A ratiometric fluorescence platform based on boric-acid-functional Eu-MOF for sensitive detection of H2O2 and glucose

Ratiometric fluorescence sensor based on deep learning for rapid and user-friendly detection of tetracycline antibiotics

The detection of tetracycline antibiotics (TCs) in food holds great significance in minimizing their absorption within the human body. Hence, this study aims to develop a rapid, convenient, real-time, and accurate detection method for detecting antibiotics in an authentic market setting. A colorimetric fluorescence sensor was devised for tetracycline detection utilizing PVA aerogels as the substrate. Its operating principle is based on the IFE effect and antenna effect. A detection device is designed to capture fluorescence images while deep learning was employed to aid in the detection process. The sensor exhibits high responsiveness with a mere 60-s requirement for detection and demonstrates substantial color changes(blue to red), achieving 99% accuracy within the range of 10-100 μM with the assistance of deep learning (Resnet18). Real sample simulation tests yielded recovery rates between 95% and 130%. Overall, the proposed strategy proved to be a simple, portable, reliable, and responsive solution for rapid real-time TCs detection in food samples.

Semiconducting polymer dots based l-lactate sensor by enzymatic cascade reaction system

BACKGROUND

l-lactate detection is important for not only assessing exercise intensity, optimizing training regimens, and identifying the lactate threshold in athletes, but also for diagnosing conditions like L-lactateosis, monitoring tissue hypoxia, and guiding critical care decisions. Moreover, l-lactate has been utilized as a biomarker to represent the state of human health. However, the sensitivity of the present l-lactate detection technique is inadequate.

RESULTS

Here, we reported a sensitive ratiometric fluorescent probe for l-lactate detection based on platinum octaethylporphyrin (PtOEP) doped semiconducting polymer dots (Pdots-Pt) with enzymatic cascade reaction. With the help of an enzyme cascade reaction, the l-lactate was continuously oxidized to pyruvic and then reduced back to l-lactate for the next cycle. During this process, oxygen and NADH were continuously consumed, which increased the red fluorescence of Pdots-Pt that responded to the changes of oxygen concentration and decreased the blue fluorescence of NADH at the same time. By comparing the fluorescence intensities at these two different wavelengths, the concentration of l-lactate was accurately measured. With the optimal conditions, the probes showed two linear detection ranges from 0.5 nM to 5.0 μM and 5.0 μM-50.0 μM for l-lactate detection. The limit of detection was calculated to be 0.18 nM by 3σ/slope method. Finally, the method shows good detection performance of l-lactate in both bovine serum and artificial serum samples, indicating its potential usage for the selective analysis of l-lactate for health monitoring and disease diagnosis.

SIGNIFICANCE

The successful application of the sensing system in the complex biological sample (bovine serum and artificial serum samples) demonstrated that this method could be used for sensitive l-lactate detection in practical clinical applications. This detection system provided an extremely low detection limit, which was several orders of magnitude lower than methods proposed in other literatures.

Dual-ligand lanthanide metal-organic framework based ratiometric fluorescent platform for visual monitoring of aminoglycoside residues in food samples

Herein, a dual-emission Eu metal-organic framework (Eu-MOF) is prepared and used as the ratiometric fluorescence probe for ultrasensitive detection of aminoglycoside antibiotics (AGs). Due to the strong hydrogen bond interactions between AGs and Eu-MOF, the blue emission is enhanced while the red emission has little fluctuation in Eu-MOF with the addition of AGs, thus a good linear relationship with the logarithm of AGs concentrations from 0.001 to 100 μg/mL can be established for quantitative analysis. Good sensitivity with the detection limit of 0.33 ng/mL for apramycin, 0.32 ng/mL for amikacin and 0.30 ng/mL for kanamycin is achieved. The proposed assay demonstrates good selectivity and applicability for determination of AGs in real milk and honey samples. The Eu-MOF materials are further fabricated as fluorescent test papers for facile visual detection. The as-established ratio fluorescence platform offers a portable and economical way for rapid monitoring AGs residues in complex food samples.

Dual-source signal amplification electrochemiluminescence sensor combined with molecularly imprinted polymers for the imidacloprid detection

A novel lanthanide metal-organic-gel (MOG)-derived material/nitrogen-doped graphdiyne (Tb-Ru-MOG/CeO2/N-GDY) composite with a dual-source signal amplification strategy was prepared and used to construct a molecularly imprinted sensor based on bifunctional monomers for the detection of imidacloprid (IMI) using electrochemiluminescence (ECL). In a green reaction environment, terbium (III) (Tb3+) can undergo multiple coordination reactions with 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine (Hcptpy) and tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium (II) dichloride (Ru(dcbpy)32+), and combine with ceria nanoparticles (CeO2 NPs) to form Tb-Ru-MOG/CeO2. Within the Tb-Ru-MOG/CeO2 framework, energy transfer from the double ligands can sensitize the central Tb3+, triggering a distinct antenna effect and energy-transfer, and its polyporous configuration offered a nanoconfined space for Ce3+/Ce4+ to effectively catalyze coreactant radicals (S2O82-), leading to in-situ endogenous activation ECL reactions. The conductive N-GDY accelerated electron movement and increased the loading on the electrode surface, enhancing the exogenous excitation of the ECL signals. Leveraging the synergistic effect of the bifunctional monomer, the synthesized molecularly imprinted polymers (MIPs) ECL sensor demonstrated a wide detection range from 10 nM to 10,000 nM for IMI, with a limit of detection (LOD) of 1.37 nM, showcasing an innovative concept for the dual-source strategy of signal amplification in integrated ECL composites to analyze food and environmental hazards.

A ratiometric fluorescence imprinted sensor based on N-CDs and metal-organic frameworks for visual smart detection of malathion

Sensitive and rapid detection of pesticide residues in food is essential for human safety. A ratiometric imprinted fluorescence sensor N-CDs@Eu-MOF@MIP (BR@MIP) was constructed to sensitively detect malathion (Mal). Europium-based metal organic frameworks (Eu-MOF) were used as supporters to improve the sensitivity of the BR@MIP. N-doped carbon dots (N-CDs) were used as fluorescent source to produce fluorescent signal. A linear relationship between the concentration of Mal and the fluorescence response of the sensor was found in the Mal concentration range of 1-10 μM with a limit of detection (LOD) of 0.05 μM. Furthermore, the sensor was successfully applied for the detection of Mal in lettuce, tap water, and soil samples, with recoveries in the range of 93.0 % - 99.3 %. Additionally, smartphone-based sensors were used to detect Mal in simulated real samples. Thus, the construction of ratiometric imprinted fluorescence sensor has provided a good strategy for the detection of Mal.

