Truxene-to-Fluorenone Energy Transfer in a Robust Mesoporous Zn-MOF

A new metal-organic framework (MOF; [Zn4O(hett)4/3(fluo)1/2(bdc)1/2]n; TFT-MOF) constructed on chromophoric ligands 5,5',10,10',15,15'-hexaethyltruxene-2,7,12-triacetate (hett), 9-fluorenone-2,7-dicarboxylate (fluo), terephthalate (bdc), and the Zn4O node has been prepared and identified by powder X-ray diffraction. This luminescent MOF exhibits large mesoporous pores of 2.7 nm based on computer modeling using density functional theory (DFT) calculations. The steady-state and time-resolved fluorescence spectra and photophysical parameters of TFT-MOF have been investigated and compared with those of the free ligands and their basic chromophores. All in all, TFT-MOF exhibits particularly efficient singlet-singlet energy-transfer processes described as 1(hett)* → (fluo) and 1(bdc)* → (fluo), leading to fluorescence arising for the fluo lumophore operating only through Förster resonance energy transfer (FRET) with an efficiency of transfer of up to >95%. This experimental conclusion was corroborated by DFT and time-dependent DFT (TDDFT). For the 1(hett)* → (fluo) process, the approximated overall rate constant of energy transfer was evaluated to be at most 2.04 × 1010 s-1 (using a Stern-Volmer approach of solution data and the relationship between distance and concentration). This process was analyzed using the Förster theory, where two intrapore energy transfer paths of center-to-center distances of 13 and 25 Å have been identified. TFT-MOF photosensitizes the formation of singlet oxygen (1O2 (1Σg)) as detected by its phosphorescence signal at 1275 nm.

Luminescent Metal-Organic Framework for the Selective Detection of Aldehydes

The detection of toxic, hazardous chemical species is an important task because they pose serious risks to either the environment or human health. Luminescent metal-organic frameworks (LMOFs) as alternative sensors offer rapid and sensitive detection of chemical species. Interactions between chemical species and LMOFs result in changes in the photoluminescence (PL) profile of the LMOFs which can be readily detected using a simple fluorometer. Herein, we report the use of a robust, Zn-based LMOF, [Zn5(μ3-OH)2(adtb)2(H2O)5·5 DMA] (Zn-adtb, LMOF-341), for the selective detection of benzaldehyde. Upon exposure to benzaldehyde, Zn-adtb experiences significant luminescent quenching, as characterized through PL experiments. Photoluminescent titration experiments reveal that LMOF-341 has a detection limit of 64 ppm and a Ksv value of 179 M-1 for benzaldehyde. Furthermore, we study the guest-host interactions that occur between LMOF-341 and benzaldehyde through in situ Fourier transform infrared and computational modeling employing density functional theory. The results show that benzaldehyde interacts more strongly with LMOF-341 compared to formaldehyde and propionaldehyde. Our combined studies also reveal that the mechanism of luminescence quenching originates from an electron-transfer process.

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.

A Ni-MOF as Fluorescent/Electrochemical Dual Probe for Ultrasensitive Detection of Picric Acid from Aqueous Media

A water-stable, microporous, luminescent Ni(II)-based metal-organic framework (MOF) (Ni-OBA-Bpy-18) with a 4-c uninodal sql topology was solvothermally synthesized using mixed N-, O-donor-directed π-conjugated co-ligands. The extraordinary performance of this MOF toward rapid monitoring of mutagenic explosive trinitrophenol (TNP) in aqueous and vapor phases by the fluorescence "Turn-off" technique with an ultralow detection limit of 66.43 ppb (K_sv: 3.45 × 10⁵ M^-1) was governed by a synchronous occurrence of photoinduced electron transfer-resonance energy transfer-intermolecular charge transfer (PET-RET-ICT) and non-covalent π···π weak interactions, as revealed from density functional theory studies. The recyclable nature of the MOF, detection from complex environmental matrices, and fabrication of a handy MOF@cotton-swab detection kit certainly escalated the on-field viability of the probe. Interestingly, the presence of electron-withdrawing TNP decisively facilitated the redox events of the reversible Ni^III/II and Ni^IV/III couples under an applied voltage based on which electrochemical recognition of TNP was realized by the Ni-OBA-Bpy-18 MOF/glassy carbon electrode, with an excellent detection limit of ∼0.6 ppm. Such detection of a specific analyte by MOF-based probe via two divergent yet coherent techniques is unprecedented and yet to be explored in relevant literature.

