Introducing bifunctional metal-organic frameworks to the construction of a novel ratiometric fluorescence sensor for screening acid phosphatase activity

Ru@UiO-66-NH2 MOFs-Based Dual Emission Ratiometric Fluorescence for Sensitive Sensing of Arginine

Arginine has been widely applied in the food industry as coloring agents, flavoring agents, and nutritional fortifiers. It is also one of the major components of feed additives. Currently, methods for the highly selective detection of arginine remain absent. For accurate and sensitive detection of L-arginine, a novel ratiometric fluorescence assay based on Ru@UiO-66-NH2 was developed and demonstrated in this study. Under optimized detection conditions, the limit of detection (LOD) of this assay for L-arginine was 2.32 μM, which is superior to most assays reported to date. Meanwhile, Ru@UiO-66-NH2 showed good stability within 30 days, demonstrating the wide applicability of the proposed assay. The spike-and-recovery rates of the proposed assay for L-arginine in real samples (e.g., tea, grape juice, and serum) were 84.27-113.09%. Overall, the proposed assay showed high sensitivity, good reproducibility, and excellent stability in the detection of L-arginine in both buffer and real samples.

Application of Nanozymes and its Progress in the Treatment of Ischemic Stroke

Nanozymes are a new kind of material which has been applied since the beginning of this century, and its birth has promoted the development of chemistry, materials science, and biology. Nanozymes can be used as a substitute for natural enzyme and has a wide range of applications; therefore, it has attracted extensive attention from all sectors of the community, and the number of studies has constantly increasing. In this paper, we introduced the outstanding achievements in the field of nanozymes in recent years from the main function, the construction of nanozyme-based biosensors, and the treatment of ischemic stroke, and we also illustrated the internal mechanism and the catalytic principle. In the end, the obstacles and challenges in the future development of nanozymes were proposed.

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.

Highly sensitive and novel dual-emission fluorescence nanosensor utilizing hybrid carbon dots-quantum dots for ratiometric determination of chlorpromazine

Herein, a ratiometric fluorimetric nanosensor is introduced for the sensitive and selective analysis of chlorpromazine (CPZ) via employing blue-emitting B-doped carbon dots (B-CDs) as the reference fluorophore and green-emitting CdTe capped thioglycolic acid (TGA) quantum dots (TGA-CdTe-QDs) as the specific recognition probe. The sensor exhibits dual emission centered at 440 and 560 nm, under a single excitation wavelength of 340 nm. Upon the addition of ultra-trace amount of CPZ, the fluorescence signal of TGA-CdTe-QDs declines due to electron transfer process from excited TGA-CdTe-QDs to CPZ molecules, whereas the fluorescence peak of B-CDs is unaffected. Therefore, a new fluorimetric platform was prepared for the assay of CPZ in the range of 2.2 × 10-10 to 5.0 × 10-9 M with a detection limit of 1.3 × 10-10 M. Moreover, the practicability of the designed strategy was investigated for the detection of CPZ in biological samples and the results demonstrate that it possesses considerable potential to be utilized in practical applications.

Molecularly imprinted metal-organic frameworks assisted cloth and paper hybrid microfluidic devices for visual detection of gonyautoxin

Marine algal toxin contamination is a major threat to human health. Thus, it is crucial to develop rapid and on-site techniques for detecting algal toxins. In this work, we developed colorimetric cloth and paper hybrid microfluidic devices (μCPADs) for rapid detection of gonyautoxin (GTX1/4) combined with molecularly imprinted polymers. In addition, the metal-organic frameworks (MOFs) composites were applied for this approach by their unique features. Guanosine serves as a dummy template for surface imprinting and has certain structural advantages in recognizing gonyautoxin. MOF@MIPs composites were able to perform a catalytic color reaction using hydrogen peroxide-tetramethylbenzidine for the detection of GTX1/4. The cloth-based sensing substrates were assembled on origami μPADs to form user-friendly, miniaturized colorimetric μCPADs. Combined with a smartphone, the proposed colorimetric μCPADs successfully achieved a low limit of detection of 0.65 μg/L within the range of 1-200 μg/L for rapid visual detection of GTX1/4. Moreover, the GTX1/4 of real shellfish and seawater samples were satisfactorily detected to indicate the application prospect of the μCPADs. The proposed method shows good potential in the low-cost, stable establishment of assays for the rapid detection of environmental biotoxins.

Chitosan-initiated gold nanoparticles with enhanced fluorescence for unique Fe3+/PPi sensing and photothermal therapy

The design of surface ligands is crucial for ligand-protected gold nanoparticles (AuNPs). Herein, following the principle of green synthesis, environmentally friendly gold nanoparticles (AuNPs@His@CC, AuHC) were fabricated based on dual ligands of histidine and carboxylated chitosan. AuHC showed the advantages of low toxicity, good photoluminescent stability and ideal biocompatibility. Compared with single histidine-coated gold nanoclusters (AuNCs@His, AuH), AuHC presented enhanced fluorescence attributed to the addition of chitosan. The blue-emitting AuHC has a unique response to Fe3+ with detection limits as low as 9.51 nM. Interestingly, the quenched fluorescence of AuHC-Fe3+ system could be restored through the introduction of PPi with a detection limit of 10.6 μM. So an "on-off-on" fluorescence sensing platform was achieved. Apart from good optical properties and sensing, the designed AuHC demonstrated outstanding photothermal conversion efficiency (27.8 %), which made it ideal material for thermal ablation of tumor. To be specific, after laser irradiation (660 nm, 0.78 W cm-2, 10 min) of AuHC, the survival rate of HeLa cells as a tumor cell model decreased to 12.7 %, indicating that AuHC has a significant tumor inhibition effect in vitro. Besides, AuHC also could be a befitting candidate for overcoming drug-resistant tumor cells such as MCF-7/ADR cells. Notably, AuHC can markedly ablate solid tumors in 4T1 tumor-bearing mice after laser irradiation (660 nm, 0.78 W cm-2, 10 min). Hence this work provides insight into the design of multifunctional AuNPs platform for simultaneously integrating the ion sensing and photothermal therapy of cancer.

