Recent advances in sensing applications of metal nanoparticle/metal–organic framework composites

High-performance electrochemical sensor based on Pt-Ag@Cu-BDC MOF composite modified glassy carbon electrode for detection of imidacloprid in citrus juice and water samples

The key factor to improve the sensitivity of electrochemical sensors for direct detection, is the introduction of new nanomaterials with enhanced catalytic properties. Accordingly, we prepared Pt-Ag@Cu-metal organic framework (MOF) as a novel nanocomposite to construct a sensitive electrochemical sensor for voltammetric determination of imidacloprid (IMI). The copper benzene-1,4-dicarboxylate framework (Cu-BDC MOF) was used as support for bearing the metal nanoparticles (NPs) including Ag and Pt. First, Ag NPs were incorporated into Cu-BDC MOF and then Pt NPs were substitute through galvanic replacement reaction between Ag NPs and Pt ions. The Pt-Ag@Cu-BDC MOF as a novel nanocomposite was utilized as a modifier to decorate glassy carbon (GC) electrode. The excellent conductivity, hierarchical and micro-mesoporous structure of Pt-Ag@Cu-BDC MOF and the synergistic effect between Ag and Pt nanoparticles were beneficial for fast electron transfer required for IMI reduction. At the Pt-Ag@Cu-BDC MOF/GCE, reduction potential of IMI was greatly shifted to positive value and the electrochemical signal increased significantly. The prepared sensor exhibited wide linear range (5 nM-10000 nM), low detection limit (1.5 nM) and high sensitivity towards IMI detection. This sensor was successfully applied for detection of IMI in citrus juice and water samples with good recoveries (92-106 %, RSD ≤4 %).

Room-temperature synthesis of Fe3O4@MOF-5 magnetic hybrid as an efficient catalyst for the one-pot green synthesis of tetrahydropyridines

In recent two decades, considerable efforts have been devoted to the room-temperature green syntheses of metal-organic frameworks (MOFs) to reduce energy consumption and increase safety. It could improve some properties (e.g., catalysis, gas adsorption) and facilitate the utilities of sensitive compounds. Herein, the magnetic hybrid catalyst (Fe3O4@MOF-5) was synthesized through a mixing procedure at room temperature and confirmed by various techniques. The SEM images exhibit cubic crystals that were uniformly coated by the Fe3O4 cores. Then, the catalytic ability of Fe3O4@MOF-5 was studied in the green synthesis of tetrahydropyridines via a domino multi-component reaction, which led to the desired products with high yield. Magnetic solid properties make it easily separated from the reaction medium, so the proposed catalyst can be reused five times while maintaining the catalytic activity over 80%.

Efficient bionic nanozyme based on AuPt NPs@ZIF-90 used for cyclic catalysis multimodal tumor therapy

Multimodal therapy based on nanozyme is expected to become a novel option for tumor treatment. However, the catalytic efficiency of nanozymes and the hypoxia microenvironment of tumors limit the therapeutic effect of nanozymes. Herein, we screened a small molecule of midazole-2-carboxaldehyde (ICA) to prepare ZIF-90 and embedded gold and platinum nanoparticles to obtain ZAAP. ZAAP possessed a multi-enzymatic cascade of catalytic processes including greatly enhanced peroxidase activity via a "bionic" catalytic microenvironment (enhanced 23-fold), catalase and glucose oxidase activities, resulting in glucose decomposition to continuously supply H2O2, peroxidases for the catabolism of H2O2 to generate ROS and peroxidase-induced oxygen generation for continuous oxidation of glucose. All the above processes built a catalysis cycle that greatly promotes the generation of ROS and oxygen as well as the consumption of glucose, leading to the chemical dynamic therapy function and alleviating tumor hypoxia. In addition to the photothermal effect of ZAAP, a synergistic treatment of chemical dynamic/photothermal/starvation therapy was achieved, and the tumor inhibition rate reached 96.4% within 2 weeks, indicating that ZAAP shows great potential in nanozyme-based synergistic multimodal tumor treatment.

