Energy Transfer in Metal-Organic Frameworks for Fluorescence Sensing

Wavelength-Based luminescence sensing via Turn-On responses for acid detection in complex Environments

One possible way to address the shortcomings of current acid detection is to add fluorescence detection capabilities, however, there is little data regarding wavelength-based luminescence sensing, which makes possible for the naked eye to perceive various colors through wavelength variations. In this paper, we achieved turn-on response and wavelength-based luminescence sensing on acids detection by using donor-accepter complex Fe-L, which display significant fluorescence discoloration in the presence of a wide range of inorganic and organic acids, including benzoic acids, providing the fluorescence response for a more intuitive and convenient acid detection. The simultaneous achievement of fluorescence enhancement and color change as the acid concentration changes enables visual detection of the acid concentration, which provides a foundation for future research into convenient detection methods for various types of acids.

Nanomaterial-based electrochemical biosensors as tools for detecting the tumor biomarker miR-21

MicroRNAs (miRNAs) are noncoding RNA transcripts with myriad physiologically important regulatory roles in the human body. These miRNAs have also recently emerged as promising biomarkers for the diagnosis of particular cancers. Conventional miRNA detection strategies, however, are characterized by many limitations. As electrochemical biosensors offer advantages including low costs, high levels of sensitivity, and amenability to miniaturization, they hold great promise as an alternative approach to miRNA detection. Nanomaterials are commonly used in the context of electrochemical sensor production, and this review provides an overview of the use of various carbon nanomaterials, metallic nanomaterials, metal-organic frameworks, magnetic nanomaterials, and conductive polymer nanocomposites to modify electrochemical biosensors in order to facilitate the detection of miRNA-21. A range of materials and detection methods for particular cancer types are discussed herein highlighting the superior sensitivity and specificity of these analytical strategies., which allow for the stable and reproducible detection of miRNAs in clinical samples. Ultimately, this review demonstrates the promising clinical prospects of these modified electrochemical biosensors as tools for early cancer diagnosis and the prognostic evaluation of affected patients.

Sequential Energy and Electron Transfer in Metal-Organic Frameworks

This study presents the design and characterization of a triad metal-organic framework (MOF) system composed of pyrene, porphyrin, and phenyl-C61-butyric acid (PCBA) for efficient energy and electron transfer processes mimicking natural photosynthesis. The triad MOF, synthesized through a mixed-ligand approach followed by postsynthetic modification, demonstrates sequential energy transfer from pyrene to porphyrin, followed by electron transfer to the PCBA acceptor. Time-resolved photoluminescence (TRPL) spectroscopy was employed to investigate the dynamics of energy and charge transfer, revealing fast interligand energy transfer and subsequent charge separation in the MOF structure. The PCBA-functionalized MOF (PCBA@nMLM) exhibited a significantly enhanced photocatalytic performance compared to the nonfunctionalized counterpart, particularly in the selective aerobic oxidation of sulfides to sulfoxides under visible light irradiation. The enhanced photocatalytic activity is attributed to the prolonged charge separation facilitated by the PCBA moieties, as confirmed by electrochemical impedance spectroscopy (EIS) and transient photocurrent measurements. This work highlights the potential of MOF-based systems in artificial photosynthesis and other photocatalytic applications by effectively harnessing solar energy through optimized energy and charge transfer mechanisms.

A new type of lanthanide-sodium metalloring organic framework featuring high proton conduction in a wide temperature range and detection of Fe3+ ions

We present the design and synthesis of two novel isostructural metalloring organic frameworks (MROFs) {[(Me2NH2)1.25(H3O)4.25Na1.5X2(μ2-OH)(H2O)(SIP)4]n·xsol} (FUT-2-X, X = Eu and Sm), which are composed of the sulfonate-carboxylate ligand 5-sulfoisophthalic acid monosodium salt (NaH2SIP) and an unprecedented lanthanide-sodium metalloring [X4Na4(H2O)(SIP)2, X = Eu and Sm]. The two MROFs possess channel walls decorated with uncoordinated sulfonic acid groups and filled with abundant guest molecules residing within the framework, which support the proton conductivity of the materials by expanding the intermolecular hydrogen bonding network. FUT-2-Eu exhibits exceptional proton conductivity over a wide temperature range, achieving conductivity from 1.91 × 10-5 S cm-1 (-40 °C) to 2.65 × 10-3 S cm-1 (90 °C). Thanks to the dominant role of the additional guest H2O molecules in FUT-2-Eu's channels, which facilitate the formation of hydrogen-bonded networks for ultra-fast proton transfer with low energy barriers, FUT-2-Eu outperforms FUT-2-Sm in both the operating temperature range and proton conductivity. It is worth noting that FUT-2-Eu has the widest operating temperature range among proton conduction MROF materials. Furthermore, FUT-2-Eu can be considered as an excellent luminescence sensor with high sensitivity (KSV = 1.66 × 104 L mol-1) and a low detection limit (3.64 μM) for detecting Fe3+.

Synthesis and applications of luminescent metal organic frameworks (MOFs) for sensing dipicolinic acid in biological and water samples: a review

The detection of trace quantities of 2,6-dipicolinic acid (DPA) in real-world samples is crucial for early disease diagnosis and routine health monitoring. Metal-organic frameworks (MOFs), recognized for their diverse structural architectures, have emerged as advanced multifunctional hybrid materials. One of the most notable properties of MOFs is their luminescence (L), which can arise from structural ligands, guest molecules, and emissive metal ions. Luminescent MOFs have shown significant promise as platforms for sensor design. This review highlights the application of luminescent MOFs in the detection of DPA in biological and aqueous environments. It provides a comprehensive discussion of the various detection strategies employed in luminescent MOF-based DPA sensors. Additionally, it explores the origins of L in MOFs, their synthesis, and the mechanisms underlying their sensing capabilities. The article also addresses key challenges and limitations in this field, offering practical insights for the development of efficient luminescent MOFs for DPA detection.

UTSA-16(Zn) for SO2 detection: elucidating the fluorescence mechanism

In this study, the potential of the metal-organic framework UTSA-16(Zn) as a fluorescence detector for SO2 is explored. The material was synthesized and characterized by powder X-ray diffraction (PXRD), infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and its fluorescence behavior was analyzed before and after SO2 exposure. A significant decrease in fluorescence intensity was observed and a LOD of 1.79 mM (∼114.6 ppm) was obtained. With the help of time-resolved photoluminescence (TRPL) experiments and X-ray photoelectron (XPS) and ultraviolet-visible (UV-vis) spectroscopy, a static quenching mechanism due to the formation of a non-fluorescent complex in the ground state (GSC) was elucidated.

Large-Area Metal-Organic Framework Glasses for Efficient X-Ray Detection

Cutting-edge techniques utilizing continuous films made from pure, novel semiconductive materials offer promising pathways to achieve high performance and cost-effectiveness for X-ray detection. Semiconductive metal-organic framework (MOF) glass films are known for their remarkably smooth surface morphology, straightforward synthesis, and capability for large-area fabrication, presenting a new direction for high-performance X-ray detectors. Here, a novel material centered on MOF glasses for highly uniform glass film fabrication customized for X-ray detection is introduced. MOF glasses, composed of zinc and imidazole derivatives, enable the transition from solid to liquid at low temperatures, facilitating the straightforward preparation of large-area and continuous MOF films with high mobility for X-ray device fabrication. Remarkably, MOF glass detectors demonstrate an exceptional sensitivity of 112.8 µC Gyair -1 cm-2 and a detection limit of 0.41 µGyair s-1, making them one of the most sensitive and with the best detection limits reported to date for MOF X-ray detectors. Clear X-ray images are successfully conducted using these developed MOF glass detectors for the first time. This breakthrough in X-ray sensitivity, and detection limit along with the spatial imaging resolution establishes a new standard for developing large-area and efficient MOF-based X-ray detectors with practical applications in medical and security screening.

