Bifunctional MIL-53(Fe) with pyrophosphate-mediated peroxidase-like activity and oxidation-stimulated fluorescence switching for alkaline phosphatase detection

A dual-mode biosensor based on metal organic framework-coated upconversion composites with near-infrared luminescence and peroxidase-like activity for the detection of alkaline phosphatase and glucose

An abnormal level of alkaline phosphatase (ALP) in serum is related to many diseases, such as breast cancer, prostate cancer, hepatitis, and diabetes. The level of glucose in the blood is related to diabetes or hypoglycemia. Given the close correlation between ALP and glucose in various diseases, it is essential to establish an accurate, sensitive, and selective assay for monitoring the levels of ALP and glucose in serum. As luminescent materials, upconversion nanoparticles (UCNPs) stand out in the design of biosensors because of their high photostability, large anti-Stokes shifts and low background interference. Additionally, metal organic frameworks (MOFs) are a class of functional porous materials, and their adjustable pore size structure and high specific surface area expose many catalytic sites, making MOFs excellent catalysts and ideal materials for constructing artificial enzymes. Herein, a fluorescent and colorimetric dual-mode probe based on a multifunctional composite (UCNP@MOF) with upconversion luminescence and peroxidase-like activity was proposed for the detection of ALP and glucose. Under the optimal conditions, the detection limits of ALP and glucose by the fluorescence method were 0.046 U/L and 0.079 μM, respectively. Furthermore, the method was used to determine ALP and glucose in serum samples, and the detection results were similar to those of commercial kits; moreover, the recoveries were in the range of 92.7-105.4 %, indicating great potential for accurate and sensitive detection of ALP and glucose in biological samples.

Advances in metal-organic frameworks for optically selective alkaline phosphatase activity monitoring: a perspective

The study of Metal-Organic Frameworks (MOFs) has gained significant momentum due to their remarkable properties, including adjustable pore sizes, extensive surface area, and customizable compositions, which have urged scientists to investigate their applicability in pertinent societal issues such as water absorption, environmental remediation, and sensor technology. MOFs have the ability to transport and detect specific biomolecules, including proteins. One such biomolecule is alkaline phosphatase (ALP) that can be influenced by various diseases and can lead to severe consequences when its regulation is disrupted. The porous nature of MOFs and their tunable nature allows them to selectively adsorb, interact directly or indirectly with ALP. This ultimately influences the electronic and optical properties of the MOF, leading to measurable changes. Early detection and continuous monitoring of ALP play a crucial role in the use of an effective treatment, and recent studies have shown that MOFs are effective in detecting alkaline phosphatases. This manuscript offers a thorough examination of the potential biomedical applications of MOFs for monitoring alkaline phosphatase and envisions possible future trends in this field.

Silver ion-regulated reliable and rapid detection technique for alkaline phosphatase based on surface-enhanced Raman spectroscopy

The primary characteristics of a clinical assay are its accuracy and speed. For alkaline phosphatase (ALP) monitoring in medical treatment, a rapid, reliable surface-enhanced Raman scattering (SERS) detection technique was designed based on the controlled "hot spot" effect caused by the mediation of silver ions (Ag+). Consisting of functionalized Au nanoparticles (NPs), Ag+, and the enzyme substrate 2-phospho-L-ascorbic acid triso-dium salt (AAP), the fabricated detection technique can achieve a reliable clinical assay for ALP detection in human serum within several minutes. Herein, due to the coordination interaction of Ag+ and the cyano group (-CN), Ag+ can coordinate with p-mercaptobenzonitrile (MBN) modified on the surface of Au NPs, leading to the connection of adjacent Au NPs in a controllable manner to form a chain structure, in which the SERS signal of MBN at 2228 cm-1 in the Raman silent region would be highly amplified. Under the enzymatic biocatalysis of ALP, AAP was converted into ascorbic acid (AA). AA triggered the reduction of Ag+ into Ag0, resulting in a decrease in the concentration of Ag+. Meanwhile, the decrease in the SERS intensity of MBN was well-controlled and was recognized with the increased amounts of ALP. Based on this, the SERS detection technique for ALP was established. The limit of detection (LOD) for the detection of ALP was as low as 1.23 pg mL-1 (0.005 U L-1). Because of all these characteristics and its ultrahigh stability, this SERS detection technique is an important point-of-care candidate for the reliable, efficacious, and highly sensitive detection of ALP.

The Exploration of Nanozymes for Biosensing of Pathological States Tailored to Clinical Theranostics

The nanozymes (NZs) are the artificial catalyst deployed for biosensing with their uniqueness (high robustness, surface tenability, inexpensive, and stability) for obtaining a better response/miniaturization of the varied sensors than their traditional ancestors. Nowadays, nanomaterials with their broadened scale such as metal-organic frameworks (MOFs), and metals/metal oxides are widely engaged in generating NZ-based biosensors (BS). Diverse strategies like fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and electrochemical sensing principles were implemented for signal transduction of NZs. Despite broad advantages, numerous encounters (like specificity, feasibility, stability, and issues in scale-up) are affecting the potentialities of NZs-based BS, and thus need prior attention for a promising exploration for a revolutionary outcome in advanced theranostics. This review includes different types of NZs, and the progress of numerous NZs tailored bio-sensing techniques in detecting abundant bio analytes for theranostic purposes. Further, the discussion highlighted some recent challenges along with their progressive way of possibly overcoming followed by commercial outbreaks.

A ratiometric fluorescence sensor for detection of organophosphorus pesticides based on enzyme-regulated multifunctional Fe-based metal-organic framework

The residues of organophosphorus pesticides (OPs) are increasing environmental pollution and public health concerns. Thus, the development of simple, convenient and sensitive method for detection of OPs is crucial. Herein, a multifunctional Fe-based MOF with fluorescence, catalytic and adsorption, is synthesized by a simple one-pot hydrothermal method. The ratiometric fluorescence sensor for detection of OPs is constructed by using only one multifunctional sensing material. The NH2-MIL-101(Fe) is able catalyze the o-phenylenediamine (OPD) into 2,3-diaminophenazine (DAP) in the presence of H2O2. The generated DAP can significantly quench the intrinsic fluorescence of NH2-MIL-101(Fe) by the fluorescence resonance energy transfer (FRET) and internal filtration effect (IFE), while producing a new measurable fluorescence. Without immobilization or molecular imprinting, pyrophosphate ion (PPi) can inhibit the peroxidase-like activity of the NH2-MIL-101(Fe) by chelating with Fe3+/Fe2+ redox couple. Moreover, PPi can also be hydrolyzed by alkaline phosphatase (ALP), the presence of OPs inhibits the activity of ALP, resulting in the increase of extra PPi preservation and signal changes of ratiometric fluorescence, the interactions of ALP with different OPs are explored by molecular docking, the OPs (e.g., glyphosate) interact with crucial amino acid residues (Asp, Ser, Ala, Lys and Arg) are indicated. The proposed sensor exhibits excellent detection performance for OPs with the detection limit of 18.7 nM, which provides a promising strategy for detection of OPs.