Synthesis of tetraphenylethylene-based small molecular sensor for the selective "turn-on" detection of pyrophosphoric acid in the aqueous solution

Pyrophosphoric acid (PPi) is a crucial indicator for monitoring adenosine triphosphate hydrolysis processes, and abnormal PPi levels in the human body seriously threaten human health. Thus the efficient detection of the concentration of PPi in the aqueous solution is important and urgent. This paper described the successful synthesis of a tetraphenylethylene (TPE) derivative, named as TPE-4B, which contained four chelate pyridinium groups exhibiting aggregation-induced emission characteristics. TPE-4B was explicitly developed for the selective and sensitive fluorescence detection of PPi in aqueous solutions, showing a fluorescence "turn-on" response, and the detection limit was 65 nM. The four chelate pyridinium moieties of TPE-4B exhibited robust electrostatic interactions and binding capacity towards PPi, leading to the formation of aggregations, which was confirmed by zeta potential, dynamic light scattering, and scanning electron microscopy. Compared with free TPE-4B in the aqueous solution, the zeta potential of aggregations decreased from 20.7 to 4.2 mV, the average diameter increased from 155 to 403 nm, and the morphology transformed from porous nanostructures into a block-like format. Leveraging these properties, TPE-4B is a promising candidate for a "turn-on" fluorescence sensor designed to detect PPi in the aqueous solution.

Simple, sensitive, colorimetric detection of pyrophosphate via the analyte-triggered decomposition of metal-organic frameworks regulating their adaptive multi-color Tyndall effect

This paper describes initially the application of the Tyndall effect (TE) of metal-organic framework (MOF) materials as a colorimetric signaling strategy for the sensitive detection of pyrophosphate ion (PPi). The used MOF NH2-MIL-101(Fe) was prepared with Fe3+ ions and fluorescent ligands of 2-amino terephthalic acid (NH2-BDC). The fluorescence of NH2-BDC in MOF is quenched due to the ligand-to-metal charge transfer effect, while the NH2-MIL-101(Fe) suspension shows a strong TE. In the presence of PPi analyte, the MOFs will undergo decomposition because of the competitive binding of Fe3+ by PPi over NH2-BDC, resulting in a significant decrease in the TE signal and fluorescence restoration from the released ligands. The results demonstrate that the new method only requires a laser pointer pen (for TE creation) and a smartphone (for portable quantitative readout) to detect PPi in a linear concentration range of 1.25-800 μM, with a detection limit of ~210 nM (3σ) which is ~38 times lower than that obtained from traditional fluorescence with a spectrophotometer (linear concentration range, 50-800 µM; detection limit, 8.15 µM). Moreover, the acceptable recovery of PPi in several real samples (i.e., pond water, black tea, and human serum and urine) ranges from 97.66 to 119.15%.

Role of Metal-Organic Frameworks (MOFs) in treating and diagnosing microbial infections

This review article highlights the innovative role of metal-organic frameworks (MOFs) in addressing global healthcare challenges related to microbial infections. MOFs, comprised of metal nodes and organic ligands, offer unique properties that can be applied in the treatment and diagnosis of these infections. Traditional methods, such as antibiotics and conventional diagnostics, face issues such as antibiotic resistance and diagnostic limitations. MOFs, with their highly porous and customizable structure, can encapsulate and deliver therapeutic or diagnostic molecules precisely. Their large surface area and customizable pore structures allow for sensitive detection and selective recognition of microbial pathogens. They also show potential in delivering therapeutic agents to infection sites, enabling controlled release and possible synergistic effects. However, challenges like optimizing synthesis techniques, enhancing stability, and developing targeted delivery systems remain. Regulatory and safety considerations for clinical translation also need to be addressed. This review not only explores the potential of MOFs in treating and diagnosing microbial infections but also emphasizes their unique approach and discusses existing challenges and future directions.

A dual-mode sensing platform based on metal-organic framework for colorimetric and ratiometric fluorescent detection of organophosphorus pesticide

Pesticide residues have raised considerable concern about environmental health and food safety. Despite a great advance in enzymatic sensors for pesticide detection, the intrinsic fragility of native enzyme and possible fake results due to single mode signal have hindered its wide application. Here, a novel dual-mode sensor is reported for organophosphorus pesticide detection by using metal-organic framework (MOF) nanozyme NH2-CuBDC as sensing element. The intrinsic peroxidase-mimicking activity and fluorescence property of NH2-CuBDC enable both colorimetric and fluorescent detection of chlorpyrifos. Compared with previously reported chlorpyrifos sensors, our sensor exhibits outstanding sensitivity, and the limits of detection (LOD, S/N = 3) in colorimetric and fluorescent modes are 1.57 ng/mL and 2.33 ng/mL, respectively. No obvious interferences from other substances were measured and chlorpyrifos analysis in real samples presented good reliability, showing practical potential. This work is anticipated to provide new insights to develop multifunctional nanozymes and integrated multi-mode sensing platforms.

