Capsulation of AuNCs with AIE Effect into Metal–Organic Framework for the Marriage of a Fluorescence and Colorimetric Biosensor to Detect Organophosphorus Pesticides

γ-cyclodextrin metal-organic framework-activated gold nanoclusters with water solubility as multi-enzyme mimics for simultaneous detection of pesticide and cholinesterase activity

Cyclodextrin metal-organic framework (CD-MOF) with environmentally friendly components has attracted enormous attention in the past few decades. However, the fragile aqueous stability has limited its application in aqueous catalysis. In this work, we have devised a novel strategy to cope with the problems by introducing the well-defined gold nanoclusters (AuNCs) onto the cyclodextrin ligand through host-guest chemistry. The combination with AuNCs endowed the fragile CD-MOF with excellent multi-enzyme mimicking catalytic abilities, including peroxidase (POD), oxidase (OXD), catalase (CAT) and glucose oxidase (GOx)-mimetic activities. Furthermore, based on its intrinsic POD-like activities, by constructing the typical enzyme cascade reaction, a colorimetric sensor based on Au38/γ-CD-MOF was developed for the rapid and sensitive of carbaryl and butyrylcholinesterase (BChE) activity, respectively. In addition, combined with the smartphone, a portable paper-based sensor was developed, which could realize the on-site and semiquantitative detection of pesticide residues by identifying the RGB value. This low-cost and easy-operation portable assay shows great potential for online detection of pesticides exposure and monitoring other disease biomarkers.

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.

Ratiometric fluorescence analysis of tetracycline by dual-ligand europium-based metal-organic framework

It is important to develop sensitive and accurate methods for the detection of tetracycline (TC). For this purpose, a dual emission probe Eu-DPA/BDC-(OH)2 was developed based on the green fluorescence of the ligand 2, 5-dihydroxyterephthalic acid (BDC-(OH)2), and the red fluorescence of Eu3+ sensitized by another ligand 2, 6-pyridine dicarboxylic acid (DPA). TC was able to quench the fluorescence of ligand BDC-(OH)2 at 545 nm by the internal filter effect (IFE), and coordinate with Eu3+ to enhance the fluorescence at 625 nm by the antenna effect (AE). I625/I545 showed a linear relationship with TC concentration with an LOD at 55 nM. At the same time, the fluorescence color of Eu-DPA/BDC-(OH)2 changed from green to yellow to red with the increase of TC concentration. On this basis, the RGB method was also developed for the visual detection of TC with an LOD at 0.2 μM. These methods have been successfully applied for the detection of TC in fish feed and pork with recovery rates of 93 % -110 %, indicating excellent applicability in the detection of real samples.

AuNCs@ZIF-8 with enhanced AIE effect to develop a lateral flow immunosensor for POC dual-modal detection of acetochlor

Regarding the high incidence of residue and serious toxicity of acetochlor (ATC) pesticide, it is urgent to explore simple and low-cost methods for their sensitive detection in food. In this study, with zeolite-like imidazole frameworks (ZIFs) as the carriers for embedding glutathione-modified luminescent gold nanoclusters (GSH-AuNCs) exhibiting aggregation-induced emission (AIE) effect, a GSH-AuNCs@ZIF-8 probe driven strip-based lateral flow immunosensor (LFIS) was developed for visual qualitative and fluorescent quantitative dual-modal detection of ATC. The encapsulation of GSH-AuNCs into ZIF-8 with restriction effect not only significantly improved the stability and anti-interference ability of AuNCs, but also remarkably enhanced the fluorescence efficiency for signal amplification due to the enhanced AIE effect of GSH-AuNCs, endowing the LFIS platform with unique performance. Under optimal conditions, the LFIS platform could realize the point-of-care visualization and quantitation of ATC within 20 min with a detection limit of 8.3 pg/mL and a broad linear range of 0.01-10.0 ng/mL. High recoveries of 96.44%-106.8 % in the spiked ginger samples confirmed the outstanding accuracy and dependability of the new platform for ATC analysis of real samples. Compared with other immunoassays, the AuNCs@ZIF-8-based dual-modal LFIS exhibited the advantages of simple preparation, simple operation, short analytical time, and low cost, which could be expanded to monitor more pesticides and more trace contaminants in diverse food and agricultural products, and medicinal material matrices.

Rational Design of MOF-Based Multifunctional Bio-Nanoreactor for Efficient Detection and Photo-Degradation of Chloramphenicol

Food safety have received increasing attention in recent years, and rapid detection and thorough removal of organic contaminants is an important part of food safety control. In this work, a novel multi-functional photo-enzymatic nanoreactor HRP@Fe-NU-1003 is developed through the co-immobilization of horseradish peroxidase (HRP) and FeCl2 on a photosensitive metal-organic frameworks (MOF) NU-1003. The bio-nanocluster can serve as an efficient biosensor in the detection of chloramphenicol (CAP), with a detection limit of 15.38 pg mL-1, which is 62 times greater than that of the conventional HRP- enzyme-linked immunosorbent assay method. Besides its detecting capability, the nanoreactor also exhibits high efficiency in the photocatalytic degradation of CAP, which can remove 50 µg mL-1 of CAP thoroughly within 30 min, and the mineralization efficiency of CAP reaches 61%. In this material, Fe-NU-1003 not only acts as a protecting shell to prevent HRP from deactivation, but improves detecting sensitivity and photocatalytic performance. Mechanism studies show that FeCl2 enhances its photocatalytic performance through promoting electron (e-)-hole (h+) separation and photocurrent transfer. More importantly, the heterogeneous material possesses high stability and can be recycled at least five rounds while its photocatalytic performance maintained at a high level. This strategy provides a new approach for the detection and degradation of pollutants.