Unveiling the Correlation between Protein, Protein Corona, and Target Signal Loss in SERS Detection

The application of surface-enhanced Raman scattering (SERS) technology is hindered by the protein corona in a protein-rich complex matrix, which is a hot and important issue that needs consideration. However, the impact of the protein corona on SERS detection has not been fully studied. Herein, we selected three proteins, α-lactalbumin (α-La), β-lactoglobulin (β-Lg), and bovine serum albumin (BSA), as models for forming a protein corona, and melamine was employed as the target in SERS detection. The results indicate that three proteins form a protein corona on gold nanoparticles (AuNPs), leading to a significant loss of melamine signals. With increasing protein concentration, the degree of loss increases. The protein corona significantly inhibits target-induced nanoparticle aggregation, increases the distance between neighboring nanoparticles, and reduces the formation of "hot-spot" regions. Moreover, the adsorption capacity of AuNPs for melamine decreases, reducing the number of molecules that can achieve direct chemical enhancement. The Raman signal loss caused by different types of proteins, varies, even at the same molecule number, which is related to the deformability of proteins. This deformability determines the density of the protein corona formed on the surface of the AuNPs. Our results advance the fundamental understanding of the relationship between proteins, protein corona, and target signal loss in SERS detection, offering valuable insights for establishing models to predict Raman signal loss in protein-rich samples.

Organic and Metal-Organic Polymer-Based Catalysts-Enfant Terrible Companions or Good Assistants?

This overview provides insights into organic and metal-organic polymer (OMOP) catalysts aimed at processes carried out in the liquid phase. Various types of polymers are discussed, including vinyl (various functional poly(styrene-co-divinylbenzene) and perfluorinated functionalized hydrocarbons, e.g., Nafion), condensation (polyesters, -amides, -anilines, -imides), and additional (polyurethanes, and polyureas, polybenzimidazoles, polyporphyrins), prepared from organometal monomers. Covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and their composites represent a significant class of OMOP catalysts. Following this, the preparation, characterization, and application of dispersed metal catalysts are discussed. Key catalytic processes such as alkylation-used in large-scale applications like the production of alkyl-tert-butyl ether and bisphenol A-as well as reduction, oxidation, and other reactions, are highlighted. The versatile properties of COFs and MOFs, including well-defined nanometer-scale pores, large surface areas, and excellent chemisorption capabilities, make them highly promising for chemical, electrochemical, and photocatalytic applications. Particular emphasis is placed on their potential for CO2 treatment. However, a notable drawback of COF- and MOF-based catalysts is their relatively low stability in both alkaline and acidic environments, as well as their high cost. A special part is devoted to deactivation and the disposal of the used/deactivated catalysts, emphasizing the importance of separating heavy metals from catalysts. The conclusion provides guidance on selecting and developing OMOP-based catalysts.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Indium nanocubes based recyclable fluorescent chemosensor for sustainable environmental monitoring: pH-induced fluorescence transition and selective detection of Pd(II) ions

Rapid modern industrialization and urbanization have escalated heavy metal pollution, with palladium (Pd2+) raising significant concerns due to its extensive usage in catalysis, hydrogen storage, and electronics, thereby imposing substantial risks on the environment and human health. In this study, we report a highly fluorescent indium nanocubes based chemosensor (InNCs) functionalized with perylene tetracarboxylic acid (PTCA) and 4-(pyridyl)ethenyl benzene (PEB). The InNCs exhibited emission maximum at 415 nm (λex ∼ 350 nm) with robust chemical and photo-stability, and acted as a fluorogenic probe for selective recognition of Pd2+ in aqueous medium. The fluorescence sensing properties of InNCs were thoroughly assessed via different techniques including steady-state absorption, emission and time-resolved emission spectroscopic methods. Among the various competitive analytes, only Pd2+ could induce a significant fluorescence quenching in the probe. This "turn-off" fluorescence sensing demonstrated a remarkably low LoD of ∼65 nM. Notably, with the addition of EDTA, the probe displayed good recyclability upto 4 cycles. The sensory probe was successfully employed as a reusable platform to estimate Pd(II) in different real water and soil samples with considerable accuracy (∼ 5-10 % error). Moreover, the probe exhibited a pH-induced fluorescence transition, indicating its potential to be applied as a pH sensor. The Pd(II) binding and pH-sensing mechanisms have also been elucidated through density functional theory (DFT) calculations.