An ultralow concentration of Al-MOFs for turn-on fluorescence detection of aflatoxin B1 in tea samples

A turn-on fluorescent sensing platform based on an ultralow concentration of Al-metal organic frameworks for the detection of aflatoxin B₁ has been developed for the first time. This fluorescence turn-on sensor exhibits the largest fluorescence enhancement (or quenching) constant value of 179404 M^-1 among all luminescence-based chemical sensors reported till date. Moreover, the sensor afforded a rapid detection of aflatoxin B₁, with a linear response in the concentration range of 0.05-9.61 μM and a low detection limit of 11.67 ppb. Additionally, the fabricated sensor showed good repeatability, reproducibility, stability, and selectivity. Most importantly, the practical application of this sensor has been demonstrated by detecting aflatoxin B₁ in complex tea samples with low relative standard deviation (≤7.72%; n = 3) and satisfactory recoveries. In summary, the proposed method has great potential as a simple, sensitive and selective strategy for monitoring aflatoxin B₁ in food samples.

Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility

An octa-nuclear zinc (Zn₈) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆]·7DMF (denoted as Zn8-as; H₂FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H₂FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆] (Zn8-de). Zn8-de displays gated adsorption for C₂H₂ and type-I adsorption for CO₂, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.

Unearth the Luminescence Potential of Metal-Organic Frameworks: Adopting a Feasible Strategy to Fabricate One Ratiometric Fluorescence Sensor for Monitoring Both 1-Hydroxypyrene and Cu2

In this work, a novel luminescent hybrid material with double emission centers (Eu(TTA)_0.2@9-1-UMOF) is successfully prepared, adopting a feasible design strategy. Initially, the second ligand 1,2,4-benzenetricarboxylic acid (H₃BTC) is encapsulated based on a solid solution approach, which effectively improves the ligand-based emission intensity of the original LMOF and provides functional sites for introducing the second luminescent center; then, Eu³⁺ as the red emission source is loaded into the frameworks through a coordination post-synthetic modification method; finally, to balance the emission intensity at 613 nm (Eu³⁺) and 465 nm (1,4-naphthalenedicarboxylic acid (H₂NDC)), 2-thenoyltrifluoroacetone (TTA) as a powerful antenna is introduced. Given the outstanding luminescence properties and structural stability of Eu(TTA)_0.2@9-1-UMOF, it is further developed as a ratiometric sensor for detecting 1-hydroxypyrene (1-HP, the biomarker of polycyclic aromatic hydrocarbons (PAHs)) and Cu²⁺, which promotes the pre-diagnosis of human health. Notably, Eu(TTA)_0.2@9-1-UMOF exhibits excellent selective recognition ability for both 1-HP and Cu²⁺ with high sensitivity (LOD = 4.06 × 10^-6 mg/mL, 3.85 × 10^-7 mol/L, respectively) and fast response speed. In addition, Eu(TTA)_0.2@9-1-UMOF as a fluorescent probe shows great potential for the determination of 1-HP and Cu²⁺ in actual samples. More importantly, this work widens the road for the development of dual/multiple LMOF-based sensors for analytical applications.

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

A europium-based CP fluorescent sensor was synthesized and exhibited excellent recognition ability for malachite green (MG) and metal cations (Cr3+, Fe3+ and Cu2+).

