Heterogeneous nano metal-organic framework fluorescence probe for highly selective and sensitive detection of hydrogen sulfide in living cells

Confining Thiolysis of Dinitrophenyl Ether to a Luminescent Metal-Organic Framework with a Large Stokes Shift for Highly Efficient Detection of Hydrogen Sulfide in Rat Brain

Hydrogen sulfide (H2S) is a gaseous signaling molecule that regulates various physiological and pathological processes in the central nervous system. It is vital to develop an effective method to detect H2S in vivo to elucidate its critical role. However, current fluorescent probes for accurate quantification of H2S still face big challenges due to complicated fabrication, small Stokes shift, unsatisfactory selectivity, and especially delayed response time. Herein, based on simple postsynthetic modification, we present an innovative strategy by confining H2S-triggered thiolysis of dinitrophenyl (DNP) ether within a luminescent metal-organic framework (MOF) to address those issues. Due to the cleavage of the DNP moiety by H2S, the nanoprobe gives rise to a remarkable fluorescence turn-on signal with a large Stokes shift of 190 nm and also provides high selectivity to H2S against various interferents including competing biothiols. In particular, by virtue of the unique structural property of the MOF, it exhibits an ultrafast sensing ability for H2S (only 5 s). Moreover, the fluorescence enhancement efficiency displays a good linear correlation with H2S concentration in the range of 0-160 μM with a detection limit of 0.29 μM. Importantly, these superior sensing performances enable the nanoprobe to measure the basal value and monitor the change of H2S level in the rat brain.

A dual-color ESIPT-based probe for simultaneous detection of hydrogen sulfide and hydrazine

Hydrogen sulfide (H2S) and hydrazine (N2H4) are toxic compounds in environmental and living systems, and hydrogen sulfide is also an important signaling molecule. However, in the absence of dual-color probes capable of detecting both H2S and N2H4, the ability to monitor the crosstalk of these substances is restricted. Herein, we developed an ESIPT-based dual-response fluorescent probe (BDM-DNP) for H2S and N2H4 detection via dually responsive sites. The BDM-DNP possessed absorbing strength in the detection of H2S and N2H4, with a large Stokes shift (156 nm for H2S and 108 nm for N2H4), high selectivity and sensitivity, and good biocompatibility. Furthermore, BDM-DNP can be utilized for the detection of hydrogen sulfide and hydrazine in actual soil, and gaseous H2S and N2H4 in environmental systems. Notably, BDM-DNP can detect H2S and N2H4 in living cells for disease diagnosis and treatment evaluation.

Construction of smartphone-adapted signal visualization platform for dual-mode detection of H2S based on integrated metal-organic framework nanoprobes

Hydrogen sulfide (H2S) is a toxic contaminant and has great influence on many physiological processes. Due to various pathophysiological roles and environmental pollution problems, it is necessary to construct and develop simple and portable monitoring sensors for the precise detection of H2S. Herein, we developed a smartphone-adapted dual-mode detection platform by integrating the colorimetric and photothermal imaging analysis into a metal-organic framework-based chip (ZIF-8/Cu). Due to the nanoconfinement effect of ZIF-8, small-sized plasmonic CuS could be in-situ formed during the detection procedure of H2S and endowed the chips with excellent photothermal properties. By constructing a smartphone-adapted photothermal imager, the metal-organic framework-based chip could achieve a portable photothermal imaging analysis of H2S. Moreover, as the formed CuS was a good peroxidase-like nanozyme, the chips could also be used to trigger the enzymic catalytic reaction toward the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2, thus providing another colorimetric sensing mode by using a smartphone App. In this smartphone-adapted visualization platform, the portable chemosensors could simultaneously achieve double detection modes at one electrode, which provided a new pathway for the accurate detection of H2S and circumvented the false-positive or negative errors during the detection process. Besides, by using the finite difference time domain (FDTD) simulation method, the in-depth mechanism, including the plasmonic effect and spatial electromagnetic field distribution, was explored to provide a possible reason for the excellent sensing performance of the dual-mode visualization platform. This work provides a new insight into the construction of the accurate, portable and smart sensing platform in the visual screening of H2S.

The luminescent principle and sensing mechanism of metal-organic framework for bioanalysis and bioimaging

Metal-organic frameworks (MOFs) porous material have obtained more and more attention during the past decade. Among various MOFs materials, luminescent MOFs with specific chemical characteristics and excellent optical properties have been regarded as promising candidates in the research of cancer biomarkers detection and bioimaging. Therefore, the latest advances and the principal biosensing and imaging strategies based on the luminescent MOFs were discussed in this review. The effective synthesis methods of luminescent MOFs were emphasized firstly. Subsequently, the luminescent principle of MOFs has been summarized. Furthermore, the luminescent MOF-based sensing mechanisms have been highlighted to provide insights into the design of biosensors. The designability of LMOFs was suitable for different needs of biorecognition, detection, and imaging. Typical examples of luminescent MOF in the various cancer biomarkers detection and bioimaging were emphatically introduced. Finally, the future outlooks and challenges of luminescent MOF-based biosensing systems were proposed for clinical cancer diagnosis.