Colorimetric-fluorescent dual-mode nanosensor-powered enzyme immunoassay for ochratoxin A via alkaline phosphatase-mediated silver nanoparticle growth and fluorescence inner filter effect

Ochratoxin A (OTA) seriously threatens public health and agricultural ecosystems, necessitating sensitive detection methods. In view of that traditional immunoassays rely on animal-derived antibodies and toxic substrates, we developed a dual-mode nanosensor integrating colorimetric and fluorescent detection via alkaline phosphatase (ALP)-mediated silver nanoparticles (AgNPs) growth and inner filter effect (IFE). The Ag+-triggered aggregation-induced emission (AIE) enhancement of gold nanoclusters (AuNCs) was investigated for constructing a dual-mode nanosensor. The nanosensor employs an OTA-specific nanobody-ALP fusion (Nb-ALP) to dephosphorylate ascorbic acid 2-phosphate into ascorbic acid (AA), which reduces Ag⁺ to abundant AgNPs with NaBH4-reduced AgNPs seeds. AgNPs amplify plasmonic absorbance for colorimetric ALP detection, while quenching Ag⁺@AuNC fluorescence via IFE for fluorescent detection. The nanosensor was further combined with the Nb-ALP-based immunoassay to develop a dual-mode nanosensor-powered enzyme immunoassay (DMN-EIA). The DMN-EIA exhibited detection limits of 0.14 ng/mL (colorimetric) and 0.28 ng/mL (fluorescent) with high selectivity for OTA, with spike recovery rates of 93.5 %-108.7 % and relative standard deviations not exceeding 20 %. Furthermore, the colorimetric (R2 = 0.96) and fluorescent DMN-EIA (R2 = 0.93) correlated well with high-performance liquid chromatography in detection of ten real pepper samples. Therefore, the developed dual-mode nanosensor and DMN-EIA represent reliable and promising tools for detecting OTA.

Poly(ionic liquid)-regulated green one-pot synthesis of Au@Pt porous nanospheres for the smart detection of acid phosphatase and organophosphorus inhibitor

Here, a green poly(ionic liquid)-regulated one-pot method is developed for the synthesis of Au@Pt core-shell nanospheres (PNSs) under mild reaction conditions in water. It is found that the poly(ionic liquid) poly[1-methyl-3-butyl (3-hydroxy) imidazole] chloride (PIL-Cl) is very vital to guide the construction of Au@Pt PNSs. The as-obtained Au@Pt-1 PNSs have perfect spherical outlines, porous core-shell structures and large specific surface area by which they exhibit excellent peroxidase-like activity in acidic media and can be used to develop a simple and reliable colorimetric sensing platform. It is shown that the colorimetric sensing platform constructed with Au@Pt-1 PNSs nanozyme can effectively evaluate ACP activity, achieving a wide linear detection range of 0.1-3.0 U/L and having a low limit of detection (LOD) of 0.047 U/L (S/N = 3). Based on the cascade reaction, the Au@Pt-1 PNSs nanozyme and ACP are integrated to develop a biosensor, which can detect organophosphate inhibitor of malathion with a wide linear detection range of 5-80 nM and low LOD of 1.96 nM (S/N = 3). More importantly, this detection method is also practically applied to detect both ACP activity in fetal bovine serum and malathion concentration in cucumber juice with satisfied results. This work presents a simple and green feature for the synthesis of nanozyme with high performance and establishes a biosensing platform based on Au@Pt-1 PNSs nanozyme to effectively monitor the ACP activity and the concentration of its organophosphate inhibitor malathion with high sensitivity, anti-interference capability and good recovery capability.

Aptamer-regulated colorimetric and electrochemical dual-mode sensor for the detection of uranyl ions utilizing AuNCs@COF composite

Uranium is the core material for the development of the nuclear industry, but its irreversible radiation damage poses a significant threat to human health. In this context, an innovative dual-mode colorimetric and electrochemical sensor was developed for the detection of uranyl ions (UO22+), utilizing a covalent organic framework@gold nanoclusters (AuNCs@COF) composite. The synthesis of AuNCs@COF was simple, and the incorporation of AuNCs imparted the composite with exceptional peroxidase-like catalytic activity and enhanced electrochemical properties. By regulating the adsorption and desorption of aptamers on the AuNCs@COF surface, both peroxidase-like activity and conductivity were modulated, enabling the detection of UO22+ utilizing colorimetric and electrochemical dual signals. Under optimal conditions, the sensor revealed a broad linear detection range and a low detection limit, with ranges of 1.36 × 10-10-1.36 × 10-5 mol/L for colorimetric detection and 5.0 × 10-10-2.5 × 10-5 mol/L for electrochemical detection, achieving detection limits for these two methods of 107 pmol/L and 347 pmol/L, respectively. Unlike other single-mode sensors for UO22+ detection, this dual-mode sensor demonstrated superior sensitivity, specificity, and repeatability. Furthermore, the results of spiked recovery experiments in real water samples highlight the promising potential of this dual-mode sensor for environmental water monitoring applications.

Development of fluorescent-photothermal probe based on photoinduced energy transfer: A dual-readout immunosensor for the detection of illegal additive

The development of advanced optical probes for point-of-care testing holds great importance in the field of diagnostic technologies. This study focused on the synthesis of a probe featuring both fluorescent and photothermal responses with single excitation wavelength, which was achieved through the combination of oxidized camellia oleifera shell powder (OC) and Prussian blue nanoparticles (PBNPs). Notably, OC derived from the direct processing of raw material showed fluorescent and phosphorescent emissions simultaneously, and the positions of the two peaks overlapped with the absorbance range of PBNPs, making the fluorescent and phosphorescent emissions of OC effectively quenched by PBNPs. Meanwhile, the photothermal property of PBNPs was activated by the phosphorescent emission of OC through photoinduced energy transfer. As a proof of concept, OC@PBNPs was applied in the dual-channel immunoassay, in which illegal addictive aminopyrine (AP) was chosen as the detection target. Furthermore, a portable device was developed to capture the fluorescent and photothermal signals of OC@PBNPs, rendering the detection method based on OC@PBNPs suitable for point-of-care testing (POCT).

Integrating Humidity-Resistant and Colorimetric COF-on-MOF Sensors with Artificial Intelligence Assisted Data Analysis for Visualization of Volatile Organic Compounds Sensing

Direct visualization and monitoring of volatile organic compounds (VOCs) sensing processes via portable colorimetric sensors are highly desired but challenging targets. The key challenge resides in the development of efficient sensing systems with high sensitivity, selectivity, humidity resistance, and profuse color change. Herein, a strategy is reported for the direct visualization of VOCs sensing by mimicking human olfactory function and integrating colorimetric COF-on-MOF sensors with artificial intelligence (AI)-assisted data analysis techniques. The Dye@Zeolitic Imidazolate Framework@Covalent Organic Framework (Dye@ZIF-8@COF) sensor takes advantage of the highly porous structure of MOF core and hydrophobic nature of the COF shell, enabling highly sensitive colorimetric sensing of trace number of VOCs. The Dye@ZIF-8@COF sensor exhibits exceptional sensitivity to VOCs at sub-parts per million levels and demonstrates excellent humidity resistance (under 20-90% relative humidity), showing great promise for practical applications. Importantly, AI-assisted information fusion and perceptual analysis greatly promote the accuracy of the VOCs sensing processes, enabling direct visualization and classification of seven stages of matcha drying processes with a superior accuracy of 95.74%. This work paves the way for the direct visualization of sensing processes of VOCs via the integration of advanced humidity-resistant sensing materials and AI-assisted data analyzing techniques.

