Query: Ratiometric fluorescence sensing of metal-organic frameworks review

title: Ratiometric fluorescence sensing of metal organic frameworks: Tactics and perspectives
abstract: Metal organic frameworks (MOFs) are an important class of inorganic organic hybrid crystals with applications in various fields. In last ten years, MOFs based fluorescence sensing has gained much attention. MOFs can exhibit luminescence by metal nodes, ligands and the inserted or absorbed guests, which offer an excellent fluorescence response in analyzing. However, MOFs based monochromatic fluorescence probes are limited by concentration, the effect of ambient and excitation light intensity, resulting in low detection accuracy. To overcome this defect, MOFs based ratiometric fluorescence (RF) sensors have been proposed and rapidly developed. This review focuses on the design tactics of MOFs based RF sensing and describes the detection mechanism of different RF sensors. Based on different strategies of synthesis, the MOFs based RF sensors are categorized into three classes: MOFs' intrinsic dual emission, single emissive MOFs with a chromophore and non emissive MOFs with two chromophores. In each categorization, the design approaches and relative merits were discussed separately. Finally, the applications of MOFs based RF sensors are summarized and prospected.

title: Ratiometric fluorescence temperature sensing based on single and dual lanthanide metal organic frameworks
abstract: The ever increasing demand for fast, noninvasive, and accurate determination of temperature at the submicrometer spatial regime, particularly in microelectronic diagnostics, is driving the development of ratiometric temperature probes. In this work, we present two types of self calibrating metal organic framework (MOF) thermometers with both the organic chromophore and lanthanide emissions, which proposed an elegant avenue to address these concerns. By employing the symmetric tetracarboxylate ligand [1,1':4',1' Terphenyl] 3,3',5,5' tetracarboxylic acid, we synthesized and investigated single and dual lanthanide MOFs, TbTPTC and GdxEu1 xTPTC, in terms of their temperature dependent luminescence. Based on the energy back transfer of lanthanide ion to ligand, the intensity ratio between the ligand and lanthanide of both the single and dual lanthanide MOF systems exhibits distinctly exponential response to temperatures in the range of 313 473 K. Given their good relative sensitivities, accurate temperature resolution, and excellent repeatability, as well as sensitivity to color change, the proposed dual emitting MOF materials can be useful for thermal mapping and hot spot monitoring of microelectronic devices.

title: Nonlinear optical metal organic frameworks for ratiometric temperature sensing in physiological range
abstract: The precise and real time sensing of the temperature within the physiological range is of great significance in biology and medicine. Here, a Zn based metal organic framework (MOF) named Zn TCOMA is synthesized with good SHG performance due to its unique structure of the ligand and 3D frameworks. By encapsulating the two photon fluorescent dye DMASE into the pores of Zn TCOMA, the composite Zn TCOMADMASE is obtained and simultaneously exhibits SHG response and two photon fluorescence. Utilizing the intensity ratio between two photon fluorescence of DMASE and SHG signal of Zn TCOMA, Zn TCOMADMASE exhibits ratiometric temperature sensing property at physiological temperature region of 20~60 degC with high sensitivity. This MOF thermometer also shows excellent repeatability, good biocompatibility, and high temperature resolution of 0.018 degC, opening a new avenue to develop diverse optical thermometric or thermographic applications in biotechnology or other areas.

title: Introducing bifunctional metal organic frameworks to the construction of a novel ratiometric fluorescence sensor for screening acid phosphatase activity.
abstract: Restricted to single sensing mechanisms, most luminescent metal organic framework (LMOF) based sensors were constructed for detection of limited targets. Here, a new biosensor is described for screening acid phosphatase (ACP) activity via bifunctional NH2 MIL 101 MOFs acting as both fluorescent indicator and biomimetic catalyst. NH2 MIL 101 possesses an inherent fluorescence emission at 456 nm (F456) As a peroxidase like nanozyme, it catalyzes oxidation of o phenylenediamine (OPD) by H2O2 to generate fluorescent 2,3 diaminophenazine with the maximum emission at 556 nm (F556) Upon introducing NH2 MIL 101 into a mixture of OPD and H2O2, F456 is quenched, while F556 increases. The ACP sensing is based on pyrophosphate ion (PPi) mediated fluorescence tuning of the NH2 MIL 101/OPD/H2O2 system. PPi inhibits the NH2 MIL 101 catalytic ability by specific binding to its Fe center, while ACP addition recovers the activity by hydrolyzing PPi. Upon addition of PPi and ACP into the NH2 MIL 101/OPD/H2O2 system, a ratiometric luminescence signal (F556/F456) is obtained, and a ratiometric fluorescent sensor can be developed for the sensitive detection of PPi and for screening ACP activity. Plots of F556/F456 vs. ACP concentration were linear over 0.01 30 U/L, with a detection limit of 0.005 U/L. The proposed sensor was successfully used for ACP detection in serum samples. This ratiometric fluorescence assay will open new applications for LMOF based biosensors.