Carbon dots with enhanced red emission for ratiometric sensing and encryption applications

The excitation-dependent emission properties of carbon dots (Cdots) are extensively reported, but their red emission is often weak, limiting their wider application. Here we introduce ethidium bromide, as a functional precursor with red emission, to enhance the red emission for Cdots, with comparable intensity at a broad wavelength range to multi-emission Cdots (M-Cdots). We found that Cdots prepared with ethidium bromide/ethylenediamine exhibited strong blue and red emission at 440 and 615 nm, with optimal excitation at 360 and 470 nm as M-Cdots, respectively, but the Cdots from single ethidium bromide (EB-Cdots) possessed weak red emission. M-Cdots exhibited a broad absorption band at 478 nm, but a band blue-shifted to 425 nm was observed for EB-Cdots, while no absorption was observed at 478-425 nm for the Cdots prepared with citric acid and ethylenediamine. Thus, we proposed that C=O and C=N formed a π-conjugation structure as the absorption band at 478 nm for the red emission of M-Cdots, as also confirmed with the excitation at 470 nm. Moreover, the π-conjugation structure is fragile and sensitive to harsh conditions, so red emission was difficult to observe for the Cdots prepared with citric acid/ethylenediamine or single ethidium bromide. M-Cdots possess two centers for blue and red emission with different structures. The dual emission was therefore used for ratiometric sensing with dichromate (Cr2O72-) and formaldehyde (HCHO) as the targets using the intensity ratio of the emissions at 615 and 440 nm. Due to the comparable intensity at a broad wavelength range, we designed encryption codes with five excitations at 360, 400, 420, 450, and 470 nm as the inputs, and the emission colors were used for information decoding. Thus, we determined why red emission was difficult to realize for Cdots, and our results could motivate the design of red-emission Cdots for extensive applications.

Ion imprinted differential modulation system based on enhanced optic-fiber evanescent wave for sensitive and label-free detection of trace nickel ions

An optical system with low cost monitoring, high sensitivity, strong selectivity and much lower nickel ion (Ni2+) content in tap water than the World Health Organization (WHO) standard (1.19 μM) has been prepared by a simple strategy. This proposed ion-imprinted differential modulation system is based on the Bragg grating (FBG) and microfiber interferometer structure, and the interferometer sensing surface is coated with a polydopamine (PDA)/graphene oxide (GO) film to enhance its sensitivity. Combined with the ion imprinting technique, the microfiber interferometer sensor sensitivity can reach 0.32 nm/nM with the detection limit of 0.66 nM in the low concentration range (Ni2+ concentration range is 0 nM-100 nM). The experiment not only studies the principle of microfiber interferometer and FBG and their refractive index and temperature performance, but also shows that the FBG power change has a good fitting relationship with wavelength change. In addition, this system performance by the amount of power difference rather than the amount of wavelength shift, which significantly saves on the high cost weight, and size associated with the use of spectral analyzers in traditional inspection systems. This study provides a novel and easy method to develop new sensors with higher comprehensive performance.

Ultrastable N-Type Semiconducting Fiber Organic Electrochemical Transistors for Highly Sensitive Biosensors

Organic electrochemical transistors (OECTs) have attracted increasing attention due to their merits of high transconductance, low operating voltage, and good biocompatibility, ideal for biosensors. However, further advances in their practical applications face challenges of low n-type performance and poor stability. Here, it is demonstrated that wet-spinning the commercially available n-type conjugated polymer poly(benzimidazobenzophenanthroline) (BBL) into highly aligned and crystalline fibers enhances both OECT performance and stability. Although BBL is only soluble in high-boiling-point strong acids, it can be wet-spun into high-quality fibers with adjustable diameters. The BBL fiber OECTs exhibit a record-high area-normalized transconductance (gm,A ) of 2.40 µS µm-2 and over 10 times higher figure-of-merit (µC*) than its thin-film counterparts. More importantly, these fiber OECTs exhibit remarkable stability with no noticeable performance attenuation after 1500 cycles over 4 h operation, outperforming all previously reported n-type OECTs. The superior performance and stability can be attributed to shorter π-π stacking distance and ordered molecular arrangement in the fibers, endowing the BBL fiber OECT-based biosensors with outstanding sensitivity while keeping a miniaturized form factor. This work demonstrates that, beyond new material development, developing new fabrication technology is also crucial for addressing the performance and stability issues in n-type OECTs.

Distinguishing the responsive mechanisms of fluorescent probes to hydrogen peroxide, proteins, and DNA/RNA

The responsive mechanisms of cationic quinolinium-vinyl-N,N-dimethylaniline boronate (QVD-B) derivative probes to hydrogen peroxide (H2O2), proteins and DNA/RNA are theoretically investigated in this study. The potential energy curves of QVD-B scanned on a dihedral angle (N+-C-CC) in the first singlet (S1) state exhibit large torsional energy barriers. Additionally, the energy of the lowest unoccupied molecular orbital (LUMO) of an acceptor moiety (-3.14 eV) is lower than that of a donor moiety (-1.13 eV) in QVD-B. This demonstrates that photoinduced electron transfer (PET) quenches the fluorescence of QVD-B, as opposed to the previous report of intramolecular single-bond rotation. After reacting with H2O2, the reaction product of quinoline-vinyl-N,N-dimethylaniline (QVD) turns off the PET pathway and turns on the fluorescence at 550 nm, which is consistent with the experimental results (580 nm). Among the possible configurations of QVD-B that forms with proteins and DNA, the calculated fluorescence values of corresponding twisted QVD-B-P (638 nm) and QVD-B-D (686 nm) are consistent with the experimental results (632 and 688 nm). The frontier molecular orbital and electron-hole analysis show that the charge transfer distance follows the order of QVD (1.88 Å) < QVD-B-P (4.49 Å) < QVD-B-D (6.39 Å), which induces the fluorescence red-shifts of QVD-B-P and QVD-B-D compared to that of QVD. The multi-detection mechanism of the fluorescent probe QVD-B is attributed to PET progress and different degrees of local charge transfer after photoexcitation.

