A selective dual-response biosensor for tyrosinase monophenolase activity based on lanthanide metal-organic frameworks assisted boric acid-levodopa polymer dots

Polarity-switchable photoelectrochemical detection of tyrosinase activity based on enzyme-triggered boronic ester bridging between In2S3 and Cu2ZnSnS4

Herein, an innovative polarity switchable strategy for photoelectrochemical (PEC) detection is reported by utilizing enzyme-triggered boronic ester bridging between two semiconductors. Monophenol-modified In2S3 is prepared by sequentially coating polyethyleneimine (PEI) and covalently conjugating 4-hydroxyphenylacetic acid (PhOH) on In2S3, whereas dihydroxy-modified Cu2ZnSnS4 is prepared through surface coating of chitosan (CS). Under the catalysis of tyrosinase (TYR), monophenol groups of In2S3@PEI-PhOH undergo the conversion to o-diphenol groups. With the aid of 1,4-phenylboronic acid, boronate ester bridges form between TYR-treated In2S3@PEI-PhOH and Cu2ZnSnS4@CS, so In2S3 can be anchored on the Cu2ZnSnS4@CS-modified electrode surface. As a result, the formation of p-n heterojunctions on the photoelectrode can reverse the photocurrent polarity, enabling polarity switchable PEC detection of TYR activity. The linear range is from 0.01 to 5 U mL-1, and the detection limit is 0.0015 U mL-1 for TYR activity detection. The established method is successfully employed for TYR activity detection in human serum samples.

Coordination-Induced Photocurrent Polarity Switching of Black Titanium Dioxide for Tyrosinase Activity Assay

Polarity-switchable photoelectrochemical (PEC) analysis has garnered significant attention owing to its enhanced accuracy and superior anti-interference capability. Developing a straightforward and efficient approach for polarity-switchable PEC analysis is critically essential. We present here a novel approach for polarity-switchable PEC assay by leveraging the coordination interactions between black titanium dioxide (b-TiO2) and o-diphenol-functionalized BiOI. Specifically, 4-hydroxyphenylacetic acid was covalently functionalized onto hydrolyzed 3-aminopropyl triethoxysilane-modified BiOI nanosheets, and the monophenol groups on BiOI are further converted into o-diphenol groups through tyrosinase (TYR) catalysis. Consequently, the o-diphenol-functionalized BiOI nanosheets are attached to a b-TiO2-based photoelectrode via coordination interactions between b-TiO2 and the o-diphenol groups, enabling photocurrent polarity switching of the b-TiO2-based electrode and polarity-switchable PEC assay of TYR activity. The developed PEC assay of TYR activity exhibits a broad linear range from 0.010 to 10 U mL-1 and a low detection limit of 0.002 U mL-1. The present work not only reports an innovative photocurrent polarity switchable strategy but also establishes an effective method for TYR activity assay.

Phage@lanthanide metal-organic framework-based fluorescent biosensor for smartphone-assisted simultaneous detection of multiple foodborne pathogens

The simple, rapid, and simultaneous detection of multiple foodborne pathogens in food is crucial for ensuring public safety. In this study, a rational design strategy for lanthanide-based metal-organic frameworks (Ln-MOFs), informed by theoretical calculations, was proposed. The calculated results were experimentally verified to screen out the optimal Ln-MOF for fluorescence efficiency. The selected Ln-MOFs were coupled with phages that exhibit specific pathogen recognition to develop phage@Ln-MOF fluorescent probes, while the magnetic nanoparticles were conjugated with phages to form capture probes. On this basis, a fluorescent biosensor was developed for the simultaneous detection of three major foodborne pathogens-Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella. This sensor facilitated the detection of all three pathogens within 15 min, with limit of detection (LOD) as low as 1 CFU/mL. Moreover, this fluorescent biosensor was compatible with on-site visual detection, utilizing a self-designed portable dark box and smartphone-assisted visualization, achieving an LOD of approximately 1-2 CFU/mL for E. coli, S. aureus, and Salmonella. This work demonstrates a novel approach for the rapid on-site detection of multiple foodborne pathogens, which holds promise for advancing field-ready diagnostic tools in food safety monitoring.