title: Multi emission metal organic framework composites for multicomponent ratiometric fluorescence sensing: recent developments and future challenges.
abstract: Ratiometric fluorescence sensors that are achieved via the ratiometric fluorescence intensity changes of emission peaks based on multi emission fluorescence probes show a huge advantage. However, the preparation of these multi emission fluorescence probes is a key challenge, as it is related to having more fluorescence groups with the same excitation but different emission wavelengths, and their assembly is not a simple mixing process. More fluorescent groups or molecules can be assembled into the multi emission fluorescence probe by covalent bonds and coordination interactions, or by loading in metal organic frameworks (MOFs) MOFs are excellent candidates for constructing complexes with the capability of multicomponent ratiometric fluorescence sensing, but there are some problems that need to be considered. For example, not all fluorophores can be stably loaded in the MOFs' pores, usually due to the size, surface charge and intrinsic properties of the fluorophore. In turn, it is also related to the structure of the MOF, metal nodes, and properties of the organic ligands. This review first introduces the advantages of the MOF based multi component fluorescence sensors, and then discusses the synthesis, classification and application of fluorescent MOFs or MOF composites for multi component ratiometric fluorescence detection. Particular emphasis is focused on the potential, types and characteristics for sensing and biological applications, and the main challenges and limitations are further explored. This review might be helpful for those researchers interested in the application of multi component ratiometric fluorescence sensing based on fluorescent MOFs or MOF composites.

title: Recent Advances in Developing Lanthanide Metal Organic Frameworks for Ratiometric Fluorescent Sensing
abstract: Fluorescent probes have attracted special attention in developing optical sensor systems due to their reliable and rapid fluorescent response upon reaction with the analyte. Comparing to traditional fluorescent sensing systems that employ the intensity of only a single emission, ratiometric fluorescent sensors exhibit higher sensitivity and allow fast visual screening of analytes because of quantitatively analyzing analytes through the emission intensity ratio at two or more wavelengths. Lanthanide metal organic frameworks (LnMOFs) are highly designable multifunctional luminescent materials as lanthanide ions, organic ligands, and guest metal ions or chromophores are all potential sources for luminescence. They thus have been widely employed as ratiometric fluorescent sensors. This mini review summarized the basic concept, optical features, construction strategies, and the ratiometric fluorescent sensing mechanisms of dual emitting LnMOFs. The review ends with a discussion on the prospects, challenges, and new direction in designing LnMOF based ratiometric fluorescent sensors.

title: Dual emissive bimetallic organic framework hybrids with Eu(III) and Zr(IV) for ratiometric fluorescence sensing of acrylamide in fried and baked foods
abstract: In order to protect human health from the threat of excessive acrylamide in heat processed foods, swift, uncomplicated, highly selective and sensitive online monitoring methods for acrylamide are urgently needed. In this study, a rare earth metal/transition metal organic frameworks Eu/Zr MOFs fluorescence sensor with dual band luminescence was prepared by the hydrothermal synthesis for detection of acrylamide in fried potatoes and cookie crumbs. This sensor exhibited two different fluorescence emission peaks at 430 and 615 nm under excitation of 365 nm, and the ratio of fluorescence intensity was linear with the experimental concentration of acrylamide in the range of 1 x 10 4 to 1 x 10 3 M. Under the optimal conditions, the proposed fluorescence analysis method showed that the detection limit of acrylamide was as low as 2.4 x 10 8 M, and the satisfactory recoveries of 94.05 104.04% were obtained for various spiked samples. More importantly, the sensor has ultra high selectivity for the detection of acrylamide while other small organic molecules hardly interfere with it in the measurement environment. These studies confirmed that the ratiometric fluorescence sensing method was expected to achieve on line rapid detection of acrylamide in real foods. In addition, the mechanism of Eu/Zr MOFs sensing acrylamide was analyzed and discussed in depth, and the analog computation was carried out by Materials Studio software, and the entire sensing system was studied at the micro level in combination with density functional theory.