Advanced Hybrid materials in electrochemical sensors: Combining MOFs and conducting polymers for environmental monitoring

The integration of conducting polymers (CPs) with metal-organic frameworks (MOFs) has arisen as a dynamic and innovative approach to overcome some intrinsic limitations of both materials, representing a transformative method to address the pressing need for high-performance environmental monitoring tools. MOFs, with their intricate structures and versatile functional groups, provide tuneable porosity and an extensive surface area, facilitating the selective adsorption of target analytes. Conversely, CPs, characterized by their exceptional electrical conductivity and redox properties, serve as proficient signal transducers. By combining these two materials, a novel class of hybrid materials emerges, capitalizing on the unique attributes of both components. These MOF/CP hybrids exhibit heightened sensitivity, selectivity, and adaptability, making them primordial in detecting and quantifying environmental contaminants. This review examines the synergy between MOFs and CPs, highlighting recent advancements, challenges, and prospects, thus offering a promising solution for developing advanced functional materials with tailored properties and multifunctionality to be applied in electrochemical sensors for environmental monitoring.

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

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

Advances in Electrochemical Biosensors for the Detection of Common Oral Diseases

Limiting and preventing oral diseases remains a major challenge to the health of populations around the world, so finding ways to detect early-stage diseases (e.g., caries, periodontal disease, and oral cancer) and aiding in their prevention has always been an important clinical treatment concept. The development and application of electrochemical detection technology can provide important support for the early detection and non-invasive diagnosis of oral diseases and make up for the shortcomings of traditional diagnostic methods, which are highly sensitive, non-invasive, cost-effective, and less labor-intensive. It detects specific disease markers in body fluids through electrochemical reactions, discovers early warning signals of diseases, and realizes rapid and reliable diagnosis. This paper comprehensively summarizes the development and application of electrochemical biosensors in the detection and diagnosis of common oral diseases in terms of application platforms, sensing types, and disease detection, and discusses the challenges faced by electrochemical biosensors in the detection of oral diseases as well as the great prospects for future applications, in the hope of providing important insights for the future development of electrochemical biosensors for the early detection of oral diseases.

An attomolar-level electrochemical DNA biosensor based on target-triggered and entropy-driven catalytic amplification integrated with AuNPs@ZIF-8 nanocomposites for oral cancer overexpressed 1 detection

It is of great interest and necessity to develop a nonenzymatic, simple but highly sensitive biosensor for early diagnosis of oral cancer. Present here is an electrochemical DNA biosensor which integrates a target-triggered, entropy-driven, nonenzymatic and isothermal amplification strategy with gold nanoparticles/zeolitic imidazolate frameworks-8 (AuNPs@ZIF-8) nanocomposites for ultra-sensitive detection of oral cancer-related biomarker (ORAOV 1) in saliva. It is worth noting that the nuclease is not involved in the whole reaction process, which is simple and flexible in design only using a series of linear single-stranded DNA, avoiding undesired secondary structure interference. Meanwhile, due to the synergistic effect of AuNPs and ZIF-8, AuNPs@ZIF-8 nanocomposites display high stability, excellent electrical conductivity and exceptional electrocatalytic activity, further enhancing the electrochemical signal and avoiding labeling electrochemical signal probes. Experimental results demonstrate that this electrochemical DNA biosensor has a wide linear range (1 fM ∼1 nM), a low limit of detection (163 aM), excellent specificity, superior reproducibility and stability to ORAOV 1. More importantly, the actual application of the newly developed electrochemical biosensor is exemplified in human saliva with satisfactory recoveries. Therefore, the newly developed electrochemical biosensor has a broad application prospect in the nondestructive and early screening of oral cancer.

Two Stable Bifunctional Zinc Metal-Organic Frameworks with Luminescence Detection of Antibiotics and Proton Conduction

