Smart Nanocomposites of Cu-Hemin Metal-Organic Frameworks for Electrochemical Glucose Biosensing

Host-Guest Synergy of Metal-Organic Frameworks for Enhanced Near-Infrared Ultrafast Laser Responsiveness

Host-guest metal-organic frameworks (MOFs) offer significant potential and value in regulating and optimizing novel material properties and functionalities, owing to the synergistic effects between the host framework and the guest units. This study reported two silver-based host-guest MOFs, [Ag(ATRZ)(BrO3)]n (CMOF-1) and [Ag(ATRZ)1.5(ClO4)]n (CMOF-2), as promising candidates for laser-responsive materials. These materials feature 1D and 3D structures, respectively, comprising Ag-ATRZ cationic MOF frameworks integrated with two distinct oxidizing anionic guests, BrO3 - and ClO4 -. CMOF-1 and CMOF-2 are synthesized through straightforward, environmentally benign methods, enabling rapid fabrication. The exceptional near-infrared (NIR) laser responsiveness of CMOF-1 and CMOF-2 was achieved through the modulation of the cationic MOFs (CMOFs) architectures and synergistic interactions between the host and guest components. Moreover, both exhibit ultrafast deflagration-to-detonation transition (DDT) capabilities, alongside excellent thermal stability. This work expands the application scope of host-guest MOFs, and provides an effective strategy for developing high-performance laser-responsive materials.

Long-lasting chemiluminescence-based portable biosensor for POCT of food contaminant azodicarbonamide

Azodicarbonamide (ADA) in flour products is easily converted to semicarbazide which greatly threatens human health. Herein, a long-lasting chemiluminescence (CL)-based biosensor was developed for quantitative point-of-care testing (POCT) of ADA. The threonine (Thr)-functionalized Cu-hemin MOFs (Cu-hemin@Thr) could induce persistent CL of luminol with excellent stability. The CL intensity was related to the competition reaction among ADA and a composite of glutathione-silver ions (GSH-Ag+). In the presence of ADA, GSH is oxidized to glutathione disulfide (GSSG), which breaks the coordination between Ag+ and GSH. The CL of the sensing system is then decreased which is expected to be used for ADA detection. By combining a homemade portable device as a detector and a smartphone as an analyzer, quantitative POCT of ADA was successfully achieved. The limit of detection was 0.562 μM (0.065 ppm), which is much lower than the maximum permissible concentration of ADA (45 ppm) in flour extract. The developed strategy demonstrated quantitative POCT capabilities along with advantages of low cost, excellent selectivity, and repeatability, presenting great potential application in food safety and environment monitoring.

A non-enzymatic hydrogen peroxide biosensor based on cerium metal-organic frameworks, hemin, and graphene oxide composite

This study presents the development of a novel non-enzymatic electrochemical biosensor for the real-time detection of hydrogen peroxide (H2O2) based on a composite of cerium metal-organic frameworks (Ce-MOFs), hemin, and graphene oxide (GO). The Ce-MOFs served as an efficient matrix for hemin encapsulation, while GO enhanced the conductivity of the composite. Characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, and thermogravimetric analysis (TGA) confirmed the successful integration of hemin into the Ce-MOFs. The Ce-MOFs@hemin/GO-modified sensor demonstrated sensitive H2O2 detection due to the exceptional electrocatalytic activity of Ce-MOFs@hemin and the high conductivity of GO. This biosensor exhibited a linear response to H2O2 concentrations from 0.05 to 10 mM with a limit of detection (LOD) of 9.3 μM. The capability of the biosensor to detect H2O2 released from human prostate carcinoma cells was demonstrated, highlighting its potential for real-time monitoring of cellular oxidative stress in complex biological environments. To further assess its practical applicability, the sensor was tested in human serum samples, yielding promising results with recovery values ranging from 94.50 % to 103.29 %. In addition, the sensor showed excellent selectivity against common interfering compounds due to the outstanding peroxidase-like activity of the composite.

Palladium Nanoparticle-Decorated Copper-Hemin Metal Organic Framework for Enzymatic Electrochemical Detection of Creatinine in Human Urine

Creatinine is indeed a crucial biomarker for kidney diseases. In this work, a novel electrochemical biosensor based on a copper-hemin metal organic framework [Cu-hemin metal-organic framework (MOF)] nanoflake decorated with palladium (Pd) (Pd/Cu-hemin MOF) was fabricated and incorporated with creatinine deiminase (CD) on a glassy carbon electrode (GCE) for creatinine detection. The formation of a Pd/Cu-hemin MOF composite was confirmed by X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The formation of the composite as nanoflakes is evident from the scanning electron microscopy image. The transmission electron microscopy image clarifies the decoration of palladium nanoparticles on Cu-hemin MOF surfaces. Thus, the proposed biosensor (Pd/Cu-hemin MOF/CD/GCE) electrochemical performances were studied with cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. As a result, the Pd/Cu-hemin MOF/CD/GCE-based electrochemical detection of creatinine exhibits a broad linear range from 0 to 130 μM (R2 = 0.99), a low limit of detection 0.08 μM, and an excellent sensitivity of 3.2 μA μM-1 cm-2. The biosensor also determines creatinine in samples of human urine with a good recovery from 99.4 to 100.8%. Thus, in this study, an electrochemical biosensing platform based on Pd/Cu-hemin MOF/CD/GCE has been designed practically for creatinine.