Bidirectional Drive Reverse-Phase Enhanced Fluorescence Lateral Flow Immunoassay with Spectral Overlap and Quantitative Balance for the Analysis of Deoxynivalenol

The capacity of the reverse-phase enhanced fluorescence (turn-on mode) to sensitively alter fluorescence intensity from "zero" to "one" has drawn increasing interest and investigation in competitive lateral flow immunoassay (LFIA). During this process, three important considerations must be made: designing an effective quenching agent, choosing a suitable fluorescence donor, and building a suitable quenching mode. In this work, we employed Au@MnO2 nanoparticles as highly effective quenchers and AuNCs as fluorescence donors to achieve the overlap of absorption and emission spectra. Furthermore, we have effectively created an immunological network-based competitive LFIA to balance the quantitative relationship for the quick and accurate detection of the deoxynivalenol (DON) toxin (Au@MnO2-GAB-CFLFIA). Notably, our proposed fluorescent turn-on mode demonstrated 11.65-fold sensitivity enhancement (0.0509 ng/mL) compared to the colorimetric mode (0.593 ng/mL). Furthermore, the immunological network mode shows 5.08-fold sensitivity enhancement compared to the non-network mode (0.259 ng/mL). Moreover, satisfactory recoveries of 93.33-109.02% are obtained in real samples (maize, wheat, and oat). In this DON detection, spectral overlap and quantitative balance offer more novel and efficient strategies for reverse-phase enhanced fluorescence LFIA.

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.

Dual-assist heterologous antigens screening: An effective strategy to improve the sensitivity of lateral flow immunoassay

Heterologous strategy has promising applications in improving the sensitivity of competitive immunoassay. In this study, the potential heterologous coating antigens (HEA) were screened from eight imidacloprid (IMI) structural analogs based on the cross-reactivity (CR) of a prepared antibody. Computer-aided molecular modeling was used to predict the optimal HEA. Compared with the homologous coating antigen (HOA), the predicted HEA prepared from acetamiprid (CR = 0.23 %) increased the detection sensitivity of the enzyme-linked immunoassay and colloidal gold nanoparticle-based lateral flow immunoassay (HOA-Au-LFIA) by 5.6 and 4.1 times, respectively. Subsequently, the HEA and aggregation-induced emission fluorescent labels were integrated into a lateral flow immunoassay platform (HEA-AIE-LFIA). The limit of detection was 0.12 ng mL-1 for HEA-AIE-LFIA, which was 7.7-fold lower than that of HOA-Au-LFIA. Furthermore, HEA-AIE-LFIA was applied to detect IMI in food samples with excellent recoveries (86.41 %-111.25 %). Overall, this strategy of screening for superior HEA has great potential for improving LFIA sensitivity.

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.

High sensitive Ratiometric fluorescent Aptasensor with AIE properties for Deoxynivalenol (DON) detection

An emerging fluorescent ratiometric aptasensor based on gold nanoclusters (AuNCs) with aggregation-induced emission (AIE) properties was prepared and studied for deoxynivalenol (DON) detection. The ratiometric aptasensor used red fluorescent AuNCs620 labelled with DON aptamer (Apt-AuNCs620) as an indicator and green fluorescent AuNCs519 modified by complementary DNA (cDNA) and magnetic beads (MBs) as internal reference, namely MBs-cDNA-AuNCs519. Under the optimal conditions, the aptasensor exhibited two good linear ranges of 0.1-50 and 50-5000 pg/mL for DON detection with coefficient of determination (R2) of 0.9937 and 0.9928, respectively, and the low detection limit (LOD) of 4.09 pg/mL was achieved. Furthermore, this aptasensor was feasible to detect DON in positive wheat samples, and the results were in line with those from HPLC and ELISA, thus providing a promising route to detect DON with high sensitivity in cereals, even for other mycotoxins by replacing the suitable aptamer and cDNA.

Electrostatic Assembly of Gold Nanoclusters in Reverse Emulsion Enabling Nanoassemblies with Tunable Structure and Size for Enhanced NIR-II Fluorescence Imaging

The precise control of the assembly structure and size of gold nanoclusters (AuNCs) can potentially amplify their near-infrared II (NIR-II) fluorescence imaging and targeting properties. However, the conventional electrostatic assembly of AuNCs and charged molecules faces challenges in balancing the inherent electrostatic repulsions among charged units and regulating the diffusion of assembly units. These difficulties limit precise control over assembly size and structure, along with limited options for coassembled molecules, thereby restricting imaging properties and targeting capability. To circumvent this challenge, we developed a reverse emulsion-confined electrostatic assembly method. This technique efficiently constructs AuNC nanoassemblies with diverse coassembled molecules, allowing for the fine-tuning of assembly size and structure, including both core-satellite and homogeneous AuNC nanoassemblies. The development of two distinct nanoassemblies can be partially attributed to the varying diffusive rates of AuNCs or the AuNCs/polymer complex within the fused emulsion droplets. This variance arises from steric hindrances encountered during the emulsion fusion process. Interestingly, core-satellite nanoassemblies exhibit the strongest NIR-II fluorescence enhancement. Finally, the introduction of a hyaluronic acid coating on the surfaces of nanoassemblies with varying sizes enables the nanoprobes to achieve enhanced lymph node imaging through size modulation and macrophage targeting, which are used for surgical navigation to remove lymph node metastases. We envision that this self-assembly strategy can be extended to a wide range of electrostatic assembly systems for the development of multicomponent functional materials.

Visual aptasensor based on PtNPs/g-C3N4 and DNase I for the field detection of acetamiprid

A visual aptasensor based on the combination of graphitic carbon nitride loaded with platinum nanoparticles (PtNPs/g-C3N4) and deoxyribonuclease I (DNase I) was developed for detecting acetamiprid. The prepared PtNPs/g-C3N4 exhibited excellent peroxidase (POD)-like activity, demonstrating the capacity to oxidize the colourless o-phenylenediamine (OPD) to produce the coloured product diaminophenazine (DAP) in the presence of hydrogen peroxide (H2O2). The DNA aptamer of acetamiprid can adsorb onto the surface of PtNPs/g-C3N4, thereby inhibiting its POD activity. The binding of acetamiprid to its aptamer results in the aptamer desorbing from the surface of PtNPs/g-C3N4 and subsequent digestion by DNase I. Ascribed to the synergistic effect of these factors, the aptasensor can achieve the rapid on-site detection of acetamiprid based on the acetamiprid-induced the colour change of the solution just with the smartphone. Furthermore, due to the remarkable fluorescence signal of DAP at 570 nm, the aptasensor under fluorescence mode enables highly sensitive and quantitative detection of acetamiprid with a linear range of 1 ng/mL to 4 µg/mL and a detection limit as low as 0.31 ng/mL. The aptasensor has successfully realized the detection of acetamiprid in river water and cucumber samples, offering a novel perspective for the rapid assessment of environmental pollution and food safety risks associated with acetamiprid residues.

