Highly Fluorescent Magnetic ATT-AuNCs@ZIF-8 for All-in-One Detection and Removal of Hg2+: An Ultrasensitive Probe to Evaluate Its Removal Efficiency

Assembling metal nanoclusters with high luminescence performance and anti-interference ability for sensing p-nitrophenol

BACKGROUND

The fluorescence quantum yield (QY) of water-soluble gold nanoclusters (AuNCs) can be prominently improved by adding l-arginine (Arg) owing to rigidifying ligands. However, these fluorescence systems exhibit poor anti-interference ability in sensing application due to exposure guanidine, amino, and carboxyl groups of Arg.

RESULTS

We have developed the encapsulation of AuNCs into zeolitic imidazolate framework-8 (ZIF-8) to improve the anti-interference property due to the protection of Arg functional groups. The ligand of 6-aza-2-thiothymine (ATT)-decorated AuNCs (ATT-AuNCs) is rigidified after introducing Arg (referred as Arg/ATT-AuNCs), yielding higher QY of 59.31 % compared to ATT-AuNCs with QY of 1.18 %. Subsequently, the shell of Arg/ATT-AuNCs encapsulated into ZIF-8 (Arg/ATT-AuNCs@ZIF-8) does not only tremendously increase green fluorescence emission, but also enhance the anti-interference capability (high salt concentration, pH change, metal ions coordination, and solution dilution) due to the structural confinement effect and protection of ligand functional groups. Interestingly, Arg/ATT-AuNCs@ZIF-8 fluorescence can be quenched by p-nitrophenol (PNP) through an internal filtration effect (IFE). Thus, a fluorescence method is established for PNP analysis. The linear detection range for PNP is 0.1-80 μM with limit of detection (LOD) at 0.033 μM, which is much lower than the maximum allowable value (0.43 μM) in drinking water by EPA. This approach has been successfully applied to the detection of PNP spiked into the real samples with excellent recovery rates. This platform opens a broad avenue for metal nanocluster-based materials in the sensing application.

Enhanced biochemical sensing using metallic nanoclusters integrated with metal-organic frameworks (NCs@MOFs): a comprehensive review

In biochemical sensing, substantial progress has been achieved in the design, development, and application of metallic nanoclusters (NCs) and metal-organic frameworks (MOFs) as distinct entities. Integration of these two nanostructured materials is a promising strategy to form innovative composites with improved properties. Some improvements include (i) supporting platform to minimize the aggregation of NCs and enhance the emission efficiency; (ii) dual-emitting NCs@MOFs from the fluorescent/non-fluorescent MOFs and/or fluorescent NCs; and (iii) stability enhancement. These improvements increase the sensitivity, signal-to-noise ratio, and color tonality, lower the limit of detection, and improve other analytical figures of merits. In this review, we outline the preparation methods of NCs@MOF composites with the improvements offered by them in the field of biochemical analysis. Analytical applications in different fields, such as bioanalysis, environmental monitoring and food safety, are presented. Finally, we address the challenges that remain in the development and application of these composites, such as ensuring stability, enhancing the fluorescence intensity, and improving selectivity and scalability. Furthermore, perspectives on future research directions in this rapidly evolving field are offered.

Encapsulating Cu NCs with aggregation-induced emission into metal-organic framework ZIF-8 as a novel fluorescent nanoprobe for the highly sensitive detection of felodipine

Fluorescent metal-organic framework nanocomposites (f-MOFs) have been gaining increasing attention in the fields of chemosensors and biosensors due to their unique signal amplification mechanisms and improved selectivity. However, most f-MOFs are constructed by encapsulating fluorescent labelling agents into frameworks via host-guest interactions. The notorious aggregation-caused quenching effect of these fluorescent labelling agents often leads to a decreased fluorescent quantum yield in f-MOFs. Herein, a novel fluorescent nanocomposite, Cu NCs@ZIF-8, was designed and prepared by encapsulating copper nanoclusters (Cu NCs) with aggregation-induced emission (AIE) effects into zeolitic imidazolate framework ZIF-8 through electrostatic attraction. Owing to the AIE effect of Cu NCs and the spatial confinement of ZIF-8, the intramolecular motion of surface ligand hydrolipidic acid (DHLA) in Cu NCs was restricted, resulting in the formation of a highly emissive nanocomposite, Cu NCs@ZIF-8. Intriguingly, the UV-Vis absorption spectrum of felodipine overlaps with the excitation spectrum of Cu NCs@ZIF-8. Therefore, a novel fluorescent nanoprobe based on Cu NCs@ZIF-8 was developed for the highly sensitive detection of felodipine via the inner-filtration effect mechanism. Under optimal detection conditions, the linear response range of Cu NCs@ZIF-8 for felodipine was found to be 1-25 μM, with a detection of limit of 0.09 μM. While determining the labelling-amount percentage in commercially available felodipine tablets, the experimental results validated that the proposed Cu NCs@ZIF-8 nanoprobe exhibits good selectivity and excellent accuracy. This expands the potential applications of fluorescent metal-organic frameworks encapsulated with metal nanoclusters exhibiting AIE properties, positioning them as fluorescent nanoprobes for pharmaceutical quality control.

Methylene blue-functionalized ZIF-8/Au nanoparticle composites based ratiometric electrochemical sensor for reliable detection of methyl parathion in vegetables

A novel ratiometric electrochemical sensor based on methylene blue-functionalized ZIF-8/Au nanoparticle composites (ZIF-8@MB/AuNPs) was constructed for reliable detection of methyl parathion (MP). The ZIF-8@MB/AuNPs composites were prepared by a simple and mild room-temperature method. Here, ZIF-8 was served as a support for loading functional nanomaterials, which helps to improve the adsorption and accumulation capacity for MP. The functional electroactive molecule methylene blue (MB) was adopted to produce a stable reference signal and form a ratiometric sensing strategy, offering more accurate and reliable detection results. The decoration of Au nanoparticles can effectively enhance the conductivity and catalytic activity of the composites. The obtained ZIF-8@MB/AuNPs composites exhibited a superior electrochemical catalytic performance toward MP. According to the ratiometric signal of IMP/IMB, the developed sensor offered a detection range of 0.05-30 μg mL-1 and exhibited favorable selectivity, reproducibility and stability, and satisfactory applicability in vegetable samples.

In Situ Encapsulation of Atomically Precise Nanoclusters in Reticular Frameworks via Mechanochemical Synthesis

The combination of atomically precise nanoclusters (APNCs) and reticular frameworks is promising for generating component-specific nanocomposites with emergent properties. However, traditional liquid-phase synthesis often hampers this potential by damaging APNCs and limiting combination diversity. Here, mechanochemical synthesis to explore the encapsulation of diverse oil- and water-soluble APNCs within various reticular frameworks is employed, establishing a database of 21 unique APNC-framework combinations, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and multivariate MOFs. These framework coatings not only spatially immobilize APNCs but also secure their structures, preventing aggregation and degradation while enhancing stability and activity. Encapsulating Au25 in HOFs resulted in a remarkable 315-fold increase in catalytic activity compared to Au25 homogeneous catalyst, highlighting the framework's crucial role in catalytic enhancement. The mechanochemical synthesis strategy facilitates tailored support screening, catering to specific needs, and shows promise for developing multifunctional systems, including enzyme-APNC@frameworks material for cascade reactions.

Engineering "three-in-one" fluorescent nanozyme of Ce-Au NCs for on-site visual detection of Hg2

Hg2+ contamination poses a serious threat to the environment and human health. Although gold nanoclusters (Au NCs) have been utilized as fluorescence probes or colorimetric nanozymes for performing Hg2+ assays by using a single method, designing multifunctional nanoclusters as fluorescent nanozyme remains challenging. Herein, Ce-aggregated gold nanoclusters (Ce-Au NCs) were reported with "three in one" functions to generate strong fluorescence, excellent peroxidase-like activity, and the highly specific recognition of Hg2+ via its metallophilic interaction. A portable fluorescence and colorimetric dual-mode sensing device based on Ce-Au NCs was developed for on-site visual analysis of Hg2+. In the presence of Hg2+, fluorescence was effectively quenched and the paper-based chips gradually darkened from green till they became completely absent, while peroxidase-like activity was significantly enhanced. Two independent signals were captured by one identification unit, which provided self-validation to improve reliability and accuracy. Therefore, this work presents a simple synthesis of a multifunctional fluorescent nanozyme, and the developed portable device for on-site visual detection has considerable potential for application in the rapid on-site analysis of heavy metal ions in the environment.

Loading of AuNCs with AIE effect onto cerium-based MOFs to boost fluorescence for sensitive detection of Hg2. Talanta 2024;273:125843. [PMID: 38492285 DOI: 10.1016/j.talanta.2024.125843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Ligand-protected gold nanoclusters (AuNCs) have become promising nanomaterials in fluorescence (FL) methods for mercury ions (Hg2+) monitoring, but low FL efficiency hinders their widespread application. Herein, AuNCs/cerium-based metal-organic frameworks (AuNCs/Ce-MOFs) were prepared by loading 6-aza-2-thiothymine-protected AuNCs (ATT-AuNCs) with aggregation-induced emission (AIE) effect on the surface of Ce-MOFs by electrostatic attraction. This strategy improved the FL intensity of AuNCs through two aspects: (i) the AIE effect of ATT-AuNCs and (ii) the confinement effect of Ce-MOFs, which improved the restriction of intramolecular motion (RIM) of ATT-AuNCs. In addition, Ce-MOFs could adsorb and aggregate Hg2+ during detection, which might increase the local concentration. Therefore, based on the high FL signal of AuNCs/Ce-MOFs and enriched Hg2+, sensitive detection of Hg2+ could be achieved. More importantly, the strong specific recognition between AuNCs and Hg2+ could guarantee selectivity. The developed FL sensor exhibited superior detection performances with a wide linear range of 0.2-500 ng mL-1 and a low detection limit of 0.067 ng mL-1. Furthermore, the FL sensor used for sensitive and selective detection of Hg2+ in real samples, and the results agreed well with the standard method. In summary, this work proposed an effective and generalized strategy for improving the FL efficiency of AuNCs, which would greatly facilitate their application in pollutant monitoring.

Rapid Determination of Cr3+ and Mn2+ in Water Using Laser-Induced Breakdown Spectroscopy Combined with Filter Paper Modified with Gold Nanoclusters

Excessive emissions of heavy metals not only cause environmental pollution but also pose a direct threat to human health. Therefore, rapid and accurate detection of heavy metals in the environment is of great significance. Herein, we propose a method based on laser-induced breakdown spectroscopy (LIBS) combined with filter paper modified with bovine serum albumin-protected gold nanoclusters (LIBS-FP-AuNCs) for the rapid and sensitive detection of Cr3+ and Mn2+. The filter paper modified with AuNCs was used to selectively enrich Cr3+ and Mn2+. Combined with the multi-element detection capability of LIBS, this method achieved the simultaneous rapid detection of Cr3+ and Mn2+. Both elements showed linear ranges for concentrations of 10-1000 μg L-1, with limits of detection of 7.5 and 9.0 μg L-1 for Cr3+ and Mn2+, respectively. This method was successfully applied to the determination of Cr3+ and Mn2+ in real water samples, with satisfactory recoveries ranging from 94.6% to 105.1%. This method has potential application in the analysis of heavy metal pollution.

Bottom-Up Construction of Metal-Organic Framework Loricae on Metal Nanoclusters with Consecutive Single Nonmetal Atom Tuning for Tailored Catalysis

The introduction of single or multiple heterometal atoms into metal nanoparticles is a well-known strategy for altering their structures (compositions) and properties. However, surface single nonmetal atom doping is challenging and rarely reported. For the first time, we have developed synthetic methods, realizing "surgery"-like, successive surface single nonmetal atom doping, replacement, and addition for ultrasmall metal nanoparticles (metal nanoclusters, NCs), and successfully synthesized and characterized three novel bcc metal NCs Au38I(S-Adm)19, Au38S(S-Adm)20, and Au38IS(S-Adm)19 (S-Adm: 1-adamantanethiolate). The influences of single nonmetal atom replacement and addition on the NC structure and optical properties (including absorption and photoluminescence) were carefully investigated, providing insights into the structure (composition)-property correlation. Furthermore, a bottom-up method was employed to construct a metal-organic framework (MOF) on the NC surface, which did not essentially alter the metal NC structure but led to the partial release of surface ligands and stimulated metal NC activity for catalyzing p-nitrophenol reduction. Furthermore, surface MOF construction enhanced NC stability and water solubility, providing another dimension for tunning NC catalytic activity by modifying MOF functional groups.

Isolation of Sensing Units and Adsorption Groups Based on MOF-on-MOF Hierarchical Structure for Both Highly Sensitive Detection and Removal of Hg2

Bifunctional materials have attracted ongoing interest in the field of detection and removal of contaminants because of their integration of two functions, but they exhibit commonly exceptional performance in only one of these two aspects. The interaction between the two functional units of the bifunctional materials may compromise their sensing and adsorption abilities. Guided by the concept of domain building blocks (DBBs), a hierarchical metal-organic framework (MOF)-on-MOF hybrid was designed by growing gold nanoclusters (AuNCs)-embedded zeolitic imidazolate framework 8 (AuNCs/ZIF-8) on the surface of Zr-MOF (UiO-66-NH2) for the simultaneous detection and removal of Hg2+. In the hybrid, the amino groups (-NH2) and AuNCs─which were the adsorption groups and sensing units, respectively, were isolated from each other. Specifically, the adsorption groups (-NH2) were assembled in the inner UiO-66-NH2 layer, while the sensing units (AuNCs) were confined in the outer ZIF-8 layer. This hierarchical structure not only spatially hindered the electron transfer between these two units but also triggered the aggregation-induced emission of AuNCs because of the confinement of ZIF-8 on the AuNCs, thus changing the fluorescence of AuNCs from quenching to enhancement. The newly prepared UiO-66-NH2@AuNCs/ZIF-8 hybrid, as expected, showed an ultralow detection limit (0.42 ppb) and a high adsorption capacity (129.9 mg·g-1) for Hg2+. Overall, this work provides a feasible approach to improve the integrated performance of MOF-based composites based on DBBs.