A cost-effective, "mix & act" G-quadruplex/Cu (II) metal-nanozyme-based ratiometric fluorescent platform for highly sensitive and selective cysteine/bleomycin detection and multilevel contrary logic computing

Versatile nanozymes with fascinating catalytic properties provide inspiring and effective options for biosensing and pharmaceutical analysis. Herein, we report the first nanozyme-based ratiometric fluorescent platform for cysteine (Cys) and bleomycin (BLM) detection by harnessing the cost-effective and "mix & act" G-quadruplex/Cu(II) (G4/Cu) metal-nanozyme with satisfactory peroxidase-like activity, which was fully proven by circular dichroism (CD), electron paramagnetic resonance (EPR) spectra and reactive oxygen species (ROS) scavenging experiments. Based on the catalytic oxidation of G4/Cu metal-nanozyme toward two fluorescent substrates (Amplex Ultrared, AU; Scopoletin, Sc) with opposite responses in the presence of H2O2, and the specific interaction between Cu2+ and targets, we achieved the highly sensitive detection of Cys and BLM. Through recording the fluorescence changes of AU (emission at 590 nm, F590) and Sc (emission at 465 nm, F465), we obtained good linear relationships between ratiometric fluorescence values (F590/F465) and variable contents of targets, resulting in the competitive LODs of Cys (6.7 nM) and BLM (10 nM), respectively. Moreover, this platform presented high selectivity (without the need for masking agent) and acceptable performance in human serum samples. Furthermore, a library of DNA contrary logic pairs (CLPs) and multilevel concatenated circuits were fabricated based on the reverse dual-output of the above platform, enriching the building blocks of biocomputing. This work not only enlightened the design of affordable, "mix & act" type nanozyme-based ratiometric biosensors with high reliability, but also facilitated the pluralistic application of nucleic acid-templated nanozymes to innovative biocomputing.

Simultaneous Detection and Decontamination of Dichromate Ions: The Fluorescence Response and Photocatalysis of Thiadiazole-Modified Zr-Metal-Organic Frameworks

The simultaneous analysis and removal of highly toxic hexavalent chromium (Cr (VI)) in contaminated water via an easy method remain a serious task. Based on the guidance of bibliometric analysis, a thiadiazole ligand-modified zirconium metal-organic framework (Zr-MOF) heralds a new and simple approach to Cr (VI) treatment. The concentration can be determined by fluorescence quenching with a low detection limit of 1.4 μM and a high quenching constant of 6.88 × 103 M-1. For the sensing mechanism, the fluorescence intensity of the Zr-MOF decreased rapidly due to the competition of Cr (VI) with the Zr-MOF for absorption excitation energy and the induction of Zr-MOF aggregation. The analysis system also displayed satisfactory stability and applicability. Apart from sensing application, Zr-MOF can convert Cr (VI) to Cr (III), and the reduction rate constant was 0.004 min-1 under irradiation. Therefore, the bifunctional Zr-MOF provided a potential application method for controlling the pollution caused by Cr (VI) in wastewater.

A ratiometric fluorescent paper sensor based on dye-embedded MOF for high-sensitive detection of arginine

Ratiometric fluorescent sensors can suppress the interference of factors unrelated to analysis due to their built-in self-calibration characteristics, which exhibit higher sensitivity and more obvious visual detection in the process of qualitative and quantitative analysis. Herein, we constructed a ratiometric fluorescence probe based on fluorescent/colorimetric dual-mode method for the determination of arginine by encapsulating rhodamine B in-situ into UiO-66-NH2 MOFs (UiO-66-NH2@RhB). The as-prepared probe showed dual-emission characteristics under a single excitation wavelength. The fluorescence intensity of UiO-66-NH2 was increased significantly by arginine, while the emission peak intensity of rhodamine B remained stable, resulting in a single-signal response with fixed reference. Furthermore, the practicality of the presented sensor was successfully validated by quantitative detection of arginine in human serum. More significantly, paper-based sensors for arginine detection were devised by using carboxymethyl cellulose modified filter papers. Under the irradiation of ultraviolet light, the paper-based sensors would produce obvious color variation from lightpink to bluish violet. This work provided a convenient and efficient method for on-site detection of arginine.

Bifunctional Cu(II)-containing PDA-PEI copolymer dots: Demonstration of a dual-mode platform for colorimetric-fluorescent detection of glyphosate in the environment

The reliable and accurate detection of glyphosate is urgently demanded because it is related to food and environmental safety. In this contribution, a PDA-PEI/Cu2+ complex that possesses peroxidase-mimetic activity and stimulus-responsive fluorescence was fabricated by coordinating Cu2+ with polydopamine-polyethyleneimine copolymer dots (PDA-PEI CPDs). With the introduction of Cu2+, the fluorescence intensity of PDA-PEI CPDs dropped sharply owing to the electron transfer effect. As a peroxidase-mimicking nanozyme, the PDA-PEI/Cu2+ complex owns catalytic capacity to oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB, leading a further fluorescence quenching by internal filtering effect by oxTMB. Once the glyphosate participated, the fluorescence signal of PDA-PEI CPDs is recovered significantly because of the formation of more stable Glyp-Cu2+ complexes, meanwhile the peroxidase-mimicking activity of PDA-PEI/Cu2+ complex could be strongly hindered. According to this principle, a novel and extremely convenient 'turn off' colorimetric and 'turn on' fluorescence sensing platform can be established for dual-mode detection of glyphosate. The favorable sensitivity and selectivity and were verified in the analysis of glyphosate in the environment through the marriage of dual-signal sensing platform. The detection limit of the dual-mode glyphosate sensing platform was 103.82 ng/mL for colorimetric assay and 16.87 ng/mL for fluorescent assay, respectively. Satisfactory recoveries in the range of 96.40%-104.66% were obtained, indicating the potential of this method for application in complicated real sample. Thereby, this strategy broadens the applications of polydopamine nanomaterials and holds a promising application in determination of pesticide residues.