Customized Controllable Pyrophosphate Nanosensor Based on Lanthanide Metal-Organic Frameworks for Accurate and Sensitive Detection of Nucleic Acids

Pyrophosphate (PPi) and nucleic acid amplification play a critical role in medical diagnostics, making the development of precise nanosensors essential. Lanthanide metal-organic frameworks (Ln-MOFs) are increasingly recognized for their potential in advanced luminescent biosensing applications. However, research on customized controllable responses in Ln-MOF nanosensors is still lacking, which is critical for the molecular-level modular design. In this work, we introduce a ligand engineering strategy to regulate coordination-induced antenna effect emission in Ln-MOFs, optimizing their pyrophosphate (PPi) sensing from fluorescence turn-off to turn-on modes. By tuning the coordination environment through ligand programming, we discovered a "near coordination compensation" effect, allowing for controllable transitions between aggregation-induced emission and quenching (AIE/AIQ). This reversible response was supported by density functional theory calculations. Using a Eu3+/Tb3+ dual-emission Ln-MOF designed with 2,6-pyridinedicarboxylic acid as the optimized ligand, we developed a self-correcting PPi nanosensor with a detection limit of 0.2 μM. Moreover, this system enabled ultrasensitive nucleic acid detection, achieving a limit of detection (LOD) as low as 1 fM, with applications in DNA pyrosequencing, qPCR, and DNA epigenetic modification (5-formylcytosine) analysis. These findings shed light on the structural and photophysical factors controlling Ln-MOF luminescence, offering a promising platform for highly accurate and sensitive nucleic acid detection in biomedical diagnostics.

Use of Quantum Dots as Nanotheranostic Agents: Emerging Applications in Rare Genetic Diseases

Rare genetic diseases (RGDs) affect a small percentage of the global population but collectively have a substantial impact due to their diverse manifestations. Although the precise reasons behind these diseases remain unclear, roughly 80% of cases are genetically linked. Recent efforts focus on understanding pathology and developing new diagnostic and therapeutic approaches for RGDs. However, there persists a gap between fundamental research and clinical therapeutic approaches, where advancements in nanotechnology offer promising improvements. In this context, nanosized light-emitting quantum dots (QDs), ranging from 2-10 nm, are promising materials for diverse applications. Their size-tunable light emission, high quantum yield, and photostability allow for precise tracking of cargo. Additionally, QDs can be functionalized with therapeutic agents, antibodies, or peptides to target specific cellular pathways, enhancing treatment efficacy while minimizing side effects. By combining diagnostic and therapeutic capabilities in a single platform, QDs thus offer a versatile and powerful approach to tackle rare genetic disorders. Despite several reviews on various therapeutic applications of QDs, their utilization in the specific domain of RGDs is not well documented. This review highlight QDs' potential in diagnosing and treating certain RGDs and addresses the challenges limiting their application.

Polarity Sensor Based on Multivariate Lanthanide Metal-Organic Framework for Constructing Biosensing Platform

It is significant but challenging to develop polarity sensors that can measure multiscenario polarity in a modular, customized, sensitive, and accurate manner. In this work, we proposed a polarity sensor based on multivariate lanthanide metal-organic framework (Ln-MOF) nanoclusters through the modular programming design of ligands. This multivariate Ln-MOF combines the advantages of modularity, ease of design, high flexibility and low cost, and can be precisely customized for different polarity systems. The MOF Eu0.1Tb0.9-isophthalic acid (IPA) and Eu0.3Tb0.7-o-phthalic acid (OPA) are suitable for the detection of trace water in dimethylsulfoxide (DMSO) and hyaluronidase activity, respectively. Especially, Eu0.3Tb0.7-OPA can achieve high-sensitivity detection of hyaluronidase activity within 8 min, with the limit of detection as low as 0.016 U/L. The results enable us to break through our previous understanding of polarity parameter, allowing us to develop more polarity-related biosensing platforms. Ln-MOFs are believed to utilize their adjustable polar intermolecular interactions to achieve the optimal compatibility and high sensitivity in polarity sensing systems, which is supported by experiments and density functional theory calculations. These polarity sensors based on multivariate Ln-MOF nanoclusters offer significant potential in biosensing and medical diagnostics, overcoming traditional biosensor limitations in synthesis and customization.