Hydroxyl radical-mediated synthesis of carbonyl functionalized graphene quantum dots-like as enzyme mimics with tunable fluorescence emission

The synthesis of graphene quantum dots-like enriched with specific oxygenated groups (o-GQDs) exhibiting great catalytic performance offers a promising tool for diagnosis and biomedicine, but introducing specific oxygen groups remains a challenge. Here, we propose a mild synthetic protocol for producing regulated fluorescence emission (from blue to yellow) carbonyl functionalized GQDs with double catalytic function through Fe3O4-catalyzed hydroxyl radical (·OH) oxidation the precursors like graphene oxide, polyaniline (PANI) and polydopamine (PDA). The method can be carried out at room temperature than the traditional high-temperature oxidation in concentrated acid. Interestingly, o-GQDs exhibit excellent peroxidase (POD)- and ascorbate oxidase-like activity. XPS characterization showed a significant increase in carbonyl content in o-GQDs compared to the precursor, even a 14-fold increase in blue-emitting iron-doped GQDs (b-Fe-GQDs). The introduction of Fe3O4 during the synthesis process results in a minor degree of Fe doping, which enhances the catalytic activity of b-Fe-GQDs through coordination with N. Based on this feature, highly sensitive single-signal and ultra-selective dual-signal methods for alkaline phosphatase detection were developed. This low cost and safe synthesis strategy paves the way for practical usage of o-GQDs.

Metal-Organic Framework Based on Ratiometric dual-Fluorescent Sensor Using for Accurate Quantification and on-Site Visual Detection of Ascorbic Acid

Ascorbic acid is very important to the metabolic process of the body, but excessive intake can lead to diarrhea, kidney calculi and stomach cramps. However, complicated production procedures and harsh experimental settings limit many detection methods, and a simpler and more accurate measurement method is needed. In this study, a smartphone-assisted ratiometric fluorescence sensor was developed for the portable analysis of ascorbic acid. Leveraging the catalytic properties of MIL-53(Fe) to expedite the conversion of H2O2 into hydroxyl radicals, thereby facilitating the oxidation of o-phenylenediamine and terephthalic acid bridging ligand. The sensor showcased exceptional sensitivity in detecting ascorbic acid within a linear range of 0.3-100 µM, boasting an impressive limit of detection at 0.15 µM. Furthermore, through the utilization of color extraction RGB values captured by smartphones, accurate detection of ascorbic acid was achieved with a detection limit of 0.4 µM. Real fruit samples exhibited robust spiked recovery rates ranging from 91 to 119%, accompanied by relative standard deviations ≤ 4.7%. The MIL-53(Fe) nanozyme-based smartphone-assisted ratiometric fluorescence sensor offers an ascorbic acid fluorescence detection device that is visible, accurate, sensitive, and reasonably priced.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

Sensing the invisible: Ultrasensitive and selective colorimetric detection of E. coli O157:H7 based on masking the peroxidase-mimetic activity of aptamer-modified Au/Fe3O4

Escherichia coli O157:H7 (E. coli O157:H7) emerges as a significantly worrisome pathogen associated with foodborne illnesses, emphasizing the imperative for creating precise detection tools. In this investigation, we developed a sensitive colorimetric biosensor for detecting E. coli O157:H7. It was constructed using a nanozyme comprised of Au@Fe3O4 NPs, which was fabricated and subsequently modified with an aptamer (Apt). The nanozyme harnesses its inherent peroxidase-like activity to facilitate the transformation of reduced TMB into its oxidized form in the presence of H2O2, resulting in a noticeable shift to a blue color. However, the presence of E. coli O157:H7 effectively diminished the absorbance of oxidized TMB. Consequently, the normalized absorbance at 652 nm demonstrates a linear decrease corresponding to concentrations of E. coli O157:H7 within the range of 101 to 108 CFU mL-1 with a low limit of detection (LOD, S/N = 3) of 3 CFU mL-1.

Based ATP-gating mechanism for detection of alkaline phosphatase in single-glass micropipettes functionalized by three-dimensional DNA network

The construction of gating system in artificial channels is a cutting-edge research direction in understanding biological process and application sensing. Here, by mimicking the gating system, we report a device that easily synthesized single-glass micropipettes functionalized by three-dimensional (3D) DNA network, which triggers the gating mechanism for the detection of biomolecules. Based on this strategy, the gating mechanism shows that single-glass micropipette assembled 3D DNA network is in the "OFF" state, and after collapsing in the presence of ATP, they are in the "ON" state, at which point they exhibit asymmetric response times. In the "ON" process of the gating mechanism, the ascorbic acid phosphate (AAP) can be encapsulated by a 3D DNA network and released in the presence of adenosine triphosphate (ATP), which initiates a catalyzed cascade reaction under the influence of alkaline phosphatase (ALP). Ultimately, the detection of ALP can be responded to form the fluorescence signal generated by terephthalic acid that has captured hydroxyl radicals, which has a detection range of 0-250 mU/mL and a limit of detection of 50 mU/mL. This work provides a brand-new way and application direction for research of gating mechanism.

The Application of Metal-Organic Frameworks in Water Treatment and Their Large-Scale Preparation: A Review

Over the last few decades, there has been a growing discourse surrounding environmental and health issues stemming from drinking water and the discharge of effluents into the environment. The rapid advancement of various sewage treatment methodologies has prompted a thorough exploration of promising materials to capitalize on their benefits. Metal-organic frameworks (MOFs), as porous materials, have garnered considerable attention from researchers in recent years. These materials boast exceptional properties: unparalleled porosity, expansive specific surface areas, unique electronic characteristics including semi-conductivity, and a versatile affinity for organic molecules. These attributes have fueled a spike in research activity. This paper reviews the current MOF-based wastewater removal technologies, including separation, catalysis, and related pollutant monitoring methods, and briefly introduces the basic mechanism of some methods. The scale production problems faced by MOF in water treatment applications are evaluated, and two pioneering methods for MOF mass production are highlighted. In closing, we propose targeted recommendations and future perspectives to navigate the challenges of MOF implementation in water purification, enhancing the efficiency of material synthesis for environmental stewardship.