Flexible Chemiresistive Cyclohexanone Sensors Based on Single-Walled Carbon Nanotube-Polymer Composites

We report a chemiresistive cyclohexanone sensor on a flexible substrate based on single-walled carbon nanotubes (SWCNTs) functionalized with thiourea (TU) derivatives. A wrapper polymer containing both 4-vinylpyridine (4VP) groups and azide groups (P(4VP-VBAz)) was employed to obtain a homogeneous SWCNT dispersion via noncovalent functionalization of SWCNTs. The P(4VP-VBAz)-SWCNT composite dispersion was then spray-coated onto an organosilanized flexible poly(ethylene terephthalate) (PET) film to achieve immobilizing quaternization between the pyridyl groups from the polymer and the functional PET substrate, thereby surface anchoring SWCNTs. Subsequent surface functionalization was performed to incorporate a TU selector into the composites, resulting in P(Q4VP-VBTU)-SWCNT, for the detection of cyclohexanone via hydrogen bonding interactions. An increase in conductance was observed as a result of the hydrogen-bonded complex with cyclohexanone resulting in a higher hole density and/or mobility in SWCNTs. As a result, a sensor device fabricated with P(Q4VP-VBTU)-SWCNT composites exhibited chemiresistive responses (ΔG/G₀) of 7.9 ± 0.6% in N₂ (RH 0.1%) and 4.7 ± 0.4% in air (RH 5%), respectively, upon exposure to 200 ppm cyclohexanone. Selective cyclohexanone detection was achieved with minor responses (ΔG/G₀ < 1.4% at 500 ppm) toward interfering volatile organic compounds (VOC). analytes. We demonstrate a robust sensing platform using the polymer-SWCNT composites on a flexible PET substrate for potential application in wearable sensors.

Tuning Chromophore-Based LMOF Dimensionality to Enhance Detection Sensitivity for Fe3+ Ions

Herein, we report the synthesis of two new manganese-based luminescent metal-organic frameworks (LMOFs) [Mn_0.5(tipe)(1,4-ndc)] _n (1) and [Mn(tipe)(1,4-ndc) (H₂O)·(DMF)₂·(H₂O)₃] _n (2) [tipe = 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethene (tipe) and 1,4-ndc = 1,4-naphthalenedicarboxylic acid] constructed from an aggregation-induced emission (AIE) chromophore ligand. Compound 1 can undergo a facile single-crystal-to-single-crystal transformation to form compound 2, which results in an increase in dimensionality from a two-dimensional (2D) network to a three-dimensional (3D) network. Both compounds demonstrate excellent performance for the solution-phase detection of Fe³⁺ ions through a significant and rapid quench in luminescence emission. Fluorescence titration experiments reveal that compound 2 is more selective toward Fe³⁺ compared to compound 1 because of its 3D stacking mode. The K _sv value for compound 2 (32 378 M^-1) is twice as large as that for compound 1 (15 854 M^-1) for the detection of Fe³⁺ ions. We attribute this significant increase in performance to the increase in dimensionality. In addition, compound 2 demonstrates high selectivity and sensitivity for the detection of Cr³⁺ cations and Cr₂O₇ ^2- anions.

Fluorescent Detection of Carbon Disulfide by a Highly Emissive and Robust Isoreticular Series of Zr-Based Luminescent Metal Organic Frameworks (LMOFs)

Carbon disulfide (CS2) is a highly volatile neurotoxic species. It is known to cause atherosclerosis and coronary artery disease and contributes significantly to sulfur-based pollutants. Therefore, effective detection and capture of carbon disulfide represents an important aspect of research efforts for the protection of human and environmental health. In this study, we report the synthesis and characterization of two strongly luminescent and robust isoreticular metal organic frameworks (MOFs) Zr6(µ3-O)4(OH)8(tcbpe)2(H2O)4 (here termed 1) and Zr6(µ3-O)4(OH)8(tcbpe-f)2(H2O)4 (here termed 2) and their use as fluorescent sensors for the detection of carbon disulfide. Both MOFs demonstrate a calorimetric bathochromic shift in the optical bandgap and strong luminescence quenching upon exposure to carbon disulfide. The interactions between carbon disulfide and the frameworks are analyzed by in-situ infrared spectroscopy and computational modelling by density functional theory. These results reveal that both the Zr metal node and organic ligand act as the preferential binding sites and interact strongly with carbon disulfide.

Conformational isomerism involving the carboxylate groups of a linker in metal organic frameworks and its distinctive influence on the detection of ketones

Selective sensing of various ketones by Zn(ii) based conformational MOF isomers.