MnO4--triggered wavelength-changeable and rapid-response fluorescence sensor for paper-based on-site sensing of tyrosinase activity in potato

Rapid-response in situ fluorogenic reactions in aqueous solution are important for designing sensitive and stable sensing platforms. Herein, a wavelength-changeable and rapid-response (within 5 s) fluorescence sensing platform for monitoring tyrosinase (TYR) activity is constructed. The developed assay is based on TYR catalyzing the hydroxylation of mono-phenol to o-diphenol and MnO4--triggered fluorogenic between dopamine (DA) and phenol derivatives in aqueous solution. The fluorescence wavelength can be changeable from 470 to 550 nm with strong fluorescence according to different phenol derivatives. Our proposed sensor not only exhibits a good recovery for TYR in high serum concentration (20 %), but also has been successfully applied to the screening of TYR inhibitors modeled on kojic acid. Furthermore, a paper-based wavelength-changeable fluorescence sensor was developed for on-site detection of TYR activity in potatoes with high recovery, which is consistent with our previously reported method. Consequently, the proposed sensing system has broad prospects in the practical application of TYR-associated food monitoring and clinical diagnosis.

Time-Resolved Levodopa Cascade Polymerization Tuned by Bimetallic MOF Fluorescent Nanozyme and Boric Acid for Butyrylcholinesterase Activity Dual-Mode Assay

A ratiometric fluorescence-photothermal dual-mode assay method is constructed for the detection of butyrylcholinesterase (BChE) activity based on time-resolved levodopa (L-DOPA) cascade polymerization. First, a newly designed bimetallic metal-organic framework (MOF), Eu/Co-DPA (DPA: pyridine-2,6-dicarboxylic acid), is screened out as a fluorescent nanozyme with high catalytic activity and superior luminescence properties. In the presence of boric acid (BA), L-DOPA forms BA-esterified L-DOPA, which is catalyzed by Eu/Co-DPA to form the oligomers with strong blue fluorescence. Meanwhile, the red fluorescence of Eu/Co-DPA is quenched by the oligomers, generating a sensitive turn-on/off ratiometric fluorescence response. As polymerization time increases, Eu/Co-DPA cleaves the borate ester bonds to expose the catechol structures of the oligomers, which facilitates the further oxidation and polymerization of the oligomers, promoting the formation of poly(L-DOPA) nanoparticles with a high photothermal conversion efficiency (30.33%). Then, by using thiocholine (butyrylthiocholine enzymolysis product) to inhibit the catalytic activity of Eu/Co-DPA, BChE activity is detected through the change in fluorescence and photothermal dual signals. Both assay modes have low detection limits (0.021 and 0.024 U L-1) and high accuracy (93.3-105.3% recovery). The detection results of real human serum indicate that both assay modes show 100.0% agreement with the standard method. To our knowledge, this work first combines bimetallic MOFs and a BA regulator to tune the structure of L-DOPA polymers, providing a pathbreaking paradigm for preparing catecholamine-based fluorescence-photothermal organic polymers.