Tunable metal-organic frameworks assist in catalyzing DNAzymes with amplification platforms for biomedical applications

Various binding modes of tunable metal organic frameworks (MOFs) and functional DNAzymes (Dzs) synergistically catalyze the emergence of abundant functional nanoplatforms. Given their serial variability in formation, structural designability, and functional controllability, Dzs@MOFs tend to be excellent building blocks for the precise "intelligent" manufacture of functional materials. To present a clear outline of this new field, this review systematically summarizes the progress of Dz integration into MOFs (MOFs@Dzs) through different methods, including various surface infiltration, pore encapsulation, covalent binding, and biomimetic mineralization methods. Atomic-level and time-resolved catalytic mechanisms for biosensing and imaging are made possible by the complex interplay of the distinct molecular structure of Dzs@MOF, conformational flexibility, and dynamic regulation of metal ions. Exploiting the precision of DNAzymes, MOFs@Dzs constructed a combined nanotherapy platform to guide intracellular drug synthesis, photodynamic therapy, catalytic therapy, and immunotherapy to enhance gene therapy in different ways, solving the problems of intracellular delivery inefficiency and insufficient supply of cofactors. MOFs@Dzs nanostructures have become excellent candidates for biosensing, bioimaging, amplification delivery, and targeted cancer gene therapy while emphasizing major advancements and seminal endeavors in the fields of biosensing (nucleic acid, protein, enzyme activity, small molecules, and cancer cells), biological imaging, and targeted cancer gene delivery and gene therapy. Overall, based on the results demonstrated to date, we discuss the challenges that the emerging MOFs@Dzs might encounter in practical future applications and briefly look forward to their bright prospects in other fields.

Rapid and sensitive detection of alkaline phosphatase and glucose oxidase activity through fluorescence and colorimetric dual-mode analysis based on CuO NPs@ZIF-8 mediated enzyme-cascade reactions

The combined application of nanozymes and natural enzymes has received widespread attention in recent years. In this work, a simple and efficient method was used to synthesize a composite material of CuO nanoparticle-modified zeolitic imidazolate framework-8 (CuO NPs@ZIF-8) with multiple enzyme activities (glucose oxidase-like and hydrolase-like activities) to detect the activity of natural enzymes through fluorescence and colorimetric (UV-vis) dual-mode detection. The hydrolase- and oxidase-like activities of CuO NPs@ZIF-8 show an acceptable affinity with l-ascorbic acid 2-phosphate trisodium (AAP) and o-phenylenediamine (OPD). Using the developed sensor, highly sensitive detection of natural enzymes glucose oxidase (GOX) and alkaline phosphatase (ALP) was achieved through both fluorescent and colorimetric analyses with a wide linear range (fluorescence for GOX: 0.86-1.23 × 105 mU mL-1, UV-vis for GOX: 0.081-1.62 × 105 mU mL-1; fluorescence for ALP: 0.042-1.20 × 104 mU mL-1, UV-vis for ALP: 0.0046-1.23 × 104 mU mL-1) and low LOQs (fluorescence for GOX: 0.86 mU mL-1, UV-vis for GOX: 0.081 mU mL-1; fluorescence for ALP: 0.042 mU mL-1, UV-vis for ALP: 0.0046 mU mL-1). Compared to the other fluorescent and colorimetric sensors, this sensor has better catalytic activity due to the addition of GOX and ALP, which can amplify the detection signal and improve the sensitivity. This is the first time that composite material CuO NPs@ZIF-8 with "tandem enzyme" activity was synthesized and applied in the detection of enzyme activity. Additionally, the proposed fluorescent and UV-vis platforms exhibit the capability to detect GOX and ALP in serum samples with satisfactory recovery, indicating potential application prospects in biochemical analysis.

Construction of Aggregation-Induced Emission Molecule-MnO2 Composite Nanoprobe and Its Application in Alkaline Phosphatase Detection

Alkaline phosphatase (ALP) is among the most studied enzymes by far, playing an important role in the metabolism of organisms and the regulation of protein activity. Herein, a label-free composite nanoprobe is constructed by combining inorganic nanomaterials and aggregation-induced emission (AIE) molecule to achieve highly sensitive and selective detection of ALP. Negatively charged 9,10-bis [2-(6-sulfonatopropoxyl) naphthylethenyl] anthracene (BSNVA) molecule is synthesized, which has the AIE performance and can be assembled on the surface of amino-SiO₂ nanoparticles through electrostatic interaction for fluorescence enhancement. MnO₂ nanosheets are rich in negative charges, enabling them to be wrapped on the surface of the amino-SiO₂ nanosphere to shield the positive charge on its surface, making it impossible for BSNVA to accumulate on the surface and then weakening the bio-fluorescence of the system. Furthermore, with catalyzed substrates induced by ALP, generating ascorbic acid and the redox reaction between ascorbic acid and MnO₂, the nanoprobe helps in realizing the high-sensitivity detection of ALP with a detection limit of 0.38 mU/mL. The proposed strategy requires no complex cleaning and modification processes and can overcome the quenching effect caused by the aggregation of traditional organic dyes, proving to be a simple, low-cost and "turn-on" fluorescent detection method for ALP.

Stimuli-responsive aggregation-induced emission of molecular probes by electrostatic and hydrophobic interactions: Effect of organic solvent content and application for probing of alkaline phosphatase activity

We suggest that aggregation-induced emission (AIE) molecular probes with single charged/reactive group can exist in the formation of nanostructures but not monomers at extremely low organic solvent content. The nanoaggregates show good dispersivity and emit week emission. Stimuli-responsive assembly of nanoaggregates by electrostatic interactions can turn on the fluorescence, facilitating the design of biosensors with single-charged molecular probes as the AIE fluorogens. To prove the concept, tetraphenylethene-substituted pyridinium salt (TPE-Py) was used as the AIE fluorogen for probing of alkaline phosphatase (ALP) activity with pyrophosphate ion (PPi) as the enzyme substrate. The dynamic light scattering and transmission electron microscope experiments demonstrated that TPE-Py probes existed in aqueous solution at nanometer size and morphology. Stimuli such as the negatively charged PPi, citrate, ATP, ADP, NADP and DNA could trigger the aggregation of the positively charged TPE-Py nanoparticles, thus enhancing the fluorescence via AIE effect. ALP-enzymatic hydrolysis of PPi into two phosphate ions (Pi) limited the aggregation of TPE-Py nanoparticles. The strategy was used for the assay of ALP with a low detection limit (1 U/L) and wide linear range (1-200 U/L). We also investigated the effect of organic solvent content on the AIE process and found that high concentration of organic solvent can prevent the hydrophobic interaction between AIE molecules but show no essential influence on the electrostatic interaction-mediated assembly. The work should be evaluable for understanding AIE phenomenon and developing novel, simple and sensitive biosensors using a molecular probe with single charged/reactive group as the signal reporter.