Fabrication of Eu-MOFs rod-shaped nanospheres with dual emissions for ratiometric fluorescence detecting Hg2+ in water

The incorporation of novel nanostructure has been proven to significantly improve the performance of fluorescence-based sensors in terms of sensitivity, selectivity, and detection capability. Herein, a lanthanide metal-organic framework (BTC-Eu-BDC-NH2) with dual ligands of 2-aminobenzoic acid (BDC-NH2) and 1,3,5-benzene tricarboxylic acid (BTC) has been prepared for ratiometric fluorescent detection of Hg2+ through the rational one-step synthetic approach. Through adjusting the ratio of two ligands, this dual-ligands strategy not only provided two independent emissions at peaks of 435 nm and 615 nm to resist the influence of external conditions, but also introduced the visual detection with an obvious color change. Moreover, the specific rod-shaped nanospheres morphology substantially enlarged the surface area of BTC-Eu-BDC-NH2 to ensure good dispersion and rapid response during sensing. Upon the addition of Hg2+, the fluorescence at 435 nm of BTC-Eu-BDC-NH2 was obviously quenched because of the interaction between Hg2+ and -NH2 from the ligand, while the red fluorescence at 615 nm remains almost unchanged. As a result, the synthesized BTC-Eu-BDC-NH2 showed excellent performances for visual sensing detection of Hg2+ with a clear luminescent color conversion from blue to red, and the detecting range was 0-40 μM with a low detection limit of 67 nM. Finally, the developed sensor was applied to actual tap water, and a handy sensing kit was constructed by hydrogel with BTC-Eu-BDC-NH2, demonstrating its potential practical applications.

Determination of H2O2 and its antioxidant activity by BCM@Au NPs ratiometric SERS sensor

As a reactive oxygen species (ROS), excessive production of H2O2 contributes to the development of several diseases such as, inflammation, cancer, and respiratory diseases. Supplementation with endogenous or exogenous antioxidants can scavenge ROS and reduce the oxidation of cellular molecules, thus alleviating the generation of diseases. Therefore, the determination of H2O2 content and its antioxidant activity is of great importance in disease diagnosis and treatment. In this paper, a ratiometric SERS sensor with a flexible cellulose membrane was designed for quantitative detection of H2O2 and assessment of antioxidant activity. First, gold seeds were reduced on bacterial cellulose membrane (BCM) and Au NPs were smoothly deposited on the bacterial cellulose membrane (BCM) using halides to reduce the reduction potential in the growth solution to form a flexible BCM@Au NPs SERS substrate. Afterwards, the oxidation of H2O2 was used to convert 3-mercaptophenylboronic acid (3-MPBA) to the corresponding phenol form 3-hydroxyphenylethanol (3-HTP). The change of substance resulted in a good linear relationship between the intensity ratio corresponding to the two Raman shifts of 881 cm-1 and 995 cm-1 and the H2O2 concentration with a detection limit of 0.0186 μM. This opens up a new method for the detection of H2O2 with high sensitivity and accuracy. In addition, this SERS platform was successfully used for the determination of antioxidant activity. It is promising to be applied to disease diagnosis and efficacy evaluation.

A Recent Advancement in Food Quality Assessment: Using MOF-Based Sensors: Challenges and Future Aspects

Monitoring food safety is crucial and significantly impacts the ecosystem and human health. To adequately address food safety problems, a collaborative effort needed from government, industry, and consumers. Modern sensing technologies with outstanding performance are needed to meet the growing demands for quick and accurate food safety monitoring. Recently, emerging sensors for regulating food safety have been extensively explored. Along with the development in sensing technology, the metal-organic frameworks (MOF)-based sensors gained more attention due to their excellent sensing, catalytic, and adsorption properties. This review summarizes the current advancements and applications of MOFs-based sensors, including colorimetric, electrochemical, luminescent, surface-enhanced Raman scattering, and electrochemiluminescent sensors. and also focused on the applications of MOF-based sensors for the monitoring of toxins such as heavy metals, pesticide residues, mycotoxins, pathogens, and illegal food additives from food samples. Future trends, as well as current developments in MOF-based materials.

Boric Acid-Functionalized Carbon Dots as a High-Performance Antibacterial Agent against Escherichia coli

Bacterial infections and antibiotic abuse are a global threat to human health. In recent years, there has been a boom in research on antimicrobial agents with low toxicity and efficient nanomaterials. Boric acid-functionalized carbon dots (B-CDs) with negative surface charge were synthesized by the hydrothermal method. Covalent bonds were formed between the boric acid groups and the cis-diol groups of the polysaccharide in the bacterial cell wall, and numerous B-CDs were trapped on the bacterial surface. In the experiments of antibacterial activity, B-CDs presented strong bactericidal activity against Escherichia coli (E. coli) with a minimum bactericidal concentration of 12.5 μg/mL. The antibacterial mechanism suggested that B-CDs entered the cell interior by diffusion and posed significant damage to the double helix structure of E. coli DNA. Furthermore, B-CDs exhibited low toxicity. The results demonstrated that the novel antimicrobial B-CDs not only fought against E. coli infection and antibiotic misuse but also provided new ideas for safe and effective antimicrobial agents of carbon nanomaterials.

Quantification of Neuronal Cell-Released Hydrogen Peroxide Using 3D Mesoporous Copper-Enriched Prussian Blue Microcubes Nanozymes: A Colorimetric Approach in Real Time and Anticancer Effect

Despite the effectiveness and selectivity of natural enzymes, their instability has paved the way for developing nanozymes with high peroxidase activity using a straightforward technique, thereby expanding their potential for multifunctional applications. Herein, meso-copper-Prussian blue microcubes (Meso-Cu-PBMCs) nanozymes were successfully prepared via a cost-effective hydrothermal route. It was found that the Cu-PBMCs nanozymes, with three-dimensional (3D) mesoporous cubic morphologies, exhibited an excellent peroxidase-like property. Based on the high affinity of Meso-Cu-PBMCs toward H2O2 (Km = 0.226 μM) and TMB (Km = 0.407 mM), a colorimetric sensor for in situ H2O2 detection was constructed. On account of the high catalytic activity, affinity, and cascade strategy, the Meso-Cu-PBMCs nanozyme generated rapid multicolor displays at varying H2O2 concentrations. Under optimized conditions, the proposed sensor exhibits a preferable sensitivity of 18.14 μA μM-1, a linear range of 10 nM-25 mM, and a detection limit of 6.36 nM (S/N = 10). The reliability of the sensor was verified by detecting H2O2 in spiked human blood serum and milk samples, as well as by detecting in situ H2O2 generated from the neuron cell SH-SY5Y. Besides, the Meso-Cu-PBMCs nanozyme facilitated the catalysis of H2O2 in cancer cells, generating •OH radicals that induce the death of cancer cells (HCT-116 colon cancer cells), which holds substantial potential for application in chemodynamic therapy (CDT). This proposed strategy holds promise for simple, rapid, inexpensive, and effective intracellular biosensing and offers a novel approach to improve CDT efficacy.