A Ni(II)MOF-based hypersensitive dual-function luminescent sensor towards the 3-nitrotyrosine biomarker and 6-propyl-2-thiouracil antithyroid drug in urine

Trace detection of bioactive small molecules (BSMs) in body fluids is of great importance for disease diagnosis, drug discovery, and health monitoring. Based on the chiral ligand of 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoic acid (H2L), an achiral 3D porous Ni(II)-MOF, with a trinuclear cluster based (3,9)-c {42·6}3{46·621·89}-xmz net, was constructed under solvothermal conditions. Benefiting from its robust framework and excellent luminescent performance, NiMOF was endowed with remarkable capabilities in efficiently, rapidly, and sensitively detecting the 3-nitrotyrosine (3-NT) biomarker and 6-propyl-2-thiouracil (6-PTU) thyroid drug based on the spectral overlap and photo-induced electron transfer (PET) caused luminescence quenching response. Notably, NiMOF exhibited exceptional performance in quantifying 3-NT and 6-PTU in urine samples, yielding highly satisfactory results. Additionally, an intelligent detection system was crafted to enhance the reliability and practicability of 3-NT/6-PTU detection in urine, based on tandem combinational logic gates. This work not only heralds a promising trajectory in the development of MOF-based luminescent sensors, but also paves the way for the intelligent monitoring of BSMs in real bodily fluids.

Construction of 2D zinc(II) MOFs with tricarboxylate and N-donor mixed ligands for multiresponsive luminescence sensors and CO2 adsorption

The solvothermal reactions of ZnCl2·6H2O, benzene-1,3,5-tribenzoic acid (H3btb), and N-heterocyclic ancillary imidazole (Im) or aminopyrimidine (a mp) ligands led to the creation of two-dimensional (2D) zinc(II) based metal-organic frameworks (MOFs), (Me2NH2)2[Zn2(btb)2(Im)2]·2DMF·3MeOH (1) and (Me2NH2)2[Zn2(btb)2(amp)]·H2O·2DMF·MeOH (2). The btb3- ligands in 1 and 2 form an anionic 2D layered structure with a (63) honeycomb (hcb) topology by linking to Zn(II) centres through their carboxylate groups. The incorporation of N-heterocyclic auxiliary ligands Im and amp into the hcb nets resulted in the formation of a 2D hydrogen-bonded and covalently pillared bilayer structure featuring two-fold interpenetrating networks. Each of these networks consists of small channels that are occupied by Me2NH2 cations and solvent molecules. Both 1 and 2 emit blue luminescence emissions in the solid state at room temperature and exhibit a great selectivity and sensitivity for the detection of acetone and multiple heavy metal ions including Hg2+, Cu2+, Fe2+, Pb2+, Cr3+, and Fe3+ ions. At 1 bar, activated 1 and 2 demonstrate moderate capacities for adsorbing CO2 at room temperature, with a preference for CO2 over N2. Notably, at higher pressures (up to 20 bar), their activated samples 1 and 2 show a temperature-dependent enhancement of CO2 uptake while retaining good stability.

A Series of Rare-Earth Metal-Based Coordination Polymers: Fluorescence and Sensing Studies

Ratiometric fluorescent sensing based on dual-emitting fluorescent coordination polymers (FL-CPs) has attracted intense attention due to their sensing accuracy and easy visualization when compared with sensing relying solely on monochromatic FL-CPs. In this work, a series of rare-earth metal-based CPs, formuled as [(CH3)2NH2][Ln(bpdc)2] (Ln3+ = Y3+, Eu3+ and Tb3+, H2bpdc = biphenyl-4,4'-dicarboxylic acid), are presented, which show dual emission aroused from the Ln3+ ions and the inefficient intermolecular energy transfer from ligands to Ln3+ metals. For clarity, the as-made Ln-CPs are named Eu-bpdc, Tb-bpdc, and Y-bpdc based on the corresponding Ln3+. Notably, Eu-bpdc, presented as an example, could be used as FL sensing material ratiometric to Fe3+ ions. The ratio of FL intensity of Eu3+ ions to bpdc2- ligands (I415/I615) showed a good linear relationship with the concentrations of Fe3+ ions. Moreover, the detection process could be visibly monitored through a change from purple to blue when Eu-bpdc was used as an FL proble. This work provides a good example for exploring visibly ratiometric sensors based on FL-CPs.

Switching from Molecules to Functional Materials: Breakthroughs in Photochromism With MOFs

Photochromic materials with properties that can be dynamically tailored as a function of external stimuli are a rapidly expanding field driven by applications in areas ranging from molecular computing, nanotechnology, or photopharmacology to programable heterogeneous catalysis. Challenges arise, however, when translating the rapid, solution-like response of stimuli-responsive moieties to solid-state materials due to the intermolecular interactions imposed through close molecular packing in bulk solids. As a result, the integration of photochromic compounds into synthetically programable porous matrices, such as metal-organic frameworks (MOFs), has come to the forefront as an emerging strategy for photochromic material development. This review highlights how the core principles of reticular chemistry (on the example of MOFs) play a critical role in the photochromic material performance, surpassing the limitations previously observed in solution or solid state. The symbiotic relationship between photoresponsive compounds and porous frameworks with a focus on how reticular synthesis creates avenues toward tailorable photoisomerization kinetics, directional energy and charge transfer, switchable gas sorption, and synergistic chromophore communication is discussed. This review not only focuses on the recent cutting-edge advancements in photochromic material development, but also highlights novel, vital-to-pursue pathways for multifaceted functional materials in the realms of energy, technology, and biomedicine.

Two Stable Pillar-Layered Zn-LMOFs for Highly Fluorescence Sensing of Inorganic Pollutants and Nitro Aromatic Compounds in Water

Luminescent metal-organic frameworks (LMOFs) are a potential class of functional materials for the photoluminescent detection of a wide range of analytes as well as for the detection of pollutants in wastewater. Herein, by using the pillar-layered strategy, two new luminescence Zn-LMOFs (JLU-MOF222 and JLU-MOF223) were successfully solvothermal synthesized. The 2D layers are both consisting of Zn2+ and TPHC [TPHC = (1,1':2',1″-terphenyl)-3,3″,4,4',4″,5'-hexacarboxylic acid] ligands and then pillared by the different N-donor ligands to form the 3D Zn-LMOFs with fsh topology. Benefiting from the uncoordinated carboxylate sites, uncoordinated N atom, or -NH2 group in the pillaring ligands and excellent stability in pH = 2-13 aqueous phase, JLU-MOF222 and JLU-MOF223 not only can sensitively detect trace amounts of inorganic pollutants (Fe3+, Cr2O72-) and nitro aromatic compounds TNP and 2,4-DNP (TNP = 2,4,6- trinitrophenol, 2,4-DNP = 2,4-dinitrophenol) through luminescence quenching but also exhibit high selectivity of other anti-interference competing analytes. The two new Zn-LMOFs can be used as potential luminescent sensors for pollutant detection in water due to their high KSV and low limit of detection (LOD).