Iron protoporphyrin IX-hyaluronan hydrogel-supported luminol chemiluminescence for the detection of nitric oxide in physiological solutions

Due to its role as a free radical signal-transducing agent with a short lifespan, precise measurement of nitric oxide (●NO) levels presents significant challenges. Various analytical techniques offer distinct advantages and disadvantages for ●NO detection. This research aims to simplify the detection process by developing a hydrogel system using iron(III)-protoporphyrin IX (hemin)-loaded hyaluronan for the detection of ●NO in solution. Various hydrogel formulations were created, and the effects of their components on hydrogel-supported luminol chemiluminescence (CL) kinetics, radical scavenging, and physicochemical properties were analysed through factorial analysis. The candidate formulations were then evaluated using two ●NO donors. An increase in the degree of crosslinking in unloaded formulations enhanced interactions with the CL reaction components, hydrogen peroxide (H2O2) and luminol, thereby affecting light generation. However, hemin loading negated these effects, resulting in more prominent luminescence kinetics in formulations with lower crosslinking degrees. Similarly, ●NO influenced the kinetics differently, interacting with both the CL reaction and hydrogel components. Hemin-loaded formulations exhibited enhanced signal propagation when exposed to ●NO, followed by H2O2 and luminol, whereas reversing the order of addition inhibited this propagation. The magnitude of these luminescence changes depended on the type and concentration of the ●NO donor, demonstrating greater sensitivity to ●NO levels compared to amperometric sensing. These findings suggest that the studied hydrogel platform has potential for the facile and accurate detection of ●NO in solution, requiring minimal sample sizes.

Metal-organic framework-interfaced ELISA probe enables ultrasensitive detection of extracellular vesicle biomarkers

The enzyme-linked immunosorbent assay (ELISA) remains the prevailing method for quantifying protein biomarkers. Enzymatic signal generation and amplification are key mechanisms that govern its analytical performance. This study reports the synthesis and application of microscale metal-organic framework (MOF)/enzyme composite particles as a novel detection probe to substantially enhance the sensitivity of ELISA. An optimal one-pot approach was established to incorporate a substantial amount of streptavidin-horseradish peroxidase (SA-HRP) either within or on the surface of the metal-azolate framework (MAF-7) microparticles. This approach enables the labeling of a single sandwich antibody-antigen complex with numerous enzymes, which markedly amplifies the enzymatic colorimetric signal generation. Moreover, MAF-7 caging was found to enhance the reactivity of the caged HRP enzyme, further promoting the overall detection sensitivity of ELISA. Compared to other developments that are often associated with more complicated detection modalities, our method is compatible with standard immunoassays and commonly used photometrical signal detection. The implementation of this strategy in the detection of CD147 results in a remarkably low limit of detection of 2.8 fg mL-1, representing a 105-fold improvement compared to that obtained with the standard ELISA. Moreover, the heightened sensitivity of this technique renders it particularly suitable for diagnosing breast cancer, thus presenting a promising tool for the early detection of the disease in clinical settings.

Carrageenan-based multifunctional packaging films containing Zn-carbon dots/anthocyanin derived from Kohlrabi peel for monitoring quality and extending the shelf life of shrimps

Carrageenan-based active/intelligent packaging films containing anthocyanin and ZnO-doped CD (Zn-CD) from purple Kohlrabi peels were prepared for freshness monitoring and shelf-life extension of shrimp, and the influence of additives on the films' physical, functional, and structural properties was investigated. The films showed excellent UV blocking ability (85.2% of UV-A and 99.4% of UV-B) and high antioxidant effect (∼99% for ABTS and ∼ 58.6% for DPPH radical scavenging activity) and showed strong antibacterial activity to stop the growth (100%) of L. monocytogenes and to reduce the growth of E. coli by 8.1 log CFU/mL after 12 h of incubation. In shrimp packaging experiments, the films were evident in the freshness monitoring, reduced spoilage, and increased shelf life. This study suggests that next-generation biopolymer films impregnated with biomass-derived CDs and natural colorants will provide broad directions for ensuring safety and extending shelf life to meet the accelerating demand for packaging products.