Dual response signal CdTe QDs@ZIF-8 with butterfly spectrum for dual-mode fluorescence/colorimetric detection of tetracycline in animal feeds

In this study, a ratiometric fluorescent sensor CdTe QDs@ZIF-8 with butterfly spectra is successfully constructed by in situ encapsulating mercaptopropionic acid-modified CdTe quantum dots in zeolitic imidazolate framework-8 (ZIF-8) with a simple strategy, and used for the detection of tetracycline in fluorescence/smartphone colorimetry dual-mode. ZIF-8 not only reduces the agglomeration of the quantum dots but also surprisingly generates a new green fluorescence signal at 524 nm while the red fluorescence of the CdTe quantum dots at 650 nm quenches when tetracycline is added. The two opposing fluorescence signals create a butterfly-shaped fluorescence spectrum, allowing the sensor to detect tetracycline over a linear range of 0-70 μM with the detection limit (LOD) of 0.0155 μM by using a ratiometric fluorescence technique. What is more, based on the obvious color change of the fluorescent sensor gradually from red to green under UV light, a highly stable point-of-care testing sensor has been developed for on-site detection of tetracycline through color recognition by smartphones, which can be used for real-time detection of this antibiotic in the range of 0-1000 μM with the LOD of 0.0249 μM. This work provides a simple and efficient method for the on-site detection of tetracycline.

Apple polysaccharide stabilized palladium nanoparticles for sensitive detection of organophosphorus pesticide

The widespread application of organophosphorus pesticides (OPs) has inflicted significant damage on human well-being and food security. Hence, it is imperative to develop a friendly and accessible biosensor for the detection of OPs. Herein, apple polysaccharide (AP) stabilized palladium nanoparticles (AP-PdnNPs) with a particle size of 2.75-5.95 nm were prepared using AP as a stabilizer and reducing agent. AP-Pd30NPs exhibited good peroxidase-like activity and effectively decomposed H2O2 to ·OH, which catalyzed the 3,3',5,5'-tetramethylbenzidine system to become blue. The catalytic kinetics of AP-Pd30NPs conformed to the typical Michelis-Menten equation. Furthermore, OPs directly inhibited the peroxidase-like activity of AP-Pd30NPs. Thus, a highly effective colorimetric biosensor was developed for the detection of OPs. The detection range of the biosensor was 0.050 μg/L - 200 mg/L, and the limit of detection was extremely low to 0.010 μg/L. Compared with other nanomaterials, the detection platform based on AP-Pd30NPs can effectively detect organophosphorus pesticides without coupling natural enzymes；this method is more economical and practical. Therefore, this established method explores good perspective for the detection of OPs.

Applications of nanomaterials with enzyme-like activity for the detection of phytochemicals and hazardous substances in plant samples

Plants such as herbs, vegetables, fruits, and cereals are closely related to human life. Developing effective testing methods to ensure their safety and quantify their active components are of significant importance. Recently, nanomaterials with enzyme-like activity (known as nanozymes) have been widely developed in various assays, including colorimetric, fluorescence, chemiluminescence, and electrochemical analysis. This review presents the latest advances in analyzing phytochemicals and hazardous substances in plant samples based on nanozymes, including some active ingredients, organophosphorus pesticides, heavy metal ions, and mycotoxins. Additionally, the current shortcomings and challenges of the actual sample analysis were discussed.

Assembly of protein-directed fluorescent gold nanoclusters for high-sensitivity detection of uranyl ions

Uranium is a key element in the nuclear industry, whose accidental release causes health and environmental problems. In this paper, a protein-directed fluorescent sensor with aggregation-induced emission characteristics (gold nanoclusters@ovalbumin, AuNCs@OVA) was synthesized for the detection of UO22+ with high sensitivity and selectivity. The sensor exhibited good fluorescence stability, and its fluorescence intensity could be selectively enhanced by UO22+. Based on FT-IR and XPS analyses, the increase in fluorescence intensity of AuNCs@OVA after the addition of UO22+ was attributed to aggregation induced by the complexation between UO22+ and the amino, carboxyl, hydroxyl, and phosphate groups of ovalbumin. The detection limit was determined to be 34.4 nM, and the sensor showed excellent ion selectivity for UO22+. In combination with a smartphone program, the sensor could realize the real-time detection of UO22+ in a quantitative and portable way.

pH-responsive dual-emission carbon dots for the ratiometric detection of organophosphorus pesticides in Brassica chinensis and Hg2+ in water

Accurate and rapid monitoring of organophosphorus pesticides (OPs) residues is crucial for regulating food safety. Herein, dual-emission carbon dots (de-CDs) were fabricated for the ratiometric detection of OPs and Hg2+. The de-CDs exhibited two emission peaks at 678 and 485 nm when excited with visible light. Interestingly, the fluorescence at 678 nm was significantly quenched by Hg2+ mainly because of the static quenching effect, whereas that at 485 nm exhibited a slight change. More significantly, the quenched fluorescence of the de-CDs recovered remarkably after introducing omethoate, diazinon and malathion. Accordingly, the ratiometric detection of the three OPs and Hg2+ was achieved with high selectivity and robust performance. In addition, the OPs residues assay in Brassica chinensis was successfully performed with satisfactory results. This study not only provides an attractive tool for the simple and rapid assay of OPs but also offers new insights into the fabrication of multi-functional carbon dots.

Regulating Arrhenius Activation Energy and Fluorescence Quantum Yields of AuNCs-MOF to Achieve High Temperature Sensitivity in a Wide Response Window

Luminescent thermometry affords remote measurement of temperature and shows huge potential in future technology beyond those possible with traditional methods. Strategies of temperature measurement aiming to increase thermal sensitivity in a wide temperature response window would represent a pivotal step forward, but most thermometers cannot do both of them. Herein, we propose a balancing strategy to achieve a trade-off between high Arrhenius activation energy (Ea), which could stretch the temperature response windows, and fluorescence quantum yields (QYs) in a manner that will increase thermal sensitivity in a wide response window. In particular, a luminescent thermometer composed of AuNCs-MOF is prepared via a facile impregnation process to enhance QYs and Ea, responsible for high relative sensitivity (Sr) (15.6% K-1) and ultrawide temperature linearity range (from 83 to 343 K), respectively. Taking fluorescence intensity and lifetime as multiple parameters, the maximum Sr can reach 22.4% K-1 by multiple linear regression. The maximum Sr and temperature response range of the proposed thermometer outperform those of the most recent luminescent thermometers. The strategy of balancing Sr and thermal response range by regulating Ea and QYs enables the construction of ultra-accurate thermal sensors in the age of artificial intelligence.