Green and sustainable smart wooden system integrated with cellulose nanowhiskers-supported polyvinyl alcohol and anthocyanin biomolecules to monitor food freshness

Smart packaging materials have been used to protect human health from environmental hazards by sending real-time colorimetric signals for changes in the food packaging environment. However, the colorimetric material sensors use synthetic sensor dyes, which are toxic, expensive, non-biodegradable, and difficult to prepare. Herein, a simple strategy is presented for the development of an environmentally-friendly halochromic wood able to change color upon exposure to spoilage of food. A combination of anthocyanin (Ac)/aluminum (Al) mordant (Ac/Al) nanoparticles and cellulose nanowhiskers (CNW)-reinforced polyvinyl alcohol (PVA) was infiltrated into a delignified wood to produce a translucent wood with halochromic properties. CNW were employed as reinforcement agent to improve the mechanical performance of PVA. Additionally, CNW function as a dispersing agent to prevent agglomeration of Ac/Al nanoparticles. The diameters of CNW are in the range of 12-19 nm, whereas Ac/Al particles showed diameters of 9-22 nm. The smart wood changed color from purplish to colorless when exposed to food spoilage. A hypsochromic change from 539 nm to 370 nm was shown by the anthocyanin receptor when the spoilage level of food increased. This could be attributed to the pH-driven molecular switching of anthocyanin, leading to charge delocalization.

Fine-Scale Aerosol-Jet Printing of Luminescent Metal-Organic Framework Nanosheets

Fabrication of metal-organic framework (MOF) thin films is an ongoing challenge to achieve effective device integration. Inkjet printing has been employed to print various luminescent metal-organic framework (MOF) films. Luminescent metal-organic nanosheets (LMONs), nanometer-thin particles of MOF materials with comparatively large micrometer lateral dimensions, provide an ideal morphology that offers enhancements over analogous MOFs in luminescent properties such as intensity and photoluminescent quantum yield. The morphology is also better suited to the formation of thin films. This work harnesses the preferential features of LMONs to access the advanced technique of aerosol-jet printing (AJP) to print luminescent films with precise geometries and patterns across the micrometer and centimeter length scales. AJP of LMONs exhibiting red (R), green (G), and blue (B) emission were studied systematically to reveal the increase of luminescence upon additive layering printing until a threshold was reached limited by self-quenching. By combining different LMON emitters, emission chromaticity and intensity were shown to be tunable, including the combination of RGB emitters to fabricate white-light-emitting films. A white-light LMON film was printed onto a UV light emitting diode (LED), producing a working white-light-emitting diode. Printing with multiple distinct photoluminescent inks produced intricate multicolor patterns that dynamically responded to excitation wavelength, acting either as micrometer-scale LED-type cells or larger visual tags. Collectively, the work offers an advancement for MOF thin films by printing MON materials using AJP, offering a precise method for manufacturing a wide range of critical functional devices, from luminescent sensors to optoelectronics, and more broadly even the opportunity for printed circuitry with conductive MONs.

Luminescent Ln-MOFs for Chemical Sensing Application on Biomolecules

At present, the application of rare-earth organic frameworks (Ln-MOFs) in fluorescence sensing has entered rapid development and shown great potential in various analytical fields, such as environmental analysis, food analysis, drug analysis, and biological and clinical analysis by utilizing their internal porosity, tunable structural size, and energy transfer between rare-earth ions, ligands, and photosensitizer molecules. In addition, because the luminescence properties of rare-earth ions are highly dependent on the structural details of the coordination environment surrounding the rare-earth ions, and although their excitation lifetimes are long, they are usually not burst by oxygen and can provide an effective platform for chemical sensing. In order to further promote the development of fluorescence sensing technology based on Ln-MOFs, we summarize and review in detail the latest progress of the construction of Ln-MOF materials for fluorescence sensing applications and related sensor components, including design strategies, preparation methods, and modification considerations and initially propose the future development prospects and prospects.

Unveiling MOF-808 photocycle and its interaction with luminescent guests

The world of metal-organic frameworks (MOFs) has become a hot topic in recent years due to the extreme variety and tunability of their structures. There is evidence of MOFs that exhibit intrinsic luminescence properties that arise directly from their organic components or from the interaction between them and metallic counterparts. A new perspective is to exploit the porous nature of MOFs by encapsulating luminescent guests, such as organic dyes, in order to explore possible changes in the luminescence activity of the combined systems. This work is focused on the optical study of zirconium-based MOF-808 and its interaction with encapsulated rhodamine B molecules. Using a plethora of different techniques, we were able to unravel its photocycle. MOF-808 displays intrinsic luminescence activity that derives from an energy transfer process from the linker to the metal sites occurring in 300 ps. The emission is a singlet-singlet transition in aqueous solution, and it is a triplet transition in powdered form. After exploring the bare MOF, we combined it with rhodamine B molecules, following an easy post-synthetic process. Rhodamine B molecules were found to be encapsulated in MOF pores and interact with the MOF's matrix through nanosecond energy transfer. We created a totally new dual-emitting system and suggested a way, based on the time-resolved studies, to clearly unravel the photocycle of MOFs from the very first photoexcitation.

Luminescence Nanothermometry: Investigating Thermal Memory in UiO-66-NH2 Nanocrystals

Metal-organic frameworks (MOFs), a diverse and rapidly expanding class of crystalline materials, present many opportunities for various applications. Within this class, the amino-functionalized Zr-MOF, namely, UiO-66-NH2, stands out due to its distinctive chemical and physical properties. In this study, we report on the new unique property where UiO-66-NH2 nanocrystals exhibited enhanced fluorescence upon heating, which was persistently maintained postcooling. To unravel the mechanism, the changes in the fluorescence signal were monitored by steady-state fluorescence spectroscopy, lifetime measurements, and a fluorescence microscope, which revealed that upon heating, multiple mechanisms could be contributing to the observed enhancement; the MOFs can undergo disaggregation, resulting in a fluorescent enhancement of the colloidally stable MOF nanocrystals and/or surface-induced phenomena that result in further fluorescence enhancement. This observed temperature-dependent photophysical behavior has substantial applications. It not only provides pathways for innovations in thermally modulated photonic applications but also underscores the need for a better understanding of the interactions between MOF crystals and their environments.

Ligand Meta-Anchoring Strategy in Metal-Organic Frameworks for Remarkable Promotion of Quantum Yields

Aggregation is a conventional method to enhance the quantum yields (QYs) of pure organic luminophores due to the restriction of intramolecular motions (RIM). However, how to realize RIM in metal-organic frameworks (MOFs) is still unclear and challenging. In this work, the ligand meta-anchoring strategy is first proposed and proved to be an effective and systematic approach to restrict the intramolecular motions of MOFs for the QY improvement. By simply shifting the substituent position in the ligand from para to meta, the QY of the resulting MOF is significantly enhanced by eleven-fold. The value is even higher than that of ligand aggregates, demonstrating the strong RIM effect of this ligand meta-anchoring strategy. The introduction of co-ligand induces the appearance of visible yellow room temperature phosphorescence with a lifetime of 222 ms due to the QY enhancement and the charge transfer between the donor and accepter units. The present work thus broadens the understanding of the RIM mechanism from a new perspective, develops a novel method to realize RIM and expands the applicable objects from pure organic materials to organic-inorganic hybrid materials.

Dramatic fluorescence enhancement of PCN-224 and its application in "turn off" immunoassay for sensitive detection of E. coli O157:H7 in milk

In this study, a type of luminescent porous coordination network-224 (PCN-224) in alkaline conditions was synthesized with the dramatic fluorescence enhancement by 20.4 times, which was explained by the fact that the decrease of Zr4+ content in alkaline conditions resulted in the partial recovery of the electron cloud density of 4,4',4'',4'''-(Porphine-5,10,15,20-tetrayl) tetrakis(benzoic acid) (TCPP). Given the large overlap between the excitation spectrum of PCN-224 and the absorption band of Ag nanoparticles (Ag NPs), the coating of the Ag layer on PCN-224 triggered the fluorescence quenching effect, which was applied to "turn off" fluorescence immunoassay for sensitive detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk. The proposed immunoassay reached a low limit of detection (LOD) of 3.3 × 102 CFU mL-1, 29.7 times more sensitive than the conventional ELISA. It will provide a novel alternative strategy for sensitively detecting pathogenic bacteria in the field of food safety.