A smartphone-based visual ratiometric fluoroprobe for rapid and sensitive detection hypochlorous acid based on dual-emission metal organic frameworks

Herein, we designed/developed a mixed fluorescence system with europium metal-organic framework (EDB) and zinc metal-organic framework (ZBNB). At the 270-nm excitation wavelength, the EDB-ZBNB dually emitted at 425 and 615 nm and displayed blue solution under 365-nm UV lamp. When HOCl was fortified, the 425-nm blue emission dropped progressively, while the 615-nm red emission was relatively stable. Upon addition of ClO-, the shortened fluorescence lifetime demonstrated that the quenched 425-nm fluorescence of ZBNB was owing to the occurrence of dynamic quenching effect. Besides, amino groups are protonated in water to form -NH3+, which interact with ClO- to form hydrogen bonds, reduce the distance between -NH3+ and ClO-, produce energy transfer and result in fluorescence quenching. The ratiometric fluoroprobe provided a significant color change from blue to red, making HOCl detection visual and rapid. This fluorescent probe overcome the disadvantage of conventional redox-based fluorescent probes that can be interfered by MnO4- and other oxidants with stronger oxidizing capacity than free ClO-. Furthermore, a smartphone-based portable sensing platform was developed based on EDB-ZBNB. By using a "Thingidentify" software on smartphone, the sensing platform was used to detect HOCl in waters with a low detection limit of 28.0 nM and the fortified recoveries of 98.87-103.60%. Thus, this study provides a novel and promising platform for the detection of free ClO- in monitoring water quality.

Smart crystalline framework materials with a triazole carboxylic acid ligand: fluorescence sensing and catalytic reduction of PNP

Triazole polycarboxylic acid ligands are widely employed in the construction of MOFs due to their strong coordination ability and flexible coordination modes. In this work, three novel complexes (Pb(MCTCA)(H2O) (1), Co(HMCTCA)2(H2O)2 (2) and Cu(HMCTCA)2(H2O)2 (3)) based on the H2MCTCA ligand (5-methyl-1-(4-carboxyl)-1H-1,2,3-triazole-4-carboxylic acid) were successfully synthesized under hydrothermal conditions, respectively. X-ray single crystal structure analysis shows that complex 1 is a 3D network structure, where the central metal Pb(II) is six coordinated to form deformed triangular prism geometry. The complexes 2 and 3 are both 2D layer supramolecular structures connected through intermolecular hydrogen, where the central metals (Co/Cu) are six coordinated to form octahedral configuration geometry. Based on functional properties, it is found that complex 1 exhibits excellent detection ability for small-molecule drugs (azithromycin, colchicine and balsalazide disodium) and actinide cations (Th4+ and UO22+) within a lower concentration range without interference from other components. In particular, the detection limits of three small-molecule drugs are all lower than 0.30 μM. In addition, complexes 2 and 3 exhibited excellent catalytic reduction performance toward p-nitrophenol (PNP), with a reduction efficiency exceeding 98%. These experimental results evidence that complexes 1-3 have potential application prospects in fluorescence sensing and catalytic reduction.

Portable, Intelligent Fluorescence Sensing Platform for Dense Convolutional Network-Capable Detection of Indophenol Sulfate and Methylmalonic Acid Using a Luminescent Eu@HOF Film

Indophenol sulfate (IS) and methylmalonic acid (MMA) are biomarkers of chronic kidney disease (CKD) and diabetes polyneuropathy (DPN), respectively. Portable and accurate monitoring of IS and MMA is very important to ensuring human health. The dense convolutional network (DenseNet) with image recognition has great potential in fluorescence sensing, but developing a platform with high precision and portability to diagnose the disease still faces huge challenges. Herein, we developed a high-sensitivity platform with a fluorescence material, a smartphone, and the DenseNet to monitor IS and MMA. A red-emitting Eu@PFC-13 (1) is prepared, and 1 shows high selectivity and low detection limits (DLs) to detect IS and MMA. The sensing mechanism of 1 toward IS and MMA is investigated by experiments and theoretical calculation. For detecting IS and MMA in serum and urine, 1 is fabricated into an Eu@PFC-13/AG (2) film with DLs of 1.4 and 1.6 μM, respectively. In addition, a portable smartphone platform is designed to monitor IS and MMA with high precision. Moreover, the DenseNet is constructed by Python, which can output the concentration of analytes by identifying fluorescence images and judge whether any is in a dangerous range. This work not only proposes a novel method that integrates a fluorescence material, a smartphone, and deep learning to detect analytes but also opens a new way for the diagnosis of CKD and DPN.

Pyrazine Functionalization in Eu-MOF for Exclusive Ratiometric Luminescence Sensing of PO43

Single-emission luminescence sensors are less than satisfactory for complex systems due to their susceptibility to environmental disturbances. Lanthanum-based metal-organic frameworks (Ln-MOFs) with highly stable ratiometric dual-emission are regarded as promising luminescence probes owing to their fascinating ligand-to-metal energy transfer behaviors (also known as the antenna effect). Herein, we report the synthesis of a pair of isostructural europium-based MOFs (termed JNU-219 and JNU-220) by utilizing two X-shaped tetracarboxylate linkers, 4,4',4″,4‴-benzene-2,3,5,6-tetrayl-tetrabenzoate (BTEB) and 4,4',4″,4‴-pyrazine-2,3,5,6-tetrayl-tetrabenzoate (BTTB). Both JNU-219 and JNU-220 present the characteristic red luminescence of Eu3+, yet the pyrazine functionalization of the BTTB linker renders JNU-220 with significantly increased luminescence emission, almost 30 times that of JNU-219. As a result, the detection limit of JNU-220 for the ratiometric luminescence sensing of PO43- was determined to be as low as 0.22 μM, which is far superior to those of other reported MOF materials. Additionally, we demonstrate the excellent stability and reusability of JNU-220, further verifying its potential as a robust ratiometric luminescence probe.