Functionalized crystalline solids based on metal-organic frameworks (MOFs) enable efficient luminescence detection and high proton conductivity, making them crucial in the realms of environmental monitoring and clean energy. Here, two structurally and functionally distinct zinc-based MOFs, [Zn(TTDPa)(bodca)]·H2O (1) and [Zn(TTDPb)(bodca)]·H2O (2), were successfully designed and synthesized using 3,6-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPa) and 2,5-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPb) as ligands, in the presence of bicyclo[2.2.2]octane-1,4-dicarboxylic acid (H2bodca). Both 1 and 2 display a three-dimensional (3D) structure with 5-fold interpenetration, and notably, 2 forms a larger one-dimensional pore measuring 17.16 × 10.81 Å2 in size. Fluorescence experiments demonstrate that 1 and 2 can function as luminescent sensors for nitrofurantoin (NFT) and nitrofurazone (NFZ) with low detection limits, remarkable selectivity, and good recyclability. A comprehensive analysis was conducted to investigate the differing sensing effects of compounds 1 and 2 and to explore potential sensing mechanisms. Additionally, at 328 K and 98% relative humidity, 1 and 2 exhibit proton conductivity values of 2.13 × 10-3 and 4.91 × 10-3 S cm-1, respectively, making them suitable proton-conducting materials. Hence, the integration of luminescent sensing and proton conductivity in monophasic 3D Zn-MOFs holds significant potential for application in intelligent multitasking devices.

Review: Synthesis of metal organic framework-based composites for application as immunosensors in food safety

Ensuring food safety continues to be one of the major global challenges. For effective food safety monitoring, fast, sensitive, portable, and efficient food safety detection strategies must be devised. Metal organic frameworks (MOFs) are porous crystalline materials that have attracted attention for use in high-performance sensors for food safety detection owing to their advantages such as high porosity, large specific surface area, adjustable structure, and easy surface functional modification. Immunoassay strategies based on antigen-antibody specific binding are one of the important means for accurate and rapid detection of trace contaminants in food. Emerging MOFs and their composites with excellent properties are being synthesized, providing new ideas for immunoassays. This article summarizes the synthesis strategies of MOFs and MOF-based composites and their applications in the immunoassays of food contaminants. The challenges and prospects of the preparation and immunoassay applications of MOF-based composites are also presented. The findings of this study will contribute to the development and application of novel MOF-based composites with excellent properties and provide insights into advanced and efficient strategies for developing immunoassays.

Design of competition nanoreactor with shell-isolated colloidal plasmonic nanomaterials for quantitative sensor platform

Shell-isolated colloid plasmonic nanomaterials-based nanoreactor is a well-established platform widely applied in catalyst or Surface Enhanced Raman Scattering (SERS) sensors. The potentials versatility of nanoreactor platform is mainly implemented by the well-defined and tailorable structure of colloid plasmonic nanomaterials. Currently, a competitive conjugative-mediated nanoreactor is introduced to determine glucose with SERS. Glucose-conjugating nanoreactor, as convertors of the sensors, are constructed by coordinated deposition colloidal gold nanoparticles with sodium nitroprusside framework (Au@SNF) and covalently bonded 4-mercaptopyridine (4-Mpy) with self-assembly strategy. The nanoreactor contained the signal-amplifier Au@SNF NPs, conjugative-mediated signal receiver 4-Mpy, and signal internal standard molecular CN^-. In addition to well-defined morphology and functionality, conjugative-mediated and internal standards method are also employed to benefit the nanoreactor. The two-parameter strategy significantly improves the signal indication and correction. Using this proposed platform, the competitive-mediated nanoreactor provides a quantitative SERS detection of glucose, and extends the applicability of SERS in more complicated and reproducibility analysis. Meanwhile, the nanoreactor based sensors also exhibited better properties to detect glucose in various food samples and bio-samples which provided strongly appliance for glucose sensors.

Multimetallic nanoparticles decorated metal-organic framework for boosting peroxidase-like catalytic activity and its application in point-of-care testing

Metal-organic frameworks (MOFs) are a sort of promising peroxidase-like nanozyme but face the challenge that the inorganic nodes in most of the MOF structures are generally blocked by the organic linkers. Further enhancement or activation of their peroxidase-like activity plays an important role in developing MOF-based nanozymes. Herein, a multimetallic nanoparticle (NP) decorated-MOF, Cu/Au/Pt NP decorated-Cu-TCPP(Fe) nanozyme (CuAuPt/Cu-TCPP(Fe)) was synthesized in situ and served as a peroxidase-like nanozyme. The peroxidase-like activity of this stable CuAuPt/Cu-TCPP(Fe) nanozyme was enhanced due to the decreased potential barriers for *OH generation in the catalytic process. Owing to the remarkable peroxidase-like activity, a CuAuPt/Cu-TCPP(Fe)-based colorimetric assay was established for the sensitive determination of H₂O₂ and glucose with the limit of detection (LOD) of 9.3 µM and 4.0 µM, respectively. In addition, a visual point-of-care testing (POCT) device was developed by integrating the CuAuPt/Cu-TCPP(Fe)-based test strips with a smartphone and was employed for a portable test of 20 clinical serum glucose samples. The results determined by this method agree well with the values deduced by clinical automatic biochemical analysis. This work not only represents an inspiration for the usage of MNP/MOF composite as a novel nanozyme for POCT diagnosis, but also provides a deeper insight and understanding into the enhanced enzyme-mimic effect of MNP-hybrid MOF composites, which in turn will guide the engineering of MOF-based functional nanomaterials. Graphical Abstract.