Upconversion-based hydrogel kit with Python-assisted analysis platform for sample-to-result detection of organophosphorus pesticide

On-site quantitative analysis of pesticide residues is crucial for monitoring environmental quality and ensuring food safety. Herein, we have developed a reliable hydrogel portable kit using NaYbF4@NaYF4: Yb, Tm upconversion nanoparticles (UCNPs) combined with MnO2 nanoflakes. This portable kit is integrated with a smartphone reader and Python-assisted analysis platform to enable sample-to-result analysis for chlorpyrifos. The novel UCNPs maximizes energy donation to MnO2 acceptor by employing 100 % of activator Yb3+ in the nucleus for NIR excitation energy collection and confining emitter Tm3+ to the surface layer to shorten energy transfer distance. Under NIR excitation, efficient quenching of upconversion blue-violet emission by MnO2 nanoflakes occurs, and the quenched emission is recovered with acetylcholinesterase-mediated reactions. This process allows for the determination of chlorpyrifos by inhibiting enzymatic activity. The UCNPs/MnO2 were embedded to fabricate a hydrogel portable kit, the blue-violet emission images captured by smartphone were converted into corresponding gray values by Python-assisted superiority chart algorithm which achieves a real-time rapid quantitative analysis of chlorpyrifos with a detection limit of 0.17 ng mL-1. At the same time, pseudo-color images were also added by Python in "one run" to distinguish images clearly. This sensor detection with Python-assisted analysis platform provides a new perspective on pesticide monitoring and broadens the application prospects in bioanalysis.

Triple modal aptasensor arrays driven by CHA-mediated DNAzyme for signal-amplified atrazine pesticide accumulation monitoring in agricultural crops

Developing sensors with high selectivity and sensitivity is of great significance for pesticide analysis in environmental assessment. Herein, a versatile three-way sensor array was designed for the detection of the pesticide atrazine, based on the integration of catalytic hairpin assembly (CHA) amplification and three-mode signal transducers. With atrazine, CHA was triggered to generate abundant G-quadruplex. The produced G-quadruplex hybrid could assemble with thioflavin T (TFT) or hemin to mimic enzyme and induce the fluorescence enhancement by TFT, or the colorimetric increase by the oxidized chromogenic substrate and the naked-eye color change by inhibiting the L-cysteine-mediated aggregation of gold nanoparticles. A distinctive three-mode array was successfully constructed with convenience, on-site accessibility and high sensitivity for enzyme-free practical analysis of atrazine. It is also effective and reliable for analyzing real samples including paddy water, paddy soil and polished rice. The detection limits for atrazine were as low as 7.4 pg/mL by colorimetric observation and 0.25 pg/mL by fluorescent detection. Furthermore, the array was exploited to monitor the residue, distribution and bioaccumulation of atrazine in maize and rice for food security and environmental assessment. Hence, this work presented a versatile example for sensitive and on-site all-in-one pesticide analysis arrays with multiple signal report modes.

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.

A self-calibrating ratiometric fluorescence sensor with photonic crystal-based signal amplification for the detection of tetracycline in food

A dual-color ratiometric fluorescence sensor based on photonic crystals (PCs) was developed to detect tetracycline (TC) in food. PC was fabricated via self-assembly of carbon dots (CDs)-loaded SiO2 nanoparticles. Gold nanoclusters (AuNCs) and copper ions (Cu2+) were then adsorbed onto the PC for sensor fabrication. The fluorescence of AuNCs was amplified by the PC with an enhancement ratio of 7.6, providing higher sensitivity. The fluorescence of AuNCs was quenched by Cu2+, whereas that of CDs remained unchanged as an internal reference. TC restored the fluorescence of AuNCs owing to its complexation with Cu2+, resulting in a change in the fluorescence intensity ratio. The sensor exhibited a good linear relationship with TC concentrations ranging from 0.1 to 10 μM, with a detection limit of 34 nM. Furthermore, the sensor was applied for TC detection in food with satisfactory recoveries and relative standard deviations, revealing great potential in practical application.

AIE fluorescent nanozyme-based dual-mode biosensor for analysis of the bioactive component hypoxanthine in meat products

The development of facile, low-cost reliable, and precise onsite assays for the bioactive component hypoxanthine (Hx) in meat products is significant for safeguarding food safety and public health. Herein, we proposed a smartphone-assissted aggregation-induced emission (AIE) fluorogen tetraphenylethene (TPE)-incorporated amorphous Fe-doped phosphotungstates (Fe-Phos@TPE) nanozyme-based ratiometric fluorescence-colorimetric dual-mode biosensor for achieving the onsite visual detection of Hx. When the Hx existed, xanthine oxidase (XOD) catalyzed Hx into H2O2 to be further catalyzed into •OH by the prominent peroxidase activity of Fe-Phos@TPE at pH = 6.5, resulting in the oxidization of nonfluorescent o-phenylenediamine (OPD, naked-eye colorless) to be yellow fluorescent emissive 2,3-diaminophenazine (DAP, naked-eye dark yellow) at 550 nm as well as the intrinsic blue fluorescence of Fe-Phos@TPE at 440 nm to be decreased via inner-filter effect (IFE) action, thereby realizing a multi-enzyme cascade catalytic reaction at near-neutral pH to overcome the traditional acidity dependence-induced time-consuming and low sensitivity troublesome.

Sensitive colorimetric and fluorescence dual-mode detection of thiophanate-methyl based on spherical Fe3O4/GONRs composite nanozyme

Pesticide detection based on nanozyme is largely limited in terms of the variety of pesticides. Herein, a spherical and well-dispersed Fe3O4/graphene oxide nanoribbons (Fe3O4/GONRs) composite nanozyme was applied to firstly develop an enzyme-free and sensitive colorimetric and fluorescence dual-mode detection of thiophanate-methyl (TM). The synthesized Fe3O4/GONRs possess excellent dual enzyme-like activities (peroxidase and catalase) and can catalyze H2O2 to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB). We found that Fe3O4/GONRs can adsorb TM through the synergistic effect of multiple forces, thereby inhibiting the catalytic activities of nanozyme. This inhibition can modulate the transformation of TMB to oxTMB, producing dual responses of absorbance decrease (oxTMB) and fluorescence enhancement (TMB). The limits of detection (LODs) of TM were 28.1 ng/mL (colorimetric) and 8.81 ng/mL (fluorescence), respectively. Moreover, the developed method with the recoveries of 94.8-100.8% also exhibited a good potential application in the detection of pesticides residues in water and food samples.