A Fluorescent Chemosensor for Detection pH and Cu2+ Ion Base on 7-((2-Aminoethyl)amino)-5-Bromo-6-Hydroxy-1-Methylquinolin-1-ium-3-Sulfonate: Experimental and DFT Calculation

A quinoline derivative 7-((2-aminoethyl)amino)-5-bromo-6-hydroxy-1-methylquinolin-1-ium-3-sulfonate (QEt) containing quinoline ring, -[Formula: see text] sulfonate, -OH phenol, and amine groups was synthesized and studied luminescence properties. The aqueous solutions QEt 10µM change luminescence color from green (λem = 490 nm) to yellow (λem = 563 nm) as increasing pH and the intensity at a peak of 563 nm is linearly proportional with pH value in the range of pH = 3,0-4,0. The QEt solution can be used as a chemosensor for Cu2+ with an LOD value at 0.66 [Formula: see text]. Along with the experiment, the structure, absorption and emission spectra of QEt have been investigated by TD-DFT calculation. The result shows that the absorption band centered at 420 nm is due to the electron transition from HOMO to LUMO (π → π*). The results also help to assign emission band centered at 490 nm is due to the S1 → S0 transition (LUMO → HOMO singlet transition), at 563 nm is due to the T1 → S0 transition (LUMO → HOMO triplet transition). The dependence of the relative intensity of each emission peak on pH, which is experimentally recorded, is explained based on the results of theoretical TD-DFT calculation.

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.

Tetrahedral DNA nanostructure-corbelled click chemistry-based large-scale assembly of nanozymes for ratiometric fluorescence assay of DNA methyltransferase activity

Ligation efficiency in a surface-based DNA click chemistry (CuAAC) reaction is extremely restricted by the orientation and density of probes arranged on a heterogeneous surface. Herein, we engineer DNA tetrahedral nanostructure (DTN)-corbelled click chemistry to trigger a hybridization chain reaction (HCR) assembling a large-scale of nanozymes for ratiometric fluorescence detection of DNA adenine methyltransferase (Dam). In this study, a DNA tetrahedron structure with an alkynyl modifying pendant DNA probe (Alk-DTN) is designed and assembled on a magnetic bead (MB) as a scaffold for click chemistry. When a CuO NP-encoded magnetic nanoparticle (CuO-MNP) substrate was methylated by Dam, CuO NPs were released and turned into a mass of Cu+. The Cu+ droves azido modifying lDNA (azide-lDNA) to connect with the Alk-DTN probe on the MB through the click reaction, forming an intact primer to initiate the HCR. The HCR product, a rigid structure double-stranded DNA, periodically assembles glucose oxidase mimicking gold nanoparticles (GNPs) into a large-scale of nanozymes for catalyzing the oxidation of glucose to H2O2. NH2-MIL-101 MOFs, a fluorescent indicator and a biomimetic catalyst, activated the product H2O2 to oxidize o-phenylenediamine (oPD) into visually detectable 2,3-diaminophenazine (DAP). The change of the signal ratio between DAP and NH2-MIL-101 is proportional to the methylation event corresponding to the MTase activity. In this study, the DTN enhances the efficiency of the surface-based DNA click reaction and maintains the catalytic activities of gold nanoparticle nanozymes due to the intrinsic nature of mechanical rigidity and well-controlled orientation and well-adjusted size. Large-scale assembly of nanozymes circumvents the loss of natural enzyme activity caused by chemical modification and greatly improves the amplification efficiency. The proposed biosensor displayed a low detection limit of 0.001 U mL-1 for Dam MTase due to multiple amplification and was effective in real samples and methylation inhibitor screening, providing a promising modular platform for bioanalysis.

Ratiometric fluorescent detection of exosomal piRNA-823 based on Au NCs/UiO-66-NH2 and target-triggered rolling circle amplification

piR-823 is a newly discovered colorectal cancer marker with high diagnostic efficacy. However, the current quantification methods have complicated operations and high cost, which restrict its clinical application. Herein, a metal-organic framework (MOF) with a UiO-66 prototype structure which supports gold nanoclusters (Au NCs), Au NCs/UiO-66-NH₂, were prepared as a model nanobiosensing platform for ratiometric detection of exosomal piR-823. The rolling circle amplification process provides high sensitivity and the ratiometric detection process ensures good accuracy of the sensor. Such biosensor showed a wide linear range of 0.04-4 pM, and a low detection limit of 10.2 fM towards piR-823. In addition, piR-823 can be used as an effective supplement to carcinoembryonic antigen (CEA) in clinical diagnosis of colorectal cancer. This study not only provides a potentially valuable ratio fluorescence platform involving enzyme catalytic reaction, but also offers a design blueprint for further expansion of nanotechnology in the diverse biological analysis.

A smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor for visual detection of mercury ions and l-penicillamine

Establishment of a rapid, sensitive, visual, accurate and low-cost fluorescence detection system to detect multiple targets was of great significance in food safety evaluation, ecological environment monitoring and human health monitoring. In this work, a smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor was proposed based on metal-organic framework (NH₂-MIL-101(Fe)) and CdTe quantum dots (CdTe QDs) for visual detection of mercury ions (Hg²⁺) and L-penicillamine (L-PA), in which NH₂-MIL-101(Fe) was used as the reference signal and CdTe QDs was used as the response signal. The down-conversion fluorescence system at excitation wavelength of 300 nm (ex: 330 nm) was used to detect Hg²⁺ and L-PA, in which the detection limit of Hg²⁺ was 0.053 nM with the fluorescence color changed from green to blue, and the detection limit of L-PA was 1.10 nM with the fluorescence color changed from blue to green. Meanwhile, the up-conversion fluorescence system at excitation wavelength of 700 nm (ex: 700 nm) was used to detect Hg²⁺ and L-PA. The detection limits of Hg²⁺ and L-PA were 0.11 nM and 2.93 nM, respectively. The detection of Hg²⁺ and L-PA were also carried out based on the color extraction RGB values identified by the smartphone with a detection limit of 0.091 nM for Hg²⁺ and 8.97 nM for L-PA. In addition, the concentrations of Hg²⁺ and L-PA were evaluated by three-dimensional dynamic analysis in complex environments. The smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor system provides a new strategy for detection Hg²⁺ and L-PA in food safety evaluation, environmental monitoring and human health monitoring.

Ratiometric fluorescence sensing of formaldehyde in food samples based on bifunctional MOF

A new fluorescence strategy was described for ratiometric sensing of formaldehyde (FA) with bifunctional MOF, which acted as a fluorescence reporter as well as biomimetic peroxidase. With the assistance of H₂O₂, NH₂-MIL-101 (Fe) catalyzes the oxidation of non-luminescent substrate o-phenylenediamine (OPD) to produce fluorescent product (oxOPD) with the maximum emission at 570 nm. Besides, intrinsic fluorescence of MOF (λem = 445 nm) was quenched by oxOPD through inner filter effect (IFE). However, FA and OPD reacted to generate Schiff bases, which competitively consumed OPD inhibiting the generation of oxOPD. Under the excitation wavelength of 375 nm, a ratiometric strategy was designed to detect FA with the fluorescence intensity ratio at 445 nm and 570 nm (F₄₄₅/F₅₇₀) as readout signal. This strategy exhibited a wide linear range (0.1-50 μM) and low detection limit of 0.03 μM. This method was confirmed for FA detection in food samples. In addition to establishing a new method to detect FA, this work will open new applications of MOF in food safety.

Tris(bipyridine)ruthenium(II)-functionalized metal-organic frameworks for the ratiometric fluorescence determination of aluminum ions

A novel ratiometric fluorescence probe was designed for the determination of Al³⁺ by self-assembling of NH₂-MIL-101(Fe) and [Ru(bpy)₃]²⁺. Under the excitation wavelength of 360 nm, the NH₂-MIL-101(Fe)@[Ru(bpy)₃]²⁺ presented a dual-emitting luminescent property at 440 and 605 nm, respectively. In the presence of Al³⁺, the blue fluorescence of NH₂-MIL-101(Fe)@[Ru(bpy)₃]²⁺ at 440 nm was enhanced remarkably, while the red emission at 605 nm was almost not influenced. Therefore, taking the fluorescence at 440 nm as the report signal and 605 nm as the reference signal, quantitative determination was achieved for Al³⁺ concentration in the ranges 0.2-25 μM and 25-250 μM. The limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 73 nM and 244 nM, respectively. The sensing mechanisms were studied by theoretical calculation and optical spectra. The analysis of real food samples confirmed the suitability of the proposed method. More importantly, portable fluorescent test papers were successfully manufactured to provide a strategy for visual, rapid, and on-site detection of Al³⁺.

Ratiometric fluorescence sensing with logical operation: Theory, design and applications

The construction of ratiometric fluorescence sensing logic systems has gradually become a hot topic in fluorescence analysis, due to the multi-target analysis potential of logic operations and the high specificity and selectivity of ratiometric fluorescence sensing. In this paper, the basic principles of various logic functions implemented in ratiometric fluorescence detection are discussed in the context of sensing mechanisms, and the strategies for constructing logic systems in different ratiometric fluorescence sensing application areas are summarized. Although there are limitations such as cumbersome operations and complicated experiments, ratiometric fluorescence sensing logic circuits that combine the visualization of logic operations and the accuracy of ratiometric fluorescence are still worthy of in-depth study. This review may be useful for researchers interested in the construction of logic operations based on ratiometric fluorescence sensing applications.

A novel polydopamine-modified metal organic frameworks catalyst with enhanced catalytic performance for efficient degradation of sulfamethoxazole in wastewater

In this study, a novel polydopamine (PDA)-modified metal organic frameworks (MOFs) catalyst (MIL/PDA) was successfully fabricated to activate persulfate (PS) for the degradation of sulfamethoxazole (SMX) in wastewater. The experimental results indicated that PDA-modified catalyst exhibited superior catalytic performance and enhanced the degradation of SMX (91.5%) compared to pure MOFs. The physical-chemical properties of the MIL/PDA catalyst were comprehensively characterized, and the applications in the catalytic degradation of SMX were evaluated. It was found that the modification of PDA enhanced the electron transfer, while promoting the redox cycle of Fe(III)/Fe(II), which in turn boosted the production of active oxygen species. Furthermore, MIL/PDA showed high stability and reusable performance over multiple cycles. Both radical and non-radical pathways were jointly involved in the activation process of PS were confirmed by quenching experiments combined with electron paramagnetic resonance (EPR). Based on this, the possible mechanism of the catalytic reaction was investigated. Finally, five degradation pathways of SMX degradation were proposed according to the results of liquid chromatography-mass spectrometry (LC-MS). This work provided a new insight into the design of novel and efficient heterogeneous catalysts for advanced wastewater treatment.

Two-dimensional metal-organic frameworks: from synthesis to bioapplications

As a typical class of crystalline porous materials, metal-organic framework possesses unique features including versatile functionality, structural and compositional tunability. After being reduced to two-dimension, ultrathin metal-organic framework layers possess more external excellent properties favoring various technological applications. In this review article, the unique structural properties of the ultrathin metal-organic framework nanosheets benefiting from the planar topography were highlighted, involving light transmittance, and electrical conductivity. Moreover, the design strategy and versatile fabrication methodology were summarized covering discussions on their applicability and accessibility, especially for porphyritic metal-organic framework nanosheet. The current achievements in the bioapplications of two-dimensional metal-organic frameworks were presented comprising biocatalysis, biosensor, and theranostic, with an emphasis on reactive oxygen species-based nanomedicine for oncology treatment. Furthermore, current challenges confronting the utilization of two-dimensional metal-organic frameworks and future opportunities in emerging research frontiers were presented.

Exploration of nanozymes in viral diagnosis and therapy

Nanozymes are nanomaterials with similar catalytic activities to natural enzymes. Compared with natural enzymes, they have numerous advantages, including higher physiochemical stability, versatility, and suitability for mass production. In the past decade, the synthesis of nanozymes and their catalytic mechanisms have advanced beyond the simple replacement of natural enzymes, allowing for fascinating applications in various fields such as biosensing and disease treatment. In particular, the exploration of nanozymes as powerful toolkits in diagnostic viral testing and antiviral therapy has attracted growing attention. It can address the great challenges faced by current natural enzyme-based viral testing technologies, such as high cost and storage difficulties. Therefore, nanozyme can provide a novel nanozyme-based antiviral therapeutic regime with broader availability and generalizability that are keys to fighting a pandemic such as COVID-19. Herein, we provide a timely review of the state-of-the-art nanozymes regarding their catalytic activities, as well as a focused discussion on recent research into the use of nanozymes in viral testing and therapy. The remaining challenges and future perspectives will also be outlined. Ultimately, this review will inform readers of the current knowledge of nanozymes and inspire more innovative studies to push forward the frontier of this field.

Waste tobacco leaves derived carbon dots for tetracycline detection: Improving quantitative accuracy with the aid of chemometric model

The recycling and reutilization of biomass wastes are significant for environmental protection and sustainable development. Recently, there have many studies on utilizing biomass wastes to produce carbon dots. Whereas, the spectrum shift effect that occurs in the quantitative application of carbon dots as fluorescent probes limits the accuracy of the quantitative analysis. In this work, waste tobacco leaves were used as the carbon source for synthesizing a novel carbon dots (CDs(WTL)) through a facile hydrothermal method. The CDs(WTL) possess a series of excellent properties, including good water solubility, well stability, and high fluorescence quantum yield. The fluorescent intensity of the CDs(WTL) can be quenched by tetracycline (TC) obviously, but there is a spectrum shift. In order to use the CDs(WTL) as fluorescent probes to quantify TC with higher accuracy, a quantification fluorescence model (QFM) was introduced to overcome this spectrum shift effect that often occurs. The coefficient of determination (R2) of traditional quantification model (TQ), partial least squares (PLS), and QFM are 0.9672, 0.9834, and 0.9991, respectively; the average relative predictive error (ARPE) of TQ, PLS, and QFM are 8.8%, 4.5%, and 3.9% for the spiked water samples, and 21.9%, 22.0%, and 2.9% for spiked tablet samples, respectively. The obtained results suggest that QFM is more accurate than PLS and TQ for the TC detection. By utilizing QFM, the spike recoveries (mean ± standard deviation) in three kinds of real tablet samples produced by different manufacturers are 98.9 ± 3.6%, 102.5 ± 6.2%, and 98.5 ± 2.7%, respectively; the spike recovery in river water samples is 99.4 ± 5.0%. In addition, high performance liquid chromatography (HPLC) was used as a reference method, the F and t tests suggest that there are no significant differences on the precision and accuracy between QFM and HPLC methods.

Fabricating multifunctional low-toxicity ratiometric fluorescent probe for individual detection of Cu2+/glutamate and continuous sensing for glutamate via Cu2+-based platform

Herein, a multifunctional ratiometric fluorescent (RF) probe Fe-MIL-88NH₂@RhB was fabricated for individual detection of Cu^2+/Glu and continuous sensing of Glu based on unique coordination principle by encapsulating RhB into the porous of metal-organic-framework-Fe-MIL-88NH₂. Designed Fe-MIL-88NH₂@RhB platform could selectively identify Cu(II)/Glu accompanying a turn-off/turn-on fluorescent behavior with good linearity. Moreover, if the Fe-MIL-88NH₂@RhB/Cu²⁺ is treated with Glu continuously, the quenching fluorescence of this platform (after Cu²⁺ sensing at blue emission) would be further in turn restored. Utilizing Fe-MIL-88NH₂@RhB probe, the imaging of intracellular Cu(II) and Glu in living A549 cells was successful conducted through divisional channels with a satisfactory low cytotoxicity, meanwhile, the sensing results of Glu in serum by the molecular logic gate was also superior, which may use for development of an medical occupational tool for amyotrophic lateral sclerosis tentative diagnosis. In addition, the MOF shows di-modal response (color and lumescence) to Cu²⁺ and Glu with excellent selectivity against a wide range of other interference analytes, and the corresponding portable low-toxicity on-line test strips for Cu²⁺ and Glu recognize has exhibited a remarkable visually chromogenic phenomena, which may utilize for monitoring these contaminants in real water sample. Finally, the feasibility of probe to monitor Cu²⁺ and Glu in foodstuffs was also evaluated.

Microfluidic encapsulated manganese organic frameworks as enzyme mimetics for inflammatory bowel disease treatment

Metal organic frameworks (MOFs) with physicochemical properties and adjustable structures have been proposed as very attractive materials. The studies on development of such functional materials tended to fabricate featured MOF objects with fascinating catalytic capabilities to utilize their biomedical values. In this paper, we present novel biocompatible manganese metal organic framework (Mn-MOF)-based catalase mimetics with microfluidic microcapsule encapsulation for intravital inflammatory bowel disease (IBD) treatment. Phosphoserine, a component of the cell membrane, served as an organic ligand to ensure biocompatibility of Mn-MOF. Owing to the core-shell structure of the microcapsule, the Mn-MOF exhibited a well-organized distribution and controlled release features, which could protect them from gastric juice and provide function in the intestine. Upon reaching the sites of the inflammatory bowel, Mn-MOF could effectively scavenge reactive oxygen species (ROS) over-produced by neutrophils and macrophages under various gastrointestinal pH environments, protecting intestinal epithelial cells from ROS damage. The Mn-MOF-encapsulated microcapsules exhibited high performances in treating spontaneous IBD in interleukin-10-deficient mice by relieving the oxidative stress, reducing the inflammation, and restoring the intestinal barrier. These results indicate that the functional Mn-MOF-encapsulated microcapsules have practical applications in the treatment of ROS-associated diseases.

Enzymatic electrochemical biosensor for glyphosate detection based on acid phosphatase inhibition

A novel enzymatic electrochemical biosensor was fabricated for the indirect detection of glyphosate-based acid phosphatase inhibition. The biosensor was constructed on a screen-printed carbon electrode modified with silver nanoparticles, decorated with electrochemically reduced graphene oxide, and chemically immobilized with acid phosphatase via glutaraldehyde cross-linking. We measured the oxidation current by chronoamperometry. The current arose from the enzymatic reaction of acid phosphatase and the enzyme-substrate disodium phenyl phosphate. The biosensing response is a decrease in signal resulting from inhibition of acid phosphatase in the presence of glyphosate inhibitor. The inhibition of acid phosphatase by glyphosate was investigated as a reversible competitive-type reaction based on the Lineweaver-Burk equation. Computational docking confirmed that glyphosate was the inhibitor bound in the substrate-binding pocket of acid phosphatase and that it was able to inhibit the enzyme efficiently. Additionally, the established method was applied to the selective analysis of glyphosate in actual samples with satisfactory results following a standard method.

Glucose oxidase decorated fluorescent metal-organic frameworks as biomimetic cascade nanozymes for glucose detection through the inner filter effect

Metal-organic frameworks (MOFs) as a peroxidase mimic have been integrated with glucose oxidase (GOx) to achieve one-step glucose detection. However, limited by the loading amount of GOx, the performances of the developed glucose sensing assays still remain to be further improved to meet sensing requirements in diverse biological samples. Herein, with Fe3+ as the metal ion and 2-amino-benzenedicarboxylic acid as a ligand, a fluorescent Fe-based organic framework (NH2-MIL-101) with peroxidase-like activity was synthesized. Due to the large specific surface area (791.75 m2 g-1), 68 μg mg-1 GOx could be immobilized through the amidation coupling reaction, and the product was designated GOx@NH2-MIL-101. With OPD as the substrate, Gox@NH2-MIL-101 achieved highly efficient biomimetic cascade catalysis for one-step glucose detection through an inner filter effect: upon reacting with glucose, GOx@NH2-MIL-101 catalytically oxidized glucose using dissolved O2, and the produced H2O2 concurrently oxidized o-phenylenediamine (OPD) to oxidized OPD (oxOPD), accompanied by the fluorescence of GOx@NH2-MIL-101 at 456 nm being quenched and that of oxOPD at 565 nm being enhanced. With the fluorescent ratio F565/F456 used as a readout signal, a wide linear range of 0.1-600 μM was obtained, and the detection limit was 0.0428 μM. Based on the excellent selectivity and high stability of GOx@NH2-MIL-101, the developed assay was successfully applied to glucose detection in human serum and saliva, presenting potential applications in diverse biological samples and even medical diagnosis.

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.

Molecularly imprinted fluoroprobes doped with Ag nanoparticles for highly selective detection of oxytetracycline in real samples

A molecularly imprinted polymer (MIP), which is synthesized by a nanomolding process around a template, has emerged as a promising analytical tool for environmental quality monitoring and food safety test. In this work, a fluoroprobe with Ag-doped MIP nanolayer (16 nm thickness) is successfully prepared for the highly selective detection of oxytetracycline (OTC) in real samples (i.e. Yangtze River water, swine urine). In the MIP nanolayer, two functional monomers (i.e. 4-(2-acrylamidoethylcarbamoyl)-3-fluorophenylboronic acid, methacrylic acid) synergistically constitute the specific recognition sites. Meanwhile, the doped Ag enhances the detection sensitivity (with a detection limit of 5.38 nM) and accelerates the detection rate (within 2.5 min) even in real samples. Therefore, the present study paves the way for the preparation of MIP-based fluoroprobes, showing great prospects in environmental quality and food safety tests.

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.

Solvothermal preparation of luminescent zinc(II) and cadmium(II) coordination complexes based on the new bi-functional building block and photo-luminescent sensing for Cu2+, Al3+ and L-lysine

In industry, over usage of Cu²⁺ and Al³⁺ will lead to toxic wastewater, which further to give serious pollution for the environment. On the other hand, L-lysine can enhance serotonin release in the amygdala, with subsequent changes in psychobehavioral responses to stress. Therefore it is the urgent problem to design a method for detecting the amount of Cu²⁺, Al³⁺, and L-lysine. In this work, through the solvothermal synthesis method, two new coordination complexes based on the new bifunctional building block 4'-(1H-1,2,4-triazole-1-yl)- [1,1'-biphenyl]-4-carboxylic acid (HL) have been synthesized, namely, [Zn(L)₂·4H₂O] (complex 1) and [Cd(L)₂·4H₂O] (complex 2). X-ray single-crystal diffractometer was used to analyze its structure, powder X-ray diffraction (PXRD) patterns confirmed that 1 and 2 powder's purity and 1 can keep stable during the detection process of Cu²⁺, Al³⁺, and L-lysine, respectively. Elemental analysis, thermogravimetric analysis, infrared analysis, ultraviolet analysis and fluorescent spectrum have been used to characterize these complexes. The photo-luminescent test showed that 1 can accurately recognize Al³⁺ and Cu²⁺ among various cations. On the other hand, 1 can distinguish L-lysine among amino acid molecules. Therefore, 1 can be utilized as a multifunctional fluorescent probe for Al³⁺(K_sv = 1.5570 × 10⁴ [M]^-1), Cu²⁺(K_sv = 1.4948 × 10⁴ [M]^-1) and L-lysine (K_sv = 4.9118 × 10⁴ [M]^-1) with low detection limits (17.5 μM, 18.2 μM, 5.6 μM) respectively.

A colorimetric sensor for acid phosphatase activity detection based on acridone derivative as visible-light-stimulated oxidase mimic

Currently, organic artificial enzymes as biocatalysts have been extensively used to construct various colorimetric sensors. However, exploiting a potential organic artificial enzyme with high catalytic efficiency still remains a challenge. To address this issue, herein, we synthesize an acridone derivative 10-benzyl-2-amino-acridone (BAA). The synthesized BAA exhibits an intrinsic visible-light-stimulated oxidase-like activity, which is capable of oxidizing various chromogenic substrates without destructive hydrogen peroxide (H₂O₂) under visible light stimulation, resulting in colored products. The reaction system can be regulated by switching light on and off, which is milder and more reliable means than others H₂O₂-dependent. The photocatalytic mechanism of BAA is investigated in detail. However, l-ascorbic acid (AA), an antioxidant generating from the acid phosphatase (ACP)-mediated hydrolysis of 2-phospho-l-ascorbic acid (AAP), is able to inhibit the catalytic activity of BAA. Based on the above properties, a facile, photo-switchable and low-cost colorimetric sensing strategy is developed for ACP detection. The linear range is 0.05-2.5 U/L (r = 0.9994), and the limit of detection (LOD) is 0.0415 U/L. Moreover, the proposed sensing system can be applied for monitoring ACP activity in practical samples, demonstrating promising applications in clinical analysis and biosensor platform.

Smartphone based highly sensitive visualized detection of acid phosphatase enzyme activity

With the rapid development of point-of-care (POC) technologies, development of sensitive method featured with fast analysis and affordable devices has become an emerging requirement for practical applications. In this study, we introduced a smartphone-based RGB analysis system for the sensitive detection of acid phosphatase (ACP) enzyme activity. In the presence of ACP, l-ascorbic acid 2-phosphate (AAP) can be converted into ascorbic acid (AA), which can reduce Ag⁺ to Ag⁰ and format the Au@Ag core-shell nanostructure. This morphology change of the Au@Ag core-shell would trigger a significant color variation (pink to yellow). A good linear relationship between the RGB model parameter and the concentration of ACP could be obtained with a detection limit of 0.1 U L^-1. Moreover, this sensing strategy is suitable for the detection of ACP in practical serum samples. Thus, this simple but powerful protocol has great potential application for on-site detection of ACP in future complex biological samples.

A ratiometric fluorescence sensor for triticonazole based on the encapsulated boron-doped and phosphorous-doped carbon dots in the metal organic framework

In this work, boron-doped carbon dots (B-CDs) with blue fluorescence and phosphorous-doped green emitting CDs (P-CDs) were encapsulated into zeolitic imidazolate framework-8 (ZIF-8) to prepare a dual-emission ratiometric fluorescence sensor for triticonazole. The B-CDs/P-CDs@ZIF-8 composite exhibited two emission peaks at 440 nm and 510 nm under a single wavelength excitation of 385 nm that respectively belong to B-CDs and P-CDs. In the presence of triticonazole, the fluorescence intensity of B-CDs remarkably declined while that of P-CDs remained unchanged. With increasing concentration of triticonazole, the fluorescence color of the ratiometric probe progressively changed from blue to green. Under the optimized conditions, B-CDs/P-CDs@ZIF-8 probe showed a high sensitivity with a linear range from 10 to 400 nM and a detection limit of 4.0 nM for triticonazole. The probe not only has an improved sensitivity through the accumulation of analyte molecules into the metal-organic framework but also has the advantages of ratiometric fluorescence measurements in terms of precision and accuracy. The applicability of the sensor was evaluated in the analysis of water and fruit juice samples.

A microfluidic biosensor for rapid and automatic detection of Salmonella using metal-organic framework and Raspberry Pi

Rapid screening of pathogenic bacteria contaminated foods is crucial to prevent food poisoning. However, available methods for bacterial detection are still not ready for in-field screening because culture is time-consuming; PCR requires complex DNA extraction and ELISA lacks sensitivity. In this study, a microfluidic biosensor was developed for rapid, sensitive and automatic detection of Salmonella using metal-organic framework (MOF) NH₂-MIL-101(Fe) with mimic peroxidase activity to amplify biological signal and Raspberry Pi with self-developed App to analyze color image. First, the target bacteria were separated and concentrated with the immune magnetic nanobeads (MNBs), and labeled with the immune MOFs to form MNB-Salmonella-MOF complexes. Then, the complexes were used to catalyze colorless o-phenylenediamine and H₂O₂ to produce yellow 2,3-diaminophenazine (DAP). Finally, the image of the catalysate was collected under the narrow-band blue light and analyzed using the Raspberry Pi App to determine the bacterial concentration. The experimental results showed that this biosensor was able to detect Salmonella Typhimurium from 1.5 × 10¹ to 1.5 × 10⁷ CFU/mL in 1 h with the lower detection limit of 14 CFU/mL. The mean recovery for Salmonella in spiked chicken meats was ~112%. This biosensor integrating mixing, separation, labelling and detection onto a single microfluidic chip has demonstrated the merits of automatic operation, fast reaction, less reagent and small size, and is promising for in-field detection of foodborne bacteria.

Design of turn-on luminescent sensor based on nanostructured molecularly imprinted polymer-coated zirconium metal-organic framework for selective detection of chloramphenicol residues in milk and honey

Herein, an optical sensor based on nanostructured molecularly imprinted polymer (MIP) coated on a luminescent zirconium metal-organic framework (MIP/Zr-LMOF) is introduced, and its performance is investigated for the fluorescent determination of chloramphenicol (CAP) antibiotic residues in milk and honey. To fabricate the sensor, the surface of Zr-LMOF is modified with MIP in the presence of CAP template, resulting in the introduction of recognition sites for antibiotic molecules. The porous structure of Zr-LMOF with specific binding sites for CAP recognition benefiting from coated MIP leads to selective and sensitive detection of antibiotic. The probe yields a linear range for detection of CAP in trace concentrations (0.16-161.56 µg.L^-1) and provides a detection limit of 0.013 µg.L^-1. Acceptable recoveries are achieved for antibiotic in real samples, which are consistent with that obtained from liquid chromatography-tandem mass spectrometry (LC-MS/MS), confirm the favorable performance of sensor for accurate determination of CAP in practical applications.

A hydrophobic polymer stabilized CsPbBr3 sensor for environmental pollutant detection

The detection of o-nitrophenol in the environment is of great significance to environmental protection.