An electrochemical microsensor based on a specific recognition element for the simultaneous detection of hydrogen peroxide and ascorbic acid in the live rat brain

A novel electrochemical microsensor was developed for the ratiometric and simultaneous determination of hydrogen peroxide (H2O2) and ascorbic acid (AA) based on the borate-phenol "switch" recognition mechanism and carbon nanotube (CNT) catalytic characteristics. First of all, a carbon fiber microelectrode (CFME) was coated with CNTs. Then, a specific probe, 9-anthraceneboronic acid pinacol ester (9-AP), was screened and decorated on CNTs through π-π stacking for the recognition of H2O2 based on the transformation of boric acid ester into electroactive phenols. CNTs not only served as the amplifiers of current signals, but also as catalysts facilitating AA oxidation. Meanwhile, ferrocenecarboxylic acid (Fc), inert to H2O2 and AA, was modified on another amino-functionalized CNT microelectrode via an amide bond as an internal reference channel for avoiding errors caused by environmental discrepancies. The two-channel ratiometric microsensor enabled the sensitive and accurate detection of H2O2 and AA simultaneously, and the detection limits were estimated to be 0.09 μM and 4.12 μM, respectively. The developed microsensor with remarkable analytical performance was finally applied for the simultaneous detection of H2O2 and AA in the live rat brain.

Sensitive detection of extracellular hydrogen peroxide using plasmon-enhanced electrochemical activity on Pd-tipped Au nanobipyramids

The fabrication of electroactive nanostructures with high electron concentration and specific electron transport is crucial for electrochemical sensing. In this study, a plasmon-enhanced electrochemical sensor has been developed for the detection of extracellular hydrogen peroxide (H2O2) from cancer cells, utilizing Pd-tipped Au nanobipyramids (PTA NBPs) as the electrocatalysts. Plasmonic PTA NBPs were synthesized by depositing Pd nanoparticles onto the tips of Au nanobipyramids (Au NBPs). Under excitation of localized surface plasmon resonance (LSPR), the PTA NBPs generate high-energy electron-hole pairs (e-/h+) on their surface. The generated electrons (e-) significantly enhance the electrochemical reduction of H2O2. Based on this, a plasmon-enhanced H2O2 electrochemical sensor is constructed with high sensitivity (986.57 μA mM-1 cm-2), low detection limit (0.02 μM), wide linear range (0.1 μM to 980 μM), and good stability and repeatability. Moreover, this sensor also enables the measurement of extracellular H2O2 derived from cancer cells (MCF-7), highlighting its potential applications in cellular biology and biomedical research.

Highly sensitive fluorescent quantification of carbendazim by two-dimensional Tb-MOF nanosheets for food safety

Carbendazim (CBZ), a well-known benzimidazole pesticide, is utilized in agriculture to prevent and cure plant diseases caused by fungi. Residual CBZ in food poses serious threat to human health. Herein, a fluorescent two-dimensional terbium-based metal-organic framework (2D Tb-MOF) nanosheet sensor was developed for the rapid and ultrasensitive detection of CBZ. The 2D Tb-MOF nanosheets, prepared with Tb³⁺ ions and 5-borono-1,3-benzenedicarboxylic acid (BBDC) as the precursors, exhibited excellent optical properties. Upon the addition of CBZ, the fluorescence of Tb-MOF nanosheets was quenched because of the inner filter effect (IFE) and dynamic quenching. The fluorescence sensor offered two linear ranges of 0.06-4 and 4-40 µg/mL with a low detection limit of 17.95 ng/mL. Furthermore, the proposed sensing platform was successfully applied to assay CBZ in apples and tea, and satisfactory results were obtained. This study provides an effective alternative strategy for the qualitative and quantitative determination of CBZ to ensure food safety.

Boric acid group-functional Tb-MOF as a fluorescent and captured probe for the highly sensitive and selective determination of propyl gallate in edible oils

This study reports the development of a Tb-metal-organic framework (Tb-MOF)-based fluorescent platform for the detection of propyl gallate (PG). The Tb-MOF using 5-boronoisophthalic acid (5-bop) as the ligand exhibited multiple emissions at 490, 543, 585, and 622 nm under an excitation wavelength of 256 nm. The fluorescence of Tb-MOF was selectively and significantly weakened in the presence of PG due to the special nucleophilic reaction between the boric acid of Tb-MOF and o-diphenol hydroxyl of PG, and the combined effect of static quenching and internal filtering. Furthermore, this sensor enabled the determination of PG within seconds in a wide linear range of 1-150 μg/mL, and with a low detection limit of 0.098 μg/mL, and high specificity against other phenolic antioxidants. This work provided a new route for the sensitive and selective determination of PG in soybean oil, thus was perspective to monitor and reduce the risk of PG overuse.

Quantitative Time-Resolved Visualization of Catalytic Degradation Reactions of Environmental Pollutants by Integrating Single-Drop Microextraction and Fluorescence Sensing

Current methods for evaluating catalytic degradation reactions of environmental pollutants primarily rely on chromatography that often suffers from intermittent analysis, a long turnaround period, and complex sample pretreatment. Herein, we propose a quantitative time-resolved visualization method to evaluate the progress of catalytic degradation reactions by integrating sample pretreatment [single-drop microextraction, (SDME)], fluorescence sensing, and a smartphone detection platform. The dechlorination reaction of chlorobenzene derivatives was first investigated to validate the feasibility of this approach, in which SDME plays a critical role in direct sample pretreatment, and inorganic CsPbBr₃ perovskite encapsulated in a metal-organic framework (MOF-5) was utilized as the fluorescent chromogenic agent (FLCA) in SDME to realize fast in situ colorimetric detection via the color switching from green (CsPbBr₃) to blue (chlorine lead bromide, inorganic CsPbCl₃ perovskite). The smartphone, which can calculate the B/G value of FLCA, serves as a data output window for quantitative time-resolved visualization. Further, a [Eu(PMA)]_n (PMA= pyromellitic acid) fluorescent probe was constructed to use as an FLCA for the in situ evaluation of cinnamaldehyde and p-nitrophenol catalytic reduction. This approach not only minimizes the utilization of organic solvents and achieves quantitively efficient time-resolved visualization but also provides a feasible method for in situ monitoring of the progress of catalytic degradation reactions.