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.

An ion synergism fluorescence probe via Cu2+ triggered competition interaction to detect glyphosate

The widespread use of glyphosate (Gly) poses significant risks to environmental and human health, underscoring the urgent need for its sensitive and rapid detection. In this work, we innovated by developing a novel material, ionic liquids, which formed the ionic probe "[P66614]2[2,3-DHN]-Cu2+ (PDHN-Cu2+)" through coordination with Cu2+. This probe capitalized on the distinctive fluorescence quenching properties of ionic liquids in the presence of Cu2+, driven by synergistic interactions between anions and cations. Glyphosate disrupted the PDHN-Cu2+ coordination structure due to its stronger affinity for Cu2+, triggering a "turn-on" fluorescence response. Impressively, PDHN-Cu2+ enabled the sensitive detection of glyphosate within just one minute, achieving a detection limit as low as 71.4 nM and excellent recovery rates of 97-103% in diverse samples. This groundbreaking approach, utilizing ionic probes, lays a robust foundation for the accurate and real-time monitoring of pesticides, employing a strategy based on synergism and competitive coordination.

A novel fluorescence sensor based on Al3+-mediated aggregation of gold nanoclusters for determination of citric acid in beverages

This paper revealed a new strategy for citric acid (CA) detection using aggregation-induced emission (AIE)-based fluorescent gold nanoclusters (AuNCs). AuNCs was synthesized using glutathione (GSH) as the template and reducing agent and used as the fluorescent probe to detect CA under aluminum ion (Al3+) mediation. The fluorescence intensity of AuNCs increased about 4 times with the addition of Al3+, but the enhanced fluorescence was quenched after the addition of CA. Based on this fluorescence phenomenon, an "on-off" fluorescence strategy was designed for the sensitive determination of CA and a linear detection range for CA was achieved within 0-80.0 μM. In addition, the developed probe exhibited high selectivity and accuracy for determination of CA. The mechanism of fluorescence enhancement and quenching of AuNCs was explored in detail. The established probe was used successfully for CA detection in beverages. The spiked recoveries from 97.50% to 103.67% were gratifying, which indicated the probe had potential prospects for detecting CA in food.

Recent advances and synergistic effect of bioactive zeolite imidazolate frameworks (ZIFs) for biosensing applications

The rapid developments in the field of zeolitic imidazolate frameworks (ZIFs) in recent years have created unparalleled opportunities for the development of unique bioactive ZIFs for a range of biosensor applications. Integrating bioactive molecules such as DNA, aptamers, and antibodies into ZIFs to create bioactive ZIF composites has attracted great interest. Bioactive ZIF composites have been developed that combine the multiple functions of bioactive molecules with the superior chemical and physical properties of ZIFs. This review thoroughly summarizes the ZIFs as well as the novel strategies for incorporating bioactive molecules into ZIFs. They are used in many different applications, especially in biosensors. Finally, biosensor applications of bioactive ZIFs were investigated in optical (fluorescence and colorimetric) and electrochemical (amperometric, conductometric, and impedance) fields. The surface of ZIFs makes it easier to immobilize bioactive molecules like DNA, enzymes, or antibodies, which in turn enables the construction of cutting-edge, futuristic biosensors.

Smartphone-Based Techniques Using Carbon Dot Nanomaterials for Food Safety Analysis

The development of portable and efficient nanoprobes to realize the quantitative/qualitative onsite determination of food pollutants is of immense importance for safeguarding human health and food safety. With the advent of the smartphone, the digital imaging property causes it to be an ideal diagnostic substrate to point-of-care analysis probes. Besides, merging the versatility of carbon dots nanostructures and bioreceptor abilities has opened an innovative assortment of construction blocks to design advanced nanoprobes or improving those existing ones. On this ground, massive endeavors have been made to combine mobile phones with smart nanomaterials to produce portable (bio)sensors in a reliable, low cost, rapid, and even facile-to-implement area with inadequate resources. Herein, this work outlines the latest advancement of carbon dots nanostructures on smartphone for onsite detecting of agri-food pollutants. Particularly, we afford a summary of numerous approaches applied for target molecule diagnosis (pesticides, mycotoxins, pathogens, antibiotics, and metal ions), for instance microscopic imaging, fluorescence, colorimetric, and electrochemical techniques. Authors tried to list those scaffolds that are well-recognized in complex media or those using novel constructions/techniques. Lastly, we also point out some challenges and appealing prospects related to the enhancement of high-efficiency smartphone based carbon dots systems.

A fluorescence ionic probe utilizing Cu2+ assisted competition for detecting glyphosate abused in green tea

Food fraud caused by the violation of glyphosate use in tea is frequently exposed, posing a potential health risk to consumers and undermining trust in food safety. In the work, an ionic fluorescent probe "[P66614] [4HQCA]-Cu2+ (PHQCA-Cu2+)" was constructed using Cu2+ and ionic liquids coordination through a competitive coordination strategy to detect glyphosate. This probe exhibited a prominent "turn-on" fluorescence response in glyphosate detection. PHQCA-Cu2+was destroyed by glyphosate with its strong coordination capability, and a new complex re-formed simultaneously between glyphosate and the Cu2+ in it, where Cu2+ served as an "invisible indicator" influencing fluorescence changes. Remarkably, PHQCA-Cu2+formed rapidly within 5 s, demonstrated exceptional sensitivity and selectivity, and satisfactory detection performance on paper strips impregnated withPHQCA-Cu2+.Importantly,PHQCA-Cu2+showed excellent recoveries in various green tea, which offered a viable method for identifying contaminated products from the supply chain quickly to enhance overall food safety surveillance.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Bimetallic Ag/Au nanoclusters encapsulated in ZIF-8 framework: A novel strategy for ratiometric fluorescence detection of doxycycline in food

This study successfully encapsulated the Ag+-doped Au nanoclusters (Ag/AuNCs) within the ZIF-8 framework to construct a novel Ag/AuNCs@ZIF-8 ratiometric fluorescent probe for the antibiotic doxycycline (DOX) detection. The incorporation of Ag+ contributed to the fluorescence enhancement of the nanoclusters through the "silver effect", consequently improving the stability of the developed bimetallic Ag/AuNCs. Furthermore, the encapsulation of bimetallic Ag/AuNCs within the ZIF-8 framework restricted their intramolecular vibrations, resulting in further amplification of fluorescence intensity at 595 nm. The ZIF-8 also sensitized the restoration of DOX green fluorescence at 515 nm. Within the concentration range of 0.001-20 μg mL-1, the ratio of fluorescence intensity (F515/F595) exhibited a favorable linearity for DOX concentration, with a detection limit of 36.8 ng mL-1. This ratiometric fluorescence approach had the promising potential for accurate and efficient quantitative detection of DOX residue in food and served as a valuable reference for rapid monitoring of food contaminants.