Eu3+-Doped Mixed-Ligand UiO-66-Type Metal-Organic Framework for Ratiometric Fluorescence Sensing Fluoride Ions with Ultralow Detection Limit

Metal-organic frameworks (MOFs) have emerged as a highly promising platform for various sensing applications due to their tunable structures and functionalities. In the present work, a Eu3+-doped mixed-ligand MOF, namely, the Eu3+@UiO-66-IPA, exhibited excellent luminescent properties and high fluorescence stability in aqueous media, displaying dual-emission peaks under 395 and 615 nm excitation that were readily visible to the naked eye. Importantly, the presence of fluoride ions (F-) promoted the "antenna effect" between the ligand and the Eu3+ centers, which significantly enhanced the emission intensity of the Eu3+ characteristic peak. In addition, the addition of F- also inhibited the quenching effect of high-energy O-H bonds existing in the aqueous environment. Notably, Eu3+@UiO-66-IPA demonstrated exceptional selectivity for F- over a range of competing anions, with a remarkable limit of detection as low as 0.22 μM. The developed Eu3+-doped mixed-ligand MOF system offers a highly promising strategy for the simple and accurate sensing of F- in practical applications.

Monitoring Enzymatic Reaction Kinetics and Activity Assays in Confined Nanospace

Enzyme-mediating biotransformations commonly occur in micro- and nanospace, which is crucial to maintain the essential biochemical processes and physiological functions in living systems. Probing enzyme-catalytic reactions in a biomimetic fashion remains challenging due to the lack of competent tools and methodology. Here, we show that studying enzymatic reaction kinetics can be readily achieved by a well-designed solid-state nanopore. Using tyrosine as a classical substrate, we quantitatively characterize the catalytic activity of tyrosinase (TYR) and tyrosine decarboxylase (TDC) in a nanoconfined space. Tyrosine was first immobilized in the nanopipette, wherein the active sites of tyrosine were left unoccupied. When successively exposed to TYR and TDC, a two-step cascade reaction can spontaneously take place. In this process, the surface wettability and charge of the nanopipette stemming from the catalytic products can sensitively regulate ion transport and ionic current rectification behavior, which were monitored by ionic current signal. In this biomimetic scenario, we obtained the enzymatic reaction kinetics of monophenyl oxidase that were not previously actualized in the conventional macroenvironment. Significantly, TYR showed higher enzyme activity, with a Km value of 1.59 mM, which was lower than that measured in a free and open space (with a Km of 3.01 mM). This suggests that tyrosine should be the most appropriate substrate of TYR, thus improving our understanding of tyrosine-associated biochemical reactions. This work offers an applicable technical platform to mimic enzyme-mediated biotransformations and biometabolisms.

Bioreaction-Compatible Bivariate Lanthanide MOF Sensor Enables Stimulus-Multiresponsive Platform for ctDNA On-Site Detection

Detection of circulating tumor DNA (ctDNA) in liquid biopsy is of great importance for tumor diagnosis but difficult due to its low amount in bodily fluids. Herein, a novel ctDNA detection platform is established by quantifying DNA amplification by-product pyrophosphate (PPi) using a newly designed bivariable lanthanide metal-organic framework (Ln-MOF), namely, Ce/Eu-DPA MOF (CE-24, DPA = pyridine-2,6-dicarboxylic acid). CE-24 MOF exhibits ultrafast dual-response (fluorescence enhancement and enzyme-activity inhibition) to PPi stimuli by virtue of host-guest interaction. The platform is applied to detecting colon carcinoma-related ctDNA (KARS G12D mutation) combined with the isothermal nucleic acid exponential amplification reaction (EXPAR). ctDNA triggers the generation of a large amount of PPi, and the ctDNA quantification is achieved through the ratio fluorescence/colorimetric dual-mode assay of PPi. The combination of the EXPAR and the dual-mode PPi sensing allows the ctDNA assay method to be low-cost, convenient, bioreaction-compatible (freedom from the interference of bioreaction systems), sensitive (limit of detection down to 101 fM), and suitable for on-site detection. To the best of our knowledge, this work is the first application of Ln-MOF for ctDNA detection, and it provides a novel universal strategy for the rapid detection of nucleic acid biomarkers in point-of-care scenarios.