Metal-organic framework-based nanomaterials as opto-electrochemical sensors for the detection of antibiotics and hormones: A review

Increasing trace levels of antibiotics and hormones in the environment and food samples are concerning and pose a threat. Opto-electrochemical sensors have received attention due to their low cost, portability, sensitivity, analytical performance, and ease of deployment in the field as compared to conventional expensive technologies that are time-consuming and require experienced professionals. Metal-organic frameworks (MOFs) with variable porosity, active functional sites, and fluorescence capacity are attractive materials for developing opto-electrochemical sensors. Herein, the insights into the capabilities of electrochemical and luminescent MOF sensors for detection and monitoring of antibiotics and hormones from various samples are critically reviewed. The detailed sensing mechanisms and detection limits of MOF sensors are addressed. The challenges, recent advances, and future directions for the development of stable, high-performance MOFs as commercially viable next-generation opto-electrochemical sensor materials for the detection and monitoring of diverse analytes are discussed.

Halloysite nanotube/black phosphorene nanohybrid modified screen-printed carbon electrode as an ultra-portable electrochemical sensing platform for smartphone-capable detection of maleic hydrazide with machine learning assistance

With the assistance of machine learning (ML), black phosphorene (BP) stabilized by silver nanoparticles (AgNPs) is used to modify halloysite nanotube (HNT) to obtain highly conductive nanomaterials, HNT/BP-AgNPs, which are morphologically characterized and elementally analyzed. Artificial neural network (ANN) and least squares support vector machine (LS-SVM) are adopted for the intelligent and rapid analysis of maleic hydrazide (MH). An ultra-portable electrochemical sensor bases on HNT/BP-AgNPs modifying screen-printed carbon electrode (SPCE), smartphone and mini-palm potentiostat for detection of MH in the linear range 0.7-55 μM with limit of detection (LOD) of 0.3 μM. For comparison, a traditional electrochemical sensor is fabricated by glass carbon electrode (GCE), desktop computer and large electrochemical potentiostat, and the linear range is 0.3-600 μM with low LOD of 0.1 μM. The ultra-portable electrochemical sensor combined with ML for the detection of MH in sweat potato and carrot gain satisfactory recoveries.

CO2 Capture and Gas Storage Capacities Enhancement of HKUST-1 by Hybridization with Functionalized Graphene-like Materials

The role of graphene related material (GRM) functionalization on the structural and adsorption properties of MOF-based hybrids was deepened by exploring the use of three GRMs obtained from the chemical demolition of a nanostructured carbon black. Oxidized graphene-like (GL-ox), hydrazine reduced graphene-like (GL), and amine-grafted graphene-like (GL-NH₂) materials have been used for the preparation of Cu-HKUST-1 based hybrids. After a full structural characterization, the hybrid materials underwent many adsorption-desorption cycles to evaluate their capacities to capture CO₂ and store CH₄ at high pressure. All the MOF-based samples showed very high specific surface area (SSA) values and total pore volumes, but different pore size distributions attributed to the instauration of interactions between the MOF precursors and the specific functional groups on the GRM surface during MOF growth. All the samples showed a good affinity toward both gases (CO₂ and CH₄) and a comparable structural stability and integrity (possible aging was excluded). The trend of the maximum storage capacity values of the four MOF samples toward CO₂ and CH₄ was HKUST-1/GL-NH₂ > HKUST-1 > HKUST-1/GL-ox > HKUST-1/GL. Overall, the measured CO₂ and CH₄ uptakes were in line with or higher than those already reported in the open literature for Cu-HKUST-1 based hybrids evaluated in similar conditions.