Linker Engineering toward Tunable Emission Behavior of Porous Interpenetrated Zr-Organic Frameworks

Conjugated molecules with donor-acceptor-donor (D-A-D) moieties have garnered significant attention for their ability to form luminescent metal-organic frameworks (LMOFs). D-A-D molecules feature tunable bandgaps, which can be varied systematically to control the fluorescence wavelength of LMOFs. In this study, we prepared and characterized the fluorescence properties of two porous interpenetrated Zr-organic frameworks (PIZOFs) constructed using 4,4'-(benzo[c][1,2,5]selenadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-Se) or 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-S) as linkers. The corresponding MOFs are denoted as PIZOF-Se and PIZOF-S, respectively. Through our investigation, we explored the correlation between the structure of the frameworks and their respective optical properties. Our findings revealed that there are distinct differences in the fluorescence properties of the two PIZOFs. Specifically, the fluorescence of PIZOF-S is red-shifted from that characteristic of the corresponding linker, L-S. By contrast, the fluorescence of PIZOF-Se is substantially blue-shifted from that of linker L-Se. The emission of mixed-linker MOFs is explored by combining L-S or L-Se with structurally analogous, but nonfluorescent linker, 4,4'-((perfluoro-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzoic acid (L-F). Based on steady-state and time-resolved photoluminescence experiments, as well as confocal fluorescence microscopy combined with fluorescence lifetime imaging (FILM), we demonstrated that linker engineering is an effective method to tune the emission behavior of LMOFs.

Amyloid detection in neurodegenerative diseases using MOFs

Neurodegenerative diseases (amyloid diseases such as Alzheimer's and Parkinson's), stemming from protein misfolding and aggregation, encompass a spectrum of disorders with severe systemic implications. Timely detection is pivotal in managing these diseases owing to their significant impact on organ function and high mortality rates. The diverse array of amyloid disorders, spanning localized and systemic manifestations, underscores the complexity of these conditions and highlights the need for advanced detection methods. Traditional approaches have focused on identifying biomarkers using imaging techniques (PET and MRI) or invasive procedures. However, recent efforts have focused on the use of metal-organic frameworks (MOFs), a versatile class of materials known for their unique properties, in revolutionizing amyloid disease detection. The high porosity, customizable structures, and biocompatibility of MOFs enable their integration with biomolecules, laying the groundwork for highly sensitive and specific biosensors. These sensors have been employed using electrochemical and photophysical techniques that target amyloid species under neurodegenerative conditions. The adaptability of MOFs allows for the precise detection and quantification of amyloid proteins, offering potential advancements in early diagnosis and disease management. This review article delves into how MOFs contribute to detecting amyloid diseases by categorizing their uses based on different sensing methods, such as electrochemical (EC), electrochemiluminescence (ECL), fluorescence, Förster resonance energy transfer (FRET), up-conversion luminescence resonance energy transfer (ULRET), and photoelectrochemical (PEC) sensing. The drawbacks of MOF biosensors and the challenges encountered in the field are also briefly explored from our perspective.

Strategic Design of Non-d10 Luminescent Metal-Organic Frameworks as Dual-Mode Ultrafast and Selective Sensing Platforms for Aldehydes at the ppb Level

Utilizing a cautious design of luminescent MOFs of non-d10 divalent transition metals based on two factors (metal nodes in an octahedral geometry to minimize nonradiative energy dissipation and tailored organic chromophores), this work reports {[Ni2(oxdz)2(tpbn)]}n (1), {[Ni2(oxdz)2(tphn)]}n (2), and {[Ni2(oxdz)2(tpon)]}n (3), synthesized at room temperature, varying the spacer length of tpbn/tphn/tpon (four, six, and eight CH2 groups, respectively). This subtle change in 1-3 is correlated to their hydrophobicity and polarizing power via water vapor sorption and selective and sensitive detection of aldehydes at the ppb level, respectively. A decrease in water vapor uptake (14.8, 8.95, and 3.19 mmol g-1 for 1-3, respectively) is observed with an increase in their hydrophobicity. On the other hand, the solution phase detection limits of acetaldehyde and benzaldehyde (2.42 and 6.71 ppb for 1, 2.77 and 4.08 ppb for 2, and 10.35 and 10.4 ppb for 3, respectively) show a similar trend for their polarizing power. The best performance of 1 is expanded to the vapor-phase detection of acetaldehyde (297% luminescence enhancement) under different pH conditions. The second mode of detection of acetaldehyde via the metal-centered electrochemical behavior of 1 provides detection limits of 38.2 and 71.5 ppb at pH 7 and 13, respectively.

Lanthanide MOF-based luminescent sensor arrays for the detection of castration-resistant prostate cancer curing drugs and biomarkers

In recent years, castration-resistant prostate cancer (CRPC) has profoundly impacted the lives of many men, and early diagnosis of medication and illness is crucial. Therefore, a highly efficient detection method for CRPC biomarkers and curing drugs is required. However, the complex and diverse structures of CRPC drugs pose significant challenges for their detection and differentiation. Lanthanide metal-organic frameworks (Ln-MOFs) show great potential for sensing applications due to their intense and characteristic luminescence. In this work, a series of new bimetallic Ln-MOFs (EuxTb1-x-MOF) based luminescent sensor arrays have been developed to identify CRPC drugs, including in mixtures, via principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods. These Ln-MOFs are built with a highly conjugated H2L linker (H2L = 5-(4-(triazole-1-yl)phenyl)isophthalic acid) and exhibit robust strong luminescence emissions (mainly located at 543 and 614 nm) and high energy transfer efficiencies. More specifically, Eu0.096Tb0.904-MOF (MOF 3) has demonstrated good sensing performances for CRPC curing drugs in real human serum samples. Furthermore, the curing drug hydroxyflutamide has been combined with MOF 3, to construct a robust composite sensing platform MOF 3@hydroxyflutamide for highly efficient detection of CRPC biomarkers such as the androgen receptor (AR) and prostate-specific antigen (PSA). Finally, luminescence lifetime measurements, zeta potential measurements, and density functional theory (DFT) calculations were performed to gain insights into the sensing mechanism.

Synergistically enhancing the selective adsorption of cationic dyes through copper impregnation and amino functionality into iron-based metal-organic frameworks

Dyes contaminating the sewages have seriously threatened the living beings and their separation from wastewater in terms of potential resource recovery is of high value. Herein, both of metal node doping and ligand group grafting were taken into account to enhance the adsorption selectivity of Fe-MOFs towards cationic dyes. The positive correlation between copper doping amount and selective coefficient (∂MOMB) for methylene blue (MB) over methyl orange (MO) within a certain range was mainly attributed to the increased surface negative charges via partial replacement of Fe(III) with Cu(II). Moreover, the amount of surface negative charges was further increased after amino functionalization and there was a synergism between Cu(II) and -NH2 in selectivity enhancement. As a result, Fe0.6Cu0.4-BDC-NH2 exhibited a 22.5-times increase in ∂MOMB and other cationic dyes including malachite green (MG) and rhodamine B (Rh. B) could also be selectively separated from binary and quaternary mixed dye systems. Moreover, Fe0.6Cu0.4-BDC-NH2 showed many superiorities like a wide pH range of 4.0-8.0, strong anti-interference ability over various inorganic ions, good recyclability, and stability. The adsorption kinetics and isotherm suggested that the MB adsorption process was a homogeneous single-layer chemisorption. Additionally, the thermodynamics manifested that the overall process was exothermic and spontaneous. According to the FT-IR and XPS spectra analysis, the electrostatic interaction and hydrogen bonding were determined as the main driving forces, and π-π interaction also contributed to the adsorption process.