Fluorescence detection platform of metal-organic frameworks for biomarkers

Sensitive and selective detection of biomarkers is crucial in the study and early diagnosis of diseases. With the continuous development of biosensing technologies, fluorescent biosensors based on metal-organic frameworks have attracted increasing attention in the field of biomarker detection due to the combination of the advantages of MOFs, such as high specific surface area, large porosity, and structure with tunable functionality and the technical simplicity, sensitivity and efficiency and good applicability of fluorescent detection techniques. Therefore, researchers must understand the fluorescence response mechanism of such fluorescent biosensors and their specific applications in this field. Of all biomarkers applicable to such sensors, the chemical essence of nucleic acids, proteins, amino acids, dopamine, and other small molecules account for about a quarter of the total number of studies. This review systematically elaborates on four fluorescence response mechanisms: metal-centered emission (MC), ligand-centered emission (LC), charge transfer (CT), and guest-induced luminescence change (GI), presenting their applications in the detection of nucleic acids, proteins, amino acids, dopamine, and other small molecule biomarkers. In addition, the current challenges of MOFs-based fluorescent biosensors are also discussed, and their further development prospects are concerned.

Green synthesize of nano-MOF-ethylcellulose composite fibers for efficient adsorption of Congo red from water

Two novel MOF- ethyl cellulose (EC)- based nanocomposites have been designed and synthesized in water by electrospinning and applied for adsorption of congo red (CR) in water. Nano- Zeolitic Imidazolate Framework-67 (ZIF-67), and Materials of Institute Lavoisier (MIL-88A) were synthesized in aqueous solutions by a green method. To enhance the dye adsorption capacity and stability of MOFs, they have been incorporated into EC nanofiber to prepare composite adsorbents. The performance of both composites in the absorption of CR, a common pollutant in some industrial wastewaters, has then been investigated. Various parameters including initial dye concentration, the dosage of the adsorbent, pH, temperature and contact time were optimized. The results indicated 99.8 and 90.9% adsorption of CR by EC/ZIF-67 and EC/MIL-88A, respectively at pH = 7 and temperature at 25 °C after 50 min. Furthermore, the synthesized composites were separated conveniently and successfully reused five times without significant loss of their adsorption activity. For both composites, the adsorption behavior can be explained by pseudo-second-order kinetics, Intraparticular diffiusion and Elovich models demonstrated that the experimental data well matched to the pseudo-second-order kinetics. Intraparticular diffiusion model showed that the adsorption of CR on EC/ZIF-67 and EC/MIL-88a took place in one and two steps, respectively. Freundlich isotherm models and thermodynamic analysis indicated exothermic and spontaneous adsorption.

A BODIPY-based fluorescent chemosensor with 2, 6-substitution for visual and highly selective detection of S2

BODIPY derivatives have often been employed as fluorescent sensors to probe toxic ions in environment and living systems, such as sulfide ion (S^2-). Whilst many structure modifications have been exploited on groups at the 3, 5, 8-positions, there are quite few examples on tailoring the 2,6-substituents for chemosensor investigations. Herein, we design and synthesize a 2,6-substituted BODIPY molecule, LM-BDP, to use as a fluorescent probe for detecting S^2- in aqueous media. The electronic and crystal structures of the probe are studied by density functional theory (DFT) calculations and single-crystal X-ray diffraction analysis. Spectroscopy investigations are performed in a variety of conditions, showing that LM-BDP exhibits a noticeable color change from pink to dark red and a fluorescence shift from yellow to pink channel with decreased intensity upon addition of S^2-. The selectivity and sensitivity measurements show that LM-BDP can only response to S^2- with a detection limit of 0.29 μM in less than 100 s. The remarkable contrast in fluorescence images in test-stripe and RAW 264.7 cell experiments indicates that the probe is a proper candidate for the application in detecting exogenous S^2-.