Photoelectrochemical aptasensing with methylene blue filled Ni-MOFs nanocomposite by spatial confinement for microcystin-LR detection

Microcystin LR (MC-LR) is a hazardous cyanotoxin produced by cyanobacteria during freshwater eutrophication, which can cause liver cancer. Here, a photoelectrochemical (PEC) aptasensor based on methylene blue (MB)-loaded Ni-MOF composite (Ni-MOF/MB) with spatial confinement was constructed for the sensitive detection of MC-LR. Ni-MOF with two-dimensional sheet structure was prepared via a liquid-liquid interface synthesis method with environmental-friendly solvent and milder reaction conditions. Benefiting from the uniform pore size, Ni-MOF acted as reaction platform to anchor the photosensitive molecule MB. The electron donor, ascorbic acid (AA), was produced by alkaline phosphatase (ALP) loaded on DNA strand catalyzing ascorbic acid phosphate. The generated AA was absorbed by Ni-MOF/MB, thereby effectively improving the utilization of AA and avoiding the external environment interferences to enlarge the photocurrent of MB. For analysis, ALP-labeled aptamer can specifically recognize MC-LR by forming a complex to strip from aptasensor, thus leading to a  decreased photocurrent. The developed PEC aptasensor offered a linear range of 10 fM-100 pM with a detection limit of 6 fM. It was successfully employed for detecting MC-LR in farm water and fish meat, and the results were validated by ultrahigh-performance liquid chromatography-mass spectrometry. This method presents a new idea of MOF-limited domain for PEC aptasensing.

The enhanced electrocatalytic performance of nanoscopic Cu6Pd12Fe12 heterometallic molecular box encaged cytochrome c

Designing molecular cages for atomic/molecular scale guests is a special art used by material chemists to harvest the virtues of the otherwise vile idea known as "the cage". In recent years, there has been a notable surge in research investigations focused on the exploration and utilization of the distinct advantages offered by this art in the advancement of efficient and stable bio-electrocatalysts. This usually is achieved through encapsulation of biologically accessible redox proteins within specifically designed molecular cages and matrices. Herein, we present the first successful method for encaging cytochrome c (Cyt-c), a clinically significant enzyme system, inside coordination-driven self-assembled Cu6Pd12Fe12 heterometallic hexagonal molecular boxes (Cu-HMHMB), in order to create a Cyt-c@Cu-HMHMB composite. 1H NMR, FTIR, and UV-Vis spectroscopy, ICP-MS, TGA and voltammetric investigations carried out on the so-crafted Cyt-c@Cu-HMHMB bio-inorganic composite imply that the presented strategy ensures encaging of Cyt-c in a catalytically active, electrochemically stable and redox-accessible state inside the Cu-HMHMB. Cyt-c@Cu-HMHMB is demonstrated to exhibit excellent stability and electrocatalytic activity toward very selective, sensitive electrochemical sensing of nitrite exhibiting a limit of detection as low as 32 nanomolar and a sensitivity of 7.28 μA μM-1 cm-2. Importantly, Cyt-c@Cu-HMHMB is demonstrated to exhibit an excellent electrocatalytic performance toward the 4ē pathway oxygen reduction reaction (ORR) with an onset potential of 0.322 V (vs. RHE) and a Tafel slope of 266 mV dec-1. Our findings demonstrate that Cu-HMHMB is an excellent matrix for Cyt-c encapsulation. We anticipate that the entrapment-based technique described here will be applicable to other enzyme systems and Cyt-c for various electrochemical and other applications.

Bacterial metabolism-triggered-chemiluminescence-based point-of-care testing platform for sensitive detection and photothermal inactivation of Staphylococcus aureus

Post-operative pathogenic infections in liver transplantation seriously threaten human health. It is essential to develop novel methods for the highly sensitive and rapid detection of Staphylococcus aureus (S. aureus). Interestingly, the combination of the property of bacteria to secrete hydrogen peroxidase, bacterial metabolism-triggered-chemiluminescence (CL)-based bioassays can be as a candidate point-of-care testing (POCT) for the detection of S. aureus against the CL substrate Luminol and hydrogen peroxide without excitation light sources. Here, a CL-based strategy with stable and visualized CL intensity was fabricated according to a hybrid biomimetic enzyme of copper-Hemin metal-organic framework, which enhances the biological enzyme activity while improving the stability and sensitivity of the assay. By further integrating S. aureus-specific capture and one-step separation of the antibody-modified Fe3O4 NPs (Fe3O4 NPs@Ab), the portable device integrated smartphone enables CL-based POCT for specific detection of S. aureus in the range of 101-106 CFU/mL with a limit of detection as low as 1 CFU/mL. Specifically, S. aureus can be eliminated after detection with high antibacterial efficiency due to the excellent photothermal properties of Fe3O4 NPs@Ab. The developed multifunctional platform has the advantages of simplicity of operation and low cost, indicating great potential in clinical applications.