Progress and opportunities for metal-organic framework composites in electrochemical sensors

Metal-organic framework composites have the advantages of large surface area, high porosity, strong catalytic efficiency and good stability, which provide a great possibility of finding excellent electrode materials for electrochemical sensors. However, MOF composites still face various challenges and difficulties, which limit their development and application. This paper reviews the application of MOF composites in electrochemical sensors, including MOF/carbon composites, MOF/metal nanoparticle composites, MOF/metal oxide composites and MOF/enzyme composites. In addition, the application challenges of MOF composites in electrochemical sensors are summarized. Finally, the application prospect for MOF composites is considered to promote the synthesis of more MOF composites with excellent properties.

A Novel Composite of Zinc-based Metal Organic Framework Embedded with SnO2 Nanoparticle as a Photocatalyst for Methylene Blue Dye Degradation as well as Fluorometric Probe for Nitroaromatic Compounds Detection

A facile bottom up synthesis technique is opted for the preparation of novel composite SnO₂@Zn-BTC. This synthesized composite is fully characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and Elemental mapping techniques. Optical analysis was performed using UV-Visible absorption spectroscopy and fluorescence studies. Further this composite was utilized for the first time as a photocatalyst for methylene blue (MB) dye degradation under sunlight irradiation. This photocatalyst shows degradation efficiency of 89% within 100 min of exposure of sunlight. In addition to that, the synthesized composite can be utilized as a fluorescence probe for detection of NACs via 'turn-off" quenching response. This composite is extremely sensitive towards 3-NA in aqueous medium with quenching efficiency of 75.42%, which is highest quenching rate till reported. There occurs no interference for detecting 3-NA in the presence of other NACs. The linear fitting of the Stern-Volmer plot for 3-NA shows large quenching constant (K_SV) of 0.0115 ppb^-1 with correlation coefficient R² = 0.9943 proves higher sensitivity of composite in sensing process. The outstanding sensitivity of composite for 3-NA is certified by the low detection limit (LOD) of 25 ppb (0.18 µM). Photoinduced Electron Transfer (PET) and Fluorescence Resonance Energy Transfer (FRET) are the mechanisms used for clarification of quenching response of PL intensity by NACs via density functional theory (DFT) calculations and extent spectral overlap, respectively. Hence, synthesized composite is verified as multi-component system to act as excellent photocatalyst as well as fluorescent sensor.

Ultrasensitive Determination of Natural Flavonoid Rutin Using an Electrochemical Sensor Based on Metal-Organic Framework CAU-1/Acidified Carbon Nanotubes Composites

Rutin, a natural flavonol glycoside, is widely present in plants and foods, such as black tea and wheat tea. The antioxidant and anti-inflammatory effects of flavonoids are well known. In this study, a new electrochemical rutin sensor was developed using multiwalled carbon nanotubes/aluminum-based metal-organic frameworks (MWCNT/CAU-1) (CAU-1, a type of Al-MOF) as the electrode modification material. The suspension of multiwalled carbon tubes was dropped on the surface of the GCE electrode to make MWCNT/GCEs, and CAU-1 was then attached to the electrode surface by electrodeposition. MWCNTs and CAU-1 were characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Due to the synergistic effect of CAU-1 and MWCNT-COOH, the prepared sensor showed an ultrasensitive electrochemical response to rutin. Under optimized conditions, the sensor showed a linear relationship between 1.0 × 10^-9~3.0 × 10^-6 M with a detection limit of 6.7 × 10^-10 M (S/N = 3). The sensor also showed satisfactory stability and accuracy in the detection of real samples.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Metal-organic frameworks based surface-enhanced Raman spectroscopy technique for ultra-sensitive biomedical trace detection

Metal-organic frameworks (MOFs) have attracted widespread interest due to their unique and unprecedented advantages in microstructures and properties. Besides, surface-enhanced Raman scattering (SERS) technology has also rapidly developed into a powerful fingerprint spectroscopic technique that can provide rapid, non-invasive, non-destructive, and ultra-sensitive detection, even down to single molecular level. Consequently, a considerable amount of researchers combined MOFs with the SERS technique to further improve the sensing performance and broaden the applications of SERS substrates. Herein, representative synthesis strategies of MOFs to fabricate SERS-active substrates are summarized and their applications in ultra-sensitive biomedical trace detection are also reviewed. Besides, relative barriers, advantages, disadvantages, future trends, and prospects are particularly discussed to give guidance to relevant researchers.