Growth of AgI semiconductors on tailored 3D porous Ti3C2 MXene/graphene oxide aerogel to develop sensitive and selective "signal-on" photoelectrochemical sensor for H2S determination

Long term exposure to hydrogen sulfide (H₂S) even in low concentration poses a serious threat to human health and the ecosystem, pointing to the significance for its effective supervision. In this study, we report a sensitive and selective "signal-on" photoelectrochemical (PEC) sensor for the determination of toxic H₂S in aqueous solution by in situ growth of AgI semiconductors on tailored three-dimensional (3D) porous Ti₃C₂ MXene/graphene oxide aerogel (MGA). Our research demonstrated that the resultant MGA with the starting feeding mass ratio of MXene and graphene oxide (GO) of 1:8 (MGA_1:8) possessed the most excellent PEC performance after the growth of AgI semiconductors than their monomers (Ti₃C₂ MXene and GO) and the MGAs with other starting feeding mass ratio. Such designed PEC sensor based on MGA_1:8/AgI heterojunction showed dramatically strengthened PEC responses with increasing concentrations of S^2-. Correspondingly, a wide linear range of 5 nM-200 μM, a low limit of detection of 1.54 nM (S/N = 3), and exclusively unique selectivity have been achieved. Our research illustrates that the PEC sensor designed with tailored MGA constitutes is an effective pathway to enhance the overall sensing performance, which will envision to boost more efforts for advanced 3D porous aerogel using in PEC sensors.

Organic-Inorganic Porphyrinoid Frameworks for Biomolecule Sensing

Porphyrinoids and their analogous compounds play an important role in biosensing applications on account of their unique and versatile catalytic, coordination, photophysical, and electrochemical properties. Their remarkable arrays of properties can be finely tuned by synthetically modifying the porphyrinoid ring and varying the various structural parameters such as peripheral functionalization, metal coordination, and covalent or physical conjugation with other organic or inorganic scaffolds such as nanoparticles, metal-organic frameworks, and polymers. Porphyrinoids and their organic-inorganic conjugates are not only used as responsive materials but also utilized for the immobilization and embedding of biomolecules for applications in wearable devices, fast sensing devices, and other functional materials. The present review delineates the impact of different porphyrinoid conjugates on their physicochemical properties and their specificity as biosensors in a range of applications. The newest porphyrinoid types and their synthesis, modification, and functionalization are presented along with their advantages and performance improvements.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.

A dual-channel probe based on copper ion-mediated metal organic framework composite for colorimetric and ratiometric fluorescence monitoring of glyphosate degradation in soil and water

A dual-channel probe was developed, based on a novel composite metal organic frameworks (ZnMOF-74@Al-MOF) for glyphosate determination through ratio fluorescence and colorimetric methods. The prepared probe can not only recognize and combine glyphosate by introducing copper ion into the MOF, but also possess peroxidase-like catalytic activity. The recognition of target glyphosate brought about changes relative to its concentration on fluorescence intensity and ultraviolet absorption. And, the high specific surface area and porosity of porphyrin MOF provides the developed probe with more response opportunities to afford a better detection performance for glyphosate. Under optimum conditions, the copper ion-mediated method exhibited good detection performance for glyphosate with low detection limits (0.070 and 0.092 μg mL^-1 for fluorescence and colorimetric techniques, respectively). Furthermore, the possible mechanisms of the fluorescence quenching and the peroxidase-like catalytic of the probe were also explored. This dual-channel method was applied to monitor glyphosate degradation in environmental samples and satisfactory results were obtained.

Tuning the Redox Chemistry of Copper Oxide Nanoarchitectures Integrated with rGOP via Facet Engineering: Sensing H2S toward SRB Detection

The ultrasensitive determination of sulfate reducing bacteria (SRB) is of great significance for their crucial roles in environmental and industrial harms together with the early detection of microbial corrosion. In this work, we report the development of highly efficient electrocatalysts, i.e., Cu₂O-CuO extended hexapods (EHPs), which are wrapped on homemade freestanding graphene paper to construct a flexible paper electrode in the electrochemical sensing of the biomarker sulfide for SRB detection. Herein Cu₂O-CuO EHPs have been synthesized via a highly controllable and facile approach at room temperature, where the redox centers of copper oxide nanoarchitectures are tuned via facet engineering, and then they are deposited on the graphene paper surface through an electrostatic adsorption to enable homogeneous and highly dense distribution. Owing to the synergistic contribution of high electrocatalytic activity from the Cu mixed oxidation states and abundant catalytically active facets of Cu₂O-CuO EHPs and high electrical conductivity of the graphene paper electrode substrate, the resultant nanohybrid paper electrode has exhibited superb electrochemical sensing properties for H₂S with a wide linear range up to 352 μM and an extremely low detection limit (LOD) of 0.1 nM with a signal-to-noise ratio of 3 (S/N = 3), as well as high sensitivity, stability, and selectivity. Furthermore, taking advantage of the good biocompatibility and mechanical flexibility, the electrochemical sensing platform based on the proposed electrode has been applied in the sensitive detection of SRB in environmental samples through the sensing of sulfide from SRB, which holds great promise for on-site and online corrosion and environmental monitoring.