Enhanced Visible and Ultraviolet Light-Induced Gas-Phase Photocatalytic Activity of TiO2 Thin Films Modified by Increased Amount of Acetylacetone in Precursor Solution for Spray Pyrolysis

TiO2 thin films, modified by acetylacetone (AcacH) in solution, were deposited on glass substrate by ultrasonic spray pyrolysis and tested for photocatalytic activity in a multi-section continuous flow reactor by degradation of acetone and acetaldehyde under ultraviolet and visible light. The increase in molar ratio of AcacH in respect of titanium (IV) isopropoxide (TTIP) from 1:5 to 1:8 modified the electronic structure of the films, favoring enhanced photocatalytic activity. The photocatalytic activity was enhanced approximately twofold on the film with molar ratio 1:8 under both irradiations; the film completely oxidized 10 ppm of acetone and acetaldehyde. The photocatalytic efficacy of TiO2 films in oxidation of air pollutants was three times higher compared to the industrial glass Pilkington ActivTM. Moreover, all the synthesized films indicate antibacterial efficiency against E. coli of over 99% under ultraviolet. TiO2 film, with TTIP:AcacH molar ratio 1:8 having great possibility for its commercial use as a material for indoor air purification.

Augmenting the Carbon Dioxide Uptake and Selectivity of Metal-Organic Frameworks by Metal Substitution: Molecular Simulations of LMOF-202

Metal organic frameworks (MOFs) are promising porous materials for the adsorption of CO_2. Here, we report the study of a luminescent MOF (LMOF), called LMOF-202. We have employed Grand Canonical Monte Carlo (GCMC) simulations to understand and explain the adsorption phenomena inside LMOF-202, and based on the phenomena happening at the molecular level, we have varied the metal ions in LMOF-202 to increase the CO₂ affinity and selectivity of the material. We show that the CO₂ adsorption capacity and selectivity can be increased by approximately 1.5 times at 1 bar and 298 K by changing the metal ion from Zn to Ba. We also report the feasibility of using this material to capture CO₂ from flue gas under realistic conditions (1 bar and 298 K). This work shows that LMOF-202 merits further consideration as a carbon capture adsorbent.

A Europium-based MOF Fluorescent Probe for Efficiently Detecting Malachite Green and Uric Acid

Lanthanide (such as Tb and Eu) metal-organic frameworks (MOFs) have been widely used in fluorescent probes because of their multiple coordination modes and brilliant fluorescence characteristic. Many lanthanide MOFs were applied in detecting metal ions, inorganic anions, and small molecules. However, it's rarely reported that Ln-MOF was devoted to detecting malachite green (MG) and uric acid (UA). We prepared a europium-based metal-organic framework (Eu-TDA) (TDA = 2,5-thiophenedicarboxylic acid group). Luminescence studies demonstrated that Eu-TDA can rapidly detect MG and UA with excellent selectivity and sensitivity, where individual quenching efficiency K_sv (MG: 5.8 × 10⁵ M^-1; UA: 4.15 × 10⁴ M^-1) and detection limit (MG: 0.0221 μM; UA: 0.689 μM) were regarded as the excellent MOF sensors for detecting MG and UA. The quenching of Eu-TDA's fluorescence emission by MG and UA was likely due to the spectral overlap, energy transfer, and competition. Among 11 metal cations and 14 anions, Eu-TDA can quickly and effectively recognize MG and UA with highly selective and sensitive properties. Our method possesses potential application in detecting UA in human blood and MG in the fishpond.

Sensing organic analytes by metal–organic frameworks: a new way of considering the topic

In this review, our goal is comparison of advantageous and disadvantageous of MOFs about signal-transduction in different instrumental methods for detection of different categories of organic analytes.

Fluorescent nanosensor forin situdetection of phosphate and alkaline phosphatase in mice with parathyroid dysfunction

A composite nanosensor based on Zr(iv)-MOFs and PNPP was developed, which successfully applied for thein situfluorescence imaging of phosphate and ALP levels in mice with parathyroid dysfunction.