Smartphone-assisted colorimetric biosensor for the determination of organophosphorus pesticides on the peel of fruits

Nowadays, the widespread use of organophosphorus pesticides (OPs) in agricultural production leads to varying degrees of residues in crops, which pose a potential threat to human health. Conventional methods used in national standard for the detection of OPs in fruits and vegetables require expensive instruments or cumbersome sample pretreatment steps for the analysis. To address these challenges, in this work, we took advantage of the peroxidase-like activity of PtCu3 alloy nanocrystals (NCs) for a colorimetric and smartphone assisted sensitive detection of OPs. With the assist of a smartphone, the concentration of OPs on the peel of fruits could be obtained by comparing the B/RG value (the brightness value of blue divided by those of red and green) of a test strip with a calibration curve. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety warning.

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.

Synergistic synthesis of gold nanoflowers as upconversion near-infrared nanoprobe energy acceptor and recognition unit for improved hydrogen sulfide sensing

A highly sensitive and selective upconversion near-infrared (NIR) fluorescence and colorimetric dual readout hydrogen sulfide (H2S) nanoprobe was constructed based on the excellent NIR fluorescence emission performance of upconversion nanomaterials (UCNPs), the specific recognition effect of synergistically synthesized gold nanoflowers (trypsin-stabled AuNFs (Try-AuNFs)) and the effective NIR fluorescence quenching capability. In this assay, the sensing strategy included three processes. First of all, the synthesized UCNPs can emit 803 nm NIR fluorescence when they were excited by 980 nm excitation light. Secondly, as a result of the principle of fluorescence resonance energy transfer (FRET), Try-AuNFs can effectively quench the NIR fluorescence of UCNPs at 803 nm, which can effectively improve the signal-to-background ratio of nanoprobes, thereby improving the sensitivity of the probes. Thirdly, in the presence of H2S, the Try protective layer on the surface of Try-AuNFs was specifically penetrated, which will subsequently cleave Try-AuNFs via the strong S-Au bond. As such, the NIR fluorescence of UCNPs will be restored, achieving high selectivity and sensitivity detection of H2S. Under optimized conditions, the linear response range of H2S was 0.1-300 μM, and the detection limit was 53 nM. It is worth noting that the Try on the surface of Try-AuNFs via the synergistic effect can increase the steric hindrance of the probe, and this can effectively prevent the interaction between the probe with biothiols (cysteine (Cys), homocysteine (Hcy)) and other natural amino acids (non-thiol-containing) with resultant in the high selectivity regarding the detection of H2S in human serum, which is unlikely to be achieved by AuNFs synthesized by the gold seed method (Se-AuNFs). This work not only provided a new type of UCNPs fluorescence quencher and recognition unit, but also exemplified that the use of the physical properties (steric hindrance) of protein ligands on the surface of nanoflowers can improve the specificity of the probe. This will provide new ideas for the design of other nanoprobes.

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.

Combined fabrication of zeolitic imidazolate framework-8 and lanthanide towards coordination polymers: A dual-signal fluorescent probe for sensing Cu2+ based on synergistic effect of aggregation-induced emission and antenna effect

Copper ion (Cu2+) detection remains an important task for monitoring water quality because of its specific toxicity. Herein, a new dual-signal fluorescent probe was developed by combining zeolitic imidazolate framework-8 (ZIF-8) and lanthanide for the detection of Cu2+ for the first time. The lanthanide coordination polymer (guanosine monophosphate and Eu3+, GMP/Eu) was initially incorporated into ZIF-8 to yield ZIF-8/GMP/Eu nanomaterials with extremely weak single emission fluorescence at 618 nm. It was found that the resulted nanomaterials could display a dual emission fluorescence at 515 nm and 618 nm after the introduction of tetracycline (TC) due to the synergistic effect of aggregation-induced emission effect (AIE, TC induced by ZIF-8) and antenna effect (AE, between TC and GMP/Eu). Interestingly, in the presence of Cu2+, the AIE of TC was destroyed because of the interaction of Cu2+ with ZIF-8 and TC. The AE between TC and GMP/Eu disappeared due to the formation of complex between TC and Cu2+. A dual-signal fluorescent probe of ZIF-8/GMP/Eu/TC was thereby established for sensing Cu2+ in the range of 0.5-100 μM. Such a dual-signal response strategy that intelligently utilized the "ON"/"OFF" of AIE and AE can not only eliminate the background interference, but also ensure the improved selectivity of Cu2+ sensing. Subsequently, the dual-signal fluorimetric strategy was applied for the detection of Cu2+ in environmental water samples, indicating the potential feasibility of applications for water quality monitoring.

Integrating Wireless Remote Sensing and Sensors for Monitoring Pesticide Pollution in Surface and Groundwater

Water constitutes an indispensable resource crucial for the sustenance of humanity, as it plays an integral role in various sectors such as agriculture, industrial processes, and domestic consumption. Even though water covers 71% of the global land surface, governments have been grappling with the challenge of ensuring the provision of safe water for domestic use. A contributing factor to this situation is the persistent contamination of available water sources rendering them unfit for human consumption. A common contaminant, pesticides are not frequently tested for despite their serious effects on biodiversity. Pesticide determination in water quality assessment is a challenging task because the procedures involved in the extraction and detection are complex. This reduces their popularity in many monitoring campaigns despite their harmful effects. If the existing methods of pesticide analysis are adapted by leveraging new technologies, then information concerning their presence in water ecosystems can be exposed. Furthermore, beyond the advantages conferred by the integration of wireless sensor networks (WSNs), the Internet of Things (IoT), Machine Learning (ML), and big data analytics, a notable outcome is the attainment of a heightened degree of granularity in the information of water ecosystems. This paper discusses methods of pesticide detection in water, emphasizing the possible use of electrochemical sensors, biosensors, and paper-based sensors in wireless sensing. It also explores the application of WSNs in water, the IoT, computing models, ML, and big data analytics, and their potential for integration as technologies useful for pesticide monitoring in water.