Improvement of the fluorescent sensing biomarker 3-nitrotyrosine for a new luminescent coordination polymer by size regulation

A new 3D luminescent coordination polymer (LCP) 1 was synthesized for detecting biomarker 3-nitrotyrosine. By adjusting the reaction conditions, Nano-LCP 1 was synthesized, which has a more lower detection limit compared with LCP 1.

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide

Hydrogen sulfide (H₂S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H₂S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H₂S-involved reactions have been reported for detection of endogenous H₂S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.

Designed multifunctional ratiometric fluorescent probe for directly detecting fluoride ion/ dichromate and indirectly monitoring urea

UiO-66-NH₂@eosin Y composite was obtained by confining eosin Y (EY) into the cavities of Zr-MOF and could emit two fluorescence peaks at 453 and 543 nm at an excitation wavelength of 355 nm. This multi-responsive and multifunctional ratiometric fluorescent nanoprobe not only enable directly distinct detection of F^-/Cr₂O₇^2- with ultra-high selectivity and sensitivity, but also could indirectly monitor the concentration of urea based on unique enzymatic hydrolysis reaction. The multifunctional probe was utilized for fluorescence labeling F-/Cr₂O₇^2- in sweat latent fingerprint through an environmentally friendly powder strategy and exhibited obvious luminescence visualization changes. Notably, the corresponding portable on-line test strips of probe for detection of F^- and Cr₂O₇^2- were made for monitoring the levels of F^- and Cr₂O₇^2-. Furthermore, the probe was applied to evaluate the degrees of F^-/Cr₂O₇^2- in HepG-2 cell and urea in serum with superior results,which indicate the potential application of the as-synthesized UiO-66-NH₂@EY as multifunctional probe for the detection of F^-, Cr₂O₇^2- and urea in biological samples. Finally, in order to extend the device-based applications of probe, an AND-OR-coupled molecular logic gate was put on agenda.

Ultrafast and nanomolar level detection of H2S in aqueous medium using a functionalized UiO-66 metal-organic framework based fluorescent chemosensor

Here, we present a 4-nitrophenyl functionalized Zr-UiO-66 MOF (MOF = metal-organic framework) and its applications towards the selective, sensitive and rapid detection of H₂S both in the aqueous medium and vapour phase. The MOF material was synthesized using the 2-(nitrophenoxy)terepththalic acid (H₂BDC-O-Ph-NO₂) linker and ZrCl₄ salt in the presence of a benzoic acid modulator. It was carefully characterized by thermogravimetric analysis (TGA), elemental analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy and surface area analysis. Noticeable thermal stability up to a temperature of 390 °C under air and the considerable chemical stability in different liquid media (H₂O, 1 M HCl, glacial acetic acid, NaOH in the pH = 8 to 10 range) confirmed the robustness of the MOF. The BET surface area (1040 m² g^-1) indicated the porous nature of the MOF. Remarkable selectivity of the MOF towards H₂S over other potential congeners of H₂S was observed in the aqueous medium. A very high fluorescence increment (∼77 fold) was observed after adding an aqueous Na₂S solution to the MOF suspension. The MOF probe displayed the lowest limit of detection (12.58 nM) among the existing MOF-based chemosensors of H₂S. Furthermore, it exhibited a very quick (60 s) response towards H₂S detection. The MOF compound could also detect H₂S in the vapour phase as well as in real water samples. Furthermore, we developed inexpensive MOF-coated paper strips for the naked-eye sensing of H₂S. A thorough investigation was carried out in order to elucidate the fluorescence turn-on sensing mechanism.

Capture of toxic gases in MOFs: SO2, H2S, NH3 and NO x

MOFs are promising candidates for the capture of toxic gases since their adsorption properties can be tuned as a function of the topology and chemical composition of the pores. Although the main drawback of MOFs is their vulnerability to these highly corrosive gases which can compromise their chemical stability, remarkable examples have demonstrated high chemical stability to SO2, H2S, NH3 and NO x . Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. Thus, the interactions of such functional groups (coordinatively unsaturated metal sites, μ-OH groups, defective sites and halogen groups) with these toxic molecules, not only determines the capture properties of MOFs, but also can provide a guideline for the desigh of new multi-functionalised MOF materials. Thus, this perspective aims to provide valuable information on the significant progress on this environmental-remediation field, which could inspire more investigators to provide more and novel research on such challenging task.