Aqueous-phase detection of antibiotics and nitroaromatic explosives by an alkali-resistant Zn-MOF directed by an ionic liquid

An alkali-resistant 3D anionic Zn-MOF directed by [BMI]Br ionic liquid has been synthesized for aqueous-phase detection of antibiotics and nitroaromatic explosives.

Fluorescent "Turn-on" Sensing Based on Metal-Organic Frameworks (MOFs)

Metal-organic frameworks (MOFs) have evolved as an exciting class of materials in the domain of porous materials. The unique features of these materials arise from the combined properties of metal ions/clusters and organic struts which form the building blocks of these fascinating architectures. Among other multifarious applications, MOFs have shown tremendous applications as sensory materials for a wide variety of species. The signal transduction induced mechanism in these confined nanospaces generate optical output in response to a particular analyte which can be detected by wide variety of detection techniques. Fluorometric methods of sensing is one of widely studied method over past few decades. MOF-based fluorometric detection is a key research theme developed over the past few years. In this review, we give a brief overview of the recent developments of MOFs as "turn-on" sensors for a wide range of analytes (viz. cations, anions, volatile organic compounds (VOCs), etc.).

A robust two-dimensional zirconium-based luminescent coordination polymer built on a V-shaped dicarboxylate ligand for vapor phase sensing of volatile organic compounds

We report herein a new two-dimensional zirconium-based luminescent coordination polymer exhibiting selective fluorescence responses towards a variety of volatile organic compounds upon exposure in the vapor phase.

A pyrene-involved luminescent MOF for monitoring 1-hydroxypyrene, a biomarker for human intoxication of PAH carcinogens

A robust pyrene-involved MOF is developed as a luminescent platform for sensitive detection of 1-hydroxypyrene, a human intoxication biomarker of PAH carcinogens, by utilizing the efficient host–guest π–π charge transfer interactions.

Photonic functional metal–organic frameworks

The recent progress in photonic MOFs for luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, and biomedicine is summarized.

The role of structure and the metal ion in the fluorescence sensing of nitro compounds for a series of lanthanide(iii) 9,10-anthracene dicarboxylate coordination polymers

Of the 9 nitro compounds tested for their efficiency to quench the photoluminescence of 28 lanthanide coordination polymers (CPs) containing 9,10-anthracene dicarboxylate (ADC), Brady's reagent was found to be the best.

Rational synthesis of a luminescent uncommon (3,4,6)-c connected Zn(ii) MOF: a dual channel sensor for the detection of nitroaromatics and ferric ions

A 3D (3,4,6)-c connected net constructed using a rigid tetracarboxylate ligand and sensing studies to detect nitroaromatics and ferric ion performed.

1-Hydroxypyrene-based micelle-forming sensors for the visual detection of RDX/TNG/PETN-based bomb plots in water

New micelle-forming fluorescence molecular sensors are reported based on 1-hydroxypyrene designed exclusively for the detection of nitro-aliphatic explosives/taggants.

Tuning the flexibility of interpenetrated frameworks by a small difference in the fluorene moiety

[Zn₂(FDC)₂(bpy)] (LMOF-202) and [Zn₂(OFDC)₂(bpy)] (LMOF-201) (FDC: fluorene-2,7-dicarboxylate, OFDC: 9-fluorenone-2,7-dicarboxylate, bpy: 4,4'-bipyridine) have interpenetrated isostructures. However, their gas sorption behaviors indicate that LMOF-202 is rigid, whereas LMOF-201 is flexible. We found that the structural flexibility of LMOF-201 was due to the addition of only one oxygen atom into the ligand.

Mixed-Ligand LMOF Fluorosensors for Detection of Cr(VI) Oxyanions and Fe3+/Pd2+ Cations in Aqueous Media