Fluorometric "AND" logic gate for detection of tyramine and tyrosinase based on in-situ formation of silicon-containing nanoparticles

BACKGROUND

Tyramine is an important index of food freshness degree, and tyrosinase that can specifically oxidized monophenolamine to catecholamine plays a crucial part in the occurrence and development of melanin-related skin diseases. Therefore, it is crucial to develop sensitive and efficient methods for the detection of tyramine and tyrosinase.

RESULTS

In this work, encouraged by tyrosinase-triggered specific oxidation of tyramine to dopamine and the unique fluorescent reaction between dopamine and amino silane, we have developed a one-step synthetic strategy of silicon containing nanoparticles (Si CNPs) for "turn-on" detection of tyramine and tyrosinase. The Si CNPs formed with thoroughly studied mechanism exhibit uniform structure and robust yellow-green fluorescence. The low detection limits for tyramine (1.87 μM) and tyrosinase (0.0029 U/mL) demonstrate admirable sensitivity outstripping most methods. The proposed assay achieves satisfactory results in the determination of tyramine and tyrosinase activity in real samples. Furthermore, we leverage this new fluorescent assay to enable the fabrication of an "AND" Boolean logic gate.

SIGNIFICANCE

The entire process can be completed at easily available temperature and pressure with rapid response, convenient operation and visual observation. This fluorescent assay featured with excellent sensitivity, selectivity and stability has considerable prospects in the application of biosensors and disease diagnosis.

Synthetic Polymer Nanoparticles as an Abiotic Artificial Inhibitor of Tyrosinase

An innovative methodology is presented for synthesizing synthetic polymer nanoparticles (TINPs) as potent tyrosinase inhibitors. This inhibition strategy combines the integration of two distinct functionalities, phenol, and phenylboronic acid, within the TINPs structure. The phenyl group mimics the natural monophenol substrate, forming a strong coordination with the catalytic copper ion, significantly inhibiting tyrosinase activity. Additionally, phenylboronic acid interacts with catechol, another tyrosinase substrate, further reducing enzyme efficiency. The shared benzene ring in phenyl and phenylboronic acid enhances binding to tyrosinase's hydrophobic pocket near its copper active site, contributing to potent inhibition. TINPs exhibit exceptional performance, boasting an impressive IC50 value of 3.5×10-8 m and an inhibition constant of 9.8×10-9 m. Validation of the approach is unequivocally demonstrated through the successful inhibition of tyrosinase activity and melanin production, substantiated in both in vitro and in vivo scenarios. The mechanism of TINP inhibition is elucidated through circular dichroism and Fourier transform infrared spectroscopy. This study introduces a versatile design approach for developing abiotic polymer-based enzyme inhibitors, expanding possibilities in enzyme inhibition research.

Amorphous amEu-NH2BDC and amTb-NH2BDC as ratio fluorescence probes for smartphone-integrated naked eye detection of bacillus anthracis biomarker

The abnormal concentration of anthrax spore biomarker 2,6-pyridinedicarboxylic acid (2,6-DPA) will seriously affect public health. Therefore, a sensitive and rapid assay for 2,6-DPA monitoring is of vital importance. In this work, novel nano-sized amorphous Eu-NH2BDC (amEu-NH2BDC) and amorphous Tb-NH2BDC (amTb-NH2BDC) metal organic frameworks are prepared by adjusting the ratio of metal and ligand, respectively. Both of them exhibit highly sensitive and selective ratiometric fluorescence detection for 2,6-DPA with wider linear range and lower detection limit in aqueous solutions and human serum. Attributed to the coordination effect of 2,6-DPA in triggering the characteristic fluorescence emissions of Eu3+or Tb3+ by replacing coordinated solvent molecules, as evidenced by ultraviolet-visible spectroscopy, the fluorescence lifetimes analysis, thermal gravimetric analysis, Fourier-transform infrared spectroscopy, density functional theory (DFT) simulations and X-ray photoelectron spectroscopy. In addition, the amEu-NH2BDC or amTb-NH2BDC loaded paper-based microsensors are constructed for real-time and sensitive detection of 2,6-DPA and coupled with a smartphone-assisted visual portable device.