Multiple-Emitting Luminescent Metal-Organic Framework as an Array-on-a-MOF for Rapid Screening and Discrimination of Nitroaromatics

Fluorescence array technologies have attracted great interest in the sensing field because of their high sensitivity, low cost, and capability of multitarget detection. However, traditional array sensing relies on multiple independent sensors and thus often requires time-consuming and laborious measurement processes. Herein, we introduce a novel fluorescence array strategy of the array-on-a-metal-organic framework (MOF), which integrates multiple array elements into a single MOF matrix to achieve facile sensing and discrimination of multiple target analytes. As a proof-of-concept system, we constructed a luminescent MOF containing three different emitting channels, including a lanthanide ion (europium/Eu3+, red emission), a fluorescent dye (7-hydroxycoumarin-4-acetic acid/HCAA, blue emission), and the MOF itself (UiO-66-type MOF, blue-violet emission). Five structurally similar nitroaromatic compounds (NACs) were chosen as the targets. All three channels of the array-on-a-MOF displayed rapid and stable fluorescence quenching responses to NACs (response equilibrium achieved within 30 s). Different responses were generated for each channel against each NAC due to the various quenching mechanisms, including photoinduced electron transfer, energy competition, and the inner filter effect. Using linear discriminant analysis, the array-on-a-MOF successfully distinguished the five NACs and their mixtures at varying concentrations and demonstrated good sensitivity to quantify individual NACs (detect limit below the advisory concentration in drinking water). Moreover, the array also showed feasibility in the sensing and discrimination of multiple NACs in real water samples. The proposed "array-on-a-MOF" strategy simplifies multitarget discrimination procedures and holds great promise for various sensing applications.

Regulating luminescence thermal enhancement in negative thermal expansion metal-organic frameworks

Overcoming thermal quenching is generally essential for the practical application of luminescent materials. It has been recently found that frameworks with negative thermal expansion (NTE) could be a promising candidate to engineer unconventional luminescence thermal enhancement. However, the mechanism through which luminescence thermal enhancement can be well tuned remains an open issue. In this work, enabled by altering ligands in a series of UiO-66 derived Eu-based metal-organic frameworks, it was revealed that the changes in the thermal expansion are closely related to luminescence thermal enhancement. The NTE of the aromatic ring part favors luminescence thermal enhancement, while contraction of the carboxylic acid part plays the opposite role. Modulation of functional groups in ligands can change the thermal vibration of aromatic rings and then achieve luminescence thermal enhancement in a wide temperature window. Our findings pave the way to manipulate the NTE and luminescence thermal enhancement based on ligand engineering.

Isolation of a Cd-Based Coordination Polymer Containing Mixed Ligands: Time- and Temperature-Dependent Synthesis, Sulfonamide Antibiotics Detection, and Schottky Diode Fabrication

In this study, we present a new cadmium(II)-based two-dimensional coordination polymer [Cd (L)(NA)(H2O)] (L = Iminol form of N-nicotinoyl glycinate, NA = nicotinate), 1, containing two linkers generated from N-nicotinoyl glycine. A comprehensive investigation was carried out during the synthesis of the coordination polymers by varying the reaction time interval and temperature, and it revealed the formation of three distinct phases, of which two phases were previously reported and one was a new compound (1). The structure of compound 1 was determined by single-crystal X-ray diffraction, and it shows a corrugated layer structure with hydrogen bond interactions leading to three-dimensional supramolecular arrangements. Compound 1 exhibited strong emission at 420 nm when excited at 260 nm in an aqueous medium. The emission behavior of this compound was used for the detection of various sulfonamide antibiotics, sulfadiazine, sulfamethazine, sulfachloropyridazine, sulfameter, sulfaquinoxaline, and sulfathiazole, in the presence of common water pollutants. The luminescence quenching response of compound 1 to sulfonamide antibiotics was significant, ranging from 81 to 94%, and the detection sensitivity reached parts per billion (ppb) levels (226-726 ppb). Compound 1 also used for the fabrication of Schottky diode devices with a barrier height of 0.86 eV along with an excellent ideality factor of 1.24.

Bacterial Cellulose-Based MOF Hybrid as a Sensitive Switch Off-On Luminescent Sensor for the Selective Recognition of l-Histidine

In this study, a stable and luminescent UiO-66-NH2 (UN) and its derivative Cu2+@UN were prepared and utilized successfully as an Off-On luminescent sensing platform for effective, selective, as well as rapid (5 min) detection of l-Histidine (l-His). The UN reveals efficient quenching in the presence of Cu2+ ions through photoinduced electron transition (PET) mechanism as a dynamic quenching process (in the range of 0.01-1 mM) forming Cu2+@UN sensing platform. However, due to the remarkable affinity between l-His and Cu2+, the luminescence of Cu2+@UN is recovered in the presence of l-His indicating Turn-On behavior via a quencher detachment mechanism (QD). A good linear relationship between the l-His concentration and luminescence intensity was observed in the range of 0.01-40 μM (R2 = 0.9978) with a detection limit of 7 nM for l-His sensing. The suggested method was successfully utilized for l-His determination in real samples with good recoveries and satisfying consequences. Moreover, the result indicates that only l-His induces a significant luminescence restoration of Cu2+@UN and that the signal is significantly greater than that of the other amino acids. Also, the portable test paper based on bacterial cellulose (BC) as the Cu2+@UNBC sensing platform was developed to conveniently evaluate the effective detection of l-His.

Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 μM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

Metal-organic framework-based advanced therapeutic tools for antimicrobial applications

The escalating concern over conventional antibiotic resistance has emphasized the urgency in developing innovative antimicrobial agents. In recent times, metal-organic frameworks (MOFs) have garnered significant attention within the realm of antimicrobial research due to their multifaceted antimicrobial attributes, including the sustained release of intrinsic or exogenous antimicrobial components, chemodynamically catalyzed generation of reactive oxygen species (ROS), and formation of photogenerated ROS. This comprehensive review provides a thorough overview of the synthetic approaches employed in the production of MOF-based materials, elucidating their underlying antimicrobial mechanisms in depth. The focal point lies in elucidating the research advancements across various antimicrobial modalities, encompassing intrinsic component release system, extraneous component release system, auto-catalytical system, and energy conversion system. Additionally, the progress of MOF-based antimicrobial materials in addressing wound infections, osteomyelitis, and periodontitis is meticulously elucidated, culminating in a summary of the challenges and potential opportunities inherent within the realm of antimicrobial applications for MOF-based materials. STATEMENT OF SIGNIFICANCE: Growing concerns about conventional antibiotic resistance emphasized the need for alternative antimicrobial solutions. Metal-organic frameworks (MOFs) have gained significant attention in antimicrobial research due to their diverse attributes like sustained antimicrobial components release, catalytic generation of reactive oxygen species (ROS), and photogenerated ROS. This review covers MOF synthesis and their antimicrobial mechanisms. It explores advancements in intrinsic and extraneous component release, auto-catalysis, and energy conversion systems. The paper also discusses MOF-based materials' progress in addressing wound infections, osteomyelitis, and periodontitis, along with existing challenges and opportunities. Given the lack of related reviews, our findings hold promise for future MOF applications in antibacterial research, making it relevant to your journal's readership.