Zn(II)/Cd(II)-based dual ligand Luminescent Metal-Organic Frameworks (LMOFs) {[M(ATA)(L)]}_n·xH₂O (1) and (2) were synthesized by versatile synthetic routes, viz., diffusion of precursor solutions, conventional reflux, and green mechanochemical (grinding) reactions from bipyridyl-based Schiff base, (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and amino functionalized 2-aminoterephthalic acid (H₂ATA) as linkers. Chemical and thermal stability, phase purity, and characterization of both LMOFs were established by various analytical methods. SXRD analysis revealed the 3D framework is composed of two-dimensional [M(ATA)]_n nets doubly pillared by L through the terminal nitrogen atom. Selective and sensitive detection of chromate anions (CrO₄^2-/Cr₂O₇^2-) and Fe³⁺/Pd²⁺ cations in the aqueous phase by fluorescent quenching of the LMOFs 1 and 2 has been established. Competitive experiments in the presence of interfering anions/cations with 1 and 2 revealed no major change in the quenching efficiency. The observed limits of detection (LOD) values by 1 for CrO₄^2-/Cr₂O₇^2- were 0.25 μM (48 ppb)/0.43 μM (126 ppb) and for Fe³⁺/Pd²⁺ were 3.76 μM (0.61 ppm)/0.20 μM (35 ppb), whereas LOD values by 2 were 0.18 μM (35 ppb)/0.19 μM (55 ppb) and 1.77 μM (0.29 ppm)/0.10 μM (18 ppb), respectively. Simple fluorescent-based test paper strips have been developed for reliable and visual detection of the mentioned analytes in practical applications. The present investigation clearly demonstrates selective detection of CrO₄^2-/Cr₂O₇^2- and Fe³⁺/Pd²⁺ in aqueous media, and the probable mechanism for the quenching phenomena based on structural aspects has also been discussed.

Ultrafast water sensing and thermal imaging by a metal-organic framework with switchable luminescence

A convenient, fast and selective water analysis method is highly desirable in industrial and detection processes. Here a robust microporous Zn-MOF (metal-organic framework, Zn(hpi2cf)(DMF)(H2O)) is assembled from a dual-emissive H2hpi2cf (5-(2-(5-fluoro-2-hydroxyphenyl)-4,5-bis(4-fluorophenyl)-1H-imidazol-1-yl)isophthalic acid) ligand that exhibits characteristic excited state intramolecular proton transfer (ESIPT). This Zn-MOF contains amphipathic micropores (<3 Å) and undergoes extremely facile single-crystal-to-single-crystal transformation driven by reversible removal/uptake of coordinating water molecules simply stimulated by dry gas blowing or gentle heating at 70 °C, manifesting an excellent example of dynamic reversible coordination behaviour. The interconversion between the hydrated and dehydrated phases can turn the ligand ESIPT process on or off, resulting in sensitive two-colour photoluminescence switching over cycles. Therefore, this Zn-MOF represents an excellent PL water-sensing material, showing a fast (on the order of seconds) and highly selective response to water on a molecular level. Furthermore, paper or in situ grown ZnO-based sensing films have been fabricated and applied in humidity sensing (RH<1%), detection of traces of water (<0.05% v/v) in various organic solvents, thermal imaging and as a thermometer.

Base-driven sunlight oxidation of silver nanoprisms for label-free visual colorimetric detection of hexahydro-1,3,5-trinitro-1,3,5-triazine explosive

Here we report a label-free method for visual colorimetric detection of hexahydro-1,3,5-trinitro-1,3,5-triazine (HTT) explosive based on base-driven sunlight oxidation of silver nanoprisms (AgNPRs). Under natural sunlight illumination, the surface plasmon of AgNPRs is excited, which populates O₂ antibonding orbitals to generate negative-ion state (O₂^-). The resultant O₂^- with a strong oxidation activity can etch AgNPRs to smaller nanodisks with the aid of NaOH aqueous solution, leading to a blue shift of the absorption peak and color change from blue to pink. However, when HTT is introduced, the resultant O₂^- will be consumed by the nitrite and formaldehyde that are produced from the alkaline hydrolysis of HTT. Under this condition, the etching of AgNPRs does not occur, and the detection solution remains blue. This assay can sensitively detect as low as 1nM HTT, a level which is three orders of magnitude lower than that of gold nanoparticle-based colorimetric assays (2.6μM), and shows linearity in the range of 0.003-3.3μM. The lowest detectable concentration with the naked eye is 0.1μM. Additionally, the present assay exhibits good selectivity, and can be applied in the detection of HTT in natural water and soil samples with recoveries ranging from 90% to 100%.