MOF-Based Platform for Kidney Diseases: Advances, Challenges, and Prospects

Kidney diseases are important diseases that affect human health worldwide. According to the 2020 World Health Organization (WHO) report, kidney diseases have become the top 10 causes of death. Strengthening the prevention, primary diagnosis, and action of kidney-related diseases is of great significance in maintaining human health and improving the quality of life. It is increasingly challenging to address clinical needs with the present technologies for diagnosing and treating renal illness. Fortunately, metal-organic frameworks (MOFs) have shown great promise in the diagnosis and treatment of kidney diseases. This review summarizes the research progress of MOFs in the diagnosis and treatment of renal disease in recent years. Firstly, we introduce the basic structure and properties of MOFs. Secondly, we focus on the utilization of MOFs in the diagnosis and treatment of kidney diseases. In the diagnosis of kidney disease, MOFs are usually designed as biosensors to detect biomarkers related to kidney disease. In the treatment of kidney disease, MOFs can not only be used as an effective adsorbent for uremic toxins during hemodialysis but also as a precise treatment of intelligent drug delivery carriers. They can also be combined with nano-chelation technology to solve the problem of the imbalance of trace elements in kidney disease. Finally, we describe the current challenges and prospects of MOFs in the diagnosis and treatment of kidney diseases.

Textural Precursor Compositions Harvested for Independent Signal Generators: Scaling Micron-Sized Flower-Like Metal-Organic Frameworks as Amplifying Units for Dual-Mode Glycoprotein Assay

In this work, a micron-sized flower-like metal-organic frameworks (MOFs)-based boronate-affinity sandwich-type immunoassay was fabricated for the dual-mode glycoprotein assay. For proof of concept, the flower-like MOFs were synthesized from transition Cu nodes and tetrakis (4-carboxyphenyl) porphyrin (TCPP) ligands by spontaneous standing assembly. In addition, the specificity toward glycoprotein involved the antigen recognition as well as covalent bonding via the boronate-glycan affinity, and the immediate signal responses were initiated by textural decomposition of the flower-like MOFs. Intriguingly, Cu nodes, of which the valence state is dominant by CuI species, can endow the Fenton-like catalytic reaction of the fluorogenic substrate for generating fluorescence signals. For benefits, TCPP ligands, in which each TCPP molecule has four guest donors, can provide multiple valences for the assembly of cyclodextrin-capped gold nanoparticles via host-guest interaction for colorimetry output. Albeit important, the scaling micrometer patterns for the flower-like MOFs carrying numerous Cu nodes and TCPP ligands can also function as amplifying units, signifying the output signal. The detection limit of the dual-mode glycoprotein assay can reach 10.5 nM for the fluorescence mode and 18.7 nM for the colorimetry mode, respectively. Furthermore, the merits of harvesting different signal generators toward the multimodal readout patterns can allow the mutual verification and make the analytical results more reliable. Collectively, our proposed assay may offer a new idea in combining the inherent textural merits from MOFs for dual signal generators, which can also emphasize accurate detection capability for glycoprotein assay.

MOF-mediated dual energy transfer nanoprobe integrated with exonuclease III amplification strategy for highly sensitive detection of DNA

Accurate quantitative detection of DNA is an advanced strategy in various fields (such as disease diagnosis and environmental monitoring), but the classical DNA detection method usually suffers from low sensitivity, expensive thermal cyclers, or strict annealing conditions. Herein, a MOF-ERA platform for ultrasensitive HBV-DNA detection is constructed by integrating metal-organic framework (MOF)-mediated double energy transfer nanoprobe with exonuclease III (Exo III)-assisted target recycling amplification. The proposed double energy transfer containing a donor and two receptors is simply composed of MOFs (UiO-66-NH2, a well-studied MOF) modified with a signal probe formed by the hybridization of carboxyuorescein (FAM)-labeled DNA (FDNA) and black hole quencher (BHQ1)-terminated DNA (QDNA), resulting in low fluorescence signal. After the addition of HBV-DNA, Exo III degradation to FDNA is activated, leading to the liberation of the numerous FAM molecules, followed by the generation of a significant fluorescence signal owing to the negligible binding of MOFs with free FAM molecules. The results certify that the MOF-ERA platform can be successfully used to assay HBV-DNA in the range of 1.0-25.0 nM with a detection limit of 97.2 pM, which is lower than that without BHQ1 or Exo III. The proposed method with the superiorities of low background signal and high selectivity holds promise for early disease diagnosis and clinical biomedicine applications.

A fluorescence and SERS dual-mode sensing on tetracycline antibiotics based on Ag@NH2-MIL-101(Al) nanoprobe

Antibiotic residues are becoming more and more concern due to the increasingly serious resistance from bacteria to organism. On-site and accurate evaluation on antibiotics is necessary and urgent to effectively solve such public issue. To provide point-of-care-test (POCT) ideas for antibiotic accurate evaluation, a fluorescence (FL)-surface-enhanced Raman scattering (SERS) dual-mode detection of tetracycline antibiotic (TCs) was realized for the first time. Based on the inner filter effect in Ag@NH2-MIL-101(Al) nanoprobe, the fluorescence quenching was induced and the SERS signal was swiftly turn on through π-π interaction and hydrogen bonding in the presence of TCs. This FL-SERS dual mode sensor displayed excellent detection limits (FL in ∼10-3 ppm, SERS in ∼10-5 ppm), and achieved a reliable detection of TCs in honey with a recovery rate of 84.45%-112.08%. This method combines the advantages of FL and SERS detection, meanwhile, two techniques verified against each other to achieve highly sensitive and specific FL-SERS dual-mode sensor for TCs. We believe that such antibody-or aptamer-independent FL and SERS complementary nanoprobe can be applied to fast, direct and multiple sensing in environment and food hazards.