Fluorescence sensing and device fabrication with luminescent metal-organic frameworks

Metal-organic frameworks (MOFs) are a novel class of hybrid porous multi-functional materials consisting of metal ions/clusters and organic ligands. MOFs have exclusive benefits due to their tunable structure and diverse properties. Luminescent MOFs (LMOFs) exhibit both porosity and light emission. They display abundant host and guest responses, making them conducive to sensing. Currently, LMOF sensing research is gaining more depth, with attention given to their device and practical applications. This work reviews recent advancements and device applications of LMOFs as chemical sensors toward ions, volatile organic compounds, biomolecules, and environmental toxins. Furthermore, the detection mechanism and the correlation between material properties and structure are elaborated. This analysis serves as a valuable reference for the preparation and efficient application of targeted LMOFs.

Post-synthetic modified luminescent metal-organic framework for the detection of berberine hydrochloride in a traditional Chinese herb

In this work, a novel fluorescence sensor UiO-66-PSM based on post-synthetic modified metal-organic frameworks was prepared for the detection of berberine hydrochloride (BBH) in the traditional Chinese herb Coptis. UiO-66-PSM was synthesized by a simple Schiff base reaction with UiO-66-NH2 and phthalaldehyde (PAD). The luminescence quenching can be attributed to the photo-induced electron transfer process from the ligand of UiO-66-PSM to BBH. The UiO-66-PSM sensor exhibited fast response time, low detection limit, and high selectivity to BBH. Moreover, the UiO-66-PSM sensor was successfully applied to the quantitative detection of BBH in the traditional Chinese herb Coptis, and the detection results obtained from the as-fabricated fluorescence sensing assay were consistent with those of high-performance liquid chromatography (HPLC), indicating that this work has potential applicability for the detection of BBH in traditional Chinese herbs.

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Tailoring the topology of ZIF-67 metal-organic frameworks (MOFs) adsorbents to capture humic acids

Chlorination is a versatile technique to combat water-borne pathogens. Over the last years, there has been continued research interest to abate the formation of chlorinated disinfection by-products (DBPs). To prevent hazardous DBPs in drinking water, it is decided to diminish organic precursors, among which humic acids (HA) resulting from the decomposition and transformation of biomass. Metal-organic frameworks (MOFs) such as zeolitic imidazolate frameworks (ZIFs) have recently received tremendous attention in water purification. Herein, customized ZIF-67 MOFs possessing various physicochemical properties were prepared by changing the cobalt source. The HA removal by ZIF-67-Cl, ZIF-67-OAc, ZIF-67-NO3, and ZIF-67-SO4 were 85.6%, 68.9%, 86.1%, and 87.4%, respectively, evidently affected by the specific surface area. HA uptake by ZIF-67-SO4 indicated a removal efficiency beyond 90% in 4  90% after 60 min mixing the solution with 0.3 g L-1 ZIF-67-SO4. Notably, an acceptable removal performance (∼72.3%) was obtained even at HA concentrations up to 100 mg L-1. The equilibrium data fitted well with the isotherm models in the order of Langmuir> Hill > BET> Khan > Redlich-Peterson> Jovanovic> Freundlich > and Temkin. The maximum adsorption capacity qm for HA uptake by ZIF-67-SO4 was 175.89 mg g-1, well above the majority of adsorbents. The pseudo-first-order model described the rate of HA adsorption by time. In conclusion, ZIF-67-SO4 presented promising adsorptive properties against HA. Further studies would be needed to minimize cobalt leaching from the ZIF-67-SO4 structure and improve its reusability safely, to ensure its effectiveness and the economy of adsorption system.

Synthesis of Metal-Organic Framework-Based ZIF-8@ZIF-67 Nanocomposites for Antibiotic Decomposition and Antibacterial Activities

Toxic antibiotic effluents and antibiotic-resistant bacteria constitute a threat to global health. So, scientists are investigating high-performance materials for antibiotic decomposition and antibacterial activities. In this novel research work, we have successfully designed ZIF-8@ZIF-67 nanocomposites via sol-gel and solvothermal approaches. The ZIF-8@ZIF-67 nanocomposite is characterized by various techniques that exhibit superior surface area enhancement, charge separation, and high light absorption performance. Yet, ZIF-8 has high adsorption rates and active sites, while ZIF-67 has larger pore volume and efficient adsorption and reaction capabilities, demonstrating that the ZIF-8@ZIF-67 nanocomposite outperforms pristine ZIF-8 and ZIF-67. Compared with pristine ZIF-8 and ZIF-67, the most active 6ZIF-67@ZIF-8 nanocomposite showed higher decomposition efficacy for ciprofloxacin (65%), levofloxacin (54%), and ofloxacin (48%). Scavenger experiments confirmed that •OH, •O2-, and h+ are the most active species for the decomposition of ciprofloxacin (CIP), levofloxacin (LF), and ofloxacin (OFX), respectively. In addition, the 6ZIF-67/ZIF-8 nanocomposite suggested its potential applications in Escherichia coli for growth inhibition zone, antibacterial activity, and decreased viability. Moreover, the stability test and decomposition pathway of CIP, LF, and OFX were also proposed. Finally, our study aims to enhance the efficiency and stability of ZIF-8@ZIF-67 nanocomposite and potentially enable its applications in antibiotic decomposition, antibacterial activities, and environmental remediation.

A Fluorescence Resonance Energy Transfer Aptasensor for Aflatoxin B1 Based on Ligand-Induced ssDNA Displacement

In this study, a fluorescence resonance energy transfer (FRET)-based aptasensor for the detection of aflatoxin B1 (AFB1) was designed using a carboxyfluorescein (FAM)-labeled aptamer and short complementary DNA (cDNA) labeled with low molecular quencher RTQ1. The sensing principle was based on the detection of restored FAM-aptamer fluorescence due to the ligand-induced displacement of cDNA in the presence of AFB1, leading to the destruction of the aptamer/cDNA duplex and preventing the convergence of FAM and RTQ1 at the effective FRET distance. Under optimal sensing conditions, a linear correlation was obtained between the fluorescence intensity of the FAM-aptamer and the AFB1 concentration in the range of 2.5-208.3 ng/mL with the detection limit of the assay equal to 0.2 ng/mL. The assay time was 30 min. The proposed FRET aptasensor has been successfully validated by analyzing white wine and corn flour samples, with recovery ranging from 76.7% to 91.9% and 84.0% to 86.5%, respectively. This work demonstrates the possibilities of labeled cDNA as an effective and easily accessible tool for sensitive AFB1 detection. The homogeneous FRET aptasensor is an appropriate choice for contaminant screening in complex matrices.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

A metal-organic framework-based fluorescence resonance energy transfer nanoprobe for highly selective detection of Staphylococcus Aureus

Survival and infection of pathogenic bacteria, such as Staphylococcus aureus (S. aureus), pose a serious threat to human health. Efficient methods for recognizing and quantifying low levels of bacteria are imperiously needed. Herein, we introduce a metal-organic framework (MOF)-based fluorescence resonance energy transfer (FRET) nanoprobe for ratiometric detection of S. aureus. The nanoprobe utilizes blue-emitting 7-hydroxycoumarin-4-acetic acid (HCAA) encapsulated inside zirconium (Zr)-based MOFs as the energy donor and green-emitting fluorescein isothiocyanate (FITC) as the energy acceptor. Especially, vancomycin (VAN) is employed as the recognition moiety to bind to the cell wall of S. aureus, leading to the disassembly of VAN-PEG-FITC from MOF HCAA@UiO-66. As the distance between the donor and acceptor increases, the donor signal correspondingly increases as the FRET signal decreases. By calculating the fluorescence intensity ratio, S. aureus can be quantified with a dynamic range of 1.05 × 103-1.05 × 107 CFU mL-1 and a detection limit of 12 CFU mL-1. Due to the unique high affinity of VAN to S. aureus, the nanoprobe shows high selectivity and sensitivity to S. aureus, even in real samples like lake water, orange juice, and saliva. The FRET-based ratiometric fluorescence bacterial detection method demonstrated in this work has a prospect in portable application and may reduce the potential threat of pathogens to human health.