Lysosome targeting metal-organic framework probe LysFP@ZIF-8 for highly sensitive quantification of carboxylesterase 1 and organophosphates in living cells

Herein, a lysosomal targeting LysFP@ZIF-8 metal-organic framework (MOF) was fabricated using fluorescent protein chromophore-based probe (LysFP) for selectively detection of carboxylesterase 1 (CES1) in living cells. Unlike the regular small molecule fluorescent probes, LysFP@ZIF-8 showed wide range pH tolerabiligy, high selectivity and sensitivity to CES1 in bio-samples, and was successfully applied to achieve the visual monitoring of CES1 activity in living cells. Low detection limit and high fluorescence quantum yield was calculated as 79 ng/mL and 0.76 for LysFP@ZIF-8, respectively. Furthermore, LysFP@ZIF-8 can also serve as a fluorescence indicator of organophosphates pesticide exposure in the way of hydrolyzing the carboxylic acid ester group in LysFP. This type of probe can inspire the development of fluorescent tools for further explore many pathological processes.

Magnetically Driven Micro and Nanorobots

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells. Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility. This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as “MagRobots”) as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement. These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields. Actuation mechanisms of flagella-inspired MagRobots (i.e., corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (i.e., surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi-)spherical, helical, flexible, wire-like, and biohybrid MagRobots. Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed. Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed.

Multi-emission metal-organic framework composites for multicomponent ratiometric fluorescence sensing: recent developments and future challenges

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.

Porphyrin-Based Metal-Organic Frameworks for Biomedical Applications

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self-quenching under physiological conditions, limit their biomedical applications. In recent years, metal-organic frameworks (MOFs) have received increasing attention. The construction of porphyrin-based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin-based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin-based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

A historical perspective on porphyrin-based metal-organic frameworks and their applications

Porphyrins are important molecules widely found in nature in the form of enzyme active sites and visible light absorption units. Recent interest in using these functional molecules as building blocks for the construction of metal-organic frameworks (MOFs) have rapidly increased due to the ease in which the locations of, and the distances between, the porphyrin units can be controlled in these porous crystalline materials. Porphyrin-based MOFs with atomically precise structures provide an ideal platform for the investigation of their structure-function relationships in the solid state without compromising accessibility to the inherent properties of the porphyrin building blocks. This review will provide a historical overview of the development and applications of porphyrin-based MOFs from early studies focused on design and structures, to recent efforts on their utilization in biomimetic catalysis, photocatalysis, electrocatalysis, sensing, and biomedical applications.

Selective dual detection of H2S and Cu2+ by a post-modified MOF sensor following a tandem process

Fabrication of metal-organic frameworks (MOFs) based multifunctional sensors for various environmental pollutants represents a promising solution to the development of novel monitoring technologies. In this work, a dual responsive sensor of UiO-66-MA has been efficiently fabricated via post-modification of the UiO-66-MOF with maleic anhydride (MA), and dual detection of H₂S and Cu²⁺ in aquatic environments has been achieved tandemly. UiO-66-MA could selectively undergo Michael addition with H₂S accompanying a linear fluorescence turn-on behavior. The sensing is highly sensitive and selective, and the detection limit value of 3.3 nM represents the lowest record among all MOF-based H₂S sensing researches. Moreover, an alternative sensor for Cu²⁺ could be further tandemly afforded after the H₂S sensing. The H₂S added product of UiO-66-MA/H₂S exhibits selective fluorescence quenching towards Cu²⁺ with a detection limit as low as 2.6 nM. UiO-66-MA exhibits dual sensing functions for H₂S and Cu²⁺ following a tandem process based on combinatorial principles of Michael addition and S-Cu coordination. Evaluation studies suggest the promising potentials of UiO-66-MA in determining the level of H₂S and Cu²⁺ in aquatic environment, and the tandemly derived dual sensing functions demonstrate the advantages of developing multifunctional MOF sensors based on combinatorial principles.

External Power-Driven Microrobotic Swarm: From Fundamental Understanding to Imaging-Guided Delivery

Untethered micro/nanorobots have been widely investigated owing to their potential in performing various tasks in different environments. The significant progress in this emerging interdisciplinary field has benefited from the distinctive features of those tiny active agents, such as wireless actuation, navigation under feedback control, and targeted delivery of small-scale objects. In recent studies, collective behaviors of these tiny machines have received tremendous attention because swarming agents can enhance the delivery capability and adaptability in complex environments and the contrast of medical imaging, thus benefiting the imaging-guided navigation and delivery. In this review, we summarize the recent research efforts on investigating collective behaviors of external power-driven micro/nanorobots, including the fundamental understanding of swarm formation, navigation, and pattern transformation. The fundamental understanding of swarming tiny machines provides the foundation for targeted delivery. We also summarize the swarm localization using different imaging techniques, including the imaging-guided delivery in biological environments. By highlighting the critical steps from understanding the fundamental interactions during swarm control to swarm localization and imaging-guided delivery applications, we envision that the microrobotic swarm provides a promising tool for delivering agents in an active, controlled manner.