Advances and Applications of Metal-Organic Frameworks (MOFs) in Emerging Technologies: A Comprehensive Review

Metal-organic frameworks (MOFs) that are the wonder material of the 21st century consist of metal ions/clusters coordinated to organic ligands to form one- or more-dimensional porous structures with unprecedented chemical and structural tunability, exceptional thermal stability, ultrahigh porosity, and a large surface area, making them an ideal candidate for numerous potential applications. In this work, the recent progress in the design and synthetic approaches of MOFs and explore their potential applications in the fields of gas storage and separation, catalysis, magnetism, drug delivery, chemical/biosensing, supercapacitors, rechargeable batteries and self-powered wearable sensors based on piezoelectric and triboelectric nanogenerators are summarized. Lastly, this work identifies present challenges and outlines future opportunities in this field, which can provide valuable references.

Metallic nanostructure-based aptasensors for robust detection of proteins

There is a significant need for fast, cost-effective, and highly sensitive protein target detection, particularly in the fields of food, environmental monitoring, and healthcare. The integration of high-affinity aptamers with metal-based nanomaterials has played a crucial role in advancing the development of innovative aptasensors tailored for the precise detection of specific proteins. Aptamers offer several advantages over commonly used molecular recognition methods, such as antibodies. Recently, a variety of metal-based aptasensors have been established. These metallic nanomaterials encompass noble metal nanoparticles, metal oxides, metal-carbon nanotubes, carbon quantum dots, graphene-conjugated metallic nanostructures, as well as their nanocomposites, metal-organic frameworks (MOFs), and MXenes. In general, these materials provide enhanced sensitivity through signal amplification and transduction mechanisms. This review primarily focuses on the advancement of aptasensors based on metallic materials for the highly sensitive detection of protein targets, including enzymes and growth factors. Additionally, it sheds light on the challenges encountered in this field and outlines future prospects. We firmly believe that this review will offer a comprehensive overview and fresh insights into metallic nanomaterials-based aptasensors and their capabilities, paving the way for the development of innovative point-of-care (POC) diagnostic devices.

Ratiometric fluorescence aptasensor for the detection of patulin in apple juice based on the octahedral UiO-66-TCPP metal-organic framework and aptamer systems

Patulin (PAT) is a potentially harmful mycotoxin to human health and is known to contaminate apple juice. In this work, we developed a ratiometric fluorescence aptasensor using tetrakis(4-carboxyphenyl)porphyrin (H2TCPP)-treated octahedral UiO-66-NH2 (defined as UiO-66-TCPP) to detect PAT. This 2-aminoterephthalic acid and H2TCPP functionalized metal-organic framework showed multiple adsorption effects (hydrogen bonding and π-π stacking) on the aptamer (Apt) and served as a quenching material. When the target PAT bound specifically to the Apt, the fluorescence of the 6-carboxyfluorescein-labeled Apt would recover, and the fluorescence of the H2TCPP ligand remained unchanged. This ratiometric fluorescence property improved the accuracy of PAT detection. Moreover, the introduction of the H2TCPP ligand enhanced the quenching efficiency of UiO-66-NH2, thus improving the sensitivity of the fluorescent aptasensor (UiO-66-TCPP vs. UiO-66-NH2: 0.0162 ng/mL vs. 1.8 ng/mL). In addition, we used UiO-66-TCPP to detect PAT in apple juice samples. This work provides a good paradigm for the construction of ratiometric fluorescence aptasensors with high sensitivity and accuracy.

A review of aptamer-conjugated nanomaterials for analytical sample preparation: Classification according to the utilized nanomaterials

BACKGROUND

Sample extraction before detection is a critical step in analysis. Since targets of interest are often found in complex matrices, the sample can not be directly introduced to the analytical instrument. Nanomaterials with unique physical-chemical properties are excellent supports for use in sorbent-based extraction. However, they lack selectivity and thus need to be functionalized with target-capturing molecules. Antibodies and molecularly imprinted polymers (MIPs) can be used for this purpose, but they have some problems that limit their practical applications. Hence, functionalization of nanomaterials for selectivity remains a problem.

RESULTS

Nucleic acid aptamers are affinity reagents that can provide superiority to antibodies since they can be selected in vitro and at a lower cost. Moreover, aptamers can be chemically synthesized and easily modified with different functional groups. Hence, aptamers are good candidates to impart selectivity to the nanomaterials. Recent studies focus on the integration of aptamers with magnetic nanoparticles, carbon-based nanomaterials, metal-organic frameworks, gold nanoparticles, gold nanorods, silica nanomaterials, and nanofibers. The unique properties of nanomaterials and aptamers make the aptamer-conjugated nanomaterials attractive for use in sample preparation. Aptamer-functionalized nanomaterials have been successfully used for selective extraction of proteins, small molecules, and cells from different types of complex samples such as serum, urine, and milk. In particular, magnetic nanoparticles have a wider use due to the rapid extraction of the sample under magnetic field.

SIGNIFICANCE

In this review, we aim to emphasize how beneficial features of nanomaterials and aptamers could be combined for extraction or enrichment of the analytes from complex samples. We aim to highlight that the benefits are twofold in terms of selectivity and efficiency when employing nanomaterials and aptamers together as a single platform.

SERS Immunoassay Based on an Enzyme-Catalyzed Cascade Reaction and Metal-Organic Framework/Alkaline Phosphatase for Ultrasensitive Detection of Adenosine Triphosphate

Herein, an adenosine triphosphate (ATP)-induced enzyme-catalyzed cascade reaction system based on metal-organic framework/alkaline phosphatase (MOF/ALP) nanocomposites was designed to establish a surface-enhanced Raman spectroscopy (SERS) biosensor for use in rapid, sensitive ATP detection. Numerous ALP molecules were first encapsulated using ZIF-90 to temporarily deactivate the enzyme activity, similar to a lock. Au nanostars (AuNSs), as SERS-enhancing substrates, were combined with o-phenylenediamine (OPD) to form AuNSs@OPD, which could significantly improve the Raman signal of OPD. When the target ATP interacted with the MOF/ALP nanocomposites, ATP could act as a key to open the MOF structure, releasing ALP, which should further catalyze the conversion of OPD to oxOPD with the aid of ascorbic acid 2-phosphate. Therefore, with the increasing concentrations of ATP, more ALP was released to catalyze the conversion of OPD, resulting in the reduced intensity of the Raman peak at 1262 cm-1, corresponding to the level of OPD. Based on this principle, the ATP-induced enzyme-catalyzed cascade reaction SERS biosensor enabled the ultrasensitive detection of ATP, with a low detection limit of 0.075 pM. Consequently, this study provides a novel strategy for use in the ultrasensitive, rapid detection of ATP, which displays considerable potential for application in the fields of biomedicine and disease diagnosis.