Integrated ratiometric luminescence sensing strategy based on encapsulation of guests in heterobinuclear lanthanide coordination polymer nanoparticles for glucose detection in human serum

Lanthanide coordination polymers (LnCPs) can be used as a host platform to encapsulate functional guest molecules for the construction of integrated sensing platforms. In this work, two guest molecules, rhodamine B (RhB) and glucose oxidase (GOx), were successfully encapsulated in a heterobinuclear lanthanide coordination polymer synthesized by self-assembly of Ce³⁺, Tb³⁺ and adenosine monophosphate (AMP) to form RhB&GOx@AMP-Tb/Ce. Both guest molecules show good storage stability and minimal leakage. The higher catalytic activity and stability of RhB&GOx@AMP-Tb/Ce is obtained due to the confinement effect compared to free GOx. RhB&GOx@AMP-Tb/Ce exhibits superior luminescence based on the internal tandem energy transfer process of the nanoparticles (Ce³⁺→Tb³⁺→RhB). Glucose can be oxidized in the presence of GOx to form gluconic acid and H₂O₂. Subsequently, Ce³⁺ in the AMP-Tb/Ce host structure can be oxidized by H₂O₂ to Ce⁴⁺, thereby interrupt the internal energy transfer process and cause ratiometric luminescence response. Benefiting from the synergistic effect, the smart integrated luminescent glucose probe exhibits a wide linear range (0.4-80 μM) and a low detection limit (74.3 nM) with high sensitivity, selectivity and simplicity, enabling the quantitative detection of glucose in human serum. This work describes a good strategy to construct an integrated luminescence sensor based on lanthanide coordination polymers.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence "turn on" detecting hydrogen peroxide

The sensitively and reliably detecting hydrogen peroxide (H₂O₂) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H₂O₂ nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO₂ nanosheets. In which, DNA modified NaYF₄@NaYF₄:Yb,Tm core-shell nanoparticles were anchored onto the MnO₂ nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO₂ nanosheets, then the luminescence could be restored by adding H₂O₂ for reducing MnO₂ to Mn²⁺, and achieving a H₂O₂ concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H₂O₂ in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H₂O₂ in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

Ln-MOF Based Ratiometric Luminescent Sensor for the Detection of Potential COVID-19 Drugs

Countless people have been affected by the COVID-19 pandemic on a global scale. Favipiravir, has shown potential as an effective drug for SARS-CoV-2, attracting scientists' attention. However, overuse of Favipiravir easily leads to serious side effects, requiring real-time monitoring in body fluids. Given this, a new lanthanide metal-organic framework (MOF) was prepared under solvothermal conditions from either Eu (Eu-MOF or (1)) or Tb (Tb-MOF or (2)) using the highly delocalized imidazoledicarboxylic acid linker H₂ L (H₂ L=5-(4-(imidazol-1-yl) phenyl) isophthalic acid) and could be successfully applied to selective optical detection of Favipiravir. In this MOF framework, the organic linker H₂ L provides a high excitation energy transfer efficiency that can sensitize luminescence in lanthanides. In addition, through deliberate tuning of Eu/Tb molar ratio and reaction concentration in the lanthanide framework, ratiometric recyclable luminescent Eu_x Tb_1-x -MOF nanoparticles with open metal sites have been constructed, which present a high detection sensitivity (K_sv =1×10⁷ [M^-1 ], detection limit is 4.63 nM) for Favipiravir. The detection mechanism is discussed with the help of Density Functional Theory (DFT) calculations that sheds light over the selective sensing of Favipiravir over other related COVID-19 drug candidates. Finally, to explore the practical application of Favipiravir sensing, MOF based thin films have been used for visual detection of Favipiravir and recycled 5 times.

CDs-Peroxyfluor Conjugation for Ratiometric Fluorescence Detection of Glucose and Shortening Its Detection Time from Reaction Dynamic Perspective

A ratiometric fluorescence probe based on the conjugation of peroxyfluor-NHS (PF) and carbon dots (CDs) was designed for selective and rapid detection of glucose. When glucose was catalytically oxidized by glucose oxidase (GOx), the product H₂O₂ would react with colorless and non-fluorescent peroxyfluor moiety to give the colored and fluorescent fluorescein moiety which would absorb the energy of CDs emission at 450 nm due to the Förster Resonance Energy Transfer (FRET) and generate a new emission peak at 517 nm. The reaction between PF and H₂O₂ was slow with a rate constant of about 2.7 × 10^-4 s^-1 under pseudo-first-order conditions (1 uM PF, 1 mM H₂O₂), which was unconducive to rapid detection. Given this, a short time detection method was proposed by studying the kinetics of the reaction between PF and H₂O₂. In this method, the detection time was fixed at three minutes. The linear detection of glucose could be well realized even if the reaction was partially done. As glucose concentration increased from 0.05 mM to 5 mM, the fluorescence intensity ratio (I₅₁₇/I₄₅₀) after 3 minutes' reaction of CDs-PF and glucose oxidation products changed linearly from 0.269 to 1.127 with the limit of detection (LOD) of 17.19 μM. In addition, the applicability of the probe in blood glucose detection was verified.

Luminescent carbon dots with excellent peroxidase mimicking property for fluorometric and colorimetric detection of glucose

The luminescent carbon dots with peroxidase mimicking property had attracted considerable attention in biomedical field. In this work, iron-doped carbon dots (Fe-CDs) were prepared by one-pot hydrothermal method with 5, 10, 15, 20-tetra (4-borate phenyl)-21H, 23H-porphyrin Fe (II) (Fe-TBPP) as precursor. The obtained Fe-CDs emitted intense blue luminescence under ultraviolet light irradiation. Moreover, the Fe-CDs exhibited remarkable peroxidase mimicking property, which can efficiently catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into blue ox-TMB in the presence of hydrogen peroxide (H₂O₂). More importantly, the emission of Fe-CDs could be gradually quenched with the addition of H₂O₂. Based on these phenomena, a new optical dual-mode (colorimetric and fluorometric) method for the detection of H₂O₂ and glucose was successfully established. The detection limits of glucose were calculated to be 3.86 and 7.27 μM (S/N = 3) respectively based on the colorimetric and fluorometric methods. Furthermore, we combined this dual-mode detection method with smartphone imaging. The colorimetric and fluorescent images were collected by recognition software of smartphone, which were then transformed into the corresponding HSL values for quantitative determination of glucose. Finally, the dual-mode approach based on Fe-CDs was used for the detection of glucose content in human serum, demonstrating the potential application of carbon dots in the biological area.