Tetranuclear Cluster-Based Eu(III)-Metal-Organic Framework: Ratiometric Platform Design and Ultrasensitive Phenylglyoxylic Acid Detection

Phenylglyoxalic acid (PGA) is a typical metabolite produced by the invasion of styrene into the human body. The detection of PGA can not only reflect the health status of the human body but also assess the level of styrene contamination in the environment. Herein, a novel Eu(III)-MOF (Eu-ttpd) with excellent fluorescence properties was designed by employing the tetrazole-based ligand of 5-((4'-(tetrazol-5'-yl)benzyl)oxy) isophthalic acid (H2ttpd), which successfully used a fluorescent sensor for PGA. The as-synthesized Eu-ttpd features the unique 10-connected tetranuclear cluster [Eu4(μ3-O)2(COO)8]4+ and exhibits a novel (3,10)-connected topological. Benefiting from the perfectly matched excited-state energy levels of the employed H2ttpd ligand with PGA, rapid photoinduced electron transfer (PET) and Dexter-ET can occur, which entitle Eu-ttpd a fast fluorescence quenching response to PGA with a remarkable LOD of 0.269 μM. More importantly, by integrating Eu-ttpd and Mg,N-CDs into the polyacrylamide hydrogel, we optimized Eu-ttpd into a hydrogel sensor which exhibited enhanced detection ability (LOD = 0.052 μM) accompanied by a distinguished color transformation (red-to-blue) and realized ultrasensitive and visual detection of PGA. This work offers an indication for the development of smart sensing materials for human health and environmental safety.

Highly stable lanthanide(III) metal-organic frameworks as ratiometric fluorescence sensors for vitamin B6

Three lanthanide(III)-based metal-organic frameworks, formulated as [(CH3)2NH2]2[Ln6(μ3-OH)8(EBTC)3(H2O)6]·4H2O·2DMF (Ln = Eu (1), Tb (2) and Ce (3)), were synthesized using a rigid tetracarboxylate organic ligand (1,1'-ethynebenzene-3,3',5,5'-tetracarboxylic acid, H4EBTC). Complexes 1-3 possess 12-connected hexanuclear [Ln6(μ3-OH)8(OOC-)12(H2O)6] clusters with the ftw topology, which were stable in water and acid/alkaline aqueous solution. Due to the antenna effect, complexes 1 and 2 presented double fluorescence emission peaks, which are the characteristic emission peaks of Ln3+ ions and the ligand H4EBTC, respectively. The doped bimetallic EuxTb1--x-MOFs were obtained by tuning the Eu(III)/Tb(III) ratio during the reaction, which exhibited a colour change from red, orange, and yellow to green. Furthermore, complexes 1, 2 and Eu2Tb8-MOF as ratiometric fluorescence sensors exhibited excellent sensing ability for vitamin B6 (VB6) in phosphate buffer solution (pH = 7.35) and real samples with high selectivity and reusability. The low detection limit (LOD) values were calculated to be 1.03 μM for complex 1, 0.25 μM for complex 2 and 0.11 μM for Eu2Tb8-MOF in aqueous solution. Finally, a visual film based on Ln-MOF@SA was prepared to detect VB6 with high reusability.

Nanoporous Crystalline Materials for the Recognition and Applications of Nucleic Acids

Nucleic acid plays a crucial role in countless biological processes. Hence, there is great interest in its detection and analysis in various fields from chemistry, biology, to medicine. Nanoporous crystalline materials exhibit enormous potential as an effective platform for nucleic acid recognition and application. These materials have highly ordered and uniform pore structures, as well as adjustable surface chemistry and pore size, making them good carriers for nucleic acid extraction, detection, and delivery. In this review, the latest developments in nanoporous crystalline materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular organic frameworks (SOFs) for nucleic acid recognition and applications are discussed. Different strategies for functionalizing these materials are explored to specifically identify nucleic acid targets. Their applications in selective separation and detection of nucleic acids are highlighted. They can also be used as DNA/RNA sensors, gene delivery agents, host DNAzymes, and in DNA-based computing. Other applications include catalysis, data storage, and biomimetics. The development of novel nanoporous crystalline materials with enhanced biocompatibility has opened up new avenues in the fields of nucleic acid analysis and therapy, paving the way for the development of sensitive, selective, and cost-effective diagnostic and therapeutic tools with widespread applications.