Mn-modified porphyrin metal-organic framework mediated colorimetric and photothermal dual-channel probe for sensitive detection of organophosphorus pesticides

Herein, a novel dual-mode probe for organophosphorus pesticides (OPs) colorimetric and photothermal detection was developed based on manganese modified porphyrin metal-organic framework (PCN-224-Mn). PCN-224-Mn had excellent oxidase-like activity and oxidized colorless 3,3,5,5-tetramethylbenzidine (TMB) to blue-green oxidation state TMB (oxTMB), which exhibited high temperature under near-infrared irradiation. l-ascorbate-2-phosphate was hydrolyzed by acid phosphatase to produce ascorbic acid, which weakened colorimetric and photothermal signals by impacting oxTMB generation. The presence of OPs blocked the production of ascorbic acid by irreversibly inhibiting the activity of acid phosphatase, causing the restoration of chromogenic reaction and the increase of temperature. Under the optimal conditions, the probe showed a good linear response to OPs in the concentration range of 5 ∼ 10000 ng/mL, using glyphosate as the analog. The detection limits of glyphosate in colorimetric mode and photothermal mode were 1.47 ng/mL and 2.00 ng/mL, respectively. The probe was successfully used for sensitive identification of OPs residues in tea, brown rice, and wheat flour. This work proposes a simple and reliable colorimetric/photothermal platform for OPs identification, which overcomes the problem that single-mode detection probes are susceptible to external factors, and has broad application potential in the field of food safety.

Acetylcholine triggered enzymatic cascade reaction based on Fe7S8 nanoflakes catalysis for organophosphorus pesticides visual detection

BACKGROUND

Organophosphorus pesticides (OPs) play important roles in the natural environment, agricultural fields, and biological prevention. The development of OPs detection has gradually become an effective strategy to avoid the dangers of pesticides abuse and solve the severe environmental and health problems in humans. Although conventional assays for OPs analysis such as the bulky instrument required analytical methods have been well-developed, it still remains the limitation of inconvenient, inefficient and lab-dependence analysis in real samples. Hence, there is an urgent demand to develop efficient detection methods for OPs analysis in real scenarios.

RESULTS

Here, by virtue of the highly efficient catalytic performance in Fe7S8 nanoflakes (Fe7S8 NFs), we propose an OPs detection method that rationally integrated Fe7S8 NFs into the acetylcholine (ACh) triggered enzymatic cascade reaction (ATECR) for proceeding better detection performances. In this method, OPs serve as the enzyme inhibitors for inhibiting ATECR among ACh, acetylcholinesterase (AChE), and choline oxidase (CHO), then reduce the generation of H2O2 to suppress the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) that catalyzed by Fe7S8 NFs. Benefiting from the integration of Fe7S8 NFs and ATECR, it enables a sensitive detection for OPs (e.g. dimethoate). The proposed method has presented good linear ranges of OPs detection ranging from 0.1 to 10 μg mL-1. Compared to the other methods, the comparable limits of detection (LOD) of OPs are as low as 0.05 μg mL-1.

SIGNIFICANCE

Furthermore, the proposed method has also achieved a favorable visual detection performance of revealing OPs analysis in real samples. The visual signals of OPs can be transformed into RGB values and gathered by using smartphones, indicating the great potential in simple, sensitive, instrument-free and on-site analysis of pesticide residues in environmental monitoring and biosecurity research.

Advancements in magnetic nanoparticle-based biosensors for point-of-care testing

The significance of point-of-care testing (POCT) in early clinical diagnosis and personalized patient care is increasingly recognized as a crucial tool in reducing disease outbreaks and improving patient survival rates. Within the realm of POCT, biosensors utilizing magnetic nanoparticles (MNPs) have emerged as a subject of substantial interest. This review aims to provide a comprehensive evaluation of the current landscape of POCT, emphasizing its growing significance within clinical practice. Subsequently, the current status of the combination of MNPs in the Biological detection has been presented. Furthermore, it delves into the specific domain of MNP-based biosensors, assessing their potential impact on POCT. By combining existing research and spotlighting pivotal discoveries, this review enhances our comprehension of the advancements and promising prospects offered by MNP-based biosensors in the context of POCT. It seeks to facilitate informed decision-making among healthcare professionals and researchers while also promoting further exploration in this promising field of study.

A Dual-Signal Sensing for the Visual and Luminescent Detection of p-Phenylenediamine Based on Cerium-Nitrogen-Co-Doped Carbon Dots

Herein, a visual and luminescent dual-mode (colorimetric and fluorometric) method for the detection of P-phenylenediamine (PPD) in hair dye was successfully established based on cerium-nitrogen co-doped carbon dots (Ce, N-CDs) that displayed remarkable luminescence and peroxidase activity. Ce, N-CDs catalyzed H2O2 to produce superoxide anion, which then oxidized the colorless 3,3,5,5-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB), capable of quenching the fluorescence through fluorescence resonance energy transfer (FRET) between Ce, N-CDs and oxTMB. The reducing properties of PPD could reduce oxTMB back to TMB, leading to a decrease in the absorption intensity of oxTMB and a fluorescence recovery of Ce, N-CDs. As a result, the quantitative detection of PPD could be achieved by measuring the absorption values of oxTMB and the fluorescence signal of Ce, N-CDs. The detection limits for PPD were calculated as 0.36 µM and 0.10 µM for colorimetry and fluorimetry, respectively. Furthermore, smartphone application (ColorPicker) capable of measuring the RGB value of the color was utilized in the detection system, facilitating on-site quantitative detection. This approach effectively shortens the detection time and simplifies the operation, offering a powerful and convenient tool for real-time monitoring of PPD.

Metal-Organic Framework-Enabled Sustainable Agrotechnologies: An Overview of Fundamentals and Agricultural Applications

With aggravated abiotic and biotic stresses from increasing climate change, metal-organic frameworks (MOFs) have emerged as versatile toolboxes for developing environmentally friendly agrotechnologies aligned with agricultural practices and safety. Herein, we have explored MOF-based agrotechnologies, focusing on their intrinsic properties, such as structural and catalytic characteristics. Briefly, MOFs possess a sponge-like porous structure that can be easily stimulated by the external environment, facilitating the controlled release of agrochemicals, thus enabling precise delivery of agrochemicals. Additionally, MOFs offer the ability to remove or degrade certain pollutants by capturing them within their pores, facilitating the development of MOF-based remediation technologies for agricultural environments. Furthermore, the metal-organic hybrid nature of MOFs grants them abundant catalytic activities, encompassing photocatalysis, enzyme-mimicking catalysis, and electrocatalysis, allowing for the integration of MOFs into degradation and sensing agrotechnologies. Finally, the future challenges that MOFs face in agrotechnologies were proposed to promote the development of sustainable agriculture practices.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.