A label-free ThT-assisted fluorescence detection strategy of alkaline phosphatase activity based on MnO2 nanosheets

Alkaline phosphatase (ALP) is a metalloenzyme, the level of which is clinically significant as an abnormality of ALP activity results in several diseases. In the present study, we introduced a MnO₂ nanosheet-based assay for ALP detection employing the adsorption and reduction characteristics of G-rich DNA probes and ascorbic acid (AA), respectively. Ascorbic acid 2-phosphate (AAP) was utilized to act as a substrate for ALP which hydrolyzes AAP generating AA. In the absence of ALP, MnO₂ nanosheets adsorb the DNA probe destructing the G-quadruplex formation and showing no fluorescence emission. On the contrary, being present in the reaction mixture ALP hydrolyzes AAP yielding AA, then the AA reduce the MnO₂ nanosheets into Mn²⁺, hence, the probe is free to react with a dye, thioflavin T (ThT), and synthesizes ThT/G-quadruplex to spark high fluorescence intensity. Therefore, under optimized conditions (250 nM DNA probe, 8 μM ThT, 96 μg/mL MnO₂ nanosheets, and 1 mM AAP) the sensitive and selective measurement of ALP activity can be achieved through the change of fluorescence intensity, with a linear range and a limit of detection of 0.1-5 U/L and 0.045 U/L. Our assay exhibited its potential to assess the ALP inhibitor when in an inhibition assay Na₃VO₄ inhibited ALP with an IC50 value of 0.137 mM and also was validated in clinical samples.

A facile and sensitive magnetic relaxation sensing strategy based on the conversion of Fe3+ ions to Prussian blue precipitates for the detection of alkaline phosphatase and ascorbic acid oxidase

Herein, a novel magnetic relaxation sensing strategy based on the change in Fe³⁺ content has been proposed by utilizing the conversion of Fe³⁺ ions to Prussian blue (PB) precipitates. Compared with the common detection approach based on the valence state change of Fe³⁺ ions, our strategy can cause a larger change in the relaxation time of water protons and higher detection sensitivity since PB precipitate can induce a larger change in the Fe³⁺ ion concentration and has a weaker effect on the relaxation process of water protons relative to Fe²⁺ ions. Then, we employ alkaline phosphatase (ALP) as a model target to verify the feasibility and detection performance of the as-proposed strategy. Actually, ascorbic acid (AA) generated from the ALP-catalyzed L-ascorbyl-2-phosphate hydrolysis reaction can reduce potassium ferricyanide into potassium ferrocyanide, and potassium ferrocyanide reacts with Fe³⁺ to form PB precipitates, leading to a higher relaxation time. Under optimum conditions, the method for ALP detection has a wide linear range from 5 to 230 mU/mL, and the detection limit is 0.28 mU/mL, sufficiently demonstrating the feasibility and satisfactory analysis performance of this strategy, which opens up a new path for the construction of magnetic relaxation sensors. Furthermore, this strategy has also been successfully applied to ascorbic acid oxidase detection, suggesting its expansibility in magnetic relaxation detection.

Recent Advances in Construction and Application of Metal-Nanozymes in Pharmaceutical Analysis

Nanozymes, made of emerging nanomaterials, have similar activity to natural enzyme and exhibit promising applications in in the fields of environment, biology and medicine, and food safety science. In recent years, with the deep finding and research to nanozymes by researchers, its application in field of pharmaceutical analysis has emerged gradually, possessing great significance in drug safety evaluation and quality control. This review summarizes the construction of metal nanozymes, strategies to improve their performance and their application in pharmaceutical detection and analysis, especially in detection of target analytes consisting of small molecule medicine macromolecule, toxic and others, which proposes theoretical foundation for development of nanozymes in this field. At the same time, it also provides opportunities and challenges for the construction and application of new nanozymes.

Bioelectrochemical systems-based metal removal and recovery from wastewater and polluted soil: Key factors, development, and perspective

Bioelectrochemical systems (BES) are considered efficient and sustainable technologies for bioenergy generation and simultaneously removal/recovery metal (loid)s from soil and wastewater. However, several current challenges of BES-based metal removal and recovery, especially concentrating target metals from complex contaminated wastewater or soil and their economic feasibility of engineering applications. This review summarized the applications of BES-based metal removal and recovery systems from wastewater and contaminated soil and evaluated their performances on electricity generation and metal removal/recovery efficiency. In addition, an in depth review of several key parameters (BES configurations, electrodes, catalysts, metal concentration, pH value, substrate categories, etc.) of BES-based metal removal and recovery was carried out to facilitate a deep understanding of their development and to suggest strategies for scaling up their specific application fields. Finally, the future intervention on multifunctional BES to improve their performances of mental removal and recovery were revealed.

Explaining chemical clues of metal organic framework-nanozyme nano-/micro-motors in targeted treatment of cancers: benchmarks and challenges

Nowadays, nano-/micro-motors are considered as powerful tools in different areas ranging from cleaning all types of contaminants, to development of Targeted drug delivery systems and diagnostic activities. Therefore, the development and application of nano-/micro-motors based on metal-organic frameworks with nanozyme activity (abbreviated as: MOF-NZs) in biomedical activities have received much interest recently. Therefore, after investigating the catalytic properties and applications of MOF-NZs in the treatment of cancer, this study intends to point out their key role in the production of biocompatible nano-/micro-motors. Since reducing the toxicity of MOF-NZ nano-/micro-motors can pave the way for medical activities, this article examines the methods of making biocompatible nanomotors to address the benefits and drawbacks of the required propellants. In the following, an analysis of the amplified directional motion of MOF-NZ nano-/micro-motors under physiological conditions is presented, which can improve the motor behaviors in the propulsion function, conductivity, targeting, drug release, and possible elimination. Meanwhile, by explaining the use of MOF-NZ nano-/micro-motors in the treatment of cancer through the possible synergy of nanomotors with different therapies, it was revealed that MOF-NZ nano-/micro-motors can be effective in the treatment of cancer. Ultimately, by analyzing the potential challenges of MOF-NZ nano-/micro-motors in the treatment of cancers, we hope to encourage researchers to develop MOF-NZs-based nanomotors, in addition to opening up new ideas to address ongoing problems.

Biocatalytic Metal-Organic Framework: Promising Materials for Biosensing

The high-efficient and specific catalysis of enzyme allow it to recognize a myriad of substrate that impels the biosensing. Nevertheless, the fragility of natural enzymes severely restricts their practical applications. Metal-organic frameworks (MOFs) with porous network and attractive functions have been intelligently employed as supports to encase enzymes for protecting them against hash environments. More importantly, the customizable construction and composition affords the intrinsic enzyme-like activity of some MOFs (known as nanozymes), which provides an alternative guideline to construct robust enzymes mimics. Herein, this review will introduce the concept of these biocatalytic MOFs, with the special emphasis on how the biocatalytic processes operated in these MOFs materials can reverse the plight of native enzymes-based biosensing. In addition, the present challenges and future outlooks in this research field are briefly put forward.