A Molecular Switch-Integrated Nanoplatform Enables Photo-Unlocked Antibacterial Drug Delivery for Synergistic Abscess Therapy

Drug delivery systems (DDSs) capable of sequential multistage drug release are urgently needed for antibacterial applications. Herein, a molecular switch-integrated, photo-responsive nanoplatform is reported based on hollow mesoporous silica nanospheres (HMSN) loaded with silver nanoparticles (Ag NPs), vancomycin (Van), and hemin (HAVH) for bacteria elimination and abscess therapy. Upon near-infrared (NIR) light irradiation, the molecular switch, hemin, can effuse from the mesopores of HMSN, triggering the release of pre-loaded Ag+ and Van, which enables photothermal-modulated drug release and synergistic photothermal-chemo therapy (PTT-CHT). The HAVH_NIR irreversibly disrupts the bacterial cell membrane, facilitating the penetration of Ag+ and Van. It is found that these compounds restrain the transcription and translation of ribosomes and lead to rapid bacterial death. Furthermore, hemin can effectively inhibit excessive inflammatory responses associated with the treatment, promoting accelerated wound healing in a murine abscess model. This work presents a new strategy for antibacterial drug delivery with high controllability and extendibility, which may benefit the development of smart multifunctional nanomedicine for diseases not limited to bacterial infections.

Dual Ni/Co-hemin metal-organic framework-PrGO for high-performance asymmetric hybrid supercapacitor

In this study, we conducted direct synthesis of a dual metal-organic framework (Ni/Co-Hemin MOF) on phosphorous-doped reduced graphene oxide (PrGO) to serve as an active material in high-performance asymmetrical supercapacitors. The nanocomposite was utilized as an active material in supercapacitors, exhibiting a noteworthy specific capacitance of 963 C g^-1 at 1.0 A g^-1, along with a high rate capability of 68.3% upon increasing the current density by 20 times, and superior cycling stability. Our comprehensive characterization and control experiments indicated that the improved performance can be attributed to the combined effect of the dual MOF and the presence of phosphorous, influencing the battery-type supercapacitor behavior of GO. Additionally, we fabricated an asymmetric hybrid supercapacitor (AHSC) using Ni/Co-Hemin/PrGO/Nickel foam (NF) and activated carbon (AC)/NF. This AHSC demonstrated a specific capacitance of 281 C g^-1 at 1.0 A g^-1, an operating voltage of 1.80 V, an impressive energy density of 70.3 Wh kg^-1 at a high power density of 0.9 kW kg^-1. Notably, three AHSC devices connected in series successfully powered a clock for approximately 42 min. These findings highlight the potential application of Hemin-based MOFs in advanced supercapacitor systems.

Copper(II)-Incorporated Porphyrin-Based Porous Organic Polymer for a Nonenzymatic Electrochemical Glucose Sensor

To date, the fabrication of multifunctional nanoplatforms based on a porous organic polymer for electrochemical sensing of biorelevant molecules has received considerable attention in the search for a more active, robust, and sensitive electrocatalyst. Here, in this report, we have developed a new porous organic polymer based on porphyrin (TEG-POR) from a polycondensation reaction between a triethylene glycol-linked dialdehyde and pyrrole. The Cu(II) complex of the polymer Cu-TEG-POR shows high sensitivity and a low detection limit for glucose electro-oxidation in an alkaline medium. The characterization of the as-synthesized polymer was done by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and ¹³C CP-MAS solid-state NMR. The N₂ adsorption/desorption isotherm was carried out at 77 K to analyze the porous property. TEG-POR and Cu-TEG-POR both show excellent thermal stability. The Cu-TEG-POR-modified GC electrode shows a low detection limit (LOD) value of 0.9 μM and a wide linear range (0.001-1.3 mM) with a sensitivity of 415.8 μA mM^-1 cm^-2 toward electrochemical glucose sensing. The interference of the modified electrode from ascorbic acid, dopamine, NaCl, uric acid, fructose, sucrose, and cysteine was insignificant. Cu-TEG-POR exhibits acceptable recovery for blood glucose detection (97.25-104%), suggesting its scope in the future for selective and sensitive nonenzymatic glucose detection in human blood.

Nanoscale coordination polymers enabling antioxidants inhibition for enhanced chemodynamic therapy

Reactive oxygen species (ROS) generation to induce cell death is an effective strategy for cancer therapy. In particular, chemodynamic therapy (CDT), using Fenton-type reactions to generate highly cytotoxic hydroxyl radical (•OH), is a promising treatment modality. However, the therapeutic efficacy of ROS-based cancer treatment is still limited by some critical challenges, such as overexpression of enzymatic and non-enzymatic antioxidants by tumor cells, as well as the low tumor targeting efficiency of therapeutic agents. To address those problems, biomimetic CuZn protoporphyrin IX nanoscale coordination polymers have been developed, which significantly amplify oxidative stress against tumors by simultaneously inhibiting enzymatic and non-enzymatic antioxidants and initiating the CDT. In this design, cancer cell membrane camouflaged nanoparticle exhibits an excellent homotypic targeting effect. After being endocytosed into tumor cells, the nanoparticles induce depletion of the main non-enzymatic antioxidant glutathione (GSH) by undergoing a redox reaction with GSH. Afterward, the redox reaction generated cuprous ion (Cu⁺) works as a CDT agent for •OH generation. Furthermore, the released Zn protoporphyrin IX strongly inhibits the activity of the typical enzymatic antioxidant heme oxygenase-1. This tetra-modal synergistic strategy endows the biomimetic nanoparticles with great capability for anticancer therapy, which has been demonstrated in both in vitro and in vivo studies.