3D ZnII-Based coordination polymer: Synthesis, structure and fluorescent sensing property for nitroaromatic compounds

A water-stable Zn^II-based coordination polymer (CP) with excellent photophysical behavior, namely [Zn₂L(atez)(H₂O)₂] (compound 1; H₃L = 4-(2',3'-dicarboxylphenoxy); atez = 5-aminotetrazole), was successfully prepared by the solvothermal reaction of Zn ions with a π-conjugated and semi-rigid multicarboxylate ligand H₃L in the presence of N-containing linker atez. Compound 1 displays a hierarchically pillared three-dimensional (3D) (3,4,5)-connected (4·6²) (4²·6⁴) (4³·6⁴·8³) net which is based on two-dimensional (2D) multicarboxylate- Zn^II layers strutted by the atez ligands. Sensing investigations of compound 1 reveal that this material can selectively and sensitively detect nitroaromatic compounds in water suspension through fluorescence quenching effect. In particular, it is worth noting that it shows highly specific detection of nitrobenzene (NB) and 2,4,6-trinitrophenol (TNP) with remarkable quenching constants (K_SV = 7.5 × 10⁴ M^-1 for NB and K_SV = 1.9 × 10⁵ M^-1 for TNP) and low limit of detection (LOD = 0.93 μM for NB and LOD = 0.36 μM for TNP). Investigations reveal that the probable mechanisms for such sensing processes are the concurrent presence of fluorescence resonance energy transfer (FRET) as well as photoinduced electron transfer (PET) between the CP and nitroaromatic molecules. This work not only offers an effective route to improve the application of fluorescent CPs but also provide one novel probable fluorescence probe for nitroaromatic compounds.

Metal-organic frameworks (MOFs) based luminescent and electrochemical sensors for food contaminant detection

With the increasing population, food toxicity has become a prevalent concern due to the growing contaminants of food products. Therefore, the need for new materials for toxicant detection and food quality monitoring will always be in demand. Metal-organic frameworks (MOFs) based on luminescence and electrochemical sensors with tunable porosity and active surface area are promising materials for food contaminants monitoring. This review summarizes and studies the most recent progress on MOF sensors for detecting food contaminants such as pesticides, antibiotics, toxins, biomolecules, and ionic species. First, with the introduction of MOFs, food contaminants and materials for toxicants detection are discussed. Then the insights into the MOFs as emerging materials for sensing applications with luminescent and electrochemical properties, signal changes, and sensing mechanisms are discussed. Next, recent advances in luminescent and electrochemical MOFs food sensors and their sensitivity, selectivity, and capacities for common food toxicants are summarized. Further, the challenges and outlooks are discussed for providing a new pathway for MOF food contaminant detection tools. Overall, a timely source of information on advanced MOF materials provides materials for next-generation food sensors.

Modulated self-assembly of three flexible Cr(III) PCPs for SO2 adsorption and detection

Modulated self-assembly protocols are used to develop facile, HF-free syntheses of the archetypal flexible PCP, MIL-53(Cr), and novel isoreticular analogues MIL-53(Cr)-Br and MIL-53(Cr)-NO2. All three PCPs show good SO2 uptake (298 K, 1 bar) and high chemical stabilities against dry and wet SO2. Solid-state photoluminescence spectroscopy indicates all three PCPs exhibit turn-off sensing of SO2, in particular MIL-53(Cr)-Br, which shows a 2.7-fold decrease in emission on exposure to SO2 at room temperature, indicating potential sensing applications.

Advance Progress on Luminescent Sensing of Nitroaromatics by Crystalline Lanthanide-Organic Complexes

Water environment pollution is becoming an increasingly serious issue due to industrial pollutants with the rapid development of modern industry. Among many pollutants, the toxic and explosive nitroaromatics are used extensively in the chemical industry, resulting in environmental pollution of soil and groundwater. Therefore, the detection of nitroaromatics is of great significance to environmental monitoring, citizen life and homeland security. Lanthanide-organic complexes with controllable structural features and excellent optical performance have been rationally designed and successfully prepared and used as lanthanide-based sensors for the detection of nitroaromatics. This review will focus on crystalline luminescent lanthanide-organic sensing materials with different dimensional structures, including the 0D discrete structure, 1D and 2D coordination polymers and the 3D framework. Large numbers of studies have shown that several nitroaromatics could be detected by crystalline lanthanide-organic-complex-based sensors, for instance, nitrobenzene (NB), nitrophenol (4-NP or 2-NP), trinitrophenol (TNP) and so on. The various fluorescence detection mechanisms were summarized and sorted out in the review, which might help researchers or readers to comprehensively understand the mechanism of the fluorescence detection of nitroaromatics and provide a theoretical basis for the rational design of new crystalline lanthanide-organic complex-based sensors.

Smartphone-assisted ratiometric sensing platform for on-site tetracycline determination based on europium functionalized luminescent Zr-MOF

Accurate on-site analysis of tetracycline (TC) is of great research value for ensuring food safety and estimating environmental pollution. Herein, a smartphone-based fluorescent platform for TC detectionhas been developed based on a europium functionalized metal-organic framework (Zr-MOF/Cit-Eu). Based on the inner filter and antenna effect between Zr-MOF/Cit-Eu and TC, the probe exhibited a ratiometric fluorescent response toward TC, resulting in an emission color change from blue to red. Excellent sensing performance was achieved with a detection limit of 3.9 nM, consistent with the linear operation spanning nearly four orders of magnitude. Subsequently, visual test strips based on Zr-MOF/Cit-Eu were prepared, possessing the potential for accurate testing of TC via RGB signals. Finally, the proposed platform was well applied in actual samples with satisfied recoveries (92.27 to 110.22%). This MOF-based on-site fluorescent platform holds great potential on constructing intelligent platform for visual and quantitative detection of organic contaminants.

Terbium-based metal-organic frameworks through energy transfer modulation for visual logical sensing zinc and fluorine ions

Zinc is the second most abundant trace element in the human central nervous system, which is closely related to various physiological activities in the human body. Fluoride ion is one of the most harmful elements in drinking water. Excessive intake of F^- may cause dental fluorosis, renal failure, or DNA damage. Therefore, it is urgent to develop sensors with high sensitivity and selectivity for the detection of Zn²⁺ and F^- ions at the same time. In this work, a series of mixed lanthanide metal-organic frameworks (Ln-MOFs) probes are synthesized using a simple method of in situ doping. The luminous color can be finely modulated by changing the molar ratio of Tb³⁺ and Eu³⁺ during synthesis. Benefiting from the unique energy transfer modulation mechanism, the probe has the continuous detection capability of zinc ions and fluoride ions. The detection of Zn²⁺ and F^- in a real environment shows that the probe has a good practical application prospect. The as-designed sensor at 262 nm excitation can sequentially detect Zn²⁺ concentrations ranging from 10^-8 to 10^-3 M (LOD = 4.2 nM) and F^- levels ranging from 10^-5 to 10^-3 M (LOD = 3.6 μM) with high selectivity. Based on different output signals, a simple Boolean logic gate device is constructed to realize intelligent visualization of Zn²⁺ and F^- monitoring.