title: Ratiometric fluorescence detection of phosphate in human serum with a metal organic frameworks based nanocomposite and its immobilized agarose hydrogels
abstract: We report a metal organic frameworks (MOFs) based nanocomposite by incorporating a fluorescent dye, rhodamine B (RhB) into a stable Zr based MOF, UiO 66 NH2. Based on weakened the LMCT process resulted from the strong binding of phosphate with Zr O node in UiO 66 NH2 and the unchangable fluorescence of RhB as the reference, this nanocomposite can be employed as a novel fluorescent sensing platform for ratiometric detection of phosphate in the range from 80 to 400 uM with a detection limit of 2.0 uM. It is particularly suitable for accurate quantification of phosphate in complex samples like human serum. Furthermore, this sensing platform is well recyclable due to reversible interaction with phosphate. Finally, this nanocomposite was encapsulated into agarose hydrogels for direct detection of phosphate in human serum with the naked eye. Thanks to the robust, portable, and instrument free characteristics, it is expected to show great potential for on site clinical diagnosis.

title: Ratiometric fluorescence detection of 2,6 pyridine dicarboxylic acid with a dual emitting lanthanide metal organic framework (MOF)
abstract: Bacillus anthracis is an extremely dangerous bacterium with high morbidity and mortality. It is thus of great importance to detect Bacillus anthracis or its major biomarker 2,6 pyridine dicarboxylic acid (DPA) in a rapid and sensitive way. Althought metal organic frameworks (MOFs) have found great applications in catalysis and sensing; nevertheless, there are only a few fluorescent MOFs can be used in DAP detections, and the key factors determining the detection sensitivity is not clear yet. In this study, we successfully synthesized a novel nano sized dual emitting lanthanide MOF, namely Eu/Tb(BTC) for the high sensitivity DPA detection. The synthesized Eu/Tb(BTC) showed a remarkable sensitivity, excellent selectivity, and a high accuracy. Through comprehensive characterizations of the microstructure, luminescence properties, and sensing performance of products with different Eu/Tb ratios, the unique capability as a sensitive fluorescent probe (limit of detection 1087 nM) for selectively detecting DPA was demonstrated. More importantly, a possible route to control the sensitivity of detection by controlling the original energy transfer efficiency between Eu3+ and Tb3+ was revealed. This work not only provides an excellent nano probe for qualitative and quantitative detection of biomarker of Bacillus anthracis, but also reveals an important rule for improving the sensitivity of sensing systems.

title: Eu3+@metal organic frameworks encapsulating carbon dots as ratiometric fluorescent probes for rapid recognition of anthrax spore biomarker.
abstract: Anthrax spores pose a serious threat to human well being and life, so it is highly desirable to develop a rapid, sensitive, and selective quantitative assay of calcium pyridine dicarboxylate (CaDPA) as a biomarker of anthrax spores. Herein, carbon dots (CDs) chelated Eu3+@metal organic framework (Eu MOFs) as dual emissive ratiometric fluorescent (RF) probe was successfully fabricated by a simple one pot in situ selective self assembly synthetic strategy. The developed RF probe has an effective self calibration function, which performs a highly sensitive and selective recognition of CaDPA in water and human serum sample. The blue emitting CDs was employed as an effective fluorescence reference, while the Eu MOFs exhibited enhanced red fluorescence signal through the coordination interaction with CaDPA chromophore. The sensing mechanism is attributed to that CaDPA can sensitize Eu3+ intrinsic luminescence due to the energy transfer from CaDPA to Eu3+ What's more interesting is that with the continuous drop of CaDPA, the emission color of CDs@Eu MOF changes from blue to red. The results revealed that CDs@Eu MOFs RF probe can detect CaDPA effectively in the range of 8 170 mg/L with good linear relationship, and exhibited a remarkable selectivity for CaDPA. More interestingly, a paper based probe has also been devised for on site detection of CaDPA. In addition, CaDPA is used as input signal to construct an IHIBITION logic gate device which performs the "off on" mode. The constructed CDs@Eu MOF probe can achieve exceptionally rapid, highly sensitive and selective detection of CaDPA, which can further expand the application prospects in environmental and biological analysis.