One-Pot Synthesis of a Magnetic, Ratiometric Fluorescent Nanoprobe by Encapsulating Fe3O4 Magnetic Nanoparticles and Dual-Emissive Rhodamine B Modified Carbon Dots in Metal-Organic Framework for Enhanced HClO Sensing

Ratiometric fluorescence assay for ciprofloxacin in human blood serum and urine samples based on sulfur-doped carbon dots/rhodamine B nanohybrid encapsulated HKUST-1 metal-organic framework

Preparation of carbon dots (CDs) from biomass waste is of great interest due to its low cost synthesis, environmental compatibility and functionalization without adding dangerous chemicals. Herein, S-doped carbon dot (SCD) was synthesized using agricultural waste as carbon precursors and modified in-situ with rhodamine B dye (SCD@RHB) to construct efficient flouresent probe. SCD@RHB was loaded into HKUST-1 metal-organic framework (SCD@RHB/HKUST-1) and the probe was employed as ratiometric flouresent (RF) sensor for the determination of ciprofloxacin (CIP) antibiotic in trace level. The sensor emits two-resolved peaks at 415 and 575 nm under excitation wavelength of 310 nm which are due to the characteristic fluorescence emissions of SCD and RHB, respectively. Under optimal conditions, the emissions of SCD and RHB change oppositely in the presence of CIP which can be used to evaluate the sensing performance of probe. The ratiometric SCD@RHB/HKUST-1 nanohybrid has a wide linear range (0.1-300 μM) with a low detection limit of 21.3 nM along with good sensitivity and selectivity for CIP. The probe was also used for the determination of CIP in human blood and urine samples. The results demonstrated rapid and accurate analysis with reasonable recoveries of 94 to 102 % for blood sample and 94-106 % for urine sample. This strategy provides a conveninet way to design RF sensors based on HKUST-1.

Construction of enzyme-MOFs composite with carbon dots: A strategy to enhance the activity and increase the growth rate of the enzyme-ZIF-8 composite

Encapsulating enzymes in metal-organic frameworks (MOFs) enhances enzyme protection and improves the accuracy of inhibitor recognition and screening. Zeolitic imidazolate framework-8 (ZIF-8) has been widely used as a host matrix for enzyme immobilization. However, challenges such as the microporous structure and hydrophobicity of ZIF-8, along with the protonation of 2-methylimidazole, hinder the maintenance of activity and the rapid formation of composite. Herein, a new strategy to synthesize novel enzyme-MOFs composite by encapsulating carbon dots (CDs)-modified enzyme and Fe3O4 nanoparticles within ZIF-8 is presented for the first time. The contribution of CDs in enzyme-MOFs composite was investigated. Characterizations reveal that the CDs-modified enzymes compete with imidazole for Zn ions, inducing mesoporous structures that alleviate diffusion limitations. Modification of enzyme with CDs also modulates enzyme-MOFs interfacial interactions, accelerating the formation of composite. Activity evaluation shows that enzyme-MOFs composite (THR@CDs/Fe3O4@ZIF-8) retains 81.76 % enzyme activity under harsh conditions and maintains 66.0 % of the initial enzyme activity after 10 reuse cycles. This synthesis strategy for the novel enzyme-MOFs composite was proven to be universal. The Km value of THR@CDs/Fe3O4@ZIF-8 (19.32 μM) is lower than that of THR/Fe3O4@ZIF-8, indicating that modification with CDs significantly increases the affinity of enzyme. Furthermore, THR@CDs/Fe3O4@ZIF-8 was effectively utilized for enzyme inhibitor recognition and screening. These results demonstrate that the proposed method is a universal approach for rapidly and controllably fabricating enzyme-ZIF-8 composite with elevated activity and exceptional stability, offering promising potential for advanced drug recognition and screening platforms.

Encapsulating Fe3O4 Nanoparticles and Carbon Dots in a Metal-Organic Framework for Magnetic Fluorescent Taggants

Magnetic fluorescent composite nanomaterials have broad application prospects in the fields of biological imaging, anticounterfeiting identification, suspicious object tracking, and identification of latent fingerprints in forensic medicine. For an effective taggant, a clearly visible identifying mark is necessary to enable observers to capture labeling information quickly and accurately, even from a distance. The preparation method of magnetic fluorescent composite materials is complicated and usually needs different surface modification and assembly processes. The limited loading capacity of fluorescent materials also limits the fluorescence properties of the composite, so it is difficult to produce obvious fluorescence as a taggant to meet the requirements of visible labeling. In this study, a core-shell structure of a magnetic fluorescent composite was prepared by using the metal-organic framework ZIF-8 as the host of fluorescent materials and an encapsulation shell coated on the Fe3O4 nanoparticles. The porous ZIF-8 is beneficial for increasing the loading capacity of fluorescent materials to ensure the fluorescence performance of the composite materials. Further modification of the composite surface prevented the desorption of fluorescent materials from the pores of ZIF-8, enabling the samples to maintain good fluorescence properties even after multiple washing cycles. The preparation method is simple, rapid, and cost-effective, and the prepared magnetic fluorescent composite nanomaterial has high magnetic separation performance and fluorescence performance, making it a promising material for identification, marking, and tracking.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Tracking the Cellular Degradation of Silver Nanoparticles: Development of a Generic Kinetic Model

Understanding the degradation of nanoparticles (NPs) after crossing the cell plasma membrane is crucial in drug delivery designs and cytotoxicity assessment. However, the key factors controlling the degradable kinetics remain unclear due to the absence of a quantification model. In this study, subcellular imaging of silver nanoparticles (AgNPs) was used to determine the intracellular transfer of AgNPs, and single particle ICP-MS was utilized to track the degradation process. A cellular kinetic model was subsequently developed to describe the uptake, transfer, and degradation behaviors of AgNPs. Our model demonstrated that the intracellular degradation efficiency of AgNPs was much higher than that determined by mimicking testing, and the degradation of NPs was highly influenced by cellular factors. Specifically, deficiencies in Ca or Zn primarily decreased the kinetic dissolution of NPs, while a Ca deficiency also resulted in the retardation of NP transfer. The biological significance of these kinetic parameters was strongly revealed. Our model indicated that the majority of internalized AgNPs dissolved, with the resulting ions being rapidly depurated. The release of Ag ions was largely dependent on the microvesicle-mediated route. By changing the coating and size of AgNPs, the model results suggested that size influenced the transfer of NPs into the degradation process, whereas coating affected the degradation kinetics. Overall, our developed model provides a valuable tool for understanding and predicting the impacts of the physicochemical properties of NPs and the ambient environment on nanotoxicity and therapeutic efficacy.

Highly sensitive fluoroprobe for detecting Sudan dyes in paprika utilizing carbon dot-embedded zeolitic imidazolate framework-8

In this manuscript, we synthesized CDs@ZIF-8 through a one-step, in-situ method by integrating green-emitting carbon dots (CDs) with zeolitic imidazolate framework-8 (ZIF-8). The resulting CDs@ZIF-8 was utilized as an ultrasensitive probe for detection, leveraging the inner filter effect. The analysis demonstrated the capability to detect Sudan dyes. Sudan I, for example, could be detected within a concentration range spanning from 0.25 to 70 μM, achieving a remarkable detection limit of 76.56 nM. This established method was effectively employed for detecting Sudan I in paprika. Compared with CDs, CDs@ZIF-8 exhibited a 3.32-fold increase in sensitivity and a wider detection range. This enhanced performance was attributed to the porous ZIF-8, which allowed for the enrichment of targets around CDs and avoided the aggregation of CDs. Additionally, embedding the CDs in ZIF-8 improved their pH stability. Our study provides a new approach for using CDs under limited conditions by leveraging metal-organic frameworks.

Design and application of dual-emission metal-organic framework-based ratiometric fluorescence sensors

Metal-organic frameworks (MOFs) are novel inorganic-organic hybridized crystals with a wide range of applications. In the last twenty years, fluorescence sensing based on MOFs has attracted much attention. MOFs can exhibit luminescence from metal nodes, ligands or introduced guests, which provides an excellent fluorescence response in sensing. However, single-signal emitting MOFs are susceptible to interference from concentration, environment, and excitation intensity, resulting in poor accuracy. To overcome the shortcomings, dual-emission MOF-based ratiometric fluorescence sensors have been proposed and rapidly developed. In this review, we first introduce the luminescence mechanisms, synthetic methods, and detection mechanisms of dual-emission MOFs, highlight the strategies for constructing ratiometric fluorescence sensors based on dual-emission MOFs, and classify them into three categories: intrinsic dual-emission and single-emission MOFs with luminescent guests, and non-emission MOFs with other luminescent materials. Then, we summarize the recent advances in dual-emission MOF-based ratiometric fluorescence sensors in various analytical industries. Finally, we discuss the current challenges and prospects for the future development of these sensors.

Orange peel-derived carbon dots/Cu-MOF nanohybrid for fluorescence determination of l-ascorbic acid and Fe3. Anal Chim Acta 2024;1287:342066. [PMID: 38182373 DOI: 10.1016/j.aca.2023.342066]

Recycling and reuse of biomass waste in synthesis of nanomaterials have recently received much attention as an effective solution for environmental protection and sustainable development. Herein, nitrogen-doped carbon dots (N-CDs) with blue emission were synthesized from the orange peels as a precursor through a simple hydrothermal method and then, modified with ethylenediamine tetraacetic acid (N-CD@EDTA). The N-CD@EDTA was embedded as a fluorophore in Cu-based metal-organic framework (MOF-199) structure (N-CD@EDTA/MOF-199) to construct fluorescence sensor toward l-ascorbic acid (L-AA) determination. The N-CD@EDTA/MOF-199 nanohybrid significantly and selectively turned on toward L-AA determination during the fluorimetric experiments. Under optimal conditions, the probe showed a suitable linear response in the concentration range of 10 nM-100 μM with a low limit of detection (LOD) of 8.6 nM and high sensitivity of 0.201 μM-1. The possible mechanism of recognition and adsorption, including the reduction of Cu 2+ nodes in the MOF-199 structure in the presence of L-AA and the release of trapped N-CD@EDTA into the solution, was explored. Moreover, the N-CD@EDTA/MOF-199/L-AA (100 μM) system was further applied as a fluorescent "on-off" sensor for Fe3+ determination with a LOD of 1.15 μM. The proposed probe was successfully used in orange juice and water samples to determine L-AA and Fe3+ with satisfactory recovery, which displays the promising capability of sensor in real samples. The recoveries obtained by suggested method are consistent with that obtained from high performance liquid chromatography (HPLC) and atomic absorption spectroscopy which confirm the favorable characteristic of the sensor for accurate determination of L-AA and Fe3+ in practical applications.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Engineering of metal-organic frameworks (MOFs) for thermometry

Metal-organic frameworks (MOFs ) are excellent candidates for use in chemistry, material sciences and engineering thanks to their interesting qualitative features and potential applications. Quite interestingly, the luminescence of MOFs can be engineered by regulation of the ligand design, metal ion selection and encapsulation of guest molecules within the MOF cavity. Temperature is a very crucial physical parameter and the market share of temperature sensors is rapidly expanding with technology and medicinal advancement. Among the wide variety of available temperature sensors, recently MOFs have emerged as potential temperature sensors with the capacity to precisely measure the temperature. Lanthanide-based thermometry has advantages because of its ratiometric response ability, high quantum yield and photostability, and therefore lanthanide-based MOFs were initially focused on to construct MOF thermometers. As science and technology have gradually changed, it has been observed that with the inclusion of dye, quantum dots, etc. within the MOF cavity, it is possible to develop MOF-based thermometry. This review consolidates the recent advances of MOF-based ratiometric thermometers and their mechanism of energy transfer for determining the temperature (thermal sensitivity and temperature uncertainty). In addition, some fundamental points are also discussed, such as concepts for guiding the design of MOF ratiometric thermometers, thermometric performance and tuning the properties of MOF thermometers.

Ratiometric fluorescent sensor based on metal-organic framework for selective and sensitive detection of CO32

Carbonate ion (CO₃^2-) is an anion essential for the maintenance of life activities and is of great importance to human health. Here, a novel ratiometric fluorescent probe Eu/CDs@UiO-66-(COOH)₂ (ECU) was prepared by introducing europium ions (Eu³⁺) and carbon dots (CDs) into the UiO-66-(COOH)₂ parent framework under the guidance of a post-synthetic modification strategy and used for the detection of CO₃^2- ion in the aqueous environment. Interestingly, when CO₃^2- ions were added to the ECU suspension, the characteristic emission of carbon dots at 439 nm was significantly enhanced, while the characteristic emission of Eu³⁺ ions at 613 nm was reduced. Therefore, the detection of CO₃^2- ions can be realized through the peak height ratio of the two emissions. The probe had a low detection limit (about 1.08 μM) and a wide linear range (0-350 μM) for the detection of carbonate. In addition, the presence of CO₃^2- ions can cause a significant ratiometric luminescence response and resulted obvious red-to-blue color shift of the ECU under UV light, which will facilitate visual analysis by the naked eye.

A water-stable dual-responsive Cd-CP for fluorometric recognition of hypochlorite and acetylacetone in aqueous media

One novel cadmium(II)-coordination polymer [Cd₃L₂(datrz)(H₂O)₃] (CP 1) is controllably synthesized by surmising the astute combination of semi-rigid tricarboxylate acid 4-(2',3'-dicarboxylphenoxy) benzoic acid (H₃L) and auxiliary ligand 3,5-diamino-1,2,4-triazole (datrz). Structure analysis shows that CP 1 has a two-dimensional (2D) layer structure with a 5-nodal (4³) (4⁴·6²) (4⁵·6⁴·8) (4⁵·6) (4⁷·6⁶·8²) topology. Further investigations reveal that CP 1 shows superordinary water stability and good thermal stability. The fluorescent explorations suggest that the as-synthesized CP 1 could emit blue light centered at 485 nm, attributing to ligand-based emission. In terms of sensing investigations, CP 1 could act as a fluorescent sensor for detecting hypochlorite (ClO^-) and acetylacetone (acac) through fluorescence turn-off process in aqueous solution, and the detection limit could reach 0.18 μM and 0.056 μM, respectively. Further research reveals that it is more likely the N-H···O-Cl hydrogen bonds between -NH₂ groups of the triazole ligands and O atoms of ClO^- plays the key role in the system, which may serve as a bridge for the energy transfer, leading to fluorescence quenching of the chemosensor. While the photoinduced electron transfer (PET) combined with inner filter effect (IFT) should be responsible for the turn-off fluorescence of CP 1 triggered by acac.

Coordination polymer nanoprobe integrated carbon dot and phenol red for turn-on fluorescence detection of urease activity

The potential of coordination polymers (CPs) as a host of integrating multiple guest species to construct a fluorescence resonance energy transfer (FRET) nanoprobe was demonstrated. The ZnCPs built from zinc(II) and adenine was employed as a model of CPs to integrate carbon dot (CD) and phenol red (PR) for producing the FRET nanoprobe (CD/PR@ZnCPs). Benefiting from the confinement effect of ZnCPs, the integrated CD and PR can be brought in close proximity to favor the occurrence of FRET process from CD to PR, which leads to the quenching of CD fluorescence. However, the FRET process was disrupted upon the red-shift of PR absorption from 428 to 562 nm in alkaline medium, and consequently switches on the fluorescence of CD/PR@ZnCPs. Based on this finding, by utilizing urease to hydrolyze urea and mediate medium pH, a turn-on fluorescent method was established for the detection of urease activity. This fluorescent method has a linear response that covers 5 to 150 U/L urease with a detection limit of 0.74 U/L and exhibits an excellent selectivity over other enzymes. The successful determination of urease in saliva samples demonstrates the applicability of the fluorescent nanoprobe in complex biological matrix.

3-Aminophenylboronic acid-functionalized molybdenum disulfide quantum dots for fluorescent determination of hypochlorite

A simple method is reported for hypochlorite determination based on fluorescence 3-aminophenylboronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs). B-MoS₂ QDs with strong fluorescence at 380 nm have been successfully synthesized by the amidation reaction between APBA and hydrothermal MoS₂ QDs. Hypochlorite sensing was proposed utilizing the fluorescent quenching effect of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB) on B-MoS₂ QDs and the fast redox reaction between hypochlorite and TMB. The fluorescent quenching effect of TMB to B-MoS₂ QDs was proved to be caused by static dynamic quenching and inner filter effect. A good linear relationship was obtained in the hypochlorite concentration range from 1 to 20 μM, and the limit of detection (LOD) was 36.8 nM. The proposed fluorescent detection assay was simple and fast, taking only 5 min at room temperature. Satisfactory results were obtained in the standard spike recovery tests on tap water and milk samples, which indicate high potential in constructing fluorescent bio-detection assays.

Sensing performance and mechanism of carbon dots encapsulated into metal-organic frameworks

Metal-organic frameworks (MOFs) can be combined with nanomaterials and the combined composites have excellent optical properties. Carbon dots (CDs) with tiny particle size, non-toxic and rich surface functional groups are novel fluorescent materials. Carbon dots@metal-organic frameworks (CDs@MOFs) are synthesized by encapsulating CDs into MOFs. CDs@MOFs are promising composites for the preparation of a new generation of fluorescence sensors, which combine the hybrid properties of MOFs and the special optical properties of CDs. Urged as such, we are encouraged to categorize according to the sensing mechanisms. These include fluorescence resonance energy transfer (FRET), aggregation-caused quenching (ACQ), static quenching, dynamic quenching, photo-induced electron transfer (PET), inner filter effect (IFE) and so on. Based on the above mechanisms, CDs@MOFs can specifically interact with target analytes to generate fluorescence quenching. This review covers the research progress of CDs@MOFs in recent five years (with 103 refs), synthetic design of CDs@MOFs and introduces the sensing mechanism. The current challenges and future research directions are discussed briefly. The sensing mechanism and applications of CDs@MOFs.

Dual-emissive EY/UiO-66-NH2 as a ratiometric probe for turn-on sensing and cell imaging of hypochlorite

Hypochlorite plays a vital role in biological systems and our daily life. The rapid and convenient detection of hypochlorite is imperative and significant for disease treatment and human health. In this work, EY/UiO-66-NH₂ (EY = eosin Y) was prepared through a hydrothermal process and could be applied to the detection and bioimaging of hypochlorite as a self-calibrating sensing nanoprobe. EY/UiO-66-NH₂ features two emissions at 432 nm and 533 nm, and the emission intensity of 533 nm is enhanced with increasing ClO^- concentration. EY/UiO-66-NH₂ could be utilized as a ratiometric fluorescence sensor of ClO^-. The linear range of EY/UiO-66-NH₂ towards ClO^- is 0.1-200 μM and its detection limit is 46.4 nM. In comparison with previously reported probes for ClO^-, EY/UiO-66-NH₂ has the advantages of a wide linear range, low detection limit, turn-on fluorescence and ratiometric response. This work provides a new method for ClO^- detection in living cells.

Designing of a high-performance fluorescent small molecule enables dual-mode and ultra-sensitive fluorescence visualizing of HSO3- and HClO in dried fruit, beverage, and water samples

Herein, a novel hemicyanine derivative (E)-3-(1,1-dimethyl-2-(4-(methylthio)styryl)-1H-benzo[e]indol-3-ium-3-yl)propane-1-sulfonate (BIS) has been reasonably designed. Compound BIS is long-wavelength emissive and water-soluble with a large Stokes shift. Intriguingly, probe BIS provides a dual-mode fluorescence response pattern for the sensing of bisulfite (HSO₃^-) and hypochlorous acid (HClO) with great limit of detections (3.6 and 57.4 nM). First, the 1,4-Michael addition of HSO₃^- on the conjugated double bond triggers a ratiometric response (I₄₆₅/I₅₇₅). Second, the rapid oxidation of HClO on the thioether moiety provides a turn-on response (I₅₇₅). Evaluation of HSO₃^- and HClO levels in dried fruit, beverage, and water samples has been carried out with satisfactory results. Moreover, motivated by an impressive chromatic variation (red to blue), smartphone-assisted signal readout system and thin-film sensing platform are facilely constructed for real-time and on-site measurement of HSO₃^- levels. Furthermore, probe BIS is used for the in vivo imaging of HSO₃^- in edible fish models.

Recent Advances in the Application and Mechanism of Carbon Dots/Metal-Organic Frameworks Hybrids in Photocatalysis and the Detection of Environmental Pollutants

Metal-organic frameworks (MOFs) are a class of crystalline porous materials with simple synthesis conditions, large specific surface area, structural diversity, and a wide range of interesting properties. The integration of MOFs with other materials can provide new multifunctional composites that exhibit both component properties and new characteristics. In recent years, the integration of carbon dots (CDs) into MOFs to form composites has shown improved optical properties and fascinating new characteristics. This review focuses on the design and synthesis strategies of CDs@MOFs composites (including pore-confined synthesis, in situ encapsulation, post-synthesis modification and impregnation method) and their recent research progress in photocatalysis and detection of environmental pollutants. Both the achievements and problems are evaluated and proposed, and the opportunities and challenges of CDs@MOF composite are discussed.

Lipid membrane anchoring and highly specific fluorescence detection of cancer-derived exosomes based on postfunctionalized zirconium-metal-organic frameworks

Cancer-derived exosomes carry a variety of important biomarkers specific to the formation, invasion and metastasis of tumor tissue. Dynamic monitoring of exosomes originated from cancer cells has clinical significance. Here we proposed a novel method to employ zirconium-metal-organic frameworks (Zr-MOFs) for extracting and identifying exosomes from blood. At first UiO-66 was magnetically modified as the adsorbent to anchor exosomes by forming Zr-O-P bonds. Then UiO-66-NH₂ modified with anti-EpCAM was used to construct the fluorescent probe to recognize the extracted EpCAM-positive exosomes by forming a "MOF-exosome-MOF" structure. The proposed fluorescence detection method was evaluated by quantifying MCF-7 cell-derived exosomes at the concentration as low as 16.72 particles/μl. This method was successfully applied to analyze exosomes in the plasma samples from healthy donors and breast cancer patients, demonstrating that our method might have a great potential in assisting the early diagnosis and in dynamically monitoring the efficacy of cancer treatment. We believe that the method could be extended to the detection of other biomarkers in exosomes derived from cancer cell.

Advances and Applications of Metal-Organic Framework Nanomaterials as Oral Delivery Carriers: A Review

Oral administration is a commonly used, safe, and patient-compliant method of drug delivery. However, due to the multiple absorption barriers in the gastrointestinal tract (GIT), the oral bioavailability of many drugs is low, resulting in a limited range of applications for oral drug delivery. Nanodrug delivery systems have unique advantages in overcoming the multiple barriers to oral absorption and improving the oral bioavailability of encapsulated drugs. Metal-organic frameworks (MOFs) are composed of metal ions and organic linkers assembled by coordination chemistry. Unlike other nanomaterials, nanoscale metal-organic frameworks (nano-MOFs, NMOFs) are increasingly popular for drug delivery systems (DDSs) due to their tunable pore size and easily modified surfaces. This paper summarizes the literature on MOFs in pharmaceutics included in SCI for the past ten years. Then, the GIT structure and oral drug delivery systems are reviewed, and the advantages, challenges, and solution strategies possessed by oral drug delivery systems are discussed. Importantly, two major classes of MOFs suitable for oral drug delivery systems are summarized, and various representative MOFs as oral drug carriers are evaluated in the context of oral drug delivery systems. Finally, the challenges faced by DDSs in the development of MOFs, such as biostability, biosafety, and toxicity, are examined.

Dual-Emitting Carbonized Polymer Dots Synthesized at Room Temperature for Ratiometric Fluorescence Sensing of Vitamin B12

Ratiometric fluorescence (FL) probes are highly desirable for highly sensitive and reliable assays. Dual-emitting carbonized polymer dots (CPDs) have great application prospects in building ratiometric FL sensors. However, dual-emitting CPDs are usually synthesized at high temperatures and high pressures, which not only increases the cost but also complicates the structure of CPDs. Here, we developed a facile strategy for the fabrication of dual-emitting CPDs at room temperature using tetrachlorobenzoquinone and ethylenediamine. The formation of CPDs was induced by Schiff base condensation reaction, enabling the following cross-linking polymerization process. The dual-emitting CPDs demonstrate good photostability and antioxidant capacity. Importantly, the typical dual-emission bands of the as-prepared CPDs are found to have a blue emission band at 445 nm with a maximum excitation of 350 nm and a yellow emission band at 575 nm with a maximum excitation of 440 nm. Based on the dual-emitting property of CPDs, a ratiometric FL nanoprobe is obtained for sensitive determination of vitamin B12 (VB12), as the inner filtering and static quenching effects between VB12 and CPDs allow effective quenching of the blue FL of CPDs, while the yellow FL is maintained. The established assay shows linear detection ranges of 0.25-100 μM with a low limit of detection of 0.14 μM. These findings provide new guidance for the facile preparation of CPDs with excellent dual-emitting optical properties, indicating good prospects in biosensing.

One-step synthesis of nitrogen-doped multi-emission carbon dots and their fluorescent sensing in HClO and cellular imaging

Tunable multicolor carbon dots (CDs) with a quantum yield reach up to 35% were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. Transmission electron microscopy images reveal that the as-prepared CDs possess a small size distribution below 10 nm with bright blue, green, and yellow color emission, designated as b-CDs, g-CDs, and y-CDs, respectively. The in-depth investigations reveal that the multicolor emission CDs with different fraction displays fluorescence emission wavelength ranges from 398 nm (b-CDs), 525 nm (g-CDs), to 553 nm (y-CDs) which could be well modulated by controlling the amount of heteroatom nitrogen especially amino nitrogen onto their surface structures. Further experiments verify the important role of nitrogen content by using rhodamine solely or substituting urea with sulfur containing compounds as precursors to produce corresponding CDs since the performance is lower than that of urea incorporation. Theoretical calculation results also reveal that the increasing amount of amino nitrogen into their surface structures of b-CDs, g-CDs to y-CDs is responsible for reduced band gaps energy, which result in the redshifted wavelength. Benefiting from the excellent photoluminescence properties, wide pH variation range, high photo stability, and low toxicity, these CDs were employed for HClO sensing at 553 nm within the range 5 to 140 μM with a limit of detection (LOD) of 0.27 ± 0.025 μM (n = 3) and multicolor cellular imaging in HeLa cells. Tunable multicolor carbon dots (CDs) were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. The as-prepared CDs exhibit bright blue, green, and yellow color emission which could be well modulated by controlling the increasing incorporation of heteroatom nitrogen especially amino nitrogen into their surface structures. These CDs were employed for HClO sensing and demonstrated to multicolor cellular imaging in HeLa cells.

Molecularly imprinted polymer coated Mn-doped ZnS quantum dots embedded in a metal-organic framework as a probe for selective room temperature phosphorescence detection of chlorpyrifos

As one of the most widely used organophosphorus pesticides, chlorpyrifos (CPF) is toxic to humans. However, the rapid, effective and sensitive detection of CPF is still a challenge. In this paper, a novel molecularly imprinted phosphorescent sensor with a core–shell structure (Mn:ZnS QDs@ZIF-8@MIP) using Mn:ZnS quantum dots (QDs) as phosphorescent emitters was prepared for the highly sensitive and selective detection of CPF, and a simple and rapid room-temperature phosphorescence (RTP) detection method for CPF was proposed. For the prepared Mn:ZnS QDs@ZIF-8@MIP, Mn:ZnS QDs had good phosphorescence emission characteristics, ZIF-8 as support materials was used to improve the dispersibility of Mn:ZnS QDs, and molecularly imprinted polymer (MIP) on the surface of ZIF-8 was used to improve the selectivity of Mn:ZnS QDs for CPF. Under the optimal response conditions, the RTP intensity of Mn:ZnS QDs@ZIF-8@MIP showed a rapid response to CPF (less than 5 min), the RTP intensity ratio of P₀/P had a good linear relationship with the concentration of CPF in the range of 0–80 μM, and the detection limit of this method was 0.89 μM with the correlation coefficient of 0.99. Moreover, this simple and rapid method has been successfully used to detect CPF in real water samples with satisfactory results, and the recoveries ranged from 92% to 105% with a relative standard deviation of less than 1%. This method combines the advantages of phosphorescence emission and molecular imprinting, and greatly reduces the potential interferences of competitive substances, background fluorescence and scattered light, which opens up a broad prospect for the highly sensitive and selective detection of pollutants in water based on molecularly imprinted phosphorescent sensors.

As one of the most widely used organophosphorus pesticides, chlorpyrifos (CPF) is toxic to humans, and Mn:ZnS QDs@ZIF-8@MIP are prepared for the highly sensitive and selective detection of CPF.

Fluorescent enzyme-linked immunosorbent assay based on alkaline phosphatase-responsive coordination polymer composite

The fabrication of alkaline phosphatase (ALP)-responsive coordination polymer (CP) composite is demonstrated for establishing a fluorescent immunoassay. The CP composite (ThT@GMP/Eu) was synthesized by encapsulating thioflavin T (ThT) into the CP host that was composed of europium ion (Eu³⁺) and guanine monophosphate (GMP). The ThT@GMP/Eu composite shows a strong fluorescence in aqueous solution due to the confinement effect of GMP/Eu CPs, which restricts the conformational rotation of ThT. However, upon the addition of ALP, the structure of GMP/Eu CPs was disrupted to release ThT into solution. This results in the quenching of the fluorescence of ThT@GMP/Eu. The fluorescence of ThT@GMP/Eu has a linear response that covers 0.8 to 120 mU/mL ALP with a detection limit of 0.26 mU/mL and exhibits excellent specificity towards ALP against other enzymes. On this basis, inspired by the wide application of ALP as an enzyme label in enzyme-linked immunosorbent assay (ELISA), an ALP-based fluorescent immunoassay was further developed for the detection of mouse immunoglobulin G (mIgG). The developed immunoassay displays a linear fluorescent response towards mIgG from 0.8 to 100 ng/mL, and the detection limit is 0.16 ng/mL. The fluorescent immunoassay was successfully applied to the determination of mIgG in serum samples. Schematic of the responsivity of ThT@GMP/Eu to ALP that hydrolyzes GMP to release ThT, which leads to fluorescent quenching, and its application in the construction of a fluorescent immunoassay for mIgG determination.

Smartphone-assisted visual ratio-fluorescence detection of hypochlorite based on copper nanoclusters

A sensitive naked eye and ratio-fluorescence sensor for Curcumin (CCM) and hypochlorite (ClO^-) determination based on copper nanoclusters (Cu NCs) was developed. The fluorescence of the Cu NCs can be quenched due to inner filter effect (IFE) between CCM and Cu NCs, and the ratio fluorescence probe was formed. After adding ClO^- to Cu NCs-CCM system, the phenolic and methoxy groups of CCM were oxidized to quinones, then the fluorescence of CCM was quenched and the fluorescence of Cu NC was restored. Moreover, the continuous detection of CCM and ClO^- is accompanied by the change of solution color. Therefore, CCM and ClO^- semiquantitative visual and fluorescence dual channel detection were realized. The detection results show that the detection based on Cu NCs-CCM probe has a wide detection range (0-412 µM) and low detection limit (24 µM), and a good recovery rate is obtained in adulterated milk and tap water detection. Furthermore, smartphone was introduced for image digital colorimetric analysis through the acquisition, recognition and RGB data processing of solution colors, providing an effective scheme for the field rapid detection of hypochlorite.

Dual-Ligand Lanthanide Metal-Organic Framework for Sensitive Ratiometric Fluorescence Detection of Hypochlorous Acid

Sensitivity, selectivity, visible detection, and rapid response are the main concerns for an analytical method. Herein, we reported a metal-organic framework (MOF)-based ratiometric fluorescence detection strategy for hypochlorous acid (HClO). The MOF was prepared with dual ligands, 2-aminoterephthalic acid (BDC-NH₂) and dipicolinic acid (DPA) and Eu³⁺ ions as a metal node, denoted as Eu-BDC-NH₂/DPA. The dual-ligand strategy realized the dual emission for ratiometric sensing and visual detection, adjusted the size and morphology of MOFs to obtain a good dispersion for a rapid response, and provided an amino group for the special recognition of HClO. Thus, the MOF exhibited a dual emission derived from BDC-NH₂ and Eu³⁺ ions at 433 and 621 nm, respectively, under a single excitation at 270 nm. A hydrogen bond forms between an -NH₂ group and HClO to weaken the blue fluorescence at 433 nm, while the antenna effect emission from Eu³⁺ ions kept stable, so ratiometric sensing was realized with an easy-to-differentiate color change for visible detection. The ratiometric sensing showed a self-calibration effect and reduced the background. Thus, the high sensitivity, visual detection, low detection limit (37 nM), and short response time (within 20 s) for the detection of HClO were realized with the MOF as a probe. The analysis of real samples demonstrated the practical application of the MOF for HClO. The introduction of mixed ligands is an effective strategy to regulate the emission behaviors of MOFs for the improved analytical performance.

Ionic Liquid-Functionalized Magnetic Metal-Organic Framework Nanocomposites for Efficient Extraction and Sensitive Detection of Fluoroquinolone Antibiotics in Environmental Water

Herein, the hydrophobic carboxyl-functionalized ionic liquid (IL-COOH) was encapsulated into the prepared Fe₃O₄@Zr-MOFs, and the novel water-stable IL-COOH/Fe₃O₄@Zr-MOF nanocomposites were first synthesized. The polydopamine-functionalized Fe₃O₄ was introduced to construct the core-shell structure via layer-by-layer modification, and the controlled growth of Zr-MOFs was achieved, which realized the adjustment of charged properties of nanocomposites and simplified the adsorption or extraction process. The IL-COOH/Fe₃O₄@Zr-MOFs were fully studied by IR, HNMR, XRD, N₂ adsorption-desorption isotherms, TEM, EDS mapping, VSM, and so on. Then, they were employed for the selective adsorption and detection of fluoroquinolone antibiotics (FQs). The adsorption isotherms and kinetics demonstrated that the adsorption process followed a pseudo-second-order kinetic model and the Langmuir isotherm model. Among them, IL-COOH/Fe₃O₄@UiO-67-bpydc showed the best adsorption performance, and the maximum adsorption capacity of ofloxacin was 438.5 mg g^-1. Coupled magnetic solid-phase extraction with HPLC-DAD, a convenient, sensitive, and efficient method for extraction and detection of FQs in environmental water, was developed based on IL-COOH/Fe₃O₄@UiO-67-bpydc. The recoveries of environmental water were ranging from 90.0 to 110.0%, and the detection limits were lower than 0.02 μg L^-1. The novel functionalized composites served as solid-phase adsorbents and liquid-phase extractants. This study also provided a promising strategy for designing and preparing multi-functionalized nanocomposites for the removal or detection of pollutants in environmental samples.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.

Carbon dots@metal–organic frameworks as dual-functional fluorescent sensors for Fe3+ ions and nitro explosives

Two novel dual-functional fluorescent composites were prepared, which exhibit excellent fluorescence sensing capabilities for Fe³⁺, p-NT and 2,4-DNP.

Eu3+@metal-organic frameworks encapsulating carbon dots as ratiometric fluorescent probes for rapid recognition of anthrax spore biomarker

Anthrax spores pose a serious threat to human well-being and life, so it is highly desirable to develop a rapid, sensitive, and selective quantitative assay of calcium pyridine dicarboxylate (CaDPA) as a biomarker of anthrax spores. Herein, carbon dots (CDs) chelated Eu³⁺@metal-organic framework (Eu-MOFs) as dual-emissive ratiometric fluorescent (RF) probe was successfully fabricated by a simple one-pot in situ selective self-assembly synthetic strategy. The developed RF probe has an effective self-calibration function, which performs a highly sensitive and selective recognition of CaDPA in water and human serum sample. The blue-emitting CDs was employed as an effective fluorescence reference, while the Eu-MOFs exhibited enhanced red fluorescence signal through the coordination interaction with CaDPA chromophore. The sensing mechanism is attributed to that CaDPA can sensitize Eu³⁺ intrinsic luminescence due to the energy transfer from CaDPA to Eu³⁺. What's more interesting is that with the continuous drop of CaDPA, the emission color of CDs@Eu-MOF changes from blue to red. The results revealed that CDs@Eu-MOFs RF probe can detect CaDPA effectively in the range of 8-170 μg/L with good linear relationship, and exhibited a remarkable selectivity for CaDPA. More interestingly, a paper-based probe has also been devised for on-site detection of CaDPA. In addition, CaDPA is used as input signal to construct an IHIBITION logic gate device which performs the "off-on" mode. The constructed CDs@Eu-MOF probe can achieve exceptionally rapid, highly sensitive and selective detection of CaDPA, which can further expand the application prospects in environmental and biological analysis.

Dual-Response Ratiometric Electrochemical Microsensor for Effective Simultaneous Monitoring of Hypochlorous Acid and Ascorbic Acid in Human Body Fluids

Redox homeostasis between hypochlorous acid (HClO/ClO^-) and ascorbic acid (AA) significantly impacts many physiological and pathological processes. Herein, we report a new electrochemical sensor for the simultaneous determination of HClO and AA in body fluids. We first coated a carbon fiber microelectrode (CFME) with a three-dimensional nanocomposite consisting of graphene oxide (GO) and carbon nanotubes (CNTs) to fabricate the CFME/GO-CNT electrode. After the electrochemical reduction of GO (ERGO), we integrated a latent 1-(3,7-bis(dimethylamino)-10H-phenothiazin-10-yl)-2-methylpropan-1-one (MBS) electrochemical molecular recognition probe to monitor HClO and employed anthraquinone (AQ) as an internal reference. The compact CFME/ERGO-CNT/AQ + MBS sensor enabled the accurate and simultaneous measurement of HClO and AA with excellent selectivity and sensitivity. Measurements were highly reproducible, and the sensor was stable and exceptionally biocompatible. We successfully detected changes in the redox cycles of HClO and AA in human body fluids. This sensor is a significant advance for the investigation of reactions involved in cellular redox regulation. More importantly, we have devised a strategy for the design and construction of ratiometric electrochemical biosensors for the simultaneous determination of various bioactive species.

Carbon Dots in Porous Materials: Host-Guest Synergy for Enhanced Performance

Carbon dots (CDs) are emerging as a new class of carbon nanomaterials, which have inspired growing interest for their widespread applications in anti-counterfeiting, sensing, bioimaging, optoelectronic and energy-related fields. In terms of the concept of host-guest assembly, immobilizing CDs into porous materials (PMs) has proven to be an effective strategy to avoid the aggregation of bare CDs in solid state, in particular, the host-guest synergy with both merits of CDs and PMs affords composites promising properties in afterglow and tunable emissions, as well as optimizes their performance in optics, catalysis, and energy storage. This Minireview summarizes the recent progress in the research of CDs@PMs, and highlights synthetic strategies of constructing composites and roles of porous matrices in boosting the applications of CDs in diverse areas. The prospect of future exploration and challenges are proposed for designing advanced CDs-based functional nanocomposite materials.

Carbon dots based ratiometric fluorescent sensing platform for food safety

Food safety has become a major global concern and the rapid detection of food nutritional ingredients and contaminants has aroused much more attention. Nanomaterials-based fluorescent sensing holds great potential in designing highly sensitive and selective detection strategies for food safety analysis. Carbon dots (CDs) possess tremendous prospects in fluorescent sensing food ingredients and contaminants due to their superior properties of chemical and photostability, highly fluorescence with tunability, and no/low-toxicity. Numerous endeavors are demanded to contribute to overcoming the challenge of lower sensitivity and selectivity of the sensors interfered by various components in intricate food matrices to ensure food safety and human health. Nanohybrid CDs based ratiometric fluorescent sensing with self-calibration is regarded as an efficient strategy for the CDs based sensors for the specific recognition of target analyte in the food matrices. This work is devoted to reviewing the development of nanohybrid CDs based ratiometric fluorescent sensing platform and the perspectives of the platform for food safety. The applications of nanohybrid CDs in sensing are summarized and the sensing mechanisms are briefly discussed.

Fluorometric determination of mercury(II) based on dual-emission metal-organic frameworks incorporating carbon dots and gold nanoclusters

Carbon dots and gold nanoclusters co-encapsulated by zeolitic imidazolate framework-8 (CDs/AuNCs@ZIF-8) have been obtained at room temperature. The composite has been applied to the ratiometric fluorescence determination of mercury(II). The composite shows fluorescence emission maxima at 440 and 640 nm under 360 nm excitation, due to the CDs and AuNCs, respectively (associated quantum yields were 18% and 17%, respectively). In the presence of Hg²⁺, the fluorescence at about 640 nm is quenched, while the fluorescence at about 440 nm is unaffected. The CDs/AuNCs@ZIF-8 composite allows the sensitive detection of Hg²⁺, with the fluorescence intensity ratio (I₆₄₀/I₄₄₀) decreasing linearly with Hg²⁺ concentration over the range 3-30 nM. The fluorescence emission of the composite changes color from red to blue with increasing Hg²⁺ under UV excitation, which can easily be discerned visually. This visual detection of Hg²⁺ is due to the high fluorescence quantum yields of the CDs and AuNCs and the ~ 200 nm separation between the two emission maxima. Graphical abstract (A) Schematic diagram showing the operating principle of the determination for Hg(II). (B) Digital graph of the solutions in absence and presence of 30 nM Hg(II) under a portable UV lamp.

A simple and sensitive sensor for lactose based on cascade reactions in Au nanoclusters and enzymes co-encapsulated metal-organic frameworks

In this work, one kind of zeolite imidazole frameworks containing bovine serum albumin stabilized Au nanoclusters (AuNCs), β-galactosidase (β-Gal) and glucose oxidase (GOx) (AuNCs/β-Gal/GOx@ZIF-8) were obtained to detect lactose. Compared with other fluorescent nano-materials, AuNCs show distinct advantages as a guest species in ZIF-8, specifically their extremely small size (<1 nm), simple synthesis, excellent biocompatibility and high stability. Furthermore, the bovine serum albumin on their surfaces can promote the formation of ZIF-8 coating; thus, AuNCs were co-encapsulated in ZIF-8 with the enzymes together. X-ray diffraction (XRD) analysis indicates the composite possesses the similar crystalline structure with pure ZIF-8. Fluorescence microscope images, Fourier transform infrared spectra and energy dispersive X-ray spectroscopy indicate the presence of AuNCs in the composite. Owing to the high local concentrations of the fluorescent probe and the quenching agent in AuNCs/β-Gal/GOx@ZIF-8, the quenching rate was enhanced 3.4-fold that of free AuNCs and enzymes in solution.

The function of metal-organic frameworks in the application of MOF-based composites

In the last two decades, metal-organic frameworks (MOFs), as a class of porous crystalline materials formed by organic linkers coordinated-metal ions, have attracted increasing attention due to their unique structures and wide applications. Compared to single components, various well-designed MOF-based composites combining MOFs with other functional materials, such as nanoparticles, quantum dots, natural enzymes and polymers with remarkably enhanced or novel properties have recently been reported. To efficiently and directionally synthesize high-performance MOF-based composites for specific applications, it is vital to understand the structural-functional relationships and role of MOFs. In this review, preparation methods of MOF-based composites are first summarized and then the relationship between the structure and performance is determined. The functions of MOFs in practical use are classified and discussed through various examples, which may help chemists to understand the structural-functional relationship in MOF-based composites from a new perspective.

Preparation, surface functionalization and application of Fe3O4 magnetic nanoparticles

This paper reviews recent developments in the preparation, surface functionalization, and applications of Fe₃O₄ magnetic nanoparticles. Especially, it includes preparation methods (such as electrodeposition, polyol methods, etc.), organic materials (such as polymers, small molecules, surfactants, biomolecules, etc.) or inorganic materials (such as silica, metals, and metal oxidation/sulfide, functionalized coating of carbon surface, graphene, etc.) and its applications (such as magnetic separation, protein fixation, magnetic catalyst, environmental treatment, medical research, etc.). In the end, some existing challenges and possible future trends in the field were discussed.

Double-Emission Ratiometric Fluorescent Sensors Composed of Rare-Earth-Doped ZnS Quantum Dots for Hg2+ Detection

Quantum dots (QDs) are a class of zero-dimensional nanocrystal materials, whose lengths are limited to 2-10 nm. Their unique advantages such as wide excitation spectra, narrow emission spectra, and high quantum yield make their application possible in fluorescence sensing, wherein QDs such as CdSe, CdTe, and CdS are used. Indeed, QDs have a wide range of applications in fluorescence sensing, and there have been many reports of applications based on QDs as ion probes. The emission spectra of QDs can be adjusted by changing the size of the QDs or doping them with other ions/elements. However, the high toxicity of Cd and the poor anti-interference ability of single-emission fluorescent probes greatly limit the applications of QDs in many fields. In this paper, ZnS QDs are doped with the rare-earth element Ce to form a low-toxicity double-emission ratiometric fluorescent sensor, ZnS:Ce, for Hg²⁺ detection. The results of transmission electron microscopy (TEM), X-ray diffractometry, X-ray photoelectron spectroscopy, and optical spectroscopy show that ZnS:Ce QDs were successfully synthesized. Under the optimal conditions, the concentration of Hg²⁺ was in the range of 10-100 μM, which had a linear relationship with the fluorescence intensity of the ZnS:Ce QDs: the linear correlation coefficient was 0.998, and the detection limit was 0.82 μM L^-1. In addition, the fluorescent sensor had good selectivity for Hg²⁺, and it was successfully applied to the detection of Hg²⁺ in laboratory water samples.

Zeolitic Imidazolate Framework-Based Composite Incorporated with Well-Dispersed CoNi Nanoparticles for Efficient Catalytic Reduction Reaction

Incorporation of metal nanocatalysts within a well-defined porous support is of great importance for stabilizing unstable metal nanocatalysts, so that they display an effective and long-lasting catalytic activity. In particular, metal-organic frameworks (MOFs) with a wide range of structures serve as excellent porous supports for stabilizing unstable nanocatalysts. In addition, the development of inexpensive metal nanocatalysts is necessary to replace expensive noble metal nanocatalysts. Herein, we report on a simple method for the preparation of porous MOF-based or carbon-based composites incorporated with catalytically active CoNi alloy nanoparticles. CoNi alloy nanoparticles were produced from the concurrent reduction of Co and Ni ions existing within a zeolitic imidazolate framework (ZIF)-based precursor material during the thermal treatment. In particular, a part of the highly porous ZIF was preserved during the thermal treatment at 400 °C, which eventually resulted in a composite of ZIF and CoNi (CoNi@ZIF). The resulting CoNi@ZIF showed excellent catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol. The synergy between the highly porous ZIF support and the well-dispersed CoNi nanoparticles within CoNi@ZIF provided an outstanding catalytic performance, even with inexpensive transition-metal nanocatalysts. Moreover, the catalytic activity of CoNi@ZIF was well conserved even after five consecutive reactions.

An Integrating Platform of Ratiometric Fluorescent Adsorbent for Unconventional Real-Time Removing and Monitoring of Copper Ions

Nondegradable heavy metals have caused great dangers to the environment and human health. Combining stimuli-responsive materials with conventional MOF-based adsorbents has been considered an effective method to generate intelligent adsorbents for superior control over the adsorption process. Herein, a smart MOF-based ratiometric fluorescent adsorbent was designed to accurately monitor the progression of the removal of copper ions with dual-emitting fluorescence signal. Unlike the traditional difunctional materials, this delicately designed platform overcomes the huge energy gap to achieve two functions simultaneously. This unconventional platform provides a reliable fluorescent response toward Cu²⁺ during the removing process, changing linearly related to the degree of the adsorption process, which holds extreme promise in effectively monitoring the adsorption process. The underlying relationship of the adsorption and fluorescence response process toward copper was investigated by density functional theory (DFT) calculations. In particular, because of the favorable ion binding affinity of ZIF-8 and self-calibrating effect of RhB, the as-prepared smart adsorbent demonstrates a superior adsorption performance of 608 mg g^-1, broad response range (0.05-200 ppm, 2.07 × 10^-7to 8.29 × 10^-4 M), ultrahigh sensitivity (0.04 ppm, 1.91 × 10^-7 M) toward Cu²⁺ and strong anti-interference ability. This smart adsorbent opens an intelligent pathway to promote substantial advancements in the fields of environmental monitoring and industrial waste management.