Efficient Eu3+-Integrated UiO-66 Probe for Ratiometric Fluorescence Sensing of Styrene and Cyclohexanone

The development of probes with sensitive and prompt detection of volatile organic compounds (VOCs) is of great importance for protecting human health and public security. Herein, we successfully prepared a series of bimetallic lanthanide metal-organic framework (Eu/Zr-UiO-66) by incorporating Eu³⁺ for fluorescence sensing of VOCs (especially styrene and cyclohexanone) using a one-pot method. Based on the multiple fluorescence signal responses of Eu/Zr-UiO-66 toward styrene and cyclohexanone, a ratiometric fluorescence probe using (I₆₁₇/I₃₂₀) and (I₆₁₇/I₃₃₀) as output signals was developed to recognize styrene and cyclohexanone, respectively. Benefitting from the multiple fluorescence response, the limits of detection (LODs) of Eu/Zr-UiO-66 (1:9) for styrene and cyclohexanone were 1.5 and 2.5 ppm, respectively. These are among the lowest reported levels for MOF-based sensors, and this is the first known material for fluorescence sensing of cyclohexanone. Fluorescence quenching by styrene was mainly owing to the large electronegativity of styrene and fluorescence resonance energy transfer (FRET). However, FRET was accounted for fluorescence quenching by cyclohexanone. Moreover, Eu/Zr-UiO-66 (1:9) exhibited good anti-interference ability and recycling performance for styrene and cyclohexanone. More importantly, the visual recognition of styrene and EB vapor can be directly realized with the naked eyes using Eu/Zr-UiO-66 (1:9) test strips. This strategy provides a sensitive, selective, and reliable method for the visual sensing of styrene and cyclohexanone.

Multifunctional Cd-CP for fluorescence sensing of Cr(VI), MnO4-, acetylacetone and ascorbic acid in aqueous solutions

The development of multifunctional fluorescent chemosensors for the detection of multiple targets remains challenging but of great importance. In this paper, one novel coordination polymer (CP), denoted as [Cd₂(edda)(phen)₂]∙H₂O (compound 1, H₄edda = 5,5' (ethane-1,2-diylbis(oxy)) diisophthalic acid, phen = 1,10-phenanthroline) is successfully designed and prepared under hydrothermal conditions. Structural analysis indicates that compound 1 possesses a one-dimensional (1D) double chain structure, then self-assembles into a three-dimensional (3D) supramolecular framework via π…π interactions between phen molecules. Interestingly, compound 1 is found to be tolerant in wide range of acidic to alkaline aqueous solutions (pH = 2-13). Fluorescent spectral investigations reveal that compound 1 exhibits highly selective and sensitive fluorescence responses toward MnO₄^-, Cr(VI) ions, acetylacetone (acac) and ascorbic acid (AA) by fluorescence quenching in the aqueous phase. The detection limits are in the very low range, reaching μM level for the detection of MnO₄^-, Cr(VI) ions, nM for AA and ppm for acac detection. The distinguished multi-responsive performance suggests compound 1 to be a potential multifunctional probe. Furthermore, the possible quenching mechanisms have also been systematically investigated in this work.

Ratiometric Luminescent Thermometer Based on the Lanthanide Metal-Organic Frameworks by Thermal Curing

The high-performance optical thermometer probes are of great significance in diverse areas; lanthanide metal-organic frameworks (Ln-MOFs) are a promising candidate for luminescence temperature sensing owing to their unique luminescence properties. However, Ln-MOFs have poor maneuverability and stability in complex environments due to the crystallization properties, which then hinder their application scope. In this work, the Tb-MOFs@TGIC composite was successfully prepared using simple covalent crosslinking through uncoordinated -NH₂ or COOH on Tb-MOFs reacting with the epoxy groups on TGIC {Tb-MOFs = [Tb₂(atpt)₃(phen)₂(H₂O)]_n; H₂atpt = 2-aminoterephthalic acid; phen = 1,10-phenanthroline monohydrate}. After curing, the fluorescence properties, quantum yield, lifetime, and thermal stability of Tb-MOFs@TGIC were remarkably enhanced. Meanwhile, the obtained Tb-MOFs@TGIC composites exhibit excellent temperature sensing properties in the low-temperature (S_r = 6.17% K^-1 at 237 K), physiological temperature (S_r = 4.86% K^-1 at 323 K), or high-temperature range (S_r = 3.88% K^-1 at 393 K) with high sensitivity. In the temperature sensing process, the sensing mode of single emission changed into double emission for ratiometric thermometry owing to the back energy transfer (BenT) from Tb-MOFs to TGIC linkers, and the BenT process enhanced with the increase of temperature, which further improved the accuracy and sensitivity of temperature sensing. Most notably, the temperature-sensing Tb-MOFs@TGIC can be easily coated on the surface of polyimide (PI), glass plate, silicon pellet (SI), and poly(tetrafluoroethylene) plate (PTFE) substrates by a simple spraying method, which also exhibited an excellent sensing property, making it applicable for a wider T range measurement. This is the first example of a postsynthetic Ln-MOF hybrid thermometer operative over a wide temperature range including the physiological and high temperature based on back energy transfer.

Tunable Photoinduced Charge Transfer at the Interface between Benzoselenadiazole-Based MOF Linkers and Thermally Activated Delayed Fluorescence Chromophore

Structural modifications to molecular systems that lead to the control of photon emission processes at the interfaces between photoactive materials play a key role in the development of fluorescence sensors, X-ray imaging scintillators, and organic light-emitting diodes (OLEDs). In this work, two donor-acceptor systems were used to explore and reveal the effects of slight changes in chemical structure on interfacial excited-state transfer processes. A thermally activated delayed fluorescence (TADF) molecule was chosen as the molecular acceptor. Meanwhile, two benzoselenadiazole-core MOF linker precursors, Ac-SDZ and SDZ, with the presence and absence of a C≡C bridge, respectively, were carefully chosen as energy and/or electron-donor moieties. We found that the SDZ -TADF donor-acceptor system exhibited efficient energy transfer, as evidenced by steady-state and time-resolved laser spectroscopy. Furthermore, our results demonstrated that the Ac-SDZ-TADF system exhibited both interfacial energy and electron transfer processes. Femtosecond-mid-IR (fs-mid-IR) transient absorption measurements revealed that the electron transfer process takes place on the picosecond timescale. Time-dependent density functional theory (TD-DFT) calculations confirmed that photoinduced electron transfer occurred in this system and demonstrated that it takes place from C≡C in Ac-SDZ to the central unit of the TADF molecule. This work provides a straightforward way to modulate and tune excited-state energy/charge transfer processes at donor-acceptor interfaces.

Charge transfer in metal-organic frameworks

Metal-organic frameworks (MOFs, also known as porous coordination polymers or PCPs) are a novel class of crystalline porous material. The tailorable porous structure, in terms of size, geometry and function, has attracted the attention of researchers across all disciplines of materials science. One of the many exciting aspects of MOFs is that through directional and reversible coordination bonding, organic linkers (chromophores with metal-coordinating functional groups) and metal ions (and clusters) can be spatially organized in a preconceived geometry. The well-defined spatial geometry of the metals and linkers is very advantageous for optoelectronic functions (solar cells, light-emitting diodes, photocatalysts) of the materials. This feature article evaluates the scope of charge transfer (CT) interactions in MOFs, involving the organic linkers and metal ion or cluster components. Irrespective of the type (size, shape, electronic property) of organic chromophores involved, MOFs provide an insightful path to design and make the CT process efficient. The selected examples of MOFs with CT characteristics do not only illustrate the design principles but render a pathway towards understanding the complex photophysical processes and implementing those for future optoelectronic and catalytic applications.