Trends in Micro-/Nanorobotics: Materials Development, Actuation, Localization, and System Integration for Biomedical Applications

Micro-/nanorobots (m-bots) have attracted significant interest due to their suitability for applications in biomedical engineering and environmental remediation. Particularly, their applications in in vivo diagnosis and intervention have been the focus of extensive research in recent years with various clinical imaging techniques being applied for localization and tracking. The successful integration of well-designed m-bots with surface functionalization, remote actuation systems, and imaging techniques becomes the crucial step toward biomedical applications, especially for the in vivo uses. This review thus addresses four different aspects of biomedical m-bots: design/fabrication, functionalization, actuation, and localization. The biomedical applications of the m-bots in diagnosis, sensing, microsurgery, targeted drug/cell delivery, thrombus ablation, and wound healing are reviewed from these viewpoints. The developed biomedical m-bot systems are comprehensively compared and evaluated based on their characteristics. The current challenges and the directions of future research in this field are summarized.

A copper-based metal-organic framework for ratiometric detection of hydrogen sulfide with high sensitivity and fast response

Metal-organic framework (MOF) is a class of crystalline porous solid materials which could be designed as sensors for bioactive molecules. In this study, charge transition between the ligand and the metal ions related emission and the ligand-based emission were formed simultaneously within a novel luminescent MOF with the copper reactive site as nodes. It can serve as a rare example of MOFs implicated ratiometric sensor for selective luminescent detection of H₂S. The luminescent detection limitations for H₂S is 0.21 μM, and it possesses a fast response of 30 s. The sensing mechanism is also discussed.

In Situ Generation of Prussian Blue by MIL-53 (Fe) for Point-of-Care Testing of Butyrylcholinesterase Activity Using a Portable High-Throughput Photothermal Device

Butyrylcholinesterase (BuChE), the primary source of serum cholinesterase activity, is an indispensable biochemical marker for clinical diagnosis of liver function and organophosphorus poisoning. The requirement for bulky and expensive instruments represents a huge hindrance for point-of-care testing (POCT) of BuChE, especially in resource-limited settings. Herein, an easy-operated, economic, and portable photothermal (PT) biosensing platform for high-throughput BuChE detection was rationally designed. BuChE could "light up" the PT signal through in situ generation of Prussian blue (PB) by MIL-53 (Fe), which allowed us to translate biological signals into temperature signals. Such temperature change signals could be monitored at high throughput (six samples for a single measurement) by a miniature self-made integrated PT device via combining separable 96-well plates, a three-dimensional (3D) printed sample bracket, 808 nm lasers, and thermometers, satisfying the requirement for rapid on-site detection in a large batch with low cost. In addition, the large specific surface area, 3D network structure, and high porosity of MIL-53 (Fe) offered a beneficial platform for its reaction with enzymatic hydrolysate, resulting in high sensing sensitivity and low detection limit (0.3 U L^-1), which was at least 20 000 times lower than the normal human serum BuChE activity. This facile, affordable, and broad applicability PT sensing platform provides a beneficial reference for the rational design of other disease diagnostic approaches suitable for POCT.

N-doped carbon dots modified with the epithelial cell adhesion molecule antibody as an imaging agent for HepG2 cells using their ultra-sensitive response to Al3

Carbon dots (CDs) are emerging as an ideal multifunctional materials due to their ease of preparation and excellent properties in medical imaging technology, environmental monitoring, chemical analysis and other fields. N-doped CDs modified with the epithelial cell adhesion molecule antibody (anti-EpCAM-NCDs) were synthesized in an ingenious and high-output approach. Due to the fluorescence enhancement effect of the introduced N atoms, the obtained anti-EpCAM-NCDs exhibited a strong green emission with an absolute quantum yield of up to 32.5%. Anti-EpCAM-NCDs have immunofluorescent properties and an active targeting function. The fluorescence effect and fluorescence quenching of anti-EpCAM-NCDs are used to image cells and detect Al³⁺, respectively. Experimental results show that this probe exhibited a wide linear response to Al³⁺over a concentration range of 0-100μM with a detection limit and quantification limit of 3 nM and 6 nM, respectively. Significantly, anti-EpCAM-NCDs, which have negligible cytotoxicity, excellent biocompatibility and high photostability, could be used for the intracellular imaging of HepG2 cells and the detection of Al³⁺in environmental and biological samples. As an efficient multifunctional material, anti-EpCAM-NCDs hold great promise for a number of applications in biological systems.