Hydrogen-Bonding 2D Coordination Polymer for Enzyme-Free Electrochemical Glucose Sensing

Regular detection of blood glucose levels is a critical indicator for effective diabetes management. Owing to the intrinsic highly sensitive nature of enzymes, the performance of enzymatic glucose sensors is...

Cu-Based Conductive MOF Grown in situ on Cu Foam as a Highly Selective and Stable Non-Enzymatic Glucose Sensor

A non-enzymatic electrochemical sensor for glucose detection is executed by using a conductive metal–organic framework (MOF) Cu-MOF, which is built from the 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) ligand and copper acetate by hydrothermal reaction. The Cu-MOF demonstrates superior electrocatalytic activity for glucose oxidation under alkaline pH conditions. As an excellent non-enzymatic sensor, the Cu-MOF grown on Cu foam (Cu-MOF/CF) displays an ultra-low detection limit of 0.076 μM through a wide concentration range (0.001–0.95 mM) and a strong sensitivity of 30,030 mA μM⁻¹ cm⁻². Overall, the Cu-MOF/CF exhibits a low detection limit, high selectivity, excellent stability, fast response time, and good practical application feasibility for glucose detection and can promote the development of MOF materials in the field of electrochemical sensors.

Metal-organic frameworks based hybrid nanocomposites as state-of-the-art analytical tools for electrochemical sensing applications

Metal-organic frameworks (MOFs) are remarkably porous materials that have sparked a lot of interest in recent years because of their fascinating architectures and variety of potential applications. This paper systematically summarizes recent breakthroughs in MOFs and their derivatives with different materials such as, carbon nanotubes, graphene oxides, carbon fibers, enzymes, antibodies and aptamers etc. for enhanced electrochemical sensing applications. Furthermore, an overview part is highlighted, which provides some insights into the future prospects and directions of MOFs and their derivatives in electrochemical sensing, with the goal of overcoming present limitations by pursuing more inventive ways. This overview can perhaps provide some creative ideas for future research on MOF-based materials in this rapidly expanding field.

Superior Non-Invasive Glucose Sensor Using Bimetallic CuNi Nanospecies Coated Mesoporous Carbon

The assessment of blood glucose levels is necessary for the diagnosis and management of diabetes. The accurate quantification of serum or plasma glucose relies on enzymatic and nonenzymatic methods utilizing electrochemical biosensors. Current research efforts are focused on enhancing the non-invasive detection of glucose in sweat with accuracy, high sensitivity, and stability. In this work, nanostructured mesoporous carbon coupled with glucose oxidase (GO_x) increased the direct electron transfer to the electrode surface. A mixed alloy of CuNi nanoparticle-coated mesoporous carbon (CuNi-MC) was synthesized using a hydrothermal process followed by annealing at 700 °C under the flow of argon gas. The prepared catalyst's crystal structure and morphology were explored using X-ray diffraction and high-resolution transmission electron microscopy. The electrocatalytic activity of the as-prepared catalyst was investigated using cyclic voltammetry (CV) and amperometry. The findings show an excellent response time of 4 s and linear range detection from 0.005 to 0.45 mM with a high electrode sensitivity of 11.7 ± 0.061 mA mM cm^-2 in a selective medium.

The Encounter of Biomolecules in Metal-Organic Framework Micro/Nano Reactors

In nature, biochemical reactions often take place in confined spaces, as typically exemplified by cells. As numerous cellular reactors can be integrated to maintain the living system, researchers have made constant efforts to construct cell-like structures for achieving similar transformations in vitro. Micro/nano reactors engineered by polymers and colloids are becoming popular and being applied in many fields, especially there has been an increasing trend toward constructing metal-organic framework (MOF) micro/nano reactors with the thriving of MOF nanotechnologies. Because of the uniform pores of MOFs, the transmission of substances can be regulated more accurately. Along with properties of large specific surface area, functional diversity and precise control of the particle size, MOFs are also ideal platforms for building distinct microenvironments for biological substances. Compared with traditional polymersomes and colloidosomes, the unique characteristics of MOFs render them potent micro/nano reactor shell materials, mimicking cells for applications in enzymatic catalysis, sensing, nanotherapy, vaccine, biodegradation, etc. This review highlights recent signs of progress on the design of MOF micro/nano reactors and their applications in biology, discusses the existing problems, and prospects their promising properties for smarter multifunctional applications.