Fluorescence Detection of Trace Disinfection Byproducts by Ag Nanoprism-Modulated Lanthanide MOFs

Disinfection byproducts (DBPs), as an emerging water pollutant, present increasing concern and risk in public health and water safety. Due to their low concentration levels and inherent similarity in molecular structures, sensitive and accurate determination of DBPs is still a challenge especially for onsite or online detection. Herein, a self-regulated fluorescent probe based on the Ag nanoprism-modified lanthanide metal-organic framework (AgNPR@EuMOF) is designed for trichloroacetic acid (TCAA) detection. The EuMOF is constructed with Eu as the metal node and 5-boronoisophthalic acid as the ligand. By introducing sulfhydryl groups into EuMOF, AgNPR can be anchored on the EuMOF surface through Ag-S bonds, enabling the synthesis of stable AgNPR@EuMOF composites. During the sensing process, the triangle AgNPR will react with the organic halogen molecule, accomplished with the blue shift of surface plasmon resonance absorption peak and the significant change in the fluorescence of EuMOF. This probe can detect TCAA in a wide concentration range (0.1-40 μM) with high sensitivity and specificity. The density functional theory calculation on binding energies between DBPs and AgNPR suggests that TCAA has the largest interaction ability with AgNPR than other DBPs. Moreover, the detection of TCAA in real tap water and swimming pool water is also demonstrated with high accuracy. The reported AgNPR@EuMOF represents one of the pioneer fluorescence probes in DBP detection, which holds great promise for onsite or online analysis of trace DBPs in water.

Ligand influence in electrocatalytic properties of Cu(II) triazole complexes for hydrogen peroxide detection in aqueous media

In this work, electrocatalytic changes of Cu(II) triazole complexes (Cu(L)₂) resulting from inductive effects were evaluated to fabricate a sensor for hydrogen peroxide (H₂O₂) determination. Three copper(II) complexes with electronically differentiated ligands were synthesized by slow diffusion method and characterized by X-ray crystallography, Fourier transformed infrared (FTIR), UV-Vis, scanning electron microscopy (SEM) and voltammetry cyclic (CV). Cu(LOMe)2/GC, Cu(LBr)2/GC and Cu(LNO2)2/GC sensors were then prepared. Under optimal conditions (pH = 11), the optimal sensor presented a response at -0.5 V, good linear range of 1-32 μM, reproducibility (1.7%), repeatability (1.2%), LOD of 0.0246 μM (S/N = 5), LOQ of 0.0747 μM (S/N = 5) and selectivity. Additionally, Cu(LNO2)2/GC sensor has been successfully applied in commercial substances, such as mouthwash, milk and tea.

Metal-Organic Frameworks-Based Optical Nanosensors for Analytical and Bioanalytical Applications

Metal-organic frameworks (MOFs)-based optical nanoprobes for luminescence and surface-enhanced Raman spectroscopy (SERS) applications have been receiving tremendous attention. Every element in the MOF structure, including the metal nodes, the organic linkers, and the guest molecules, can be used as a source to build single/multi-emission signals for the intended analytical purposes. For SERS applications, the MOF can not only be used directly as a SERS substrate, but can also improve the stability and reproducibility of the metal-based substrates. Additionally, the porosity and large specific surface area give MOF a sieving effect and target molecule enrichment ability, both of which are helpful for improving detection selectivity and sensitivity. This mini-review summarizes the advances of MOF-based optical detection methods, including luminescence and SERS, and also provides perspectives on future efforts.

A luminescent Eu@SOF film fabricated by electrophoretic deposition as ultrasensitive platform for styrene gas quantitative monitoring through fluorescence sensing and ANNs model

Styrene is a harmful gas widely existing in the air, which can damage human organs. Therefore, it is very crucial to develop a sensitive, portable and simple sensor for monitoring styrene. Herein, we design and fabricate a luminescent Eu@TMA-ME/FTO film (F) through EPD method. F emits bright red light of Eu(III) ions and shows superior fluorescence response to styrene gas as a sensor, which enable real-time and quantitative monitoring for styrene gas. More importantly, F exhibits a linear response to styrene gas in a wide concentration range of 10^-7 to 10^-2 M and a low DL with 0.20 ppm. The efficient PET process to styrene induced by ME and the competitive absorption between styrene and F are responsible for the sensing mechanism. Besides, the detection of styrene solution is also investigated in deionized water, tap water and river water. For the further application, an intelligent ANNs model has been constructed to process the fluorescence sensing results, which can convert fluorescence sensing images to the concentration of styrene gas. The data demonstrates that ANNs model can accurately monitor the concentration of styrene gas via deep ML without tedious data processing.

Europium (III) complex-based fluorescent probe for instantaneous, selective, and sensitive detection of phosgene

Phosgene (carbonyl chloride, COCl₂) is a widely used colorless gas in organic synthesis. However, its high toxicity sets a severe potential damage of public safety. As the fluorescence method has the advantages of simple operation and real-time detection of phosgene, it is extremely important to develop a fluorescent phosgene probe for public health and safety. This study aimed to present a simple Eu³⁺ complex (1) with 2-hydroxyl-1H-benzimidazole moiety as a novel phosgene probe. Probe 1 exhibited characteristic emission of Eu³⁺ in CH₃CN solution, which was specifically quenched after encountering phosgene. The change in the solution color from light red to dark could be easily distinguished with the naked eye under a 365 nm ultraviolet lamp. Finally, the test paper with probe 1 was fabricated for effortless, selective, and visual detection of phosgene gas.