DNA-Functionalized Porphyrinic Metal-Organic Framework-Based Drug Delivery System for Targeted Bimodal Cancer Therapy

A DNA-functionalized porphyrinic MOF (porMOF) drug delivery system was successfully constructed. porMOF as a photosensitizer and drug delivery carrier can integrate photodynamic therapy (PDT) and chemotherapy. Via the strong coordination interaction between the zirconium cluster of porMOF and the terminal phosphate group of DNA, the stable modification of the DNA layer on the porMOF surface is achieved. Meanwhile, the introduction of C/G-rich base pairs into the DNA double-stranded structure provides more binding sites of chemotherapeutic drug doxorubicin (DOX). AS1411, an aptamer of nucleolin proteins that are overexpressed by cancer cells, is introduced in the double-stranded terminal, which can endow the nanosystem with the ability to selectively recognize cancer cells. C-rich sequences in DNA double strands form an i-motif structure under acidic conditions to promote the highly efficient release of DOX in cancer cells. In vitro and in vivo experiments demonstrate that the synergistic PDT/chemotherapy modality achieves highly efficient cancer cell killing and tumor ablation without undesirable side effects.

Construction of a nanoscale metal-organic framework aptasensor for fluorescence ratiometric sensing of AFB1 in real samples

Aflatoxins B1 (AFB1) that could contaminate agricultural products has received sustained attention due to its high toxicity and wide distribution. Therefore, sensitive and facile detection method for AFB1 is significant for food safety and control. In this work, a ratiometric fluorescence NMOFs-Aptasensor was developed based on the combination of Cy3-modified aptamer and zirconium-based nanoscale metal-organic frameworks (NMOFs). NMOFs served as energy donors, and Cy3 labeled on the AFB1 aptamer was used as an acceptor. An energy donor-acceptor pair was fabricated in the NMOFs-Aptasensor. With AFB1 selectively caught by the AFB1 aptamer, the fluorescence of the NMOFs-Aptasensor changed via fluorescence resonance energy transfer (FRET), and the fluorescence spectra changed accordingly. The ratiometric fluorescence signal was utilized to quantitatively measure AFB1. The reported NMOFs-Aptasensor presented great detection performance from 0 to 3.33 ng mL^-1, with an LOD of 0.08 ng mL^-1. Moreover, the fluorescence sensor was successfully applied to detect AFB1 in real samples.

DNA-directed assembly of nanomaterials and their biomedical applications

In the past decades, DNA has been widely used in the field of nanostructures due to its unique programmable properties. Besides being used to form its own diverse structures such as the assembly of DNA origami, DNA can also be used for the assembly of nanostructures with other materials. In this review, different strategies for the functionalization of DNA on nanoparticle surfaces are listed, and the roles of DNA in the assembly of nanostructures as well as the influencing factors are discussed. Finally, the biomedical applications of DNA-assembled nanostructures were summarized. This review provided new insight into the application of DNA in nanostructure assembly.

Insight into the Sensing Behavior of DNA Probes Based on MOF-Nucleic Acid Interaction for Bioanalysis

Adsorption of DNA probes onto nanomaterials is a promising strategy for bioassay establishment typically using fluorescence or catalytic activities to generate signals. Albeit important, there is currently a lack of systematic understanding of the sensing behaviors building on nanomaterial-DNA interactions, which greatly limits the rational method design and their subsequent applications. Herein, the issue was investigated by employing multifunctional metal-organic frameworks (MOFs) (FeTCPP⊂UiO-66) as a model that was synthesized via integrating heme-like ligand FeTCPP into commonly used MOFs (UiO-66). Our results demonstrated that the fluorescently labeled DNA adsorbed onto FeTCPP⊂UiO-66 was quenched through photoinduced electron transfer, fluorescence resonance energy transfer, and the internal filtration effect. Among different DNA structures, double-stranded DNA and hybridization chain reaction products largely retained their fluorescence due to desorption and conformational variation, respectively. In addition, ssDNA could maximally inhibit the peroxidase activity of FeTCPP⊂UiO-66, and this inhibition was strongly dependent on the strand length but independent of base composition. On the basis of these discoveries, a fluorescence/colorimetric dual-modal detection was designed against aflatoxin B1 with satisfactory performances obtained to further verify our results. This study provided some new insights into the sensing behaviors based on MOF-DNA interactions, indicating promising applications for rational bioassay design and its performance improvement.

Metal-Organic Frameworks Nanocarriers for Functional Nucleic Acid Delivery in Biomedical Applications

Metal-organic frameworks (MOFs), a distinctive funtionalmaterials which is constructed by various metal ions and organic molecules, have gradually attracted researchers' attention from they were founded. In the last decade, MOFs emerge as a biomedical material with potential applications due to their unique properties. However, the MOFs performed as nanocarriers for functional nucleic acid delivery in biomedical applications rarely summarized. In this review, we introduce recent developments of MOFs for nucleic acid delivery in various biologically relevant applications, with special emphasis on cancer therapy (including siRNA, ASO, DNAzyme, miRNA and CpG oligodeoxynucleotides), bioimaging, biosensors and separation of biomolecules. We expect the accomplishment of this review could benefit certain researchers in biomedical field to develop novel sophisticated nanocarriers for functional nucleic acid delivery based on the promising material of MOFs.