Multicolor diagnosis of salivary alkaline phosphatase triggered by silver-coated gold nanobipyramids

Alkaline phosphatase (ALP) is one of the most versatile biomarkers for early detection of several diseases, such as oral carcinomas and periodontitis; therefore, great efforts have been dedicated for developing an ALP biosensor. Multicolor detection of ALP in saliva is ideal for a point-of-care diagnosis; however, this approach is very challenging since spectral responses over wavelengths of several tens of nanometers have thus far remained difficult to achieve. In this work, a colorimetric biosensor for ALP assay has been developed based on ALP affinity to dephosphorylate glucose phosphate into glucose, which has the affinity to deposit Ag nanoshells onto Au nanobipyramids with a multicolor response. This approach provides a blue shift of localized surface plasmon resonance (LSPR) as large as 190 nm corresponding to distinctive color changes, from yellowish brown to red based on the thickness of the formed Ag shell around the Au nanobipyramids. The change in the LSPR has been conducted for highly sensitive quantitative bioassay of ALP with a detectable multicolor change with linear dynamic range of 0.1-20 U/L and low limit of detection (LOD) of 0.085 U/L. Furthermore, the developed multicolor ALP biosensor exhibits high selectivity with high recovery of 98.6% demonstrating  its reliability and suitability for a point-of-care diagnosis.

Nano-octahedral bimetallic Fe/Eu-MOF preparation and dual model sensing of serum alkaline phosphatase (ALP) based on its peroxidase-like property and fluorescence

Herein a nano-scale bimetallic Fe/Eu-MOF with a regular octahedral structure was synthesized for the first time. The synthesized Fe/Eu-MOF has both peroxidase-like activity and fluorescence properties. Fe/Eu-MOF can catalyze H₂O₂ to oxidize the chromogenic substrate TMB to produce blue oxTMB, which has ultraviolet absorption at 652 nm. Unexpectedly, the generated oxTMB can effectively quench the fluorescence of the catalyst Fe/Eu-MOF at 450 nm. The quenching mechanism is mainly the internal filtration effect (IFE), accompanied by static quenching (SQE), Förster resonance energy transfer (FRET) and photoelectron transfer (PET). Fe/Eu-MOF has a high affinity for sodium pyrophosphate (PPi). PPi can be adsorbed to the surface of Fe/Eu-MOF, destroying the structure of Fe/Eu-MOF and inhibiting its catalytic activity, resulting in a decrease in UV absorbance and the decline of fluorescence quenching. In contrast, phosphoric acid (Pi) has almost no effect on the reaction system. Alkaline phosphatase (ALP) can catalyze the hydrolysis of PPi to Pi, thereby reducing the inhibitory effect of PPi. Based on this, we successfully constructed a dual-mode ALP sensor with high selectivity. The linear ranges based on the 652 nm absorption or the fluorescence detection are from 1 to 200 U/L, and the detection limits are 0.6 for the absorption method and 0.9 U/L for the fluorescence method, respectively.

Multifunctional lanthanide metal-organic framework based ratiometric fluorescence visual detection platform for alkaline phosphatase activity

A turn-on/off ratiometric fluorescence detection platform based on multifunctional lanthanide metal-organic framework (Ln-MOF) and an enzymatic cascade reaction is proposed for alkaline phosphatase (ALP) activity assay. L-phosphotyrosine is hydrolyzed to levodopa (L-dopa) by two steps of enzymatic reaction. L-dopa further reacts with naphthoresorcinol to produce carboxyazamonardine with strong emission at 490 nm. In this process, multifunctional Ln-MOF (Cu@Eu-BTC, BTC is the 1,3,5-benzenetricarboxylic acid) acts not only as a nanozyme to catalyze the fluorogenic reaction between L-dopa and naphthoresorcinol but also as a fluorescence internal standard. The emission of Cu@Eu-BTC at 620 nm is quenched by phosphate anions, and the dual-response ratiometric fluorescence (F₄₉₀/F₆₂₀) can be achieved. A good linear relationship was obtained between Δ(F₄₉₀/F₆₂₀) and ALP activity in the range 0.3-24 U L^-1 with the detection limit of 0.02 U L^-1. In addition, a portable assay tube was designed for visual and point-of-care testing of ALP activity by color variation (ratiometric chromaticity). Both the ratiometric fluorescence detection and the visual detection methods were successfully applied to monitor ALP activity in human serum samples with recovery between 95.5%-109.0% and 94.0%-110.1%, and relative standard deviation less than 8.1% and 9.5%, respectively. As far as we know, this is the first report of ALP activity assay assisted by multifunctional Ln-MOF.Graphical abstract.

One-pot construction of acid phosphatase and hemin loaded multifunctional metal-organic framework nanosheets for ratiometric fluorescent arsenate sensing

Exploring high-performance sensors for toxic arsenic detection is highly desired because of its great threat to the environment. Herein, we report a ratiometric fluorescent biosensor based on acid phosphatase and hemin loaded multifunctional Zn-based metal-organic framework (ACP/hemin@Zn-MOF) for high-performance arsenate (As(Ⅴ)) sensing. ACP/hemin@Zn-MOF is constructed by self-assembly, where hemin exhibits peroxidase-like activity and 2-aminoterephthalic acid ligand endows ACP/hemin@Zn-MOF with an intrinsic fluorescence (452 nm). When ACP/hemin@Zn-MOF catalyzes the oxidation of o-phenylenediamine (OPD), fluorescent 2,3-diaminophenazine (DAP) with an emission signal (564 nm) is produced and weakens ACP/hemin@Zn-MOF intrinsic fluorescence (452 nm) due to inner filter effect; after adding ascorbic acid 2-phosphate (AAP), ACP can hydrolyze AAP and produce ascorbic acid, which competitively suppresses the oxidation of OPD, resulting in the decrease of DAP signal (564 nm) and the recovery of ACP/hemin@Zn-MOF signal (452 nm); when As(V) is added, it irreversibly poisons ACP against hydrolyzing AAP, and the fluorescence signal at 564 nm recovers and the one at 452 nm is suppressed again. High-sensitivity and high-selectivity detection of As(V) (3.33-300 μg L^-1) is realized, with a detection limit of 1.05 μg L^-1. The biosensor was also successfully employed to detect total arsenic and As(V) in rice.