Three-pole wheel paddle luminescent metal organic frameworks (LMOFs) based on the oxygen substituted triazine tricarboxylic acid ligand: recognition and detection of small drug molecules and aromatic amine molecules

Luminescent metal organic frameworks (LMOFs) are considered to be a type of promising optical sensing material due to their designable and tunable functions, and stable pore structures. Therefore, the preparation of LMOFs has become a research hotspot in recent years. As we know, triazine carboxylic acid ligands are conducive for constructing LMOF materials due to their large π electron conjugated system. In this work, two crystalline materials [Cd₃(TCPT)₂]·0.5DMF·4H₂O (1) and (H₃O)[Zn₂(TCPT)(μ₂-OH)₂]·0.5DMF·3H₂O (2) were obtained by the reaction of the triazine carboxylic acid ligand 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine (H₃TCPT), as an extended carboxylate arm, and d¹⁰ transition metal salts. Their structures were determined by single crystal X-ray diffraction and characterized by infrared spectroscopy (IR), ultraviolet visible spectroscopy (UV-vis), fluorescence spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG). The experimental results showed that complexes 1 and 2 show excellent fluorescent emission behavior. Thus, we explored their fluorescence sensing properties. To our delight, the results showed that they both had the ability to sense small organic drug molecules and aromatic amine molecules containing o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD). In general, the practical applications of a MOF material are usually limited because of the relatively harsh synthesis methods. In this aspect, we studied the synthesis method in detail to obtain the optimal reaction conditions for the large-scale synthesis of 1 and 2. The preparation of the two LMOF materials only required about 3 hours of heating time and they could be prepared on a large scale, which is significant for the practical applications of LMOFs.

Size-Controllable Eu-MOFs through Machine Learning Technology: Application for High Sensitive Ions and Small-Molecular Identification

Metal-organic frameworks (MOFs) with the aggregation-induced emission (AIE) activities exhibit potential applications in the fields of energy and biomedical technology. However, the controllable synthesis of MOFs in the varied particle sizes not only affects their AIE activities, but also restricts their application scenarios. In this work, the varied particle sizes of Eu-MOFs are synthesized by adjusting the synthesis process parameters, and their variation rules combining the single factor analysis method with machine learning technology are studied. Based on the R² score, the gradient boosting decision tree (GBDT) regression model (0.9535) is employed to calculate the weight and correlation between different synthesis process parameters and it is shown that all these parameters have synergic effects on the particle sizes of Eu-MOFs, and the Eu-precursors concentration dominates in their synthesis process. Furthermore, it is indicated that the large size of Eu-MOFs and strong structural stability contribute to their high AIE activities. Finally, a screen-printed pattern is fabricated using the sample of "120-0.3-6," and this pattern exhibits a bright red fluorescence under the UV light. More importantly, this kind of Eu-MOFs can also be used to identify varied ions (Fe³⁺ , F^- , I^- , SO₄^2- , CO₃^2- , and PO₄^3- ) and citric acid.

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

H₂O₂ sensing is required in various biological and industrial applications, for which electrochemical sensing is a promising choice among various sensing technologies. Electrodes and electrocatalysts strongly influence the performance of electrochemical H₂O₂ sensors. Significant efforts have been devoted to electrode nanostructural designs and nanomaterial-based electrocatalysts. Here, we review the design strategies for electrodes and electrocatalysts used in electrochemical H₂O₂ sensors. We first summarize electrodes in different structures, including rotation disc electrodes, freestanding electrodes, all-in-one electrodes, and representative commercial H₂O₂ probes. Next, we discuss the design strategies used in recent studies to increase the number of active sites and intrinsic activities of electrocatalysts for H₂O₂ redox reactions, including nanoscale pore structuring, conductive supports, reducing the catalyst size, alloying, doping, and tuning the crystal facets. Finally, we provide our perspectives on the future research directions in creating nanoscale structures and nanomaterials to enable advanced electrochemical H₂O₂ sensors in practical applications.

Efficient Electrochemical Detection of Hydrogen Peroxide Based on Silver-Centered Preyssler-Type Polyoxometalate Hybrids

Four polyoxometalate (POM)-based organic-inorganic hybrid compounds, namely, (H₂bimb)₆H₈[((Mn(H₂O)₃(μ-bimb))_0.5(Mn(H₂O)₄)(Mn(H₂O)₅)_0.5(AgP₅W₃₀O₁₁₀))₂]·29H₂O (1), [(Cu(Hbimb)(H₂O)₂(μ-bimb)Cu(Hbimb)(H₂O))(Cu(H₂O)₂(μ-bimb)Cu(H₂O)₃)((Cu(H₂O)₂)_0.5(μ-bimb)(Cu(H₂O)₃)_0.5)H₂(AgP₅W₃₀O₁₁₀)]·12.5H₂O (2), (H₂bimb)₂H[(Zn(Hbimb)(H₂O)₄(Zn(Hbimb)(H₂O)₂)_0.5)₂(AgP₅W₃₀O₁₁₀)]·12H₂O (3), and (H₂bimb)₃H₂[(Ag(H₂O)₂)_0.5(Ag(Hbimb)Ag(Hbimb)(μ-bimb)Ag)(Ag(H₂O)₂)_0.5(AgP₅W₃₀O₁₁₀)]·7H₂O (4) (bimb = 1,4-bis(1H-imidazol-1-yl)benzene), were hydrothermally synthesized using a silver-centered Preyssler-type POM K₁₄[AgP₅W₃₀O₁₁₀]·18H₂O (abbreviated as K-{AgP₅W₃₀}) as a precursor. In 1-4, {AgP₅W₃₀} clusters integrating the merits of Ag⁺ and {P₅W₃₀} units are modified by different transition metal (TM)-organic fragments to extend the structures into three-dimensional frameworks. As nonenzymatic electrochemical sensor materials, 1-4 show good electrocatalytic activity, high sensitivity, and a low detection limit for detecting hydrogen peroxide (H₂O₂); 4 possesses the highest sensitivity of 195.47 μA·mM^-1·cm^-2 for H₂O₂ detection. Most importantly, the average level of H₂O₂ detection of these {AgP₅W₃₀}-based materials outperforms that of Na-centered Preyssler-type {NaP₅W₃₀} and most Keggin-type POM-based materials. The performances of such {AgP₅W₃₀} materials mainly stem from the unique advantage of high-negatively charged {AgP₅W₃₀} clusters together with the good synergistic effect between {AgP₅W₃₀} and TMs. This work expands on the research of high-efficiency POM-based nonenzymatic electrochemical H₂O₂ sensors using Ag-containing POMs with high negative charges, which is also of great theoretical and practical significance to carry out health monitoring and environmental analysis.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.