Construction of multifunctional NH2-UiO-66 metal organic framework: sensing and photocatalytic degradation of ketorolac tromethamine and tetracycline in aqueous medium

Existence of pharmaceutical residues in water has endangered environmental pollution worldwide, which makes it ineludible to develop prospective bifunctional materials which not only possess excellent fluorescence behaviour to monitor pharmaceuticals but also exhibit simultaneous photocatalytic removal efficiency. Strengthened by functionalized metal organic framework (MOF) materials, we present here an amine functionalized zirconium-based MOF NH₂-UiO-66 which has been successfully synthesized using solvothermal approach. The as prepared MOF was subjected to numerous structural, morphological and compositional characterizations. Interestingly, featured by the excellent fluorescent intensity of MOF modulated by LMCT effect, NH₂-UiO-66 was screened to detect pharmaceutical compounds with KTC and TC in aqueous solution. The prepared functionalized MOF showcased excellent sensing platform with magnificent response range (0‒3 µM), lower limit of detection (160 nM; KTC and 140 nM; TC), excellent selectivity and influential anti-interference capability. More importantly, the practical utility of the proposed sensor was further explored for the determination of pharmaceutical drugs in real water samples with suitable recoveries. Simultaneously, the synthesized MOF also exhibited high photocatalytic efficiency towards the removal of KTC and TC under solar light irradiation. The degradation efficiency for KTC and TC was found to be 68.3% and 71.8% within 60 and 280 min of solar light, respectively. Moreover, excellent recyclability was demonstrated by the current synthesized system over five cycles. Overall, this study presents a feasible route for the utilization of functionalized MOFs as potential dual functional materials towards the simultaneous detection and degradation of specific pharmaceuticals from aqueous medium.

A signal-on fluorescent biosensor for mercury detection based on a cleavable phosphorothioate RNA fluorescent probe and metal-organic frameworks

Mercury contamination is a major environmental concern. In this work, we used a cleavable phosphorothioate (PS) fluorescence probe quenched by UiO-66-NH₂ to develop a "signal-on" fluorescent biosensor for Hg²⁺ detection. The probe was bound to UiO-66-NH₂ through π-π stacking and hydrogen bonding, thereby extinguishing the fluorescence of the FAM-labelled probe. The PS site was cleaved in the presence of Hg²⁺, releasing the FAM group and significantly enhancing the fluorescence signal. The intensity of the fluorescence linearly rose as the Hg²⁺ concentration increased in the range of 1-100 nM (R² = 0.994), and the limit of detection was 0.118 nM (S/N = 3). This biosensor demonstrated high selectivity for Hg²⁺ and was effectively applied to quantification of Hg²⁺ in various water samples with acceptable recovery rates. These results suggest that this practical, straightforward technology is a good option for monitoring mercury ions in the environment.

Rapid and efficient isolation platform for plasma extracellular vesicles: EV-FISHER

Extracellular vesicles (EVs) have found diverse applications in clinical theranostics. However, the current techniques to isolate plasma EVs suffer from burdensome procedures and limited yield. Herein, we report a rapid and efficient EV isolation platform, namely, EV-FISHER, constructed from the metal-organic framework featuring cleavable lipid probes (PO4 3- -spacer-DNA-cholesterol, PSDC). The EV-FISHER baits EVs from plasma by cholesterol and separates them with an ordinary centrifuge. The captured EVs could be released and collected upon subsequent cleavage of PSDC by deoxyribonuclease I. We conclude that EV-FISHER dramatically outperforms the ultracentrifugation (UC) in terms of time (∼40 min vs. 240 min), isolation efficiency (74.2% vs. 18.1%), and isolation requirement (12,800 g vs. 135,000 g). In addition to the stable performance in plasma, EV-FISHER also exhibited excellent compatibility with downstream single-EV flow cytometry, enabling the identification of glypican-1 (GPC-1) EVs for early diagnosis, clinical stages differentiation, and therapeutic efficacy evaluation in breast cancer cohorts. This work portrays an efficient strategy to isolate EVs from complicated biological fluids with promising potential to facilitate EVs-based theranostics.

Recent Progress in Aptamer-Functionalized Metal-Organic Frameworks-Based Optical and Electrochemical Sensors for Detection of Mycotoxins

Mycotoxin contamination in foodstuffs and agricultural products has posed a serious hazard to human health and raised international concern. The progress of cost-effective, facile, rapid and reliable analytical tools for mycotoxin determination is in urgent need. In this regard, the potential utility of metal-organic frameworks (MOFs) as a class of crystalline porous materials has sparked immense attention due to their large specific surface area, adjustable pore size, nanoscale framework structure and good chemical stability. The amalgamation of MOFs with high-affinity aptamers has resulted in the progress of advanced aptasensing methods for clinical and food/water safety diagnosis. Aptamers have many advantages over classical approaches as exceptional molecular recognition constituents for versatile bioassays tools. The excellent sensitivity and selectivity of the MOF-aptamer biocomposite nominate them as efficient lab-on-chip tools for portable, label-free, cost-effective and real-time screening of mycotoxins. Current breakthroughs in the concept, progress and biosensing applications of aptamer functionalized MOFs-derived electrochemical and optical sensors for mycotoxins have been discussed in this study. We first highlighted an overview part, which provides some insights into the functionalization mechanisms of MOFs with aptamers, offering a foundation to create MOFs-based aptasensors. Then, we discuss various strategies to design high-performance MOFs-based aptamer scaffolds, which serve as either signal nanoprobe carriers or signal nanoprobes and their applications. We perceived that applications of optical aptamers are in their infancy in comparison with electrochemical MOFs-derived aptasensors. Finally, current challenges and prospective trends of MOFs-aptamer sensors are discussed.

Metal-organic frameworks for pharmaceutical and biomedical applications

Metal-organic framework (MOF) materials provide unprecedented opportunities for evaluating valuable compounds for various medical applications. MOFs merged with biomolecules, used as novel biomaterials, have become particularly useful in biological environments. Bio-MOFs can be promising materials in the global to avoid utilization above toxicological substances. Bio-MOFs with crystallin and porosity nature offer flexible structure via bio-linker and metal node variation, which improves their wide applicability in medical science.

Nanomaterials and metal-organic frameworks for biosensing applications of mutations of the emerging viruses

The world today lives in a state of terrible fear due to the mutation of the emerging COVID-19. With the continuation of this pandemic, there is an urgent need for fast, accurate testing devices to detect the emerging SARS-CoV-2 pandemic in terms of biosensors and point-of-care testing. Besides, the urgent development in personal defense tools, anti-viral surfaces and wearables, and smartphones open the door for simplifying the self-diagnosis process everywhere. This review introduces a quick COVID-19 overview: definition, transmission, pathophysiology, the identification and diagnosis, mutation and transformation, and the global situation. It also focuses on an overview of the rapidly advanced technologies based on nanomaterials and MOFs for biosensing, diagnosing, and viral control of the SARS-CoV-2 pandemic. Finally, highlight the latest technologies, applications, existing achievements, and preventive diagnostic strategies to control this epidemic and combat the emerging coronavirus. This humble effort aims to provide a helpful survey that can be used to develop a creative solution and to lay down the future vision of diagnosis against COVID-19.

Fluorescence Biosensor for One-Step Simultaneous Detection of Mycobacterium tuberculosis Multidrug-Resistant Genes Using nanoCoTPyP and Double Quantum Dots

The diagnosis of multidrug-resistant tuberculosis (MDR-TB) is crucial for the subsequent drug guidance to improve therapy and control the spread of this infectious disease. Herein, we developed a novel florescence biosensor for simultaneous detection of Mycobacterium tuberculosis (Mtb) multidrug-resistant genes (rpoB531 for rifampicin and katG315 for isoniazid) by using our synthesized nanocobalt 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (nanoCoTPyP) and double quantum dots (QDs). Several nanoCoTPyPs with different charges and morphology were successfully prepared via the surfactant-assisted method and their quenching ability and restoring efficiency for DNA detection were systematically analyzed. It was found that spherical nanoCoTPyP with positive charge exhibited excellent quenching effect and sensing performance for the two DNAs' detection due to its affinity differences towards single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). ssDNA attached on QDs (QDs-ssDNA) was specifically hybridized with targets to form QDs-dsDNA, resulting in fluorescence recovery due to the disruption of the interactions between nanoCoTPyP and ssDNA. Two drug-resistant genes could be simultaneously quantified in a single run and relatively low limits of detection (LODs) were obtained (24 pM for T1 and 20 pM for T2). Furthermore, the accuracy and reliability of our method were verified by testing clinical samples. This simple and low-cost approach had great potential to be applied in clinical diagnosis of MDR-TB.

Modulating the Biomimetic and Fluorescence Quenching Activities of Metal-Organic Framework/Platinum Nanoparticle Composites and Their Applications in Molecular Biosensing

Nanoscale metal-organic frameworks (nMOFs) have gained considerable attention with significant potential applications. Although great efforts have been devoted to designing and fabricating nanoscaffold structures, approaches of deliberately regulating the intrinsic functionality of nMOFs have been poorly explored. Herein, we report a simple and novel strategy to regulate the catalytic and fluorescence quenching behaviors of nMOFs through coordination-driven self-assembly. As a proof-of-concept, we synthesized a synergistic and stable MOF-metal nanocomposite by loading platinum nanoparticles (PtNPs) on a commonly used Fe-MOF, i.e., MIL-88B-NH₂/Pt, as a MOF composite model for exploration. On one hand, the complexation with ATP effectively broke the pH limitation of the peroxidase-mimicking MIL-88B-NH₂/Pt nanozyme, bringing a 10-fold increased catalytic activity under alkaline condition. Based on the distinct catalytic enhancement between ATP and other nucleotides, real-time monitoring of apyrase activity as well as colorimetric detection of alkaline phosphatase (ALP) was performed. On the other hand, interactions of MIL-88B-NH₂/Pt with fluorescent DNA were tolerant of different nucleic acids and, more importantly, were further manipulated by inorganic molecules. As a result, H₂O₂ could only trigger the release of a G-rich sequence, while phosphates could readily induce desorption of various DNA molecules with varying lengths, sequences, and fluorescent dyes. Accordingly, fluorescent DNA and MIL-88B-NH₂/Pt as functional probe-quencher pairs were proposed, allowing the establishment of a fluorescence bioassay for ALP and PPase detection and Boolean logic calculations. This work offers a means to tune the intrinsic activities of nMOFs by surface engineering, benefiting design of functional nanomaterials and development of advanced biosensing systems.

Biofunctionalized metal-organic frameworks and host-guest interactions for advanced biomedical applications

Owing to highly favourable properties such as enormous internal surface areas, high porosity and large flexibility, when it comes to the choice of precursors and high control over their structures and porosity, metal-organic frameworks (MOFs) have emerged as promising materials for applications such as gas storage and separation, catalysis, wastewater filtration, etc. The applications of MOFs, despite being so lucrative materials, are very limitedly explored in biomedical applications owing to several concerns such as their biocompatibility, rate of degradation and rate of accumulation in tissues and biological systems. Newer methods are being developed to make MOFs more biologically palatable by their surface functionalization using biomolecules such as nucleic acids, amino acids and lipids. Here we present the progress in biofunctionalization methods of MOFs for improving their physical and chemical properties for biomedical applications, with special focus on their formation via covalent and non-covalent routes. Following this, we discuss in detail the applications of these biofunctionalized MOFs in areas of drug delivery, bio-sensing and bio-imaging. We conclude by presenting a brief outlook of the major challenges that lie ahead for mainstream usage of these materials for advanced biomedical applications.

Rapid and ultrasensitive detection of DNA and microRNA-21 using a zirconium porphyrin metal-organic framework-based switch fluorescence biosensor

Sensitive and accurate detection of nucleic acid biomarkers is critical for early cancer diagnosis, disease monitoring, and clinical treatment. In this study, we developed a switch fluorescence biosensor for simple and high-efficient detection of nucleic acid biomarkers using 6-carboxyfluorescein (FAM)-modified single-stranded DNA (ssDNA) probes (FAM-P1/P2), and zirconium porphyrin metal-organic framework nanoparticles (ZrMOF) acted as fluorescence quencher. FAM-P1/P2 probes were adsorbed on ZrMOF surface because of π-π stacking, hydrogen bonding, and electrostatic interactions. Fluorescence quenching event occurred by fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) processes, thereby achieving the "off" fluorescence status. Once the specific binding was formed between the fluorescence probes and the targets, the rigid double-stranded DNA (dsDNA) structures were released from ZrMOF surface, resulting in the recovery of fluorescence and the "on" status. Because of the superior adsorption ability of ZrMOF toward ssDNA than dsDNA, the switch of fluorescence signals from "off" to "on" allowed rapid and ultrasensitive detection of ssDNA (T1) and microRNA-21 (miR-21) within 30 min. The limit of detection (signal-to-noise ratio = 3) for T1 and miR-21 were 2 fM and 11 aM, respectively. Moreover, the proposed strategy was very simple as it worked by the facile adsorption-quenching-recovery mechanism without difficult and complicated immobilization processes. Also, this biosensor showed an excellent analytical performance in the detection of miR-21 in human serum samples. Therefore, this biosensor might be considered a potential tool for the detection of DNA and miRNA biomarkers in clinical samples.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers' health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

A sensor array based on DNA-wrapped bimetallic zeolitic imidazolate frameworks for detection of ATP hydrolysis products

Most current biosensors were designed for the detection of individual analytes, or a group of chemically similar analytes. We reason that sensors designed to track both reactants and products might be useful for following chemical reactions. Adenosine triphosphate (ATP) is a key biomolecule that participates in various biochemical reactions, and its hydrolysis plays a fundamental role in life. ATP can be converted to adenosine diphosphate (ADP) and inorganic phosphate (Pi) via the dephosphorylation process. ATP can also be hydrolyzed to adenosine monophosphate (AMP) and pyrophosphate (PPi) through depyrophosphorylation, depending on where the bond is cleaved. The detection of ATP-related hydrolysates would enable a better understanding of the different reaction pathways with a high level of robustness and confidence. Herein, we prepared a fluorescent sensor array based on a series of bimetallic zeolite imidazole frameworks M/ZIF-8 (M = Ni, Mn, Cu) and ZIF-67 to discriminate ATP hydrolysis and detect ATP hydrolysis related analytes. A fluorescently-labeled DNA oligonucleotide was used for signaling. Interestingly, Cu/ZIF-8 exhibited an ultrahigh selectivity for recognizing pyrophosphate with a detection limit of 2.5 μM. Moreover, the practicality of this sensor array was demonstrated in fetal bovine serum, clearly discriminating ATP hydrolysis products.

Smart Metal-Organic Frameworks for Biotechnological Applications: A Mini-Review

In this pandemic situation it is evident that viruses and bacteria, more specifically, multiple drug resistant (MDR) bacteria, endanger human civilization severely. It is high time to design smart weapons to combat these pathogens for the prevention and cure of allied ailments. Metal-organic frameworks (MOFs) are porous materials designed from metal ions or inorganic clusters and multidentate organic ligands. Due to some unique features like high porosity, tunable pore shape and size, numerous possible metal-ligand combinations, etc., MOFs are ideal candidates to design "smart biotechnological tools". MOFs construct promising fluorescence based biosensing platforms for detection of viruses. MOFs also exhibit excellent antibacterial activity due to their ability for sustained release of active biocidal agents. There are several reviews that summarize the antibacterial applications of MOFs, but the biosensing platforms based on MOFs for detection of viruses have scarcely been summarized. This review carefully covers both the aspects including virus detection (nucleic acid recognition and immunological detection) with underlying mechanisms as well as antibacterial application of MOFs and doped MOFs or composites. This review will deliver valuable information and references for designing new, smarter antimicrobial agents based on MOFs.

An electrochemical aptasensor for Mycobacterium tuberculosis ESAT-6 antigen detection using bimetallic organic framework

A label-free electrochemical aptasensor is reported for sensitive detection of the 6-kDa early secreted antigenic target (ESAT-6). For the first time, the bimetallic organic framework (b-MOF) of Zr-MOF-on-Ce-MOF was decorated with nitrogen-doped graphene (NG) and applied as the matrix for electroactive toluidine blue (Tb) to form the NG@Zr-MOF-on-Ce-MOF@Tb nanohybrid. The prepared nanohybrid with excellent hydrophilicity, dispersibility, and large specific surface exhibited significant electrochemical response. This nanohybrid could be directly used for anchoring ESAT-6 binding aptamers (EBA) through the interaction between the 5'-phosphate group (PO₄^3-) of EBA and Zr⁴⁺ of Zr-MOF. The signal response before and after incubating the ESAT-6 antigen has been evaluated by cyclic voltammetry at a scan rate of 100 mV s^-1 from - 0.7 to 0.3 V (vs. SCE). Under optimal conditions, the proposed aptasensor displayed a wide linear range from 100 fg mL^-1 to 10 ng mL^-1 with a limit of detection (LOD) of 12 fg mL^-1. The developed method showed good reproducibility with a relative standard deviation (RSD) of 2.27%. The aptasensor showed favorable results in the analysis of the real samples. With these merits, the aptasensor has exceptional potential as a diagnostic tool for tuberculosis in clinical practice.

Group 4 Metal-Based Metal—Organic Frameworks for Chemical Sensors

Metal-organic frameworks (MOFs) have attracted great attention for their applications in chemical sensors mainly due to their high porosity resulting in high density of spatially accessible active sites, which can interact with the aimed analyte. Among various MOFs, frameworks constructed from group 4 metal-based (e.g., zirconium, titanium, hafnium, and cerium) MOFs, have become especially of interest for the sensors requiring the operations in aqueous media owing to their remarkable chemical stability in water. Research efforts have been made to utilize these group 4 metal-based MOFs in chemosensors such as luminescent sensors, colorimetric sensors, electrochemical sensors, and resistive sensors for a range of analytes since 2013. Though several studies in this subfield have been published especially over the past 3–5 years, some challenges and concerns are still there and sometimes they might be overlooked. In this review, we aim to highlight the recent progress in the use of group 4 metal-based MOFs in chemical sensors, and focus on the challenges, potential concerns, and opportunities in future studies regarding the developments of such chemically robust MOFs for sensing applications.

Au@Zr-based metal-organic framework composite as an immunosensing platform for determination of hepatitis B virus surface antigen

An ultrasensitive electrochemical immunosensor has been prepared using an immunofunctionalized zirconium (Zr)-based metal-organic framework (MOF) with gold (Au) decoration Au@UiO-66(NH2) composite-coated glassy carbon electrode (GCE) for the determination of infectious hepatitis B surface antigen (HBsAg). We fabricated GCE with specific composite via immune-functionalization using anti-HBsAg with Au nanoparticles embedded in UiO-66(NH2). The electrochemical sensing performance of the immunofunctionalized Au@UiO-66(NH2)/GCE with HBsAg was characterized by cyclic voltammetry and differential pulse voltammetry. Under optimized conditions, there was a linear dynamic relationship in the buffer system between the electrical signal and HBsAg levels over the range 1.13 fg mL-1-100 ng mL-1 (R2 = 0.999) with a detection limit of 1.13 fg mL-1. The total analysis time was 15 min per sample. Further validations were performed with HBsAg-spiked human serum samples, and similar detection limits as in the buffer system were observed with reduced signal intensities at lower concentrations of HBsAg (1, 10, and 100 fg mL-1) and minimal interference. The HBsAg electrochemical immunosensing assay had good selectivity and excellent reproducibility, thereby indicating its significant potential in the super-fast diagnosis of hepatitis B.

A fluorescence aptasensor based on controlled zirconium-based MOFs for the highly sensitive detection of T-2 toxin

T-2 toxin is one of class A trichothecene mycotoxins produced by Fusarium, presenting genotoxic, cytotoxicity, and immunotoxicity for animals and humans. Therefore, It is urgent to establish a rapid test method with high sensitivity, good selectivity and reliability. In this research, by adjusting the synthesis conditions, a kind of NH₂-UiO-66 with high quenching efficiency was screened out. On this basis, we constructed a novel fluorescence sensor via Cy3-labeled aptamer (Cy3-aptamer). With the help of π-π interaction, hydrogen bond and coordination, NH₂-UiO-66 could adsorb and quench the fluorescence of Cy3-aptamer based on FRET and PET. In the presence of T-2 toxin, it recognized and bound to Cy3-aptamer, leading to the disintegration of the NH₂-UiO-66/Cy3-aptamer compound. As the energy transfer process was blocked, the fluorescence intensity was restored, enabling a highly sensitive response to T-2 toxin. There was a good linear correlation between fluorescence intensity and T-2 toxin concentration in the range of 0.5-100 ng ml ^-1. The LOD of this fluorescence aptasensor was 0.239 ng ml^-1 (S/N = 3). Besides, the recoveries of milk and beer were 89.86-108.99% (RSD = 2.0-2.6%) and 92.31-111.51% (RSD = 2.3-2.9%), respectively. The fluorescence aptasensor exhibited advantages of excellent analytical performance, convenient operation procedure and good selectivity. Predictably, the aptasensor was supposed to detect antibiotics and other pollutants, describing an intriguing blueprint and potential application prospect in food safety, biochemical sensing and environmental conservation.

One-pot bottom-up synthesis of a 2D graphene derivative: application in biomolecular recognition and nanozyme activity

The synthesis of two-dimensional (2D) nanosheets such as graphene and its derivatives through a bottom-up approach has many advantages such as growth control and functionalization, but it is always challenging to get the desired material. Herein, we have reported the synthesis of water soluble 2D-nanosheets through a bottom-up approach from 2,4,6-tribromo-3-hydroxybenzoic acid via a self-coupling pathway and characterized them using several techniques. AFM and TEM analyses reveal that the synthesized material has a layered structure with a thickness of ∼1.2 nm. Also, the prepared nanosheets are amorphous in nature with high negative charge (-38 ± 2.5 mV). The flexible nature of 2D-nanosheets and their functionality can be used in many related applications. Therefore, we have utilized the synthesized 2D-nanosheets in biomolecular recognition studies. It was found that the enzymatic activity of α-chymotrypsin can be controlled reversibly in the presence of the synthesized 2D-nanosheets. The kinetic study revealed that the nanosheet surface selectively binds to the active sites of the enzyme through a competitive pathway. Furthermore, we explored the nanozyme activity of the material in a peroxidase-like activity assay of two bio-active molecules: Nicotinamide Adenine Dinucleotide Phosphate (NADH) and dopamine. The results suggest that the prepared material efficiently catalyzed the oxidation of NADH to biological cofactor NAD⁺ and dopamine to aminochrome in the presence of H₂O₂. These synthesized graphene-like 2D-nanosheets with functional groups can be further tuned with other functionalities, which can open a new window for other related applications.

Metal-organic frameworks for diagnosis and therapy of infectious diseases

Infectious diseases are one of the leading cause of mortality and morbidity worldwide. Metal-Organic Frameworks (MOFs), which are porous coordination materials composed of bridging organic ligands and metallic ions or clusters, exhibits great potential to be used against several pathogens, such as bacteria, viruses, fungi and protozoa. MOFs can show sustained release capability, high surface area, adjustable pore size and structural flexibility, which makes them good candidates for new therapeutic systems. This review provides a detailed summary of the biological application of MOFs, focussing on diagnosis and treatment of infectious diseases. MOFs have been reported for usage as antimicrobial agents, drug delivery systems, therapeutic composites, nanozymes and phototherapies. Furthermore, different MOF-based biosensors have also been developed to detect specific pathogens by electrochemical, fluorometric and colorimetric assays. Finally, we present limitations and perspectives in this field.

An amine-functionalized metal-organic framework and triple-helix molecular beacons as a sensing platform for miRNA ratiometric detection

Herein, a metal-organic framework (UiO-66-NH₂) with two functions (intrinsic fluorescence and fluorescence quenching ability) is designed to establish a ratiometric fluorescent platform for high-performance miRNA detection. The use of a fluorescent organic ligand endows the MOF material with a strong intrinsic fluorescence at 440 nm. In the presence of target miRNA, the fluorescence signal of the FAM is restored with the triple helix molecular beacons bind to the target. Using the I_FAM/I_MOF signal as the output, the prepared ratiometric probe was able to eliminate disturbance caused by the sensing environment. Under the optimal reaction conditions, including buffer pH of 7.4, temperature of 37 °C, and response time of 1 h, the best detection results can be obtained. The ratiometric fluorescence probe presented showed good sensitivity and selectivity for detecting miRNA-203 and the limit of detection was 400 pM with a wide linear range from 1 nM to 160 nM. In addition, this method was applied to diluted human serum and cell lysates, and good detection effect was realized.

State-of-the-art progress of switch fluorescence biosensors based on metal-organic frameworks and nucleic acids

Metal-organic frameworks (MOFs) have captured substantial attention of an increasing number of scientists working in sensing analysis fields, due to their large surface area, high porosity, and tunable structure. Recently, MOFs as attractive fluorescence quenchers have been extensively investigated. Given their high quenching efficiency toward the fluorescence intensity of dyes-labeled specific biological recognition molecules, such as nucleic acids, MOFs have been widely developed to switch fluorescence biosensors with low background fluorescence signal. These strategies not only lead to specificity, simplicity, and low cost of biosensors, but also possess advantages such as ultrasensitive, rapid, and multiple detection of switch fluorescence methods. At present, researches of the analysis of switch fluorescence biosensors based on MOFs and nucleic acids mainly focus on sensing of different types of in vitro and intracellular analytes, indicating their increasing potential. In this review, we briefly introduce the principle of switch fluorescence biosensor and the mechanism of fluorescence quenching of MOFs, and mainly discuss and summarize the state-of-the-art advances of MOFs and nucleic acids-based switch fluorescence biosensors over the years 2013 to 2020. Most of them have been proposed to the in vitro detection of different types of analytes, showing their wide scope and applicability, such as deoxyribonucleic acid (DNAs), ribonucleic acid (RNAs), proteins, enzymes, antibiotics, and heavy metal ions. Besides, some of them have also been applied to the bioimaging of intracellular analytes, emerging their potential for biomedical applications, for example, cellular adenosine triphosphate (ATP) and subcellular glutathione (GSH). Finally, the remaining challenges in this sensing field and prospects for future research trends are addressed. Graphical abstract.

Aptamer-functionalized metal-organic frameworks (MOFs) for biosensing

As a class of crystalline porous materials, metal-organic frameworks (MOFs) have attracted increasing attention. Due to the nanoscale framework structure, adjustable pore size, large specific surface area, and good chemical stability, MOFs have been applied widely in many fields such as biosensors, biomedicine, electrocatalysis, energy storage and conversions. Especially when they are combined with aptamer functionalization, MOFs can be utilized to construct high-performance biosensors for numerous applications ranging from medical diagnostics and food safety inspection, to environmental surveillance. Herein, this article reviews recent innovations of aptamer-functionalized MOFs-based biosensors and their bio-applications. We first briefly introduce different functionalization methods of MOFs with aptamers, which provide a foundation for the construction of MOFs-based aptasensors. Then, we comprehensively summarize different types of MOFs-based aptasensors and their applications, in which MOFs serve as either signal probes or signal probe carriers for optical, electrochemical, and photoelectrochemical detection, with an emphasis on the former. Given recent substantial research interests in stimuli-responsive materials and the microfluidic lab-on-a-chip technology, we also present the stimuli-responsive aptamer-functionalized MOFs for sensing, followed by a brief overview on the integration of MOFs on microfluidic devices. Current limitations and prospective trends of MOFs-based biosensors are discussed at the end.

Highly-sensitive and fast detection of human telomeric G-Quadruplex DNA based on a hemin-conjugated fluorescent metal-organic framework platform

The formation of G-quadruplex (G4) structures in Human telomeric DNA (H-Telo) has been demonstrated to inhibit the activity of telomerase enzyme that is associated with the proliferation of many cancer cells. Accordingly, G-quadruplex structures have become one of the well-established targets in anticancer therapeutic strategies. And, the development of simple and selective detection platforms for G4 structures has become a significant focus of research in recent years. In this study, a simple "off-on" fluorometric method was developed for the selective detection of picomolar quantities of H-Telo G4 DNA based on a fluorescent cerium-based metal organic framework (Ce-MOF) conjugated with hemin to form the sensing probe, Hemin@Ce-MOF. The solvothermal synthesis of the Ce-MOF took advantage of 5-aminoisophtlalic acid (5AIPA) as the organic bridging ligand, (Ce₂(5AIPA)₃(DMF)₂). Characterization of Ce-MOF and Hemin@Ce-MOF was performed by XRD, XPS, TEM, SEM, BET and FTIR techniques. The detection and quantification of the H-Telo was carried out through the adsorption/incorporation of hemin molecules on the pores and surface of Ce-MOF resulting in the fluorescent quenching of the system followed by the restoration of the fluorescence upon addition of H-Telo probably due to a competition between H-Telo and Ce-MOF to bind to hemin. The impact of the key variables including MOF quantity, hemin concentration and detection time was investigated and optimized. Under the optimized conditions, the developed probe provides a limit of detection (LOD) of 665 pM, linear dynamic range (LDR) of 1.6-39.7 nM and excellent selectivity towards H-Telo. Taken together, these results present a simple, novel and superior platform for the selective detection of H-Telo G4 DNA.

A porous organic polymer nanosphere-based fluorescent biosensing platform for simultaneous detection of multiplexed DNA via electrostatic attraction and π–π stacking interactions

One key challenge in oligonucleotide sequence sensing is to achieve multiplexed DNA detection in one sensor. Herein, a simple and efficient fluorescent biosensing platform is constructed to simultaneously detect multiplexed DNA depending on porous organic polymer (POP) nanospheres. The developed sensor is based on the concept that the POP nanospheres can efficiently quench the fluorescence emission of dye-labeled single-stranded DNA (ssDNA). Fluorescence quenching is achieved by the non-covalent assembly of multiple probes on the surface of POP nanospheres through electrostatic attraction and π–π stacking interactions, in which the electrostatic attraction plays a more critical role than π–π stacking. The formed dsDNA could be released off the surface of POP via hybridizing with the target DNA. Consequently, the target DNA can be quickly detected by fluorescence recovery. The biosensor could sensitively and specifically identify three target DNAs in the range of 0.1 to 36 nM, and the lowest detection limits are 50 pM, 100 pM, and 50 pM, respectively. It is noteworthy that the proposed platform is successfully applied to detect DNA in human serum. We perceive that the proposed sensing system represents a simple and sensitive strategy towards simultaneous and multiplexed assays for DNA monitoring and early clinical diagnosis.

This communication reports a simple and efficient fluorescent biosensing platform to simultaneously detect multiplexed DNA depending on porous organic polymer (POP) nanospheres by electrostatic attraction and π–π stacking interaction.