Functionalized Tumor-Targeting Nanosheets Exhibiting Fe(II) Overloading and GSH Consumption for Ferroptosis Activation in Liver Tumor

Liver tumor is difficult to cure for its high degree of malignancy and rapid progression characteristics. Ferroptosis as a new model of inducing cell death is expected to break the treatment bottleneck of liver tumors. Here, a strategy to induce ferroptosis in HepG2 cells with acid-degradable tumor targeted nanosheets Cu-Hemin-PEG-Lactose acid (Cu-Hemin-PEG-LA) is proposed. After highly ingested by HepG2 cells, Cu-Hemin-PEG-LA nanosheets are degraded by weak acid and release Cu(II) and hemin, which consuming intracellular glutathione (GSH) content and increasing the expression of heme oxygenase 1 (HMOX1) protein, respectively. Furthermore, the expression of glutathione peroxidase 4 protein (GPX4) is down-regulated by consumption intracellular GSH content via converting GSH into glutathione oxidized (GSSG), which is named the classical mode. The intracellular Fe²⁺ content is overloaded by the significant up-regulation of HMOX1 expression, which is denoted as nonclassical mode. The synergistic effect of classical and nonclassical mode increased the intracellular lipid reactive oxide species, induced the occurrence of ferroptosis and up-regulated the expression of BH3 interacting domain death agonist (BID), apoptosis-inducing factor (AIF), and endonuclease G proteins (EndoG). The synergistic strategy demonstrate the excellent ferroptosis induction ability and antitumor efficacy in vivo, which provides great potential for the clinical transformation of ferroptosis.

Fabrication of Cu-hemin metal-organic-frameworks nanoflower supported on three-dimensional reduced graphene oxide for the amperometric detection of H2O2

A novel electrochemical sensor based on Cu-hemin metal-organic-frameworks nanoflower/three-dimensional reduced graphene oxide (Cu-hemin MOFs/3D-RGO) was constructed to detect H₂O₂ released from living cells. The nanocomposite was synthesized via a facile co-precipitation method using hemin as the ligand, then decorated with 3D-RGO. The prepared Cu-hemin MOFs showed a 3D hollow spherical flower-like structure with a large specific surface area and mesoporous properties, which could load more biomolecules and greatly enhance the stability by protecting the activity of hemin. In addition, the introduction of 3D-RGO effectively enhanced the conductivity of Cu-hemin MOFs. Thus, the proposed sensor (Cu-hemin MOFs/3D-RGO/GCE) showed excellent electrochemical performances towards H₂O₂ with a wide linear range (10-24,400 μM), high sensitivity (207.34 μA mM^-1 cm^-2), low LOD (0.14 μM), and rapid response time (less than 3 s). Most importantly, we prepared a Cu-hemin MOFs/3D-RGO/ITO electrode with cells growing on it. Compared with detecting H₂O₂ in cell suspension by GCE-based electrode, adhesion of cells on ITO could shorten the diffusion distance of H₂O₂ from solution to the surface of the electrode and achieve in situ and a real-time monitor of H₂O₂ released by living cells. This self-supported sensing electrode showed great potential applications in monitoring the pathological and physiological dynamics of cancer cells.

Recent Advances in the Design and Sensing Applications of Hemin/Coordination Polymer-Based Nanocomposites

The fabrication of biomimetic catalysts as substituents for enzymes is of critical interest in the field due to the problems associated with the extraction, purification, and storage of enzymes in sensing applications. Of these mimetics, hemin/coordination polymer-based nanocomposites, mainly hemin/metal-organic frameworks (MOF), have been developed for various biosensing applications because of the unique properties of each component, while trying to mimic the normal biological functions of heme within the protein milieu of enzymes. This critical review first discusses the different catalytic functions of heme in the body in the form of enzyme/protein structures. The properties of hemin dimerization are then elucidated with the supposed models of hemin oxidation. After that, the progress in the fabrication of hemin/MOF nanocomposites for the sensing of diverse biological molecules is discussed. Finally, the challenges in developing this type of composites are examined as well as possible proposals for future directions to enhance the sensing performance in this field further.

Indirect Quantification of Glyphosate by SERS Using an Incubation Process With Hemin as the Reporter Molecule: A Contribution to Signal Amplification Mechanism

The indirect determination of the most used herbicide worldwide, glyphosate, was achieved by the SERS technique using hemin chloride as the reporter molecule. An incubation process between hemin and glyphosate solutions was required to obtain a reproducible Raman signal on SERS substrates consisting of silicon decorated with Ag nanoparticles (Si-AgNPs). At 780 nm of excitation wavelength, SERS spectra from hemin solutions do not show extra bands in the presence of glyphosate. However, the hemin bands increase in intensity as a function of glyphosate concentration. This allows the quantification of the herbicide using as marker band the signal associated with the ring breathing mode of pyridine at 745 cm-1. The linear range was from 1 × 10-10 to 1 × 10-5 M and the limit of detection (LOD) was 9.59 × 10-12 M. This methodology was successfully applied to the quantification of the herbicide in honey. From Raman experiments with and without silver nanoparticles, it was possible to state that the hemin is the species responsible for the absorption in the absence or the presence of the herbicide via vinyl groups. Likewise, when the glyphosate concentration increases, a subtle increase occurs in the planar orientation of the vinyl group at position 2 in the porphyrin ring of hemin over the silver surface, favoring the reduction of the molecule. The total Raman signal of the hemin-glyphosate incubated solutions includes a maximized electromagnetic contribution by the use of the appropriate laser excitation, and chemical contributions related to charge transfer between silver and hemin, and from resonance properties of Raman scattering of hemin. Incubation of the reporter molecule with the analyte before the conjugation with the SERS substrate has not been explored before and could be extrapolated to other reporter-analyte systems that depend on a binding equilibrium process.

