a portable infrared thermal imager to monitor temperature changes. The detection limits for the fluorescence, colorimetric, and photothermal modes were 4.2, 3.3, and 5.7μM, respectively. The self-calibration ability of the sensor across different modes markedly enhanced its detection accuracy and robustness. The developed sensor successfully has detected and quantified urine glucose, effectively distinguishing between healthy individuals and patients with diabetes, providing a convenient and efficient tool for diabetes management.

Fe(II) Induced Porphyrin Nanoaggregates Assembled in the Liquid-Liquid Interface with Dual Enzyme-like Activity for Colorimetric Determination of Methimazole.

The liquid-liquid interface offers a confined space to control the growth of nanomaterials. In this study, Fe(II) (water phase) induced Meso-tetra (4-carboxyphenyl) porphyrin (H2TCPP) (CHCl3, organic phase) into nanoaggregates (Fe-TCPP) in the liquid-liquid interface. By tuning the ratio of DMF in organic solvents, Fe(II) induced H2TCPP into two nanoaggregates (Fe-TCPP-1 and Fe-TCPP-2) with different morphologies via coordination interaction occurring at the water-CHCl3 interface. Interestingly, the Fe-TCPP nanoaggregates possess dual enzyme-like activity (peroxidase-like and oxidase-like activity). In particular, both Fe-TCPP-1 and Fe-TCPP-2 demonstrate a peroxidase-/oxidase-like activity under visible light irradiation that is higher than that in the dark. Comparatively, Fe-TCPP-2 exhibits enhanced peroxide-like (POD) activity together with oxidase-like (OXD) activity compared with that of Fe-TCPP-1 under the corresponding similar conditions. The excellent enzyme mimic activity of Fe-TCPP nanozymes is ascribed to the generated hydroxyl radicals (·OH) and superoxide anions (O2•-). Remarkably, the catalytic activity of Fe-TCPP-2 remains more than 90% even in the higher temperature range of 35-40 °C, which is significant for biological detection under physiological conditions. Based on the outstanding dual enzyme-like activity of Fe-TCPP-2, a colorimetric sensing platform for methimazole (an antithyroid medicine) has been developed, demonstrating a linear detection range of 10-100 μM and a detection limit of 4.44 μM.

A colorimetric platform using highly active Prussian blue composite nanocubes for the rapid determination of ascorbic acid and acid phosphatase.

Cobalt-doped Prussian blue composite nanocubes (Co-PB NCs) were synthesized, which can quickly convert O2 to O2•- and 1O2. Due to the presence of cobalt and iron transition metal redox electron pairs, Co-PB NCs with high oxidase mimetic activity can rapidly oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue products (ox-TMB) without the assistance of unstable H2O2. Using ascorbic acid-2-phosphate trisodium salt (AAP) as a substrate, it can be converted to reduced ascorbic acid (AA) under acid phosphatase (ACP) hydrolysis, resulting in suppression of TMB oxidation. Therefore, an enzyme cascade signal amplification strategy for rapid colorimetric detection of AA/ACP was developed based on the high-efficiency oxidase-like activity of Co-PB NCs combined with the hydrolysis effect of ACP. The color changes at low concentrations of AA and ACP could be observed by the naked eye, and the detection limits of AA and ACP were 1.67μM and 0.0266 U/L, respectively. The developed colorimetric method was applied to the determination of AA in beverages and ACP in human serum, and the RSDs were less than 3%, showing good reproducibility. This work provides a promising strategy for the use of metal-doped Prussian blue composite material for the construction of rapid colorimetric sensing platforms that avoid the use of unstable hydrogen peroxide.

Developing oxygen vacancy-rich CuMn2O4/carbon dots dual-function nanozymes via Chan-Lam coupling reaction for the colorimetric/fluorescent determination of D-penicillamine

Defect engineering is a promising approach to construct high performance nanozymes due to its ability to regulate their physical and chemical properties. However, how to construct defects to improve the activity of nanozymes remains a challenge. Herein, for the first time, the Chan-Lam coupling reaction is used to construct the oxygen vacancy (OV)-rich CuMn2O4/carbon dots (CDs) (OV-CuMn2O4/CDs) dual-function nanozymes with fluorescent (FL) and oxidase-like properties, via regulating the low-valent metal ions (Cu+ and Mn2+) and Ov contents in the spinel CuMn2O4 and in-situ growth of β-cyclodextrin (β-CD)-derived CDs. Expectedly, relative to CuMn2O4, the OV-CuMn2O4/CDs exhibited 35.8%, 8.5%, and 14.6% rise in the contents of Cu+, Mn2+ and Ov, respectively. Abundant Ov provides more O2 adsorption/activation sites, and the charge transfer between Ov and metal atoms increases the charge density around metal atoms. This produces more low-valent metals (like Cu+ and Mn2+) to promote the electron transfer from metal to O atoms and O-O bond cleavage. Thus, the oxidase-like activity of OV-CuMn2O4/CDs is 4.1 times that of CuMn2O4. Also, the in-situ growth of β-CD-derived carbon dots on CuMn2O4 endows OV-CuMn2O4/CDs selective target recognition. Thus, a sensitive and selective colorimetric and fluorescence dual-mode method was established for determining D-penicillamine (D-PA), with the limit of detection of 0.25 and 0.048 μM, respectively. The method was applied to D-PA determination in real samples. This work demonstrates the Chan-Lam coupling reaction can be used to construct high performance nanozymes for developing dual-mode sensor for the detection of targets.

Dual-mode fluorescent and colorimetric sensing of thiourea and aluminum ion in natural water based on CuO nanoparticles.

CuO nanoparticles with good water solubility and uniform particle size were successfully prepared. Interestingly, the oxidase-like activity of CuO NPs was continuously enhanced by the addition of thiourea (TU), and the enzyme activity was further enhanced by the addition of aluminum ion (Al3+). By systematically exploring and optimizing the experimental conditions, including the key parameters such as temperature, reaction time, and pH, a fluorescence-colorimetric dual-mode sensing system based on CuO nanoparticles was constructed. The detection range of TU and Al3+ were 1-100 µM and 1-100 µM, respectively, and the selectivity and precision of detection were further improved. In addition, the catalytic mechanism of CuO NPs as oxidase-like catalysts and the specific process in the reaction were investigated. Finally, the nano-sensing system was successfully applied to the analysis of three real environmental samples, namely, tap water, lake water and river water, which provided an effective new strategy for the future development of nano-sensing technology for TU and Al3+.

Transformative personalized oxalate biomarker analysis through a wrist-worn microneedle device integrated with duplex nanozyme toolbox

The interstitial fluid (ISF) is valuable for disease diagnosis due to its unique biomarkers. Microneedles (MNs) offer a painless method for ISF sampling, facilitating primary diagnostics. This study introduces a minimally invasive, biocompatible MN patch made from a swellable hydrogel of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), which effectively extracts ISF. The hydrogel selectively permits small molecules like oxalate, a kidney disease biomarker, while blocking large biomolecules. The MN patch is integrated with a multilayer sensor via microfluidic channels, featuring cotton fiber, agarose, and Mn3[Fe(CN)6]2, alongside Fe3[Fe(CN)6]3 (AGH-CP/MnFeCN/FeFeCN). These nanozymes exhibit oxidase-like activity, reacting with 3,3′,5,5′-tetramethylbenzidine (TMB) to indicate oxalate levels through a color change from green (no oxalate) to light or dark blue, based on concentration. The designed sensor demonstrates high performance with a detection limit of 0.897 μM and an RSD of 1.22 %, enabling accurate quantification via smartphone image analysis as readout platforms for more accessibility and user-friendliness which helps to reach personalized healthcare goals. This integration facilitates real-time, remote, precise disease detection, biochemical analysis and forsooth miniaturization, leading to the development of portable, flexible, and wearable sensors. The MN patch and integrated sensor show excellent stability, selectivity, sensitivity, reliability, and long-term durability. This minimally invasive sensing system, designed for wristband integration, opens new avenues for precision point-of-care monitoring, enhancing personal healthcare.

Manganese-arginine nanozymes as oxidase mimics for smartphone-based intelligent detection of 4'-O-methylpyridoxine.

Byself-assembly of MnCl2 and arginine under alkaline conditions, ultra-small MnArg nanoparticles were successfully constructedas oxidase (OXD) mimics for intelligent detection of the Ginkgo toxin 4'-O-methylpyridoxal (MPN). The obtained MnArg nanozymes possessed excellent OXD-like activity and thermal stability. Based on the inhibitory effect of MPN for the catalytic activity of MnArg, this system wasutilized for the colorimetric sensing of MPN with a low limit of detection (LOD) of 2.16µgmL-1. Thedetection system exhibited good selectivity against other potential interferents. FTIR data showed that the presence of MPN binds with MnArg and shields the active sites, thereby interfering with the oxidase-like activity. Combined with a smartphone and the ColorMax software, this nanozyme-based intelligent detection platform could effectively detect MPN with a LOD of 2.1µgmL-1. Our MnArg nanozyme-based system wasapplied to detect real ginkgo nut samples with recoveries of 92.4-108.7%, and the relative standard deviations were less than 0.7%. This work may promote the development of novel nanozymes and expand their applications in the field of food safety detection.

Co nanoparticles confined in N-doped hollow carbon nanospheres as multifunctional oxidase mimic for colorimetric detection of L-Cysteine and Hg2+

In contrast to peroxidase-mimicking nanozymes, oxidase mimics directly employ molecular oxygen (O2) as oxidant to generate reactive oxygen species (ROS). Generally, transition metal-based nanozymes exhibit poor oxidase-like activity. We herein constructed a colorimetric sensor based on Co-based oxidase mimic, where the Co nanoparticles were encapsulated in hollow N-doped carbon nanospheres (Co-N/C). Co nanoparticles confined catalyst effectively anchored the active part, which greatly influenced the catalytic activity of the oxidase-mimic nanozymes. Due to the antioxidative property of L-Cysteine (L-Cys) and the specific complexation between L-Cys and Hg2+, the rationally designed Co-N/C could be utilized to detect L-Cys and Hg2+. The proposed sensing platform exhibited wide linear ranges of 1–30 μM for L-Cys and 0.6–30 μM for Hg2+, respectively. The excellent selectivity of the constructed sensor showed the reliability and practicality for the assay of L-Cys and Hg2+ in fetal bovine serum. The spatial confinement can prevent the aggregation of Co nanoparticles, boosting the stability and catalytic performance in colorimetric sensing.

Cu3(HITP)2 with peroxidase- and ascorbic acid oxidase-like catalytic activity for fluorescence/chemiluminescence sensing of ascorbic acid

Nanomaterials with intrinsic enzyme mimicking activity have achieved widespread application. However, developing novel nanomaterials with multienzyme mimicry activity remains challenging. Herein, Cu3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with ascorbic acid oxidase (AAO)- and peroxidase (POD)-like activity are successfully synthesized. Cu3(HITP)2 exhibits excellent AAO-like activity and can specifically catalyze the oxidation reaction of ascorbic acid (AA). Dehydroascorbic acid (DHAA) obtained from the oxidation of AA is allowed to react with nonfluorescent o-phenylenediamine (OPD) to form 3-(1,2-dihydrox-yethyl) furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission. Moreover, Cu3(HITP)2 is able to catalyze the chemiluminescence (CL) reaction of ABEI-H2O2 to generate a strong and glow-type emission based on its POD activity. Inspired by the multienzyme mimicry activity of Cu3(HITP)2, the simple and sensitive fluorescence and chemiluminescence sensing platforms are successfully constructed and applied for the detection of AA. The sensors show high sensitivity and excellent selectivity. We believe that this multienzyme mimicry activity nanomaterial not only can be used to construct the multiple-mode biosensing platform, but also enables the extensive applications in the fields of biomedicine, energy, and environment.

Nanozyme-mediated ratiometric fluorescence hydrogel for on-site detection of sulfite in food

In this work, a ratiometric fluorescence hydrogel nanosensor was developed by integrating a composite consisting of o-phenylenediamine (OPD), manganese dioxide nanoflakes (MnO2 NFs), and N-doped carbon dots (N-CDs) into an agarose hydrogel for sulfite detection. MnO2 NFs demonstrated intense oxidase-like activity, facilitating the conversion of non-fluorescent OPD into yellow-emissive 2,3-diaminophenazine (DAP). As a result, a significant emission peak belongs to DAP, alongside the fluorescence quenching of N-CDs through FRET. Upon interaction with sulfite, MnO2 NFs lost their oxidase-like function. This process decreased the fluorescence of DAP and restored the blue fluorescence of N-CDs, producing a typical ratiometric response, ranging from 3 nM ∼ 400 μM, with a detection limit (LOD) of 3.79 nM. Employing a smartphone, the fluorescence color change demonstrated by the hydrogel sensor was translated into quantitative data (LOD: 8.44 nM). This hydrogel sensor offers an affordable, portable, and user-friendly solution for sulfite detection and food safety monitoring.

Three in one: A multifunctional oxidase-mimicking Ag/Mn3O4 nanozyme for colorimetric determination, precise identification, and broad-spectrum inactivation of foodborne pathogenic bacteria

A multifunctional oxidase-mimicking Ag/Mn3O4 was prepared, catalyzing the 3, 3′, 5, 5′-tetramethylbenzidine (TMB) chromogenic reaction. Six foodborne pathogenic bacteria species, including Escherichia coli, Staphylococcus aureus, Salmonella enterica, Listeria monocytogenes, Bacillus cereus, and Cronobacter sakazakii, were observed to differentially inhibit its oxidase-like activity, resulting in decelerating the TMB chromogenic reaction. Owing to these properties, the following achievements were achieved: colorimetric determination of these bacteria with high sensitivity can be achieved using Ag/Mn3O4 + TMB reaction system; precise identification of these bacteria at different concentrations, including individual bacterium, binary mixtures, and even multivariate mixtures, can be effectively realized by combining the Ag/Mn3O4-based colorimetric sensor array with principal component analysis (PCA); broad-spectrum inactivation of these bacteria can be remarkably realized through catalyzation of Ag/Mn3O4 to generate superoxide anion free radicals. Therefore, our proposed Ag/Mn3O4 holds significant application potential in the colorimetric determination, precise identification, and broad-spectrum inactivation of foodborne pathogenic bacteria.

When MnSiO3 meets ratiometric fluorescence: A facile, cost-effective ratiometric fluorescent platform based on oxidase-like MnSiO3 nanozyme for versatile Total Antioxidant Capacity (TAC) measurements

The level alterations of antioxidants are highly associated with various oxidative stress-related diseases, food quality and drug safety problems, which enables the reliable and accurate determination of total antioxidant capacity (TAC) become progressively significant. Herein, for the first time, we explored the catalytic effect of MnSiO3 nanozyme with oxidase-like activity towards different fluorescent substrates, and introduced ratiometric fluorescence to MnSiO3-based biosensing. By harnessing MnSiO3-propelled catalytic oxidation of two fluorescent substrates with contrary responses (Scopoletin, SC and o-phenylenediamine, OPD), we constructed a facile, cost-effective ratiometric fluorescent (RF) platform for TAC measurement. In the absence of antioxidants, SC and OPD can be oxidized, and the synergistic effect of fluorescence resonance energy transfer (FRET) and inner-filter-effect (IFE) between SC and oxidized OPD (Ox-OPD) will result in the weak fluorescence of Ox-SC at 465 nm and the strong one of Ox-OPD at 562 nm, respectively. However, the addition of antioxidants will dissociate MnSiO3, generating the recovered high/low fluorescence values of both substrates. Through monitoring the FI465/FI562 changes, the RF analysis of different antioxidants (Cys, AA, GSH) with satisfactory sensitivity is performed and the TAC measurements in diverse real samples (human serums, beverages, and drugs) are successfully accomplished. Moreover, the system demonstrates high selectivity and could compete with the commercial TAC test kits.

Pd nanocubes supported on the porous V2CTx nanosheets with enhanced nanozyme activity and photothermal property for antibacterial application

Rational design and controllable construction of supported nanostructures with excellent antibacterial property remain a great challenge. Recently, transition metal carbides/nitrides/carbonitrides (MXenes) have attracted much interest in many fields due to their large specific surface areas and good photothermal property. Herein, a simple yet effective surface engineering strategy based on the tuning of MXene surface chemistry is presented, which allows in-situ controlled growth of the Pd nanocubes on the V2CTx nanosheets. Briefly, the exfoliated V2CTx nanosheets by HF are annealed, which changes the composition of surface terminations while creating the mesoporous structures. The annealing largely affects the exposure and oxidation states of the adjacent V atoms and allows the controllable growth of Pd nanocubes. Interestingly, the obtained Pd@V2CTx nanocomposites show enhanced peroxidase-/oxidase-like activities and intrinsic photothermal effect in the near infra-red (NIR) region due to the strong metal-support interaction. Furthermore, the combined nanocatalytic-photothermal treatment by their versatilities remarkably improves the antibacterial efficacy, giving a high killing rate (above 98 % for both Escherichia coli and Staphylococcus aureus). This work provides a new avenue to develop the supported metal nanostructures based on MXenes for antibacterial application.