Development of biological metal-organic frameworks designed for biomedical applications: from bio-sensing/bio-imaging to disease treatment

Metal-organic frameworks (MOFs) are built using various organic ligands and metal ions (or clusters). With properties of high porosity, tunable chemical composition, and potential for post-synthetic modification, they have been applied in biomedicine, especially in bio-sensing, bio-imaging, and drug delivery. Since organic ligands and metal centers (ions or clusters) in the structure of MOFs can directly influence the property, function, and performance of MOFs, strict screening of organic ligands and metal centers is necessary. Especially, to improve the application of MOFs in the field of biomedicine, biocompatible organic ligands with low toxicity are desirable. In recent years, biological metal-organic frameworks (bio-MOFs) with ideal biocompatibility and diverse functionality have attracted wide attention. Endogenous biomolecules, including nucleobases, amino acids, peptides, proteins, porphyrins and saccharides, are employed as frameworks for MOF construction. These biological ligands coordinate with diverse metal centers in different ways, leading to the structural diversity of bio-MOFs. In this review, we summarize the organic ligand selectivity in constructing different types of bio-MOFs and their influence in biomedical applications with attractive new functions.

Carbon dots with red emission for bioimaging of fungal cells and detecting Hg2+ and ziram in aqueous solution

It is of importance for bioimaging of fungal cells using biocompatible and low toxic carbon dots (CDs) as labels in plant protection field because a clearer understanding on the infection mechanism of fungi on plant can be achieved. Meanwhile, long wavelength, especially, red/near-infrared (NIR) emissive CDs are more biocompatible than short wavelength emissive ones. In this work, CDs with red emission were synthesized by solvothermal pyrolysis of citric acid, acrylamide dissolved in formamide. Fungal cells stained by the CDs with red emission were brightly illuminated when imaged on a fluorescent microscope with excitation by a green laser pulse, suggesting the CDs are of an excellent label for bioimaging of fungal cell in red color region. Moreover, the CDs show a selective response to Hg²⁺ in the NaAc-HAc buffer solution, while ziram can form a more stable complex with Hg²⁺, leading to a recovery of the quenched fluorescence of the CDs. Therefore, methods for the detections of Hg²⁺ and ziram based on the "off-on" fluorescence of the CDs were established with limits of detection as low as 0.19 μM and 0.55 μg/mL.

Fluorinated ZnFeIII Hollow Metal-Organic Framework as a 19F NMR Probe for Highly Sensitive and Selective Detection of Hydrogen Sulfide

Hydrogen sulfide (H2S) is considered as a highly toxic environmental pollutant and an important signal transmitter in physiological processes, and the selective and reliable detection of H2S is of great concern and remains challenging. Herein, we report a smart sensitive "off-on" 19F NMR sensor for H2S by partially introducing a fluorinated ligand to construct a hollow dual metal-organic framework (MOF) nanosystem, F-ZnFeIII hMOF, in which the fluorinated ligand acts as the 19F signal source but is initially quenched due to the strong paramagnetic relaxation enhancement (PRE) effect from neighboring Fe3+ nodes. Upon exposure to sulfide ions, reduction of Fe3+ to Fe2+ is specifically triggered, which attenuates PRE efficiency, thus turning on the 19F NMR signal. The unique hollow MOF architecture benefits the mobility of 19F atoms, thereby improving the response sensitivity. Meanwhile, the desirable H2S-sorption feature and appropriate redox potential of Fe3+/Fe2+ account for the favorable selectivity. The increase in the 19F signal is linear with the concentration of sulfide in the range of 20 to 150 μM with a detection limit of 2.8 μM. The probe is well demonstrated by analyzing H2S in complex matrixes such as biological and foodstuff samples.

Metal-Organic Frameworks for Biomedical Applications

Metal-organic frameworks (MOFs) are an interesting and useful class of coordination polymers, constructed from metal ion/cluster nodes and functional organic ligands through coordination bonds, and have attracted extensive research interest during the past decades. Due to the unique features of diverse compositions, facile synthesis, easy surface functionalization, high surface areas, adjustable porosity, and tunable biocompatibility, MOFs have been widely used in hydrogen/methane storage, catalysis, biological imaging and sensing, drug delivery, desalination, gas separation, magnetic and electronic devices, nonlinear optics, water vapor capture, etc. Notably, with the rapid development of synthetic methods and surface functionalization strategies, smart MOF-based nanocomposites with advanced bio-related properties have been designed and fabricated to meet the growing demands of MOF materials for biomedical applications. This work outlines the synthesis and functionalization and the recent advances of MOFs in biomedical fields, including cargo (drugs, nucleic acids, proteins, and dyes) delivery for cancer therapy, bioimaging, antimicrobial, biosensing, and biocatalysis. The prospects and challenges in the field of MOF-based biomedical materials are also discussed.