Materials for Chemical Sensing: A Comprehensive Review on the Recent Advances and Outlook Using Ionic Liquids, Metal–Organic Frameworks (MOFs), and MOF-Based Composites

The ability to measure and monitor the concentration of specific chemical and/or gaseous species (i.e., “analytes”) is the main requirement in many fields, including industrial processes, medical applications, and workplace safety management. As a consequence, several kinds of sensors have been developed in the modern era according to some practical guidelines that regard the characteristics of the active (sensing) materials on which the sensor devices are based. These characteristics include the cost-effectiveness of the materials’ manufacturing, the sensitivity to analytes, the material stability, and the possibility of exploiting them for low-cost and portable devices. Consequently, many gas sensors employ well-defined transduction methods, the most popular being the oxidation (or reduction) of the analyte in an electrochemical reactor, optical techniques, and chemiresistive responses to gas adsorption. In recent years, many of the efforts devoted to improving these methods have been directed towards the use of certain classes of specific materials. In particular, ionic liquids have been employed as electrolytes of exceptional properties for the preparation of amperometric gas sensors, while metal–organic frameworks (MOFs) are used as highly porous and reactive materials which can be employed, in pure form or as a component of MOF-based functional composites, as active materials of chemiresistive or optical sensors. Here, we report on the most recent developments relative to the use of these classes of materials in chemical sensing. We discuss the main features of these materials and the reasons why they are considered interesting in the field of chemical sensors. Subsequently, we review some of the technological and scientific results published in the span of the last six years that we consider among the most interesting and useful ones for expanding the awareness on future trends in chemical sensing. Finally, we discuss the prospects for the use of these materials and the factors involved in their possible use for new generations of sensor devices.

In-situ synthesis of metal nanoparticle embedded soft hybrid materials via eco-benign approach

The unique optical and electronic properties of metal nanoparticles and tunable properties of the organic templates encourage the scientific community to generate metal nanoparticle embedded soft hybrid materials for various novel utilities. Here, we discuss the in-situ synthesis of metal nanoparticle embedded soft hybrid materials via eco-benign approach which exclude the use of toxic reducing/capping agents or toxic reaction media. In this protocol, the gel matrix composed of benign organic templates act as reducing as well as stabilizing agent for the in-situ generation and stabilization of metal nanoparticles. As the incorporation of metal salts (as nanoparticle precursor) in the gel medium is required in this process, in most of the cases aqueous media were used for the generation of metal nanoparticle embedded soft hybrid materials. This discussion includes interesting findings from our laboratory where hybrid gel matrix composed of renewable chemicals was utilized for the in-situ synthesis of palladium nanoparticle embedded soft trihybrid material. The hybrid gel matrix rich in polyphenols/flavonoids was exploited to generate palladium nanoparticle embedded trihybrid gel through in-situ reduction of doped Pd (II) salts to stable PdNPs. The xerogel of this trihybrid material was utilized as recyclable heterogeneous catalyst for C-C coupling reaction in air under phosphene free condition and reduction reaction.

Coordination polymers derived from alkali metal complexes of redox-active ligands

Treatment solutions of (dpp-bian)M (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene; M = Li, Na, K) with 4,4′-bipyridine (4,4′-bipy) affords coordination polymers [(dpp-bian)M(4,4′-bipy)m]n, (M = Li or K, m = 1; M = Na, m = 2).

Present and Perspectives of Photoactive Porous Composites Based on Semiconductor Nanocrystals and Metal-Organic Frameworks

This review focuses on the recent developments in synthesis, properties, and applications of a relatively new family of photoactive porous composites, integrated by metal halide perovskite (MHP) nanocrystals and metal-organic frameworks (MOFs). The synergy between the two systems has led to materials (MHP@MOF composites) with new functionalities along with improved properties and phase stability, thus broadening their applications in multiple areas of research such as sensing, light-harvesting solar cells, light-emitting device technology, encryption, and photocatalysis. The state of the art, recent progress, and most promising routes for future research on these photoactive porous composites are presented in the end.