Controllable Synthesis of TbIII Metal-Organic Frameworks with Reversible Luminescence Sensing for Benzaldehyde Vapor

Two novel lanthanide metal-organic frameworks (MOFs) with the formulas [Tb(bidc)(Hbidc)(H₂O)]_n (JXUST-20) and {[Tb₃(bidc)₄(HCOO)(DMF)]·solvents}_n (JXUST-21) were synthesized based on 2,1,3-benzothiadiazole-4,7-dicarboxylic acid (H₂BTDC) under solvothermal conditions. Interestingly, benzimidazole-4,7-dicarboxylic acid (H₂bidc) was formed in situ using H₂BTDC as the starting material. The self-assembly process of the targeted MOFs with different topological structures can be controlled by the solvents and concentration of the reactants. Luminescence experiments show that JXUST-20 and JXUST-21 exhibit strong yellow-green emission. JXUST-20 and JXUST-21 can selectively sense benzaldehyde (BzH) via a luminescence quenching effect with detection limits of 15.3 and 1.44 ppm, respectively. In order to expand the practical application of MOF materials, mixed-matrix membranes (MMMs) have been constructed by mixing targeted MOFs and poly(methyl methacrylate) in a N,N-dimethylformamide (DMF) solution, which can also be used for BzH vapor sensing. Therefore, the first case of MMMs derived from Tb^III MOFs has been developed for the reversible detection of BzH vapor, providing a simple and efficient platform for the future detection of volatile organic compounds.

In Situ Formation of o-Phenylenediamine Cascade Polymers Mediated by Metal-Organic Framework Nanozymes for Fluorescent and Photothermal Dual-Mode Assay of Acetylcholinesterase Activity

A fluorescent and photothermal dual-mode assay method was established for the detection of acetylcholinesterase (AChE) activity based on in situ formation of o-phenylenediamine (oPD) cascade polymers. First, copper metal-organic frameworks of benzenetricarboxylic acid (Cu-BTC) were screened out as nanozymes with excellent oxidase-like activity and confinement catalysis effect. Then, an ingenious oPD cascade polymerization strategy was proposed. That is, oPD was oxidized by Cu-BTC to oPD oligomers with strong yellow fluorescence, and oPD oligomers were further catalyzed to generate J-aggregation, which promotes the formation of oPD polymer nanoparticles with a high photothermal effect. By utilizing thiocholine (enzymolysis product of acetylthiocholine) to inhibit the Cu-BTC catalytic effect, AChE activity was detected through the fluorescence-photothermal dual-signal change of oPD oligomers and polymer nanoparticles. Both assay modes have low detection limitation (0.03 U L^-1 for fluorescence and 0.05 U L^-1 for photothermal) and can accurately detect the AChE activity of human serum (recovery 85.0-111.3%). The detection results of real serum samples by fluorescent and photothermal dual modes are consistent with each other (relative error ≤ 5.2%). It is worth emphasizing that this is the first time to report the high photothermal effect of oPD polymers and the fluorescence-photothermal dual-mode assay of enzyme activity.

A New Microporous Lanthanide Metal-Organic Framework with a Wide Range of pH Linear Response

Lanthanide metal-organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H₃TATB) as an organic ligand, coordinated with lanthanide ions (Eu³⁺/Tb³⁺), and synthesized a new metal-organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH^- and ligand (TATB^3-) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0-14), which can be used as a potential fluorescence sensing material for pH detection.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.