Linker-Eliminated Nano Metal-Organic Framework Fluorescent Probe for Highly Selective and Sensitive Phosphate Ratiometric Detection in Water and Body Fluids

Phosphate is an important anion in both the aquatic environment and biological systems. The search for a selective and sensitive phosphate ratiometric fluorescent probe to quantify the phosphate level in water samples and body fluids is of great significance for the protection of the ecological environment and human health. Here, a porphyrin-based nano metal-organic framework (NMOF), PCN-224, was successfully exploited as a simple but highly sensitive and selective single-component ratiometric fluorescent probe with accurate composition and measurable structure for the quantitative determination of phosphate, based on the interesting double-emission fluorescence of the porphyrin ligand itself. Compared with other zirconium-based NMOF probes for phosphate, the reduced number of connections for ZrO clusters with the ligand in PCN-224 obtained by a linker-elimination strategy simultaneously provides more active recognition sites for phosphate, which effectively improves the sensitivity of the zirconium-based NMOF probes. The detection limit of the probe is only 54 nM. Additionally, the accuracy of the ratiometric detection based on this probe was further proved by the detection of phosphate in human serum and drinking water.

A two-dimensional zinc(II)-based metal-organic framework for fluorometric determination of ascorbic acid, chloramphenicol and ceftriaxone

A two-dimensional zinc(II)-based metal-organic framework [Zn • (BA) • (BBI)] was synthesized from 1,2-benzenediacetic acid and 1,1'-(1,4-butanediyl) bis(imidazole) via a solvothermal reaction. The crystal exhibits good chemical stability in the pH range from 2 to 12, and strong fluorescence with excitation/emission maxima of 270/290 nm. The crystal is shown to by a viable fluorescent probe for the detection of ascorbic acid (AA) and the antibiotics chloramphenicol (CHL) and ceftriaxone (CRO). Fluorescence intensity of crystal dispersion is significantly quenched with increasing concentrations of AA/CHL/CRO. Quenching occurs even in the presence of other substances. The assay is fast (5 s) and has a low detection limit (1.6 ppb for AA, 12 ppb for CHL and 3.9 ppb for CRO). The crystal still has a good quenching effect on AA/CHL/CRO after washing and using for five times. The response of the probe is related to the interplay between the MOF and analytes via energy absorption competition. Graphical abstractSchematic diagram of preparing Zn • (BA) • (BBI) and responding to target analytes. BA: 1,2-phenyldiacetic acid; BBI: 1,1'-(1,4-butanediyl)bis(imidazole); Zn • (BA) • (BBI): Crystal chemical formula.

Fe3+-Sensitive Carbon Dots for Detection of Fe3+ in Aqueous Solution and Intracellular Imaging of Fe3+ Inside Fungal Cells

In this article, the Fe3+-sensitive carbon dots were obtained by means of a microwave-assisted method using glutamic acid and ethylenediamine as reactants. The carbon dots exhibited selective response to Fe3+ ions in aqueous solution with a turn-off mode, and a good linear relationship was found between (F0-F)/F0 and the concentration of Fe3+ in the range of 8-80 μM. As a result, the as-synthesized carbon dots can be developed as a fluorescent chemosensor for Fe3+ in aqueous solution. Moreover, the carbon dots can be applied as a fluorescent agent for fungal bioimaging since the fungal cells stained by the carbon dots were brightly illuminated on a confocal microscopy excited at 405 nm. Furthermore, an increase in the concentration of intracellular Fe3+ could result in fluorescence quenching of the carbon dots in the fungal cells when incubated in the Tris-HCl buffer solution containing Fe3+. However, due to EDTA might hinder Fe(III) to enter the fungal cells, incubation in Fe(III)-EDTA complex solution exerted negligible effect on the fluorescence of fungal cells labeled by the carbon dots. Therefore, the carbon dots can serve as a potential probe for intracellular imaging of Fe3+ inside fungal cells.

An accurate and portable colorimetric chemosensor for S2− detection via two complementary mechanisms

A chemosensor based on two complementary mechanisms of color mixing and the recovery of uncoordinated carboxyl groups has been developed, which makes S²⁻ detection in water more accurate.

Post-synthetic modification of a metal–organic framework with a chemodosimeter for the rapid detection of lethal cyanide via dual emission

A post-synthetically modified chemodosimeter grafted MOF is presented for the selective, visual and fluorogenic detection of cyanide via dual emission.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.

Size-controlled synthesis of metal–organic frameworks and their performance as fluorescence sensors

Fluorescent sensing experiments were carried out to compare the sensing performance for folic acid between bulk and nano Tb-MOFs.