Glucose oxidase@Cu-hemin metal-organic framework for colorimetric analysis of glucose

The work presents a novel glucose oxidase@Cu-hemin metal-organic frameworks (GOD@ Cu-hemin MOFs) with a ball-flower structure as bienzymatic catalysts for detection of glucose. The GOD@Cu-hemin MOFs exhibits great stability as compared with free horseradish peroxidase and GOD toward harsh conditions because the ball-flower-like shell of Cu-hemin MOF effectively protects from GOD. Thus, the GOD@Cu-Hemin MOFs can be used in external harsh conditions such as high temperature and acid/base. The GOD@Cu-hemin MOFs is capable of sensitive and selective detection of glucose via peroxidase-like of Cu-hemin MOFs and GOD by using 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate. Under the existence of glucose, O₂ is reduced into H₂O₂ via GOD@Cu-hemin MOFs. The produced H₂O₂ as well as Cu-hemin MOFs oxidize TMB into blue oxTMB which shows UV-Vis absorbance at 652. The absorption intensity of oxTMB linearly increases with the increasing concentration of glucose from 0.01 to 1.0 mM with detection limit of 2.8 μM. An integrated agarose hydrogel film (Aga/GOD@Cu-hemin MOF/TMB) sensor is rationally designed for colorimetric detection of glucose. The sensor displays a response range of 30 μM-0.8 mM with a detection limit of 0.01 mM. The result indicates that the Cu-hemin MOFs are an ideal carrier for the encapsulation of enzymes.

Tunable Polymeric Scaffolds for Enzyme Immobilization

The number of methodologies for the immobilization of enzymes using polymeric supports is continuously growing due to the developments in the fields of biotechnology, polymer chemistry, and nanotechnology in the last years. Despite being excellent catalysts, enzymes are very sensitive molecules and can undergo denaturation beyond their natural environment. For overcoming this issue, polymer chemistry offers a wealth of opportunities for the successful combination of enzymes with versatile natural or synthetic polymers. The fabrication of functional, stable, and robust biocatalytic hybrid materials (nanoparticles, capsules, hydrogels, or films) has been proven advantageous for several applications such as biomedicine, organic synthesis, biosensing, and bioremediation. In this review, supported with recent examples of enzyme-protein hybrids, we provide an overview of the methods used to combine both macromolecules, as well as the future directions and the main challenges that are currently being tackled in this field.

A novel Fe-hemin-metal organic frameworks supported on chitosan-reduced graphene oxide for real-time monitoring of H2O2 released from living cells

Herein, a kind of novel hemin-based metal organic frameworks (Fe-hemin-MOFs) with unique peroxidase-like bioactivity was developed for the first time. The synthesized Fe-hemin-MOFs exhibited satisfactory catalytic activity toward hydrogen peroxide (H₂O₂). When it was further supported on Chitosan-reduced graphene oxide (CS-rGO), amplified electrochemical signal could be obtained. The Fe-hemin-MOFs/CS-rGO composite was used to construct a novel H₂O₂ electrochemical sensor. The electrocatalytic reduction of H₂O₂ displayed two segments linearity range from 1 to 61 μM and 61-1311 μM, as well as a low detection limit of 0.57 μM. Furthermore, the proposed sensor was successfully used for real-time monitoring of H₂O₂ released from living cells, which extended the practical application of MOFs-based sensors in monitoring the pathological process in living cells.

Iron-porphyrin-based covalent-organic frameworks for electrochemical sensing H2O2 and pH

Here, a novel iron-porphyrin-based covalent organic framework (COF_{p-Fepor NH2-BTA}) was synthesized and applied for electrochemical sensing H₂O₂ and pH which involved in many biological processes. The COF_{p-Fepor NH2-BTA} was obtained by post-modification of porphyrin-based COF (COF_{p-por NH2-BTA}) which was firstly synthesized by aldehyde-ammonia condensation reaction between 1,3,5-benzenetricarboxaldehyde and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H- porphine. The COF_{p-por NH2-BTA} was proved to be regular and uniform spherical particles with diameter about 1 μm, as well as possessed good crystalline structure and abundant micropores of about 1.4 nm. The resulted COF_{p-Fepor NH2-BTA} after post-modification with Fe²⁺ maintained the original shape and crystalline structure of COF_{p-por NH2-BTA}, while the micropores decreased to be about 0.89 nm. Electrochemical results indicated that the synthesized COF_{p-Fepor NH2-BTA} had good electrochemical redox and proton activity owing to iron-porphyrin, enabling to simultaneously be used as mimic peroxidase to catalyze the reduction of hydrogen peroxide (H₂O₂) and evaluate pH using current and potential as signal, respectively. The prepared sensor showed good performance for H₂O₂ detection from 6.85 nM to 7 μM with the detection limit of 2.06 nM (S/N = 3), and pH test from 3.0 to 9.0. This work demonstrated that the iron-porphyrin-based COF could be used as a mimic peroxidase to apply in biological fields.

Computational characterization of halogen vapor attachment, diffusion and desorption processes in zeolitic imidazolate framework-8

Computational simulation methods are used for characterizing the detailed attachment, diffusion and desorption of halogen vapor molecules in zeolitic imidazolate framework-8 (ZIF-8). The attachment energies of Cl2, Br2 and I2 are -55.2, -48.5 and -43.0 kJ mol-1, respectively. The framework of ZIF-8 is disrupted by Cl2, which bonds with Zn either on the surface or by freely diffusing into the cage. A framework deformation on the surface of ZIF-8 can be caused by the attachment of Br2, but only reorientation of the 2-methylimidazolate linkers (mIms) for I2. In diffusion, the halogen molecules have a tendency to vertically permeate the apertures of cages followed with swing effect implemented by the mIms. Larger rotation angles of mIms are caused by Br2 because of its stronger interaction with mIms than I2. A maximum of 7 Br2 or 5 I2 molecules can be accommodated in one cage. Br2 are clinging to the mIms and I2 are arranged as crystal layout in the cages, therefore in desorption processes molecules attached to the surface and free inside are desorbed while some remained. These results are beneficial for better understanding the adsorption and desorption processes of halogen vapors in the porous materials.

Hemin-Bridged MOF Interface with Double Amplification of G-Quadruplex Payload and DNAzyme Catalysis: Ultrasensitive Lasting Chemiluminescence MicroRNA Imaging

Here, we report a double-amplified sensing platform for ultrasensitive chemiluminescence (CL) miRNA detection in real patients' blood in which a hemin-bridged metal-organic framework (MOF) is employed as a functional interface to boost the payload and catalysis of G-quadruplex (G4) DNAzymes. Hemin is here used as the organic ligand for the MOF synthesis, which endows the MOF with an intrinsic peroxidase-like catalytic activity. Most importantly, the MOF surface provides a large amount of binding sites for polymeric G4 DNAzymes that are produced by miRNA-triggered rolling circle amplification reactions, and meanwhile, the interfaced G4 DNAzymes on MOFs (G4/MOFzymes) display an about 100-fold higher catalytic activity than those in solution. By using the G4/MOFzyme catalysts in the luminol/H₂O₂ CL system, the amplification detection of two acute myocardial infarction (AMI)-related miRNAs (low to 1 fM seen with naked eyes) is achieved in human serum with a smartphone as a portable imaging detector, which provides a facile methodology for point-of-care (POC) diagnosis of AMI. Compared with previous smartphone-based counterparts not requiring sophisticated equipment, this new facile methodology shows both 6 orders of magnitude higher sensitivity and an ∼50-fold longer duration for CL miRNA imaging. These unique features allow our developed G4/MOFzymes to be further employed as a novel luminescent ink for printing commonly used patterns.

Enzyme-free glucose sensor based on layer-by-layer electrodeposition of multilayer films of multi-walled carbon nanotubes and Cu-based metal framework modified glassy carbon electrode

A high-performance nonenzymatic glucose sensor was successfully prepared by a layer by layer strategy through electrodeposition assembling multilayer films of Cu-metal-organic frameworks/multi-walled carbon nanotubes (Cu-MOF/MWNTs) modified glassy carbon electrodes (GCE). Different multilayer films of Cu-MOF/MWNTs modified GCE (Cu-MOF/MWNTs/GCE) were prepared by repeating the electrodeposition of MWNTs onto the GCE in an MWNTs solution (MWNTs/GCE) and electrodeposition of the Cu-MOF layer onto the MWNTs film surface to form a Cu-MOF/MWNTs composite layer in the crystallization solution of Cu-MOF. Results confirmed that this method to fabricate multilayer composite films on the GCE was fast and convenient, and that multilayer composite films were stable and unified. The electrode modified by the multilayer composite films could effectively increase the exposure of active sites and increase the surface area of reactive contact. The GCE modified by eight layers (four multilayers Cu-MOF/MWNTs films) showed the optimum catalytic performance in the oxidation of glucose. The novel glucose sensor exhibited a wider detection linear range of 0.5 μM-11.84 mM, with a detection limit of 0.4 μM and a sensitivity of 3878 μA cm^-2 mM^-1. Moreover, the electrochemical response of the sensor on glucose was fast (within 0.3 s) and stable, exhibited good selectivity and was free of interference.