Metal-Organic Frameworks Enhance Biomimetic Cascade Catalysis for Biosensing

Multiple enzymes-induced biological cascade catalysis guides efficient and selective substrate transformations in vivo. The biomimetic cascade systems, as ingenious strategies for signal transduction and amplification, have a wide range of applications in biosensing. However, the fragile nature of enzymes greatly limits their wide applications. In this regard, metal-organic frameworks (MOFs) with porous structures, unique nano/microenvironments, and good biocompatibility have been skillfully used as carriers to immobilize enzymes for shielding them against hash surroundings and improving the catalytic efficiency. For another, nanomaterials with enzyme-like properties and brilliant stabilities (nanozymes), have been widely applied to ameliorate the low stability of the enzymes. Inheriting the abovementioned merits of MOFs, the performances of MOFs-immboilized nanozymes could be significantly enhanced. Furthermore, in addition to carriers, some MOFs can also serve as nanozymes, expanding their applications in cascade systems. Herein, recent advances in the fabrication of efficient MOFs-involving enzymes/nanozymes cascade systems and biosensing applications are highlighted. Integrating diversified signal output modes, including colorimetry, electrochemistry, fluorescence, chemiluminescence, and surface-enhanced Raman scattering, sensitive detection of various targets (including biological molecules, environmental pollutants, enzyme activities, and so on) are realized. Finally, challenges and opportunities about further constructions and applications of MOFs-involving cascade reaction systems are briefly put forward.

A colorimetric alkaline phosphatase biosensor based on p-aminophenol-mediated growth of silver nanoparticles

Alkaline phosphatase (ALP) is an enzyme that catalyzes the dephosphorylation of proteins, nucleic acids, and biomolecules. It is a potential biomarker for diverse diseases such as breast cancer, osteopenia, and hepatobiliary. Herein, we developed a colorimetric sensor for the ALP assay based on its enzymatic activity to dephosphorylate the p-aminophenol phosphate (pAPP) into pAP. In a solution containing silver nanoparticles (AgNPs) and Ag⁺ ions prepared using a low concentration of NaBH₄, pAP mediates the growth of AgNPs by reducing the concentration of Ag⁺ ions to enhance the intensity of localized surface plasmon resonance as the pAPP cannot induce a reduction of the remaining Ag⁺ due to the masking of the hydroxyl with phosphate. The quantitative assay of the ALP was demonstrated via the colorimetric detection of the pAP-mediated growth of AgNPs in the presence of an ALP. The highly sensitive enzymatic growth of AgNPs provided a wider dynamic linear range of 0.5-225 U/L with a lower limit of detection of 0.24 U/L than that previously reported. The use of pAP resulted in excellent selectivity of the sensor for the ALP assay in human serum, yielding a high recovery rate and a high precision of 99.2 ± 1.5 % for the standard addition method.

Target-induced synergetic modulation of electrochemical tag concentration and electrode surface passivation for one-step sampling filtration-free detection of acid phosphatase activity

As a biomarker of several diseases, the activity of acid phosphatase (ACP) is generally used to assistantly diagnose these diseases. Thus, developing reliable ACP activity analytical methods becomes quite significant. Herein, we recommend a one-step sampling filtration-free electrochemical method for ACP activity determination based on the target-induced synergetic modulation of tag concentration and surface passivation. Mn₃O₄ microspheres with favorable oxidase-mimicking activity are synthesized to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to its product TMBox, resulting in a remarkable re-reduction signal of TMBox to TMB recorded by an integrated electrochemical system consisting of screen-printed electrode (SPE) and 3D-printed holder. When hexametaphosphate ions (HMPi) with rich negative charges are employed to interact positively charged TMBox, the formed flocculent precipitate TMBox-HMPi automatically sedimentates onto SPE surface, and both the decreased concentration of free TMBox in solution and the increased electrode surface passivation triggered by TMBox-HMPi sedimentation synergistically reduce the re-reduction signal of TMBox. When ACP is present, it hydrolyzes the HMPi substrate, greatly relieving the formation of the TMBox-HMPi precipitate and its sedimentation onto SPE surface. As a result, the electrochemical re-reduction signal of TMBox becomes remarkable again. With the strategy of using one stimulus to generate two-fold signal change, highly sensitive ACP activity detection was realized, with a wide linear range from 0.05 to 50 U/L and a limit of detection down to 0.024 U/L. Reliable monitoring of ACP activity in clinical serum was also demonstrated.

One-step colorimetric detection of Staphylococcus aureus based on target-induced shielding against the peroxidase mimicking activity of aptamer-functionalized gold-coated iron oxide nanocomposites

Staphylococcus aureus (S. aureus) is one of the most threatened food-borne pathogens. Thus, it is necessary to establish fast, portable and reliable tools to realize the identification of S. aureus. Herein, the authors describe an effective colorimetric-based biosensor for the detection of S. aureus in multiple types of samples. Initially, a nanozyme composed of gold and iron oxide nanoparticles was synthesized and further modified with S. aureus-specific aptamer via Au-S bond. By utilizing the intrinsic peroxidase-like activity of the above magnetic conjugates, 3,3',5,5'-tetramethylbenzidine (TMB) can be transferred to oxTMB by oxidation of hydrogen peroxide (H₂O₂), resulting in a visible blue color. However, the introduction of S. aureus can turn off the UV-vis absorbance signals of TMB-H₂O₂ system, due to the identification property of the nanozyme probe. Consequently, the optical density of the mixed solution measured at 652 nm decreased linearly as the concentration of S. aureus increased from 10 to 10⁶ CFU mL^-1, with the visible limit of detection as low as 10 CFU mL^-1. The as-prepared sensor can detect S. aureus in spiked water, milk and urine samples quantitatively during 12 min without any pre-enrichment, separation or washing steps. In our perception, the one-step colorimetric assay show promise in practical on-site detection of S. aureus.

In Situ Fluorogenic Reaction Generated via Ascorbic Acid for the Construction of Universal Sensing Platform

A highly fluorescent emission reaction between terephthalic acid (PTA) and ascorbic acid (AA) via simple control of the reaction temperature was first revealed with the detailed formation mechanism and various characterizations including electron paramagnetic resonance and mass spectrometry. Based on the AA-responsive emission, the alkaline phosphatase (ALP) triggered the transformation of l-ascorbic acid 2-phosphate trisodium salt to AA was integrated with the present system for developing a sensitive, selective, and universal platform. The monitoring of the activity of ALP and the fabrication of ALP-based enzyme-linked immunoassay (ELISA) with carcinoembryonic antigen (CEA) as the model target was performed. The fluorescence intensity correlated well to the CEA concentration in the ranges of 0.25-30 ng/mL, with a detection limit of 0.08 ng/mL. Such a facile protocol based on the fluorescent reaction between PTA and AA without the assistance of catalysis of nanomaterials avoided the laborious synthesis procedure and provided a direct strategy for the early clinical diagnosis coupled with ALP-related catalysis.

Metal-Organic Frameworks for Liquid Phase Applications

In the last two decades, metal-organic frameworks (MOFs) have attracted overwhelming attention. With readily tunable structures and functionalities, MOFs offer an unprecedentedly vast degree of design flexibility from enormous number of inorganic and organic building blocks or via postsynthetic modification to produce functional nanoporous materials. A large extent of experimental and computational studies of MOFs have been focused on gas phase applications, particularly the storage of low-carbon footprint energy carriers and the separation of CO2-containing gas mixtures. With progressive success in the synthesis of water- and solvent-resistant MOFs over the past several years, the increasingly active exploration of MOFs has been witnessed for widespread liquid phase applications such as liquid fuel purification, aromatics separation, water treatment, solvent recovery, chemical sensing, chiral separation, drug delivery, biomolecule encapsulation and separation. At this juncture, the recent experimental and computational studies are summarized herein for these multifaceted liquid phase applications to demonstrate the rapid advance in this burgeoning field. The challenges and opportunities moving from laboratory scale towards practical applications are discussed.

Universal Platform for Ratiometric Sensing Based on Catalytically Induced Inner-Filter Effect by Cu2

Integrating two kinds of fluorescent probes in one system to develop a ratiometric sensing platform is of prime importance for achieving an accurate assay. Inspired by the efficient overlapped spectrum of 2-aminoterephthalic acid (PTA-NH₂) and 2,3-diaminophenazine (DAP), a new sensitive ratiometric fluorescent sensor has been developed for Cu²⁺ on the basis of in situ converting o-phenylenediamine (OPD) into DAP through the catalysis of Cu²⁺. Here, the presence of Cu²⁺ induced the emission of DAP, which acted as an energy acceptor to inhibit the emission of PTA-NH₂. This dual-emission reverse change ratiometric profile based on the inner-filter effect improved sensitivity and accuracy, and the highly sensitive determination of Cu²⁺ with a detection limit of 1.7 nmol·L^-1 was obtained. The proposed sensing platform displayed the wide range of detection of Cu²⁺ from 5 to 200 nmol·L^-1 by modulating the reaction time between Cu²⁺ and OPD. Moreover, based on the specific interaction between glutathione (GSH) and Cu²⁺, this fluorescent sensor showed high response toward GSH in a range of 0.5-80 μmol·L^-1 with a detection limit of 0.16 μmol·L^-1. The successful construction of this simple ratiometric sensing platform without the participation of enzymes provides a new route for the detection of small biological molecules that are closely related to human health.

Tri-functional Fe-Zr bi-metal-organic frameworks enable high-performance phosphate ion ratiometric fluorescent detection

Metal-organic frameworks (MOFs) featured with flexible design and versatile properties are finding increasing applications. In particular, integrating multiple functions into one framework can bring them improved detection efficiency towards various analytes. Herein, for the first time, a Fe-Zr bi-metal-organic framework (UiO-66(Fe/Zr)-NH2) with three functions (intrinsic fluorescence, peroxidase-mimicking activity, and specific recognition) is designed to establish a ratiometric fluorescent platform for high-performance phosphate ion (Pi) sensing. The use of a fluorescent organic ligand endows the MOF material with a strong intrinsic fluorescence at 435 nm. The presence of Fe3+/Fe2+ nodes offers good enzyme-like capacity to catalyze the o-phenylenediamine (OPD) substrate to fluorescent OPDox (555 nm), which then quenches the intrinsic fluorescence of UiO-66(Fe/Zr)-NH2 due to the inner filter effect. The Zr4+ nodes in the MOF material act as selective sites for Pi recognition. When Pi exists, it specifically adsorbs onto UiO-66(Fe/Zr)-NH2 and decreases the latter's peroxidase-mimetic activity, resulting in the less production of fluorescent OPDox. As a consequence, the intrinsic fluorescence of UiO-66(Fe/Zr)-NH2 at 435 nm is restored, and the signal from OPDox at 555 nm is reduced inversely. With the ratiometric strategy, efficient determination of Pi with outstanding sensitivity and selectivity was realized, giving a detection limit down to 85 nM in the concentration range of 0.2-266.7 μM. Accurate measurement of the target in practical water matrices was also validated, indicating its promising application for Pi analysis in environmental and other fields.

A dual-mode resonance Rayleigh scattering and colorimetric alkaline phosphatase assay based on in situ ascorbic acid-induced signal generation from manganese dioxide nanosheets

Multimode sensing has attracted extensive attention because they provide more than one transduction channel, thus improving accuracy and sensitivity. Due to the structural diversity, MnO2 nanosheets and nanoneedles were successively obtained via one-step redox reaction and different self-assembly methods. MnO2 nanosheets possess outstanding optical properties including extremely strong resonance Rayleigh scattering (RRS) and absorbance signal, and were selected as a dual-mode sensing material. Inspired by the selectivity of alkaline phosphatase (ALP) towards dephosphorylate ascorbic acid 2-phosphate (AAP) to generate ascorbic acid (AA), which has the ability to decompose MnO2 nanosheets along with optical signals and colour change, a dual-mode optical ALP sensing platform has been designed. Therefore, MnO2 nanosheets can serve as colorimetric probes by directly visualizing the colour variation with bare eyes. Moreover, the detection limit obtained by the RRS sensing mode can be as low as 0.17 mU L-1, which is far superior to that obtained by previously reported methods. The strategy not only has good feasibility and sensitivity, but also shows good prospects for a series of ALP-extended sensing applications.

A novel alkaline phosphatase activity sensing strategy combining enhanced peroxidase-mimetic feature of sulfuration-engineered CoOx with electrostatic aggregation

Given alkaline phosphatase (ALP) takes part in the phosphorylation/dephosphorylation processes in the body, its activity is universally taken as an important indicator of many diseases, and thus developing reliable and efficient methods for ALP activity determination becomes quite important. Here, we propose a new sensing strategy for ALP activity by integrating the improved peroxidase-mimicking catalysis of sulfuration-engineered CoO_x with the hexametaphosphate ion (HMPi)-mediated electrostatic aggregation. After sulfuration engineering, the CoO_x composite coming from the pyrolysis of ZIF-67 exhibits enhanced peroxidase-mimetic catalytic ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to its oxide TMBox, offering a remarkable color change from colorless to mazarine; with the presence of HMPi, the rapid electrostatic assembly of negatively charged HMPi and positively charged TMBox leads to the aggregation of the latter, resulting in a color fading phenomenon; when ALP is added in advance to hydrolyze the HMPi mediator, the aggregation procedure is significantly suppressed, and such that the solution color can be recovered. Based on this principle, efficient determination of ALP activity was gained, giving a wide detection scope from 0.8 to 320 U/L and a detection limit as low as 0.38 U/L. Reliable analysis of the target in serum samples was also achieved, verifying the feasibility and practicability of our strategy in measuring ALP activity for clinical applications. Graphical abstract.

Combining CeVO4 oxidase-mimetic catalysis with hexametaphosphate ion induced electrostatic aggregation for photometric sensing of alkaline phosphatase activity

In the present work, a novel alkaline phosphatase (ALP) activity colorimetric assay is proposed by integrating the oxidase-mimicking catalytic characteristic of CeVO₄ nanoparticles with the hexametaphosphate ion (HMPi) mediated electrostatic aggregation. The CeVO₄ nanoparticles exhibit good oxidase-mimetic catalytic ability to promote the 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to TMBox, offering a significant change from colorless to blue. After a small amount of HMPi is added, the strong electrostatic interaction between the negatively charged HMPi species and the positively charged TMBox product leads to the aggregation of the latter, generating an aubergine HMPi-TMBox agglomerate. After the agglomerate is filtered out, the reaction solution turns to be almost colorless. When ALP is used to hydrolyze the HMPi species in advance, the electrostatic aggregation process is remarkably restrained, thus retaining the blue color of the CeVO₄ catalyzed TMB solution. According to the new sensing strategy, highly selective and sensitive analysis of ALP activity was realized, providing a wide detection range from 1 to 210 U/L and a detection limit of 0.68 U/L. Accurate measurement of ALP activity in clinical serum matrices was also validated, demonstrating the practicability of the proposed assay in practical applications.

ATP induced alteration in the peroxidase-like properties of hollow Prussian blue nanocubes: a platform for alkaline phosphatase detection

Breaking the pH limitation of the enzyme-like activity of nanomaterials is of great importance for extending their applications in environmental and biomedical fields. Herein, to mimic the role of histidine residues in horseradish peroxidase (HRP), adenosine 5'-triphosphate (ATP) is reported to improve the peroxidase-like activity of hollow Prussian blue nanocubes (hPBNCs). Due to the inherited porous structures, hPBNCs can expose all the binding sites as far as possible to ATP to significantly amplify their catalytic activity and broaden their applicable pH range up to pH 12. Introduction of ATP provides the possibility of realizing efficient catalytic reactions under alkaline conditions. Upon binding with hPBNCs, ATP can enhance the stability of hPBNCs, increase the affinities of the catalysts towards substrates and improve the conductivity of hPBNCs as well as change the decomposed product from H₂O₂. Moreover, on the basis of the different catalytic activities of hPBNCs towards ATP, adenosine 5'-diphosphate and adenosine 5'-monophosphate, hPBNCs-ATP is utilized to construct a novel colorimetric sensor for the detection of alkaline phosphatase (ALP) activity in biological fluids, which is significantly important for the clinical diagnosis of ALP-related diseases.

A smartphone-based platform for point-of-use determination of alkaline phosphatase as an indicator of water eutrophication

A smartphone-based detection platform for the determination of alkaline phosphatase (ALP) is described. The method is based on the rational design of the stimulus-response of 7-methoxycoumarin-3-carboxylic acid (7-MC-3-COOH)-functionalized Eu-AMP infinite coordination polymer (ICP) nanoparticles. The blue fluorescence of 7-MC-3-COOH at 403 nm was suppressed, while the red fluorescence of Eu³⁺ at 615 nm was sensitized after the formation of 7-MC-3-COOH@Eu-AMP ICP. Upon exposure to ALP, the dephosphorylation of AMP resulted in the destruction of 7-MC-3-COOH@Eu-AMP ICP, and thereby, the blue fluorescence of 7-MC-3-COOH recovered; in the meantime, the sensitized red fluorescence was quenched. With the fluorescence intensity ratio F₆₁₅/F₄₃₀ as the signal readout, ALP can be detected within a concentration range 0.001 to 0.15 U mL^-1, and the limit of detection (LOD) was 0.00035 U mL^-1. Moreover, fluorescence color changes from red to blue could also be recognized by a portable device with the smartphone as a signal reader, and direct point-of-use testing (POUT) for ALP within a concentration range 0.005 to 0.7 U mL^-1 could be realized, with LOD of 0.0015 U mL^-1. Endowed with high sensitivity and superior reliability, the assay enabled direct monitoring of P-related water eutrophication in a freshwater lake with ALP as an indicator. Graphical abstract A smartphone-based platform for point-of-use determination of alkaline phosphatase.

Construction of a recyclable oxidase-mimicking Fe3O4@MnOx-based colorimetric sensor array for quantifying and identifying chlorophenols

Chlorophenols (CPs) are known as a class of pollutants posing a great threat to the environment and human health because of their carcinogenesis and teratogenesis, and thus exploring convenient and efficient methods for their detection and identification becomes particularly important. Herein, we report a recyclable colorimetric sensor array according to the oxidase-mimicking catalytic characteristics of Fe₃O₄@MnO_x for the high-performance quantification and differentiation of typical CPs. The core-shell Fe₃O₄@MnO_x prepared by growing oxidase-like MnO_x nanoflakes on the surface of magnetic Fe₃O₄ particles via a hydrothermal process can exhibit excellent catalytic activity to trigger the color reaction of CPs and 4-aminoantipyrine with the participation of O₂. By utilizing the Fe₃O₄@MnO_x-catalyzed color reaction, high-sensitivity quantitative analysis of CPs, taking 2-chlorophenol as a model, was realized, providing a detection limit as low as 0.85 μM. Given different chlorine substitution places and numbers in CPs impact the reaction kinetics diversely, a new nanozyme-based colorimetric sensor array was further constructed for the successful differentiation of various CPs with the help of hierarchical cluster analysis and principal component analysis. Accurate double-blind identification of unknown samples using the proposed sensor array was also demonstrated, indicating its reliability for practical practice.

Ultrasensitive Assay of Alkaline Phosphatase Based on the Fluorescent Response Difference of the Metal-Organic Framework Sensor

The assay of alkaline phosphatase (ALP) is important in clinical diagnosis because the abnormal expression of this enzyme is related to many serious diseases. In this work, using a luminescent metal-organic framework (MOF) as the sensor, a fluorescent method was developed for the activity assay of ALP. With nanoscale particle size, the prepared MOF sensor exhibited good dispersability and stable photoluminescence in aqueous suspension. The emission of this MOF is inert to p-nitrophenylphosphate (NPP) but could be efficiently quenched by its dephosphorylated product, p-nitrophenol. Taking advantage of this feature, this MOF was added to the system of ALP-catalyzed NPP dephosphorylation to transduce the proceeding of the reaction real-timely to the fluorescent signal. The enzyme activity could be calculated based on the recorded kinetic trace. This method presented a low detection limit (2 × 10-3 U L-1) and a wide quantification range (0.6-90 U L-1) in our experiments, showing its quantification capability challenges the best of current ALP analytical methods. As a practical application, our method was successfully applied to the ALP analysis in human serum samples.