Encapsulating gold nanoclusters into metal-organic frameworks to boost luminescence for sensitive detection of copper ions and organophosphorus pesticides

Confinement effect of zirconium metal-organic frameworks derived enhanced oxidase-like activity and stability of gold nanoclusters for biosensing

Gold nanoclusters (AuNCs), as an attractive material in heterogeneous catalysis, exhibit great potential in biosensing and biomedicine. However, controllable regulation of catalytic activity and preferable stabilization of AuNCs remain challenging. Benefiting from porous structures and ultrahigh specific surfaces, metal-organic frameworks (MOFs) have shown promising potential in the tailoring of catalytic activity and improving the stability of AuNCs. However, preferable catalytic activity and excellent stability are still challenging, due to the easy leaching of AuNCs from MOFs. Enhancing the combination between AuNCs and MOFs is of great significance. Herein, biomimic nanozymes of AuNCs@UiO-68 were designed through strong coordination between Zr atoms of the MOFs and phosphonate O atoms of DNA backbones from the DNA-templated AuNCs. Compared with control materials of AuNCs and AuNCs/UiO-68, a significant enhancement of oxidase-mimicking activity was achieved in AuNCs@UiO-68, owing to the confinement effect of Zr-MOFs. Additionally, it was found that the catalytic activity of AuNCs could be regulated by altering ligands of the Zr-MOFs. Based on the favorable catalytic activity of AuNCs@UiO-68, a highly sensitive and selective detecting platform for small uremic toxin molecule of hydroquinone was established, with a low detection limit of 0.85 μM. The stability of AuNCs was greatly improved by the proposed synthetic strategy. Besides, preferable and controllable catalytic activity was also obtained, attributed to the confinement effect of MOFs. This work provides a new way for rational regulation of catalytic activity and ameliorating the stability of metal clusters based nanozymes.

Nanocatalysts encapsulated in metal-organic frameworks: Size control and positive influences

Beyond traditional porous materials, metal-organic frameworks (MOFs) have attracted considerable attention for fabricating encapsulated nanocatalysts in the pores/cavities/channels of MOFs due to the high surface area, porous structure, and a large variety of organic linkers. As the host for nanocatalyst encapsulation, MOFs can provide uniform hierarchical pores and channels that can accelerate the mass transfer and migration of reactants or products and various metal‑oxygen clusters and organic linkers, which may interact strongly with nanocatalysts. Herein, state-of-the-art advancements in the encapsulation of nanocatalysts, including catalyst nanoparticles, clusters, quantum dots, and single-atom catalysts, have been summarized. The synthetic methods for nanocatalysts in MOFs and the enhanced properties are especially discussed. Then, positive effects upon the encapsulation of nanocatalysts in MOFs, including tunable chemical environment and encapsulation effects have been explored. Notably, the catalytic activity and product selectivity can be much improved by regulating the chemical environment around nanocatalysts and the interaction between the active nanocatalysts and metal nodes or organic linkers. Finally, challenges and future perspectives in encapsulated nanocatalysts in MOFs are proposed. This review could shed light on the construction of stable nanocatalysts encapsulation in MOFs with maximum exposed active sites and excellent activity in significant reactions.

Ultrasensitive adsorptive stripping voltammetry-free electrochemical sensor for Cu2 + based on its specific catalytic etching to cytosine-rich oligonucleotide templated silver nanoparticles

The development of reliable and highly sensitive copper ions (Cu2+) detection technologies is crucial for both environmental conservation and health surveillance. To address the challenges associated with conventional adsorptive stripping voltammetry, such as potential matrix interference, lengthy pre-electrolysis times, and limited detection sensitivity, we herein introduce an innovative electrochemical sensing approach for Cu2+. This method utilizes the unique catalytic etching capability of Cu2+ on cytosine-rich oligonucleotide (CRO)-templated silver nanoparticles (AgNPs). The thiolated CRO was assembled onto the Au electrode through the Au-S bond. Subsequently, the AgNPs were generated by in-situ chemical reduction of Ag+, which pre-absorbed on CRO via the cytosine-Ag+-cytosine (C-Ag+-C) structure. The results demonstrated that Cu2+ could markedly speed up the etching of AgNPs, which in turn reduced the solid-state electrochemical response of AgNPs. This reduction allowed for the detection of Cu2+ within a wide concentration range from 0.1 pM to 1.0 nM, with an impressively low detection limit of 0.03 pM. The practicality of this method has been validated through its successful application in analyzing Cu2+ levels of the actual water samples.

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.

A sensitive fluorescent probe of gold nanoclusters encapsulated by zeolitic imidazolate framework-8 for ATP detection

Adenosine triphosphate (ATP) actively involve into cellular processes. Abnormal levels of ATP related to a variety of diseases, therefore determining the ATP level is of pivotal significance for diagnoses. Here, a highly sensitive fluorescence probe based on gold nanoclusters (Au NCs) was constructed for the detection of ATP, and an expanded detection range and low limit of detection (LOD) were realized in our work. Zeolitic imidazolate framework-8 (ZIF-8) enhanced the fluorescence intensity of Au NCs by the encapsulation and less ATP cause to a stronger fluorescence change, which guaranteed detection reproducibility and facilitated lower LOD. The LOD of Au NCs encapsulated ZIF-8 (AZ) for ATP detection was expanded to 2 μM, which was only 0.05 % of sole Au NCs (4000 μM). Significantly, ATP of high concentration quenched AZ by disrupting the structure of ZIF-8 which expanded the detection range. Moreover, the linear range of high concentration ATP detection in serum was 600-4000 μM, which was closed to the normal level of ATP in physiological. Therefore, due to its low LOD and high sensitivity, AZ can be applied for fluorescence detection and initial diagnosis of disease related to ATP.

Sensitive discrimination of hazardous explosives by a sensor array based on siloles with aggregate-induced emission

The utilization of cationic amidinourea as side chain of fluorophore has rarely been reported, which might be an efficient and feasible strategy for detecting hazardous explosives. In this work, we present an organic sensor bearing a cationic amidinourea group-specifically, silole UMPS-synthesized via a rapid and convenient method. Its analogues with novel and symmetric structures were also reported. One is neutral and the other two carry hydrocarbon side chains that are positively charged. All four derivatives exhibit aggregation-induced emission and were employed for the detection of nitroaromatic explosives in water. These silole-based derivatives demonstrate excellent sensitivity and effective discriminatory capabilities in detecting explosives. We constructed a cross-reactive sensor array consisting of four derivatives, enabling the differentiation of nine closely related nitro explosives through linear discriminant analysis (LDA). This sensor array not only effectively distinguishes individual explosives of different concentrations and complex explosive mixtures, but also has the capability to identify individual explosives in real water samples with the assistance of machine learning algorithms. Moreover, two siloles were fabricated into test strips for sensing nitroaromatics in practical applications. We anticipate that the current work will pave the way for the development of cation sensors and provide a convenient detection platform for environmental analysis.

Rapid fluorescent sensing through heparin and chitosan encapsulated Eu3+ complexes for pesticide detection

Vegetables and fruits are essential sources of nutrients, minerals, vitamins, and dietary fiber for a well-balanced diet. However, excessive pesticide use, particularly 2,6-dichloro-4-nitroaniline (DCN), poses serious health and environmental risks. Traditional pesticide detection methods require expensive equipment, trained personnel and making them unsuitable for on-site sensing. In this study, we synthesized europium (Eu3+) complexes incorporating heparin sodium and chitosan to develop a rapid, cost-effective, and highly sensitive fluorescent sensor for DCN detection. The optimized Eu3+ complex (ETP-HS3) demonstrated excellent water stability, strong red fluorescence, and a long fluorescence lifetime (888.09 μs). It exhibited a low limit of detection (LOD = 0.9049 μM), a rapid sensing response (20 s), and a high quenching constant (Ksv = 1.226 × 104 M-1), rendering it an effective and portable fluorescence sensor for real-time pesticide monitoring. The fluorescence quenching mechanism was thoroughly investigated, confirming the selectivity and efficiency of the sensor.

Iron/manganese-zeolitic imidazolate framework (Fe/Mn-ZIF) nanozyme combined with acetylcholinesterase for colorimetric rapid detection of organophosphorus pesticides

Organophosphorus pesticides (OPs) are extensively utilized in agricultural production, but they pose significant threats to environment and organisms. This study aims to develop a novel method for the rapid and efficient detection of OPs. Initially, an iron/manganese zeolitic imidazolate framework (Fe/Mn-ZIF) with excellent oxidase-like activity was synthesised. The catalytic performance was evaluated, and the main factors influencing catalytic activity were investigated. Subsequently, a combined acetylcholinesterase assay was employed to detect three OPs. The specificity and recyclability of Fe/Mn-ZIF were also studied. The proposed colorimetric strategy demonstrated strong linear relationships: 0.1-2 mg/L for trichlorfon, 0.2-14 mg/L for glyphosate, and 0.4-10 mg/L for glufosinate, with the low detection limits of 0.024, 0.080, and 0.121 mg/L (3 S/N) respectively. Good recoveries were observed in real sample detection. This work lays a foundation for enhancing the catalytic performance of Fe/Mn-ZIF, which holds promise for biosensing applications.

Synchronously Delivering Melittin and Evoking Ferroptosis via Tumor Microenvironment-Triggered Self-Destructive Metal-Organic Frameworks to Boost Cancer Immunotherapy

The primary goal of treating malignant tumors is to efficiently eliminate the primary tumor and prevent metastasis and recurrence. Unfortunately, the immunosuppressive tumor microenvironment (TME) is a significant obstacle to effective oncotherapy. Herein, a therapeutic strategy based on melittin (MLT) encapsulated in hyaluronic acid-modified metal-organic frameworks (MOFs) is pioneered, focusing on the safe delivery and TME-responsive release of MLT to reshaping the immunosuppressive TME and simultaneously activating the immune system to eradicate cancerous cells. Iron-based MOFs respond to glutathione and pH, degrade within a moderately acidic TME, and achieve tumor-specific release of MLT. Additionally, the iron-mediated Fenton reaction produces reactive oxygen species that augment oxidative stress, ultimately leading to tumor-specific ferroptosis, whereas MLT-induced membrane disruption promotes immunogenic cell death to activate the immune system. In combination with the immune checkpoint inhibitor anti-PD-L1, this nanodrug elicits potent antitumor immune responses, facilitating the infiltration of effector T cells and enhancing systemic antitumor T cell immunity to suppress both primary and distant tumors. This study demonstrates the tremendous potential of nanoscale self-destructive MOFs for the targeted transport and controlled release of MLT and reveals the promoting effect of combined MLT and ferroptosis delivery on cancer immunotherapy.

Sensing array based on imidazole-regulated Cu@MOFs nanozymes with enhanced laccase-like activity for the discrimination of phenolic pollutants

BACKGROUND

Phenolic pollutants with high toxicity and low biodegradability can disrupt environmental balance and severely affect human health, whereas existing methods are difficult to implement the rapid and high-throughput detection of multiple phenolic pollutants.

RESULTS

Herein, we developed a four-dimensional colorimetric sensor array based on imidazole-modulated Cu@MOFs for distinguishing and determining phenolic pollutants. Wherein, four Cu@MOFs (ATP@Cu, ADP@Cu, AMP@Cu, and GMP@Cu) nanozyme with laccase-like activity were firstly prepared, and a novel strategy of imidazole-containing molecules-regulated was proposed to improve the laccase-like activity of Cu@MOFs nanozymes. Interestingly, imidazole (IM) exhibited the strongest enhancing effects on the laccase-like activity of the four Cu@MOFs by accelerating electron transfer on the surface of laccase nanozymes and producing more reactive oxygen species. Subsequently, by using Cu@MOFs@IM as the recognition elements of the sensor array, a colorimetric sensor array based on imidazole-modulated Cu@MOFs was developed, and differentiation and classification of phenolic pollutants were carried out using LDA and HCA methods. More importantly, the proposed sensor array could accomplish the identification of 6 phenolic pollutants and their mixtures.

SIGNIFICANCE

Additionally, the designed sensor array was applied to identify these phenolic pollutants in real water samples, further highlighting the potentials for assessing water pollution.

Integrating Zeolitic Imidazolate Framework-8 with DES-Treated Loofah Sponge for Enhanced Toluene Adsorption

The pervasive presence of toluene in aquatic environments, primarily due to oil spills and industrial effluents, necessitates the development of effective and sustainable remediation strategies. This study introduces ZIF-8@DES-treated loofah sponge (ZIF-8@DLS), a novel adsorbent composite material, synthesized via an in situ process that integrates the high surface area of ZIF-8 with the natural loofah sponge. The composite was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), confirming the successful loading of ZIF-8 onto the loofah substrate. The adsorption capacity of ZIF-8@DLS for toluene was evaluated, achieving a maximum of 145.3 mg/g with an efficiency of 72% under standard conditions. Kinetic studies revealed that the adsorption process predominantly followed a pseudo-second-order model, indicative of chemisorption. The adsorption isotherm data were found to align more closely with the Freundlich model, suggesting a multilayer adsorption mechanism on the composite's heterogeneous surface. The ZIF-8@DLS composite demonstrates a promising synergy of high adsorption performance, cost-effectiveness, facile synthesis, and environmental benignity, positioning it as a candidate for practical applications in wastewater treatment and adsorptive separation processes.

Metal-organic frameworks encapsulating gold nanoclusters and carbon dots for ratiometric fluorescent detection of formaldehyde in real food samples, construction materials and indoor environments

A novel fluorescence sensing nanoplatform (CDs/AuNCs@ZIF-8) encapsulating carbon dots (CDs) and gold nanoclusters (AuNCs) within a zeolitic imidazolate framework-8 (ZIF-8) was developed for ratiometric detection of formaldehyde (FA) in the medium of hydroxylamine hydrochloride (NH2OH·HCl). The nanoplatform exhibited pink fluorescence due to the aggregation-induced emission (AIE) effect of AuNCs and the internal filtration effect (IFE) between AuNCs and CDs. Upon reaction between NH2OH·HCl and FA, a Schiff base formed via aldehyde-diamine condensation, releasing hydrochloric acid. The acid triggered the degradation of ZIF-8, releasing CDs and AuNCs, and thereby shifting the fluorescence to blue as the CDs disperse. The nanoplatform demonstrated high sensitivity (LOD of 0.26-2.19 μM), exceptional selectivity, and rapid response time (<1 min) toward FA. Additionally, test strips and hydrogel films integrated with smartphones were prepared for on-site and visual detection of FA. The portable and smartphone-assisted test strips effectively detected indoor FA gas, while wearable and intelligent hydrogel films provided reliable surface measurements of FA on fruits and vegetables. Real sample analyses achieved satisfactory FA recoveries (99.06-115.30%) with relative standard deviations (RSD) from 1.86% to 3.81%. The innovative sensing nanoplatform served as a promising approach for FA detection in food, construction materials, and indoor air quality, offering both analytical accuracy and convenient visualization.

Advances in the synthesis and properties of sulfur quantum dots for food safety detection and antibacterial applications

Food safety is closely related to human health and has become a worldwide, pressing concern. Food safety analysis is essential for ensuring food safety. Sulfur quantum dots (SQDs), a new type of zero-dimensional metal-free nanomaterials, have recently become the focus of scientific research due to their good luminescence properties, dispersibility, biocompatibility, and inherent antibacterial properties. This review focuses on recent advances in SQDs, with emphasis on their practical applications in the food field. First, commonly used methods for the synthesis of SQDs are presented, including traditional and emerging strategies. The properties of SQDs are then analyzed in detail, particularly their luminescence properties, catalytic activities, and reducing properties. Next, the use of SQDs in food safety detection and antibacterial fields are elaborated. Finally, this review discusses the challenges associated with the use of SQDs in food safety detection and antimicrobial applications.

Safeguarding food safety: Nanomaterials-based fluorescent sensors for pesticide tracing

Pesticide residue contamination has emerged as a critical concern due to its potential negative effects on both public health and the natural environment. Consequently, the detection of pesticide residue is of utmost importance. Nanomaterial-based fluorescence sensors, including metal nanoparticles (MNPs), metal nanoclusters (MNCs), carbon dots (CDs), and quantum dots (QDs), are particularly effective for detecting pesticide residues. Herein, we provide a comprehensive review of the recent advances (2018-2024) in fluorescence-based sensors utilizing MNPs, MNCs, CDs and QDs and their composites for the purpose of detecting various pesticides including organophosphates, carbamates, organochlorines, and pyrethroids in food. This review delves into the evolution of nanomaterials, their corresponding fluorescence-based sensing mechanisms, including Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), inner filter effect (IFE), aggregation induced emission (AIE), and the detection principle, focusing on aspects of sensitivity and specificity. We also address the challenges and future perspectives of nanomaterials-based fluorescence sensors.

Mediated self-assembled gold nanoclusters with mesoporous silica particles to boost fluorescence for enhanced on-site monitoring of organophosphate pesticides

Accurate detection of organophosphate pesticides (OPs) is paramount for ensuring food safety. Dendritic mesoporous silica sphere was employed to confine gold nanoclusters (AuNCs@dmSiO2) to ameliorate fluorescent property of AuNCs. A AuNCs@dmSiO2-based fluorescent method was developed for OPs sensing. Identification of Cu2+ by AuNCs quenched AuNCs@dmSiO2 fluorescence. Interaction between Cu2+ and generated thiocholine in catalysis of acetylcholinesterase (AChE) caused fluorescence enhancement. OPs, an inhibitor of AChE, suppressed thiocholine production to cause fluorescence quenching. Based on fluorescent variation, a fluorescent method was proposed for OPs by selecting paraoxon as a model within range of 0.05-25.0 ng/mL with a limit of detection (LOD) of 0.032 ng/mL. Besides, a portable test swab was prepared for on-site monitoring OP paraoxon with a smartphone-based 3D-printing portable device with a LOD of 0.65 ng/mL. This work is highlighted by the inspiration of designing highly fluorescent AuNCs, and the provision of a viable avenue for OPs-related food analysis.

Luminescent Cu nanoclusters-encapsulated ZIF-8 as on-off-on fluorescent probe for efficient and selective quantification of E. coli

Rapid and accurate detection of Escherichia coli (E. coli) is critical for maintaining water quality, and protecting aquatic ecosystems and public health. This research focuses on the development of a Förster resonance energy transfer (FRET)-based "turn-on" fluorescent nanosensor for real time, sensitive detection of E. coli. Copper nanoclusters-encapsulated metal organic frameworks (CuNCs@ZIF-8) were sythesized as a fluorescent donor with excellent luminescence properties. Further, MnO2 nanospheres were synthesized as a receptor with good adsorption and quenching abilities. This novel nanoconjugate (CuNCs@ZIF-8@ MnO2) was employed for the construction of a sensitive, accurate, and rapid sensing platform against E. coli in water on the basis of p-benzoquinone/hydroquinone (p-BQ/HQ) redox pair formation. Fluorescence is quenched by energy transfer when MnO2 nanospheres are added to CuNCs@ZIF-8. Upon contact with E. coli, NADH-quinone reductase converts p-BQ to HQ, which reduces MnO2 to Mn2+, releasing the nanospheres and restoring fluorescence in the composite. Based on this FRET ON-OFF-ON fluorescent probe, E. coli can be detected across a broad concentration range (5 × 101 to 5 × 105 CFU/mL), with a detection limit as low as 8 CFU/mL within 50 min. The sensor's practicality was verified through the investigation of E. coli in real water samples, with recoveries in the range 94.3 to 106.5%. This approach offers an efficient method for on-site detection and quantification of E. coli in both environment and food safety domains.

Tailoring the photoluminescence of AIE-type gold nanoclusters via biomineralization-inspired polymorphism

Tailoring the aggregation-induced emission (AIE) characteristics of well-defined metal nanoclusters (MNCs) is highly sought after for numerous practical applications. Studies have primarily focused on assembling AIE-type MNCs using monomorphic molecules. Achieving polymorphic assemblies, with different molecular arrangements could provide valuable insights into the role of external molecular matrices on the photoluminescence (PL) behaviour of these NCs. In this study, by mimicking biomineralization, we successfully embedded AIE-type Au22SG18 NCs within different polymorphic environments of CaCO3. Upon incorporation into CaCO3 matrices such as, calcite, vaterite and a mixture of both, the PL was enhanced in all the inorganic composites accompanied by a significant blue shift. In the metastable vaterite matrix, Au22SG18 NCs exhibited the highest blue shift in the PL spectrum while in the stable crystalline matrix of calcite, the NCs showed the highest PL intensity as well as excited state lifetime. Time-resolved spectroscopic and single-molecule Raman studies revealed that variations in the PL of NCs are linked to the stability of their polymorphic structures, progressing from vaterite to a vaterite/calcite mixture, and finally to calcite. These findings shed light on the crucial role of external molecular arrangement in the AIE behaviour of MNCs.

Design of aggregation-induced emission materials for biosensing of molecules and cells

In recent years, aggregation-induced emission (AIE) materials have gained significant attention and have been developed for various applications in different fields including biomedical research, chemical analysis, optoelectronic devices, materials science, and nanotechnology. AIE is a unique luminescence phenomenon, and AIEgens are fluorescent moieties with relatively twisted structures that can overcome the aggregation-caused quenching (ACQ) effect. Additionally, AIEgens offer advantages such as non-washing properties, deep tissue penetration, minimal damage to biological structures, high signal-to-noise ratio, and excellent photostability. Fluorescent probes with AIE characteristics exhibit high sensitivity, short response time, simple operation, real-time detection capability, high selectivity, and excellent biocompatibility. As a result, they have been widely applied in cellular imaging, luminescent sensing, detection of physiological abnormalities in the human body, as well as early diagnosis and treatment of diseases. This review provides a comprehensive summary and discussion of the progress over the past four years regarding the detection of metal ions, small chemical molecules, biomacromolecules, microbes, and cells based on AIE materials, along with discussing their potential applications and future development prospects.

Integrating L-Cys-AuNCs in ZIF-8 with Enhanced Fluorescence and Strengthened Stability for Sensitive Detection of Copper Ions

Gold nanoclusters (AuNCs) have been widely investigated because of their unique photoluminescence properties. However, the applications of AuNCs are limited by their poor stability and relatively low fluorescence. In the present work, we developed nanocomposites (L-Cys-AuNCs@ZIF-8) with high fluorescence and stability, which were constructed by encapsulating the water-dispersible L-Cys-AuNCs into a ZIF-8 via Zn2+-triggered growth strategy without high temperature and pressure. The maximum emission wavelength of the L-Cys-AuNCs@ZIF-8 composite was at 868 nm, and the fluorescence intensity of L-Cys-AuNCs@ZIF-8 was nearly nine-fold compared with L-Cys-AuNCs without the ZIF-8 package. The mechanism investigation by fluorescence spectroscopy and X-ray photoelectron spectroscopy showed that L-Cys-AuNCs@ZIF-8 impeded ligand rotation, induced energy dissipation, and diminished the self-quenching effect, attributing to the spatial distribution of L-Cys-AuNCs. Based on the high fluorescence efficiency of L-Cys-AuNCs@ZIF-8, a "signal off" detective platform was proposed with copper ions as a model analyte, achieving a sensitive detection limit of Cu2+ at 16.7 nM. The quenching mechanism was confirmed, showing that the structure of the L-Cys-AuNCs@ZIF-8 nanocomposites was collapsed by the addition of Cu2+. Attributing to the strong adsorption ability between copper ions and pyridyl nitrogen, the as-prepared L-Cys-AuNCs@ZIF-8 was shown to accumulate Cu2+, and the Zn2+ in ZIF-8 was replaced by Cu2+.

Rapid redox-response featured visual ascorbic acid sensor based on simple-assembled europium metal-organic framework

A facile, fast and visible sensing platform for ascorbic acid (AA) detection has been developed based on self-assembled hydrangea-like europium metal-organic framework (HL-EuMOF). HL-EuMOF was synthesized through a simple one-step mixing process with Eu3+ and 1, 10-phenanthroline-2, 9-dicarboxylic acid at room temperature, which exhibited excellent properties including strong red fluorescence, long decay lifetime (548.623 μs) and good luminescent stability. Based on the specific redox reaction between Fe3+ and AA, the HL-EuMOF@Fe3+ was fabricated with "turn-off" response for AA, where the resulting Fe2+ displayed effective fluorescence quenching ability toward HL-EuMOF. The sensor demonstrated low detection limit (31.94 nM), rapid response time (30 s) and high selectivity. Integration of smartphone-assisted RGB analysis with HL-EuMOF@Fe3+ permitted convenient and visible quantitative determination of AA level. This approach also presented good detection performances in complex human serum and beverage samples, which could provide a valuable tool for AA detection in biomedical research and food industry.

Highly Sensitive Determination of Copper Ions as MnO2 Etching Inhibitor in Single-Particle Nanoplasmonic Imaging

Dark-field microscopy (DFM) imaging based on plasmonic metal nanoparticles has garnered significant attention. Here, we exploit the susceptibility of MnO2 to reduction to modulate the local dielectric environment of an Au nanoparticle core through the etching/antietching effects of specific targets on the encapsulated MnO2 shell. The presence of d-penicillamine promotes MnO2 etching, while the chelation of d-penicillamine with Cu2+ effectively inhibits this etching. By recording the Cu2+-induced color shift of scattered light from orange to bright green at the single-particle level and performing the statistical analysis of the green-to-red (G/R) values in DFM images, we achieved quantitative determination of Cu2+ with a wide linear range (0.1-10 μM) and a low limit of detection (4.55 nM). With the facile and reliable Cu2+ assay in real-world samples exemplifying the practicality of the single-particle nanoplasmonic imaging method, this work may inspire future DFM-based investigations of nanoshell etching inhibition processes.

Portable hydrogel kit based on Michael addition reaction for (E)-2-hexenal gas detection

Plants exhibit rapid responses to biotic and abiotic stresses by releasing a range of volatile organic compounds (VOCs). Monitoring changes in these VOCs holds the potential for the early detection of plant diseases. This study proposes a method for identifying late blight in potatoes based on the detection of (E)-2-hexenal, one of the major VOC markers released during plant infection by Phytophthora infestans. By combining the Michael addition reaction with cysteine-mediated etching of aggregation-induced emission gold nanoclusters (Au NCs), we have developed a portable hydrogel kit for on-site detection of (E)-2-hexenal. The Michael addition reaction between (E)-2-hexenal and cysteine effectively alleviates the etching of cysteine-mediated Au NCs, leading to a distinct fluorescence color change in the Au NCs, enabling a detection limit of 0.61 ppm. Utilizing the superior loading and diffusion characteristics of the three-dimensional structure of agarose hydrogel, our sensor demonstrated exceptional performance in terms of sensitivity, selectivity, reaction time, and ease of use. Moreover, quantitative measurement of (E)-2-hexenal was made easier by using ImageJ software to transform fluorescent images from the hydrogel kit into digital data. Such method was effectively used for the early detection of potato late blight. This study presents a low-cost, portable fluorescent analytical tool, offering a new avenue for on-site detection of plant diseases.

Organophosphorus Hydrolase-like Nanozyme with an Activity-Quenched Aggregation-Induced Emission Effect: A Self-Reporting and Specific Assay of Nerve Agents

Given the promising prospect of aggregation-induced emission luminogens (AIEgens) in fluorescence assays, it is interesting and significant to endow AIEgens with molecular recognition capability (such as enzyme-like activity). Here, an AIE nanomaterial with intrinsic enzyme-like activity (named as "AIEzyme") is designed and synthesized via a facile coordination polymerization of Zr4+ and AIE ligands. AIEzyme possesses enhanced and stable fluorescence in different solvents because of the AIE effect of ligands in the rigid structure of a coordination polymer. On the other hand, the organophosphorus hydrolase (OPH)-mimicking activity of AIEzyme exhibits excellent affinity and specific activity. Interestingly, the OPH-like activity can quench the inherent fluorescence of AIEzyme by the hydrolysate of a typical organophosphorus nerve agent (OPNA), diethyl-4-nitrophenylphosphate. Due to the sensitive activity-induced quenching effect for AIE, the self-reporting fluorescence assay method based on AIEzyme was established, which shows ultrahigh sensitivity, high selectivity, good storage stability, and acceptable reliability for a real sample assay. Moreover, the simultaneous colorimetric method broadens the detection range and the application scenarios. The proposed assay method avoided the interference of O2 during detection because the OPH-like activity does not derive from the generation of ROS. As a bonus, AIEzyme can also be used for the degradation of OPNAs by OPH-like activity, and the process can be self-monitored by AIE quenching. This work would provide a new opportunity for expanding the application of AIEgens and artificial enzymes by endowing AIEgens with enzyme-like activity.

Luminescent Metal-Organic Framework-Based Fluorescent Sensor Array for Screening and Discrimination of Bisphenols

Extensive applications of bisphenols in industrial products have led to their release into aquatic environments, causing a great threat to human health due to their endocrine-disrupting effects, whereas existing methods are difficult to implement the rapid and high-throughput detection of multiple bisphenols. To circumvent this issue, we constructed a sensor array using two luminescent metal-organic frameworks (LMOFs) (Zr-BUT-12 and Ga-MIL-61) for the rapid discrimination of six bisphenol contaminants (BPA, BPS, BPB, BPF, BPAF, and TBBPA). Wherein, Zr-BUT-12 and Ga-MIL-61 exhibited different fluorescence-emission properties and good luminescent stability. Interestingly, bisphenols with different structures had diverse quenching effects on the fluorescence intensity of Zr-BUT-12 and Ga-MIL-61 via the adsorptive interaction, resulting in unique fluorescent fingerprints. Based on pattern recognition methods, different bisphenols were successfully identified, with the limit of detection in the range of 1.59-16.7 ng/mL for six bisphenols. More importantly, the developed sensor array could be effectively utilized for distinguishing different ratios of mixed bisphenols, which was further applied for bisphenol discrimination in real water samples. Consequently, our finding provides a promising strategy for the simultaneous recognition of multiple bisphenols, which encourages the development of a sensor array for the detection of multiple contaminants in environmental monitoring and food safety.

Deep learning assisted logic gates for real-time identification of natural tetracycline antibiotics

The overuse and misuse of tetracycline (TCs) antibiotics, including tetracycline (TTC), oxytetracycline (OTC), doxycycline (DC), and chlortetracycline (CTC), pose a serious threat to human health. However, current rapid sensing platforms for tetracyclines can only quantify the total amount of TCs mixture, lacking real-time identification of individual components. To address this challenge, we integrated a deep learning strategy with fluorescence and colorimetry-based multi-mode logic gates in our self-designed smartphone-integrated toolbox for the real-time identification of natural TCs. Our ratiometric fluorescent probe (CD-Au NCs@ZIF-8) encapsulated carbon dots and Au NCs in ZIF-8 to prevent false negative or positive results. Additionally, our independently developed WeChat app enabled linear quantification of the four natural TCs using the fluorescence channels. The colorimetric channels were also utilized as outputs of logic gates to achieve real-time identification of the four individual natural tetracyclines. We anticipate this strategy could provide a new perspective for effective control of antibiotics.

Digitalization of Colorimetric Sensor Technologies for Food Safety

Colorimetric sensors play a crucial role in promoting on-site testing, enabling the detection and/or quantification of various analytes based on changes in color. These sensors offer several advantages, such as simplicity, cost-effectiveness, and visual readouts, making them suitable for a wide range of applications, including food safety and monitoring. A critical component in portable colorimetric sensors involves their integration with color models for effective analysis and interpretation of output signals. The most commonly used models include CIELAB (Commission Internationale de l'Eclairage), RGB (Red, Green, Blue), and HSV (Hue, Saturation, Value). This review outlines the use of color models via digitalization in sensing applications within the food safety and monitoring field. Additionally, challenges, future directions, and considerations are discussed, highlighting a significant gap in integrating a comparative analysis toward determining the color model that results in the highest sensor performance. The aim of this review is to underline the potential of this integration in mitigating the global impact of food spoilage and contamination on health and the economy, proposing a multidisciplinary approach to harness the full capabilities of colorimetric sensors in ensuring food safety.

Smartphone-integrated visual inspection for enhancing agricultural product quality and safety: a review

The increasing emphasis on the quality and safety of agricultural products, which are vital to global trade and consumer health, has driven the innovation of cost-effective, convenient, and rapid smart detection technologies. Smartphones, with their interdisciplinary functionalities, have become valuable tools in quantification and analysis research. Acting as portable, affordable, and user-friendly analytical devices, smartphones are equipped with high-resolution cameras, displays, memory, communication modules, sensors, and operating systems (Android or IOS), making them powerful, palm-sized remote computers. This review delves into how visual inspection technology and smartphones have enhanced the quality and safety of agricultural products over the past decade. It also evaluates the key features and limitations of existing smart rapid inspection methods for agricultural products and anticipates future advancements, offering insights into the application of smart rapid inspection technology in agriculture.

Gold Nanocluster-Based Self-Assembly Fluorescence Microbeads for Sensor Array Discrimination of Multicomponent Metal Ions

Benefiting from easy visualization and simultaneous detection of multiple targets, fluorescence microbeads are commonly used as fluorescence-sensing elements to detect pollutants in the environment. However, the application of fluorescence microbead-based sensor arrays is still limited because fluorescence dyes always suffer from self-quenching, photobleaching, and spectral overlap. Herein, three kinds of gold nanoclusters (Au NCs) were assembled with polystyrene microspheres (PS NPs) by electrostatic interaction to prepare fluorescence microbeads (PS-Au NCs), developing a sensor array for the simultaneous analysis of multiple metal ions. In this work, different PS-Au NCs showed an enhancing or quenching fluorescence response to various metal ions, owing to distinct binding capacities. Combined with the recognition algorithm from linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA), this sensor assay could realize single-component and multicomponent qualitative detection for 8 kinds of heavy metal ions (HMIs) including Cu2+, Co2+, Pb2+, Hg2+, and Ce3+. Particularly, the large surface area of PS NPs could provide a direct reaction microenvironment to improve the efficiency of the detection process. Meanwhile, the fluorescence property of Au NCs could also be enhanced by a partially effective aggregation-induced emission (AIE) effect to give better fluorescence signal output. Under optimal conditions, 8 kinds of heavy metals and their multicomponent mixtures could be identified at concentrations as low as 0.62 μM. Meanwhile, the analytical performance of this sensor assay in water samples was also verified, meeting the requirement of actual analysis. This study provides a great potential and practical example of single-batch, multicomponent identification for HMIs.

Encapsulation of Enzymes into Hydrophilic and Biocompatible Metal Azolate Framework: Improved Functions of Biocatalyst in Cascade Reactions and its Sensing Applications

Multiple enzyme-triggered cascade biocatalytic reactions are vital in vivo or vitro, considering the basic biofunction preservation in living organisms and signals transduction for biosensing platforms. Encapsulation of such enzymes into carrier endows a sheltering effect and can boost catalytic performance, although the selection and preparation of an appropriate carrier is still a concern. Herein, focusing on MAF-7, a category of metal azolate framework (MAF) with superiority against the topologically identical ZIF-8, this enzyme@MAF system can ameliorate the sustainability of encapsulating natural enzymes into carriers. The proposed biocatalyst composite AChE@ChOx@MAF-7/hemin is constructed via one-pot in situ coprecipitation method. Subsequently, MAF-7 is demonstrated to exhibit an excellent capacity of the carrier and protection against external factors in the counterpart of ZIF-8 through encapsulated and free enzymes. In addition, detections for specific substrates or inhibitors with favorable sensitivity are accomplished, indicating that the properties above expectation of different aspects of the established platform are successfully realized. This biofunctional composite based on MAF-7 can definitely provide a potential approach for optimization of cascade reaction and enzyme encapsulation.

Raspberry-shaped ZIF-8/Au nanozymes with excellent peroxidase-like activity for simple and visual detection of glutathione

Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5-60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions.

A Ratiometric Fluorescence Probe Based on Silver Nanoclusters and CdSe/ZnS Quantum dots for the Detection of Hydrogen Peroxide by Aggregation and Etching

In this study, a ratiometric fluorescence nanoprobe is developed for the analysis of hydrogen peroxide (H2O2). Silver nanoclusters (AgNCs) were synthesized by chemical reduction method using sodium borohydride (NaBH4) as reducing agent, and were coupled with CdSe/ZnS quantum dots (QDs) to form the ratiometric fluorescence nanoprobe silver nanoclusters-quantum dots (AgNCs-QDs). The effect of the volume ratio of CdSe/ZnS QDs to AgNCs on the fluorescence ratio of AgNCs-QDs was investigated. The fluorescence characterization results show that two emission peaks of AgNCs-QDs are located at 473 nm and 661 nm, respectively. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) results show that H2O2 can cause the fluorescence probe to aggregate, while etching AgNCs to produce silver ions, which together cause the fluorescence of the QDs in the ratiometric fluorescent probe to be quenched. Based on this strategy, the fluorescence intensity ratio of the two emission peaks F473/F661 exhibits a strong linear correlation with the concentration of H2O2. The detection range is 3.32 µM ~ 2.65 mM with a detection limit of 3.32 µM. In addition, the ratiometric fluorescence probe can specifically recognize H2O2 and has excellent anti-interference performance and good fluorescence stability. Importantly, the probe was utilized for the detection of H2O2 in serum, showing the possibility of the probe in clinical detection applications.

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.

Metal-organic framework-based multienzyme cascade bioreactor for sensitive detection of methyl parathion

In this study, a cascade nanobioreactor was developed for the highly sensitive detection of methyl parathion (MP) in food samples. The simultaneous encapsulation of acetylcholinesterase (AChE) and choline oxidase (CHO) in a zeolitic imidazole ester backbone (ZIF-8) effectively improved the stability and cascade catalytic efficiency of the enzymes. In addition, glutathione-stabilized gold nanoclusters (GSH-AuNCs) were encapsulated in ZIF-8 by ligand self-assembly, conferring excellent fluorescence properties. Acetylcholine (ATCh) is catalyzed by a cascade of AChE/CHO@ZIF-8 as well as Fe(II) to generate hydroxyl radicals (·OH) with strong oxidizing properties. The ·OH radicals then oxidize Au(0) in GSH-AuNCs@ZIF-8 to Au(I), resulting in fluorescence quenching. MP, as an inhibitor of AChE, hinders the cascade reaction and thus restores the fluorescence emission, enabling its quantitative detection. The limit of detection of the constructed nanobioreactor for MP was 0.23 µg/L. This MOF-based cascade nanobioreactor has great potential for the detection of trace hazards.

Morphology Control of Zr-Based Luminescent Metal-Organic Frameworks for Aflatoxin B1 Detection

Metal-organic frameworks (MOFs) have gained significant prominence as sensing materials owing to their unique properties. However, understanding the correlation between the morphology, properties, and sensing performance in these MOF-based sensors remains a challenge, limiting their applications and potential for improvement. In this study, Zr-MOF was chosen as an ideal model to explore the impact of the MOF morphology on the sensing performance, given its remarkable stability and structural variability. Three luminescent MOFs (namely rod-like Zr-LMOF, prismoid-like Zr-LMOF, and ellipsoid-like Zr-LMOF) were synthesized by adjusting the quantities of the benzoic acid and the reaction time. More importantly, the sensing performance of these Zr-LMOFs in response to aflatoxin B1 (AFB1) was thoroughly examined. Notably, the ellipsoid-like Zr-LMOF exhibited significantly higher sensitivity compared to other Zr-LMOFs, attributed to its large specific surface area and pore volume. Additionally, an in-depth investigation into the detection mechanism of AFB1 by Zr-LMOFs was conducted. Building upon these insights, a ratiometric fluorescence sensor was developed by coordinating Eu3+ with ellipsoid-like Zr-LMOF, achieving a remarkably lower detection limit of 2.82 nM for AFB1. This study contributes to an improved comprehension of the relationship between the MOF morphology and the sensing characteristics while presenting an effective approach for AFB1 detection.

Eu3+-based InP/ZnS quantum dot fluorescence platform for multi-color and sensitive visualization of tetracycline

A turn-on type ratiometric fluorescence sensing system of blue quantum dot Eu-MPA-InP/ZnS was established for multi-color visualization determination of tetracycline (TC). Mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) both modify the hydrophilicity of InP/ZnS QDs and serve as a scaffold for coordinating of Eu3+ ions. The blue fluorescence of Eu-MPA-InP/ZnS at 478 nm is reduced by the TC through the inner filter effect (IFE) under a single excitation wavelength of 365 nm. Rich colour gradients and a highly discriminative colour change were features of this multicolour response to TC, which allowed visual quantification of TC in a dose-dependent manner. Furthermore, by cross-linking Eu-MPA-InP/ZnS with agarose (Aga.), a mouldable Eu-MPA-InP/ZnS@Aga 96-well gel sensing device was designed to serve as a handheld sensor for on-site detection of TC. This probe expands the use of InP QDs in analytical sensing and has been effectively applied to the visual detection of tetracycline in milk and the environment.

Four birds with one stone: Aggregation-induced emission-type zeolitic imidazolate framework-8 based bionic nanoreactor for portable detection of olaquindox in environmental water and swine urine by smartphone

The abuse of olaquindox (OLA) as both an antimicrobial agent and a growth promoter poses significant threats to the environment and human health. While nanoreactors have proven effective in hazard detection, their widespread adoption has been hindered by tedious chemical processes and limited functionality. In this study, we introduce a novel green self-assembly strategy utilizing invertase, horseradish peroxidase, antibodies, and gold nanoclusters to form an aggregation-induced emission-type zeolitic imidazolate framework-8 nanoreactor. The results demonstrate that the lateral flow immunoassay not only allows for qualitative naked eye detection but also enables optical analysis through the fluorescence generated by aggregated gold nanoclusters and enzyme-catalyzed enhancement of visible colorimetric signals. To accommodate more detection scenarios, the photothermal effects and redox reactions of the nanoreactor can fulfill the requirements of thermal sensing and electrochemical analysis for smartphone applications. Remarkably, the proposed approach achieves a detection limit 17 times lower than conventional methods. Besides, the maximum linear range spans from 0.25 to 5 μg/L with high specificity, and the recovery is 85.2-112.9% in environmental water and swine urine. The application of this high-performance nanoreactor opens up avenues for the construction of multifunctional biosensors with great potential in monitoring hazardous materials.

Recent advancements in modifications of metal-organic frameworks-based materials for enhanced water purification and contaminant detection

Metal-organic frameworks (MOFs) have emerged as a key focus in water treatment and monitoring due to their unique structural features, including extensive surface area, customizable porosity, reversible adsorption, and high catalytic efficiency. While numerous reviews have discussed MOFs in environmental remediation, this review specifically addresses recent advancements in modifying MOFs to enhance their effectiveness in water purification and monitoring. It underscores their roles as adsorbents, photocatalysts, and in luminescent and electrochemical sensing. Advancements such as pore modification, defect engineering, and functionalization, combined synergistically with advanced materials, have led to the development of recyclable MOF-based nano-adsorbents, Z-scheme photocatalytic systems, nanocomposites, and hybrid materials. These innovations have broadened the spectrum of removable contaminants and improved material recyclability. Additionally, this review delves into the creation of multifunctional MOF materials, the development of robust MOF variants, and the simplification of synthesis methods, marking significant progress in MOF sensor technology. Furthermore, the review addresses current challenges in this field and proposes potential future research directions and practical applications. The growing research interest in MOFs underscores the need for an updated synthesis of knowledge in this area, focusing on both current challenges and future opportunities in water remediation.

A facile fluorescence microplate immunoassay based on an in situ fluorogenic reaction for the detection of two highly toxic anticoagulant rodenticides in food and biological matrix

Bromadiolone and brodifacoum, the most frequently used anticoagulant rodenticides, are highly toxic and pose a threat to public health by causing food poisoning incidents. Here, we developed a fluorescence microplate immunoassay for facile and sensitive detection of bromadiolone and brodifacoum by introducing three commercial chemicals (p-phenylenediamine, polyethyleneimine, H2O2) as a new substrate of horseradish peroxidase and then generating fluorescence signals based on an in situ fluorogenic reaction (detection time within 75 min). This assay exhibited higher efficiency in generating fluorescence signals, thereby exhibiting a 6-fold improvement in sensitivity compared with colorimetric ELISA. The limit of detection was 0.23-0.28 ng/mL (ng/g) for bromadiolone and 0.34-0.61 ng/mL (ng/g) for brodifacoum in corn and human serum, with recovery ratios higher than 82.3 %. These satisfactory results illustrated our proposed assay was a potential tool for food analysis and poisoning diagnosis caused by bromadiolone and brodifacoum.

Dual-Emission Single Sensing Element-Assembled Fluorescent Sensor Arrays for the Rapid Discrimination of Multiple Surfactants in Environments

Surfactants are considered as typical emerging pollutants, their extensive use of in disinfectants has hugely threatened the ecosystem and human health, particularly during the pandemic of coronavirus disease-19 (COVID-19), whereas the rapid discrimination of multiple surfactants in environments is still a great challenge. Herein, we designed a fluorescent sensor array based on luminescent metal-organic frameworks (UiO-66-NH2@Au NCs) for the specific discrimination of six surfactants (AOS, SDS, SDSO, MES, SDBS, and Tween-20). Wherein, UiO-66-NH2@Au NCs were fabricated by integrating UiO-66-NH2 (2-aminoterephthalic acid-anchored-MOFs based on zirconium ions) with gold nanoclusters (Au NCs), which exhibited a dual-emission features, showing good luminescence. Interestingly, due to the interactions of surfactants and UiO-66-NH2@Au NCs, the surfactants can differentially regulate the fluorescence property of UiO-66-NH2@Au NCs, producing diverse fluorescent "fingerprints", which were further identified by pattern recognition methods. The proposed fluorescence sensor array achieved 100% accuracy in identifying various surfactants and multicomponent mixtures, with the detection limit in the range of 0.0032 to 0.0315 mM for six pollutants, which was successfully employed in the discrimination of surfactants in real environmental waters. More importantly, our findings provided a new avenue in rapid detection of surfactants, rendering a promising technique for environmental monitoring against trace multicontaminants.

A portable colorimetric sensing platform for rapid and sensitive quantification of dichlorvos pesticide based on Fe-Mn bimetallic oxide nanozyme-participated highly efficient chromogenic catalysis

BACKGROUND

Dichlorvos (DDVP), as a highly effective insecticide, is widely used in agricultural production. However, DDVP residue in foodstuffs adversely affects human health. Conventional instrumental analysis can provide highly sensitive and accurate detection of DDVP, while the need of bulky and expensive equipment limits their application in resource-poor areas and on-site detection. Therefore, the development of easily portable sensing platforms for convenient, rapid and sensitive quantification of DDVP is very essential for ensuring food safety.

RESULT

A portable colorimetric sensing platform for rapid and sensitive quantification of DDVP is developed based on nanozyme-participated highly efficient chromogenic catalysis. The Fe-Mn bimetallic oxide (FeMnOx) nanozyme possesses excellently oxidase-like activity and can efficiently catalyze oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue oxide with a very low Michaelis constant (Km) of 0.0522 mM. The nanozyme-catalyzed chromogenic reaction can be mediated by DDVP via inhibiting the acetylcholinesterase (AChE) activity. Thus, trace DDVP concentration-dependent color evolution is achieved and DDVP can be sensitively detected by spectrophotometry. Furthermore, a smartphone-integrated 3D-printed miniature lightbox is fabricated as the colorimetric signal acquisition and processing device. Based on the FeMnOx nanozyme and smartphone-integrated lightbox system, the portable colorimetric sensing platform of DDVP is obtained and it has a wide linear range from 1 to 3000 ng mL-1 with a low limit of detection (LOD) of 0.267 ng mL-1 for DDVP quantification.

SIGNIFICANCE

This represents a new portable colorimetric sensing platform that can perform detection of DDVP in foodstuffs with simplicity, sensitivity, and low cost. The work not only offers an alternative to rapid and sensitive detection of DDVP, but also provides a new insight for the development of advanced sensors by the combination of nanozyme, 3D-printing and information technologies.

Portable sensors equipped with smartphones for organophosphorus pesticides detection

Organophosphorus pesticides (OPs) play an important role in agricultural production and the accurate detection of OP residues is essential to ensure food safety. Portable sensors are expected to be a potential device due to their high detection efficiency, easy-to-use processes and low cost. Due to the widespread popularity and powerful capabilities of smartphones, smartphone-based sensing systems have rapidly developed into ideal tools for portable detection, however, a systematic review on the detection of OPs is still lacking. Therefore, a comprehensive overview of sensors equipped with smartphones for OP detection in recent year is provided; this overview includes their sensing signals (colorimetric, fluorescent, chemiluminescent and electrochemical signals), detection mechanism, analysis applications, advantages/disadvantages and perspectives. Moreover, the progress of sensors equipped with smartphones for the detection of OPs in food is thoroughly summarized. This review contributes to food safety and the development of efficient and reliable methods for smartphone-based OPs detection.

Fluorometric and colorimetric dual-mode sensing of α-glucosidase based on aggregation-induced emission enhancement of AuNCs

Herein, a fluorometric and colorimetric dual-mode assay platform used for α-glucosidase (α-Glu) activity sensing based on aggregation-induced emission enhancement (AIEE) of AuNCs was developed for the first time. The quantum yield (QY) and fluorescence lifetime of AuNCs were successfully ameliorated by Ce3+-triggered AIEE (Ce@AuNCs). Subsequently, on the basis of the inner filter effect (IFE) and dynamic quenching effect (DQE) between 2,6-dichlorophenolindophenol (DCIP) and Ce@AuNCs as well as the reduction of DCIP by ascorbic acid (AA) generated from α-Glu-catalyzed hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl (AA2G), the marriage of fluorometric and colorimetric modes applied for α-Glu activity monitoring was achieved. Besides, the feasibility of this dual-mode sensing system was confirmed by the assays versus potential interfering substances and in real samples. In particular, this system was further applied to evaluate natural α-Glu inhibitors (AGIs) including luteolin, apigenin, and hesperidin. Overall, the multi-mode optical sensor newly designed here has the potential for the accurate discovery of natural anti-diabetes drugs and the therapy of diabetes.

A Novel Ion Species- and Ion Concentration-Dependent Anti-Counterfeiting Based on Ratiometric Fluorescence Sensing of CDs@MOF-Nanofibrous Films

Traditional fluorescent anti-counterfeiting labels based on "on-off" fluorescence can be easily cloned. It is important to explore advanced anti-counterfeiting fluorescent labels with high-level security. Here, a pioneering ion species- and ion concentration-dependent anti-counterfeiting technique is developed. By successive loading Cu2+ -sensitive yellow emitted carbon dots (Y-CDs) and Cu2+ non-sensitive blue emitted carbon dots (B-CDs) into metal-organic frameworks (MOFs) and followed by electrospinning, the B&Y-CDs@MOF-nanofibrous films are prepared. The results show that the use of MOF not only avoids the fluorescence quenching of CDs but also improves the fluorescence stability. The fluorescence Cu2+ -sensitivity of the CDs@MOF-nanofibrous films can be regulated by polymer coating or lamination. The fluorescent label consisting of different Cu2+ -sensitivity films will show Cu2+ concentration-dependent decryption information. Only at a specific ion species and concentration (Cu2+ solution of 40-90 µm), the true information can be read out. Less or more concentration (<40 or >90 µm) will lead to false information. The identification of the real information depends on both the species and the concentration. After Cu2+ treatment, the fluorescence of the label can be recovered by ethylenediaminetetraacetic acid disodium (EDTA-2Na) for further recycling. This work will open up a new door for designing high-level fluorescent anti-counterfeiting labels.

Recent advances in metal-organic framework (MOF)-based agricultural sensors for metal ions: a review

Metal ions have great significance for agricultural development, food safety, and human health. In turn, there exists an imperative need for the development of novel, sensitive, and reliable sensing techniques for various metal ions. Agricultural sensors for the diagnosis of both agricultural safety and nutritional health can establish quality and safety traceability systems of both agro-products and food to guarantee human health, even life safety. Metal-organic frameworks (MOFs) are utilized widely for the design of diversified sensors due to their distinctive structural characteristics and extraordinary optical and electrical properties. To serve agricultural sensors better, this review is dedicated to providing a brief overview of the synthesis of MOFs, the modification of MOFs, the fabrication of MOF-based film electrodes, the applications of MOF-based agricultural sensors for metal ions, which are centered on electrochemical sensors and optical sensors, and current challenges of MOF-based agricultural sensors. In addition, this review also provides potential future opportunities for the development and practical application of agricultural sensors.

Fabrication of Biomimetic Cascade Nanoreactor Based on Covalent Organic Framework Capsule for Biosensing

The cooperation of biocatalysis and chemocatalysis in a catalytic cascade reaction has received extensive attention in recent years, whereas its practical applications are still hampered due to the fragility of the enzymes, poor compatibility between the carriers and enzymes, and limited catalytic efficiency. Herein, a biomimetic cascade nanoreactor (GOx@COFs@Os) was presented by integrating glucose oxidase (GOx) and Os nanozyme with covalent organic framework (COF) capsule using metal-organic framework (ZIF-90) as a template. The obtained GOx@COFs@Os capsule provided a capacious microenvironment to retain the conformational freedom of GOx for maintaining its activity, wherein the enzyme activity of GOx in COF capsules was equal to 92.9% of the free enzyme and was 1.88-folds higher than that encapsulated in ZIF-90. Meanwhile, the COF capsule could protect the GOx against incompatible environments (high temperature, acid, and organic solvents), resulting in improved stability of the packaged enzymes. Moreover, the COF capsule with great pore structure significantly improved the affinity to substrates and facilitated efficient mass transfer, which achieved 2.19-folds improvement in catalytic efficiency than the free cascade system, displaying the great catalytic performance in the cascade reaction. More importantly, the biomimetic cascade capsule was successfully employed for glucose monitoring, glutathione sensing, and bisphenol S detection in the immunoassay as a proof-of-concept. Our strategy provided a new avenue in the improvement of biocatalytic cascade performance to encourage its wide applications in various fields.

Aggregates-based fluorescence sensing technology for food hazard detection: Principles, improvement strategies, and applications

Aggregates often exhibit modified or completely new properties compared with their molecular elements, making them an extraordinarily advantageous form of materials. The fluorescence signal change characteristics resulting from molecular aggregation endow aggregates with high sensitivity and broad applicability. In molecular aggregates, the photoluminescence properties at the molecular level can be annihilated or elevated, leading to aggregation-causing quenching (ACQ) or aggregation-induced emission (AIE) effects. This change in photoluminescence properties can be intelligently introduced in food hazard detection. Recognition units can combine with the aggregate-based sensor by joining the aggregation process, endowing the sensor with the high specificity of analytes (such as mycotoxins, pathogens, and complex organic molecules). In this review, aggregation mechanisms, structural characteristics of fluorescent materials (including ACQ/AIE-activated), and their applications in food hazard detection (with/without recognition units) are summarized. Because the design of aggregate-based sensors may be influenced by the properties of their components, the sensing mechanisms of different fluorescent materials were described separately. Details of fluorescent materials, including conventional organic dyes, carbon nanomaterials, quantum dots, polymers and polymer-based nanostructures and metal nanoclusters, and recognition units, such as aptamer, antibody, molecular imprinting, and host-guest recognition, are discussed. In addition, future trends of developing aggregate-based fluorescence sensing technology in monitoring food hazards are also proposed.

Identification of multi-component metal ion mixtures in complex systems using fluorescence sensor arrays

The growing co-contamination of multiple metal ions seriously influences human health due to their synergistic and additive toxicological effects, whereas the rapid discrimination of multiple heavy metal ions in complex aquatic systems remains a major challenge. Herein, a high- throughput fluorescence sensor array was fabricated based on three gold nanoclusters (GSH-Au NCs, OVA-Au NCs, and BSA-Au NCs) for the direct identification and quantification of seven heavy metal ions (Pb²⁺, Fe³⁺, Cu²⁺, Co²⁺, Ag⁺, Hg²⁺ and As³⁺) from environmental waters without sample pretreatment other than filtration. At the detection system, three gold nanoclusters with various ligands possessed distinct binding capacities against metal ions and induced aggregation-induced fluorescence enhancement and quenching, resulting in a unique pattern of fluorescence variations. Meanwhile, integrated the collected fluorescence fingerprints with linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA), a discrete database was obtained for the accurate recognition and sensitive detection of metal ions. Under the optimized conditions, the limit of detection (LOD) of the proposed fluorescence sensor array for metal ions detection at nM concentration level along with a satisfactory accuracy. Importantly, our study indicated that the fluorescence sensor array could be widely used as a general platform in environmental monitoring against multiple targets at low concentrations.

Degradation kinetics and transformation pathway of methyl parathion by δ-MnO2/oxalic acid reaction system

Methyl parathion (MP) is a typical organophosphorus pesticide that is widely used worldwide, and hydrolysis, oxidation and reduction are the main abiotic degradation processes. Manganese dioxide (MnO₂) and organic acid can participate in various geochemical processes of pollutants, a reaction system was constructed to degrade MP using δ-MnO₂ and oxalic acid. The δ-MnO₂/oxalic acid reaction system could efficiently degrade MP, and the removal rate of MP (20 μM) reached 67.83% within 30 h under the optimized conditions (pH 5, [δ-MnO₂] = 2 mM, [oxalic acid] = 100 mM). MP was hydrolyzed by substitution reactions of S_N@P and S_N@C, and reduced by conversion of the nitro groups (-NO₂) in MP and its hydrolysates to amino groups (-NH₂). The primary active substance produced in the reaction system was the complexes dominated by Mn(III)-oxalic acid. This study provides a scientific basis for the degradation of organophosphorus pesticides using MnO₂ and an organic acid. The results have important theoretical significance and application value for pollution control and remediation of organophosphorus pesticides.