Doping Engineering To Modulate Surface Plasmon Resonance and Enzyme-like Activities for Enhancing Photoacoustic Imaging-Guided Targeted Cancer Therapy in the Second Near-Infrared Window.

Biological imaging-guided targeted tumor therapy has been a soughtafter goal in the field of cancer diagnosis and treatment. To this end, we proposed a strategy to modulate surface plasmon resonance and endow WO3-x nanoparticles (NPs) with enzyme-like catalytic properties by doping Fe2+ in the structure of the NPs. Doping of the Fe2+ introduced oxygen vacancies into the structure of the NPs, inducing a red shift of the maximum absorption wavelength into the near-infrared II (NIR-II) region and enhancing the photoacoustic (PA) and photothermal properties of the NPs for more effective imaging-guided cancer therapy. Under NIR-II laser irradiation, the Fe-WO3-x NPs produced very strong NIR-II PA and photothermal effects, which significantly enhanced the PA imaging and photothermal treatment effects. On the other hand, Fe2+ in Fe-WO3-x could undergo Fenton reactions with H2O2 in the tumor tissue to generate ·OH for chemodynamic therapy. In addition, Fe-WO3-x can also catalyze the above reactions to produce more reactive oxygen species (ROS) and induce the oxidation of NADH to interfere with intracellular adenosine triphosphate (ATP) synthesis, thereby further improving the efficiency of cancer therapy. Specific imaging of tumor tissue and targeted synergistic therapy was achieved after ligation of a MUC1 aptamer to the surface of the Fe-WO3-x NPs by the complexing of -COOH in MUC1 with tungsten ions on the surface of the NPs. These results demonstrated that Fe-WO3-x NPs could be a promising diagnosis and therapeutic agent for cancer. Such a study opens up new avenues into the rational design of nanodiagnosis and treatment agents for NIR-II PA imaging and cancer therapy.

MOF derivatization of multifunctional nanozyme: Peroxidase-like catalytic activity combined with magnetic solid phase extraction for colorimetric detection of Hg2.

Nanozyme-based colorimetric sensing has drawn immense attention due to the rapid development of nanozyme in recent years. However, the selectivity of nanozyme-based colorimetric sensing greatly limits its subsequent practical application. It is well known that sample pretreatment can not only improve selectivity by eliminating the sample matrix interference, but also improve sensitivity by enriching trace targets. Based on the easy facile surface modification properties of nanozyme, we rationally designed nanozyme combined with sample pretreatment for colorimetric biosensing, through separation and enrichment, thereby improving the selectivity and sensitivity of the nanozyme colorimetric biosensing. As a proof of concept, the detection of Hg2+ by nanozyme-based colorimetric sensing was used as an example. Magnetic peroxidase-like nanozyme Fe3S4 was designed and synthesized. The selectivity is improved by the specific adsorption of S-Hg bond and the interference elimination after magnetic separation. In addition, the sensitivity is improved by magnetic solid-phase extraction enrichment. Our established colorimetric sensing based on Fe3S4 nanozyme integrated sample pretreatment with an enrichment factor of 100 and the limit of detection (LOD) is 26 nM. In addition, this strategy was successfully applied to detect Hg2+ in environmental water samples. Overall, the strategy showed good selectivity and sensitivity, providing a new practical method for the application of nanozyme-based biosensing in sample pretreatment.

A Macrophage Membrane-Coated Cu-WO3-x-Hydro820 Nanoreactor for Treatment and Photoacoustic/Fluorescence Dual-Mode Imaging of Inflamed Liver Tissue.

A disease-targeting nanoplatform that integrates imaging with therapeutic activity would facilitate early diagnosis, treatment, and therapeutic monitoring. To this end, a macrophage membrane-coated Cu-WO3-x-Hydro820 (CWHM) nanoreactor was prepared. This reactor was shown to target inflammatory tissues. The reactive oxygen species (ROS) such as H2O2 and ·OH in inflammatory tissues can react with Hydro820 in the reactor to form the NIR fluorophore IR820. This process allowed photoacoustic/fluorescence dual-mode imaging of H2O2 and ·OH, and it is expected to permit visual diagnosis of inflammatory diseases. The Cu-WO3-x nanoparticles within the nanoreactor shown catalase and superoxide enzyme mimetic activity, allowing the nanoreactor to catalyze the decomposition of H2O2 and ·O2- in inflammatory cells of hepatic tissues in a mouse model of liver injury, thus alleviating the oxidative stress of damaged liver tissue. This nanoreactor illustrates a new strategy for the diagnosis and treatment of hepatitis and inflammatory liver injury.

Rational design of nanozyme with integrated sample pretreatment for colorimetric biosensing.

Nanozymes have been widely used in the field of biosensing owing to their high stability, low cost, adjustable catalytic activity, and convenient modification. However, achieving high selectivity and sensitivity simultaneously in nanozyme-based colorimetric sensing remains a major challenge. Nanozymes are nanomaterials with enzyme-simulating activity that are often used as solid-phase adsorbents for sample pretreatment. Our design strategy integrated sample pretreatment function into the nanozyme through separation and enrichment, thereby improving the selectivity and sensitivity of nanozyme-based colorimetric biosensing. As a proof-of-concept, glucose was used as the model analyte in this study. A phenylboric acid-modified magnetic nanozyme (Cu/Fe3O4@BA) was rationally designed and synthesized. Selectivity was enhanced by boronate-affinity specific adsorption and the elimination of interference after magnetic separation. In addition, magnetic solid-phase extraction enrichment was used to improve the sensitivity. A recovery rate of more than 80% was reached when the enrichment factor was 50. The synthesized magnetic Cu/Fe3O4@BA was recyclable at least five times. The proposed method exhibited excellent selectivity and sensitivity, simple operation, and recyclability, providing a novel and practical strategy for designing multifunctional nanozymes for biosensing.

Rational design of cuprofullerene bipyridine nanozyme with high peroxidase-like activity for colorimetric sensing of bleomycin.

The high catalytic activity of Cu-based nanozymes mainly depends on the efficient Fenton-like reaction of Cu+/ H2O2, but Cu+ cannot exist stably. Trying to find a material that can stably support Cu+ while promoting the electron cycle of Cu2+/Cu+ still faces serious challenges. C60 is expected to be an ideal candidate to solve this problem due to its unique structure and rich physicochemical properties. Here, we designed and synthesized a C60-doped Cu+-based nanozyme (termed as C60-Cu-Bpy) by loading high catalytic active site Cu+ onto C60 and coordinating with 2,2'-bipyridine (Bpy). The single crystal diffraction analysis and a series of auxiliary characterization technologies were used to demonstrate the successful preparation of C60-Cu-Bpy. Significantly, the C60-Cu-Bpy exhibited superior peroxidase-like activity during the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Then, the catalytic mechanism of C60-Cu-Bpy as peroxidase was elucidated in detail, mainly benefiting from the dual function of C60. On the one hand, C60 acted as a carrier to directly support Cu+, which has the ability to efficiently decompose H2O2 to produce reactive oxygen species. The other was that C60 acted as an electron buffer, contributing to promoting the Cu2+/Cu+ cycle to facilitate the reaction. Furthermore, a colorimetric sensor for the quantitative analysis of bleomycin was established based on the principle of bleomycin specific inhibition of C60-Cu-Bpy peroxidase-like activity, with satisfactory results in practical samples. This study provides a new strategy for the direct synthesis of Cu+-based nanozymes with high catalytic performance.

Analyte-induced laccase-mimicking activity inhibition and conductivity enhancement of electroactive nanozymes for ratiometric electrochemical detection of thiram.

Most nanozyme-based electrochemical sensing strategies depend on the catalytic formation of electroactive substances, while the electrochemical properties of nanozymes have rarely been explored. In this study, magnetic nanoparticles encapsulated metal-organic framework served as precursors to prepare bioinspired nanozymes with both laccase-mimicking activity and electroactivity. Owing to the strong affinity between thiram (THR) and Cu(II) active sites in the nanozymes, the binding of THR inhibited nanozyme catalytic activity toward catechol (CT) oxidation and enhanced nanozyme conductivity. A lower oxidation current (ICT) of CT was accompanied by a higher oxidation signal (ICu) of Cu(II), allowing a ratiometric electrochemical response of the electroactive nanozymes toward the incoming THR. The signal ratio (ICu/ICT) displayed a good linear relationship over a THR concentration range of 10.0 nM-3.0 µM with a limit of detection of 0.15 nM, and the entire THR detection process was rapidly accomplished within 5 min. The high sensitivity and selectivity of the developed electrochemical strategy guaranteed the reliable detection of THR in fruit, vegetable, and river water samples. This study provides new insights into the development of nanozymes for electrochemical analysis.

A Ce-MOF@polydopamine composite nanozyme as an efficient scavenger for reactive oxygen species and iron in thalassemia disease therapy.

Patients with ß-thalassemia are prone to complications such as cardiovascular diseases and secretory gland injury due to iron overload (IO) and reactive oxygen species (ROS) production caused by blood transfusions. Simultaneously scavenging ROS and eliminating IO using nanomedicine remains challenging. Herein, we designed a dual-functional Ce-based metal-organic framework@polydopamine (Ce-MOF@PDA) composite that integrates oxidative stress reduction and IO elimination and evaluated its protective effect on IO injury in thalassemia. Using Ce-MOF with multiple active sites as the core, dopamine, which can coordinate iron ions, was modified on the surface of Ce-MOF and spontaneously polymerized to obtain PDA with iron elimination ability. Dopamine modification also adjusted the Ce3+/Ce4+ ratio to further enhance the catalytic activity for scavenging ROS. Ce-MOF@PDA exhibited multiple nanozyme activities, such as superoxide dismutase- and catalase-like activities, and decreased iron-mediated oxidative stress levels in vitro. Furthermore, the serum ferritin levels and iron concentrations in the liver of IO mice were reduced following treatment with Ce-MOF@PDA, and the fecal clearance ability was comparable to that of deferoxamine. These results indicate that Ce-MOF@PDA can eliminate IO while scavenging ROS and reduce tissue damage caused by oxidative stress. Therefore, the Ce-MOF@PDA nanozyme is a promising therapeutic nanomedicine for treating thalassemia IO.

Enhanced peroxidase-like activity of MOF nanozymes by co-catalysis for colorimetric detection of cholesterol.

Metal-organic frameworks (MOFs) have been widely used as nanozymes with a great development prospect due to their unique advantages. It is known that the current Fe-based or Cu-based MOF, etc., exhibits the catalytic activity of nanozymes through the Fenton catalytic reaction. And the conversion efficiency of the Fe3+/Fe2+ or Cu2+/Cu+ cycle is key to the catalytic activity. Therefore, we proposed a novel co-catalytic method to promote the reaction rate of the rate-limiting step of Cu2+/Cu+ conversion in the Fenton reaction of Cu2+/H2O2 to enhance the catalytic activity of the nanozymes. As a proof of concept, the MoCu-2MI nanozyme with high catalytic activity was successfully synthesized using Mo-doped Cu-2MI (2-methylimidazole). By using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, MoCu-2MI exhibited higher peroxidase-like activity than pure Cu-2MI. Then, it was confirmed that the newly introduced Mo played a crucial co-catalytic role by characterizing the possible catalytic mechanism. Specifically, Mo acted as a co-catalyst to accelerate the electron transfer in the system, and then promote the Cu2+/Cu+ cycle in the Cu-Fenton reaction, which was conducive to accelerating the production of a large number of reactive oxygen species (ROS) from H2O2, and finally improve the activity. Ultimately, a biosensor platform combined with MoCu-2MI and cholesterol oxidase realized the one-step colorimetric detection of cholesterol in the range of 2-140 µM with the detection limit as low as 1.2 µM. This study provides a new strategy for regulating the activity of MOF nanozymes.

Three-in-one covalent organic framework nanozyme: Self-reporting, self-correcting and light-responsive for fluorescence sensing 3-nitrotyrosine.

Most current redox-type nanozyme-based colorimetric sensing platforms are susceptible to interference from the reductant when using chromogenic probe, and the unstable H2O2 used in the peroxidase-like nanozyme-based systems is prone to difficulty in sensing signal reproducibility, while peroxidase-like nanozyme with oxidase-mimicking activity is easy to bring background interference by O2. Since the strong structural designability of covalent organic frameworks (COFs) endows them great application value in the sensing fields, therefore, we envision the construction a COF oxidase-like nanozyme-based controllable sensing system that integrates self-reporting, self-correcting and light-responsive functions to avoid these affects. Herein, 3-nitrotyrosine (3-NT) biomarker was selected as model analyte. 1,3,5-triformylphloroglucinol (Tp) and 3,6-diaminoacridine (DA) were acted as building monomers of the multifunctional COF nanozyme (termed as TpDA). Owing to the excellent light-responsive oxidase-mimicking property of TpDA, 3-NT can be efficiently oxidized, the inner filter effect (IFE) between TpDA and the 3-NT oxidation product greatly quenches the intrinsic fluorescence of TpDA, making it a controllable self-reporting system for fluorescence turn-off sensing 3-NT. Additionally, the excessive reactive oxygen species (ROS) that generated continuously during photocatalysis can resist the interference of endogenous reductants. This study not only provides new insights to avoid the interference of H2O2, background and reductants from conventional redox-type nanozyme-based colorimetric systems but also opens avenues to rational construct versatile COF nanozyme-based sensor.

Rational synthesis of FeNiCo-LDH nanozyme for colorimetric detection of deferoxamine mesylate.

The accurate surveillance and sensitive detection of deferoxamine mesylate (DFO) is of great significance to ensure the safety of thalassemia major patients. Herein, we report a new nanozyme-based colorimetric sensor platform for DFO detection. First, a metal-organic framework (ZIF-67) was used as a precursor for the synthesis of FeNiCo-LDH (Layered Double Hydroxide, LDH) via an ion exchange reaction stirring at room temperature. The results of electron microscopy and nitrogen adsorption-desorption showed that FeNiCo-LDH exhibited a 3D hollow and mesopores structure, which supplied more exposed active sites and faster transfer of mass. The as-prepared FeNiCo-LDH showed superior peroxidase-like activity with a low Km and high υmax. It can catalyze the decomposition of H2O2 to generate reactive oxygen species (ROS) and further react with 3,3',5,5'-tetramethylbenzidine (TMB) to form blue oxidized TMB (oxTMB), which has a characteristic absorption at 652 nm. Once DFO was introduced, it can complex with FeNiCo-LDH and inhibit the peroxidase-like activity of FeNiCo-LDH, making the color of oxTMB lighter. The quantitative range of DFO was 0.8-28 µM with a detection limit of 0.71 µM. This established method was applied to the detection of DFO content in urine samples of thalassemia patients, and the spiked recoveries were falling between 97.7% and 109.6%, with a relative standard deviation was less than 5%, providing a promising tool for the clinical medication of thalassemia patients.

A Single Aptamer-Dependent Sandwich-Type Biosensor for the Colorimetric Detection of Cancer Cells via Direct Coordinately Binding of Bare Bimetallic Metal-Organic Framework-Based Nanozymes.

A typical colorimetric sandwich-type sensor relies on dual antibodies/aptamers to specifically visualize the targets. The requirement of dual antibodies/aptamers and low signal intensity inevitably increases the design difficulty and compromises the sensing sensitivity. In this work, a novel sandwich-type aptasensor was developed using single aptamer-functionalized magnetic nanoparticles as a specific recognition unit to target cancer cells and a bimetallic metal-organic frameworks (MOFs)-based nanozymes as a colorimetric signal amplification unit. The well-defined crystalline structure of UIO-66 MOFs enabled the introduction of Fe/Zr bimetal nodes, which possessed integrated properties of the peroxidase-like nanozyme activity and direct coordinately binding to the cell surface. Such a novel construction strategy of sandwich-type aptasensors achieved simple, sensitive, and specific detection of the target cancer cells, which will inspire the development of biosensors.

Dextran-coated Gd-based ultrasmall nanoparticles as phosphatase-like nanozyme to increase ethanol yield via reduction of yeast intracellular ATP level.

Nanozymes-functional materials that possess intrinsic enzyme-like characteristics-have gained tremendous attention in recent years owing to their unique advantages; however, further research is required to understand their scope in biological applications. In this study, dextran-coated nanogadolinia (DCNG) was synthesised, and its phosphatase mimetic activity was demonstrated. Specifically, the dephosphorylation of adenosine triphosphate (ATP), an important biomolecule, by DCNG was investigated. The results showed that DCNG could selectively catalyse the hydrolysis of the terminal high-energy phosphate bonds of ATP under physiological conditions. Furthermore, the biocompatible DCNG, with remarkable phosphatase mimicking activity, decreased the intracellular ATP content by dephosphorylation and increased ethanol yield during glucose fermentation by S. cerevisiae. These results indicate potential alternatives for improving ethanol yields and exploring novel biological applications of nanozymes.

Preparation of cationic hierarchical porous covalent organic frameworks for rapid and effective enrichment of perfluorinated substances in dairy products.

Perfluorinated substances (PFASs) are harmful pollutants that have environmental persistence and high bioaccumulation. Effective sample pretreatment must be performed to detect trace or even ultra-trace PFASs in actual samples because of their extremely low contents in complex samples. In this study, a cationic hierarchical porous covalent organic frameworks (C-H-COF) were customized via a template-assisted strategy using polystyrene spheres (PS) as sacrificial materials and a post-synthetic modification method. C-H-COF showed good adsorption selectivity for PFASs owing to the dual effects of the full utilization of the internal adsorption sites and electrostatic interaction. The key role of electrostatic attraction in the extraction of PFASs using C-H-COF was further proven by density functional theory (DFT) calculations. The maximum adsorption capacity of the C-H-COF for perfluorooctanoic acid (PFOA) was 400 mg·g⁻1, which was superior to that of microporous COFs (M-COF) and hierarchical porous COFs without cationic functionalization (H-COF). Accordingly, an analytical method for sensitively detecting five PFASs was established by employing C-H-COF as a dispersive solid phase extraction (DSPE) adsorbent combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the limits of detection were 0.011‒0.29 ng·L⁻1. Moreover, the hierarchical porous structure of the C-H-COF accelerated the mass transfer of analytes so that the extraction process could be completed within 10 min. This method was employed to analyze PFASs in dairy products, in which the ultra-trace levels of analytes were quickly determined with spiked recoveries of 80.1‒112.6%. This work not only provides a rational synthetic strategy for novel ionic hierarchical porous COFs but also helps to expand the application of COFs in sample pretreatment.

Ultrasmall phosphatase-mimicking nanoceria with slight self-colour for nonredox nanozyme-based colorimetric sensing.

Nanozyme-based colorimetric sensing has attracted significant interest in recent years, and a number of redox-type nanozyme-based colorimetric sensors based on peroxidase and oxidase mimics have been reported. However, conventional redox-type nanozyme-based colorimetric sensing is affected by interference from the endogenous reductants present in actual samples. Herein, we describe the development of a homogeneous nonredox-type nanozyme-based colorimetric sensor that exploits the intrinsic phosphatase-like activity of CeO2. Specifically, colorimetric detection platforms for fluoride ions, zearalenone, and hydrogen peroxide were constructed based on activity inhibition, aptamer-assisted gate control, and plasmonic nanoparticle growth, respectively. Thus, this study reports a versatile route for constructing nonredox nanozyme-based colorimetric sensors that are not affected by interference from endogenous reductants and are thus highly promising for use in food safety and bioassay applications.

Colorimetric detection of creatinine based on specifically modulating the peroxidase-mimicking activity of Cu-Fenton system.

Creatinine (CR) has always been considered as a prime important indicator for evaluating of renal dysfunction. Nevertheless, the literature still lacks in methods that fulfill the requirements for detecting CR effectively. Therefore, the development of a visual sensing method for the detection of CR specifically and sensitively is definitely desirable. To provide a solution, a colorimetric sensing platform for monitoring CR was constructed based on the regulation effect of CR on the peroxidase-mimicking activity of MoO3-Cu2+ system. Here, the prepared MoO3 itself does not have the catalytic activity of peroxidase mimics, but it can be used as a co-catalyst. In the presence of CR, the Cu2+ Fenton-like reaction can be promoted through co-catalysis of MoO3, so as to facilitate the production of more reactive oxygen species (ROS) and accelerate the oxidation process of 3,3',5,5'-tetramethylbenzidine (TMB). As a result, the regulation of MoO3-Cu2+ peroxidase-like activity can be achieved by adding different concentrations of CR. The higher the concentrations of CR, the stronger the catalytic activity for MoO3-Cu2+/CR. Experimental results showed that the colorimetric sensing strategy proposed in this paper can be successfully applied to the analysis of CR in human serum samples.

Enhancing the peroxidase-like activity of MIL-88B by ligand exchange with polydopamine.

Metal-organic frameworks (MOFs) as nanozymes have been widely used in biosensing. However, MOFs have inherent defects of easy agglomeration, leading to the stacking of active surfaces. In addition, the low conductivity of MOFs is not conducive to the electron migration in the Fenton-like reaction, which leads to a further decrease in catalytic activity and severely restricts their application. In response to the above problems, it makes sense to develop a method to improve both the dispersion and conductivity of MOFs. Here, a simple ligand exchange method with polydopamine (PDA) was used to synthesize MOF PDA-MIL-88B. PDA-MIL-88B shows stronger peroxidase-like activity than MIL-88B. One reason is the good dispersibility of PDA-MIL-88B, which is conducive to exposing the active surface. In addition, the reduced electrochemical impedance of PDA-MIL-88B increases its electrical conductivity, which is favorable for electron migration in the Fenton-like reaction. As a result, PDA-MIL-88B can better catalyze 3,3',5,5'-tetramethylbenzidine to achieve redoximorphic color changes. PDA-MIL-88B can be used to detect glucose in human serum with good sensitivity and selectivity. This work can provide a strategy for MOFs to enhance the enzyme-like activity.

MOF-derivated MnO@C nanocomposite with bidirectional electrocatalytic ability as signal amplification for dual-signal electrochemical sensing of cancer biomarker.

Dual-signal strategy has great potential in improving the accuracy and sensitivity of cancer biomarker determination. However, most sensors based on nanomaterials as signal amplification usually output single detectable signal. It is still a challenge to achieve dual-signal sensing of biomarkers with nanomaterials as signal amplification. Herein, MnO@C nanocomposite was prepared with Mn-MOF-74 as precursor by pyrolysis. It possesses bidirectional electrocatalytic ability toward both oxidation and reduction of H2O2 for its fully exposed crystal facets. After loading AuNPs, MnO@C@AuNPs can connect aptamer (Apt) via Au-S and then as a signal amplification for the construction of sandwich-type aptasensor for dual-signal electrochemical sensing of cancer biomarker. Thus, taking mucin 1 (MUC1) as a model system. The aptasensor has the parallel output of differential pulse voltammetry (DPV) and chronoamperometry responses based on oxidation and reduction of H2O2, respectively, which implemented sensitive and accurate measurements to avoid false results. The linear response ranges of 0.001 nM-100 nM (detection limit of 0.31 pM) for DPV technique and 0.001 nM-10 nM (detection limit of 0.25 pM) for chronoamperometry technique were obtained. It opens up a new way to design elegant dual-signal aptasensors with potential applications in early disease diagnosis.

A gas-pressure-assisted ratiometric atomic flame assay for the point-of-care testing of tumor-cell-derived exosomes.

The multicolor-based point-of-care testing (POCT) of tumor cell-derived exosomes is of vital importance for understanding tumor growth and metastasis. Multicolor-based ratiometric signals most often rely on molecular optics, such as fluorescence resonance energy transfer (FRET)-dependent molecular fluorescence and localized surface plasmon resonance (LSPR)-related molecular colorimetry. However, finding acceptable FRET donor-acceptor fluorophore pairs and the kinetically slow color responses during size-related molecular colorimetry have greatly impeded POCT applications. Herein, an atomic flame was used to develop a visual sensing platform for the POCT of tumor-cell-derived exosomes. In comparison with common molecular optics, the atomic flame possessed the advantages of providing both a variety of ratiometric flame signals and fast response sensitivity. The integration of a gas-pressure-assisted flame reaction and dual-aptamer recognition guaranteed the sensitive and selective analysis of exosomes with a low limit of detection (LOD) of 7.6 × 102 particles per mL. Such a novel optical signal will inspire the development of more user-friendly POCT approaches.

Multicolor and photothermal dual-mode assay of alkaline phosphatase based on the UV light-assisted etching of gold nanorods.

A multicolor and photothermal dual-mode assay for sensitive alkaline phosphatase (ALP) determination was realized based on the 3,3',5,5'-tetramethylbenzidine (TMB)-induced etching of gold nanorods (AuNRs). TMB was oxidized under ultraviolet light irradiation to form TMB+. In the presence of ALP, ascorbic acid phosphate (AAP) is converted to ascorbic acid, which can then reduce the levels of TMB+, resulting in lower concentrations of TMB+. The remaining TMB+ was transformed into TMB2+ after the addition of HCl solution. AuNRs were etched by TMB2+ to produce a multicolor and photothermal change. Based on the degree of AuNRs etching, this highly sensitive dual-mode assay provided a linear range of 1.0-8.0 mU/mL, with detection limits of 0.34 mU/mL for the multicolor assay and 0.11 mU/mL for the photothermal assay. This method was successfully applied to the determination of ALP in serum samples.

Ce-MOF with Intrinsic Haloperoxidase-Like Activity for Ratiometric Colorimetric Detection of Hydrogen Peroxide.

Metal-organic framework (MOF) nanozymes, as emerging members of the nanozymes, have received more and more attention due to their composition and structural characteristics. In this work, we report that mixed-valence state Ce-MOF (MVCM) has intrinsic haloperoxidase-mimicking activity. MVCM was synthesized by partial oxidation method using Ce-MOF as a precursor. In the presence of H2O2 and Br-, MVCM can catalyze oxidative bromination of chromogenic substrate phenol red (PR) to produce the blue product bromophenol blue (Br4PR), showing good haloperoxidase-like activity. Because of the special chromogenic substrate, we constructed a ratiometric colorimetric-sensing platform by detecting the absorbance of the MVCM-(PR, Br-) system at wavelengths of 590 and 430, for quantifying H2O2, where the detection limit of the H2O2 is 3.25 µM. In addition, the haloperoxidase-mimicking mechanism of the MVCM is proposed. Moreover, through enzyme kinetics monitoring, the Km (H2O2 and NH4Br) of the MVCM is lower than that of cerium oxide nanomaterials, indicating that the MVCM has a stronger binding affinity for H2O2 and NH4Br than other materials. This work provides more application prospects for the development of nanozymes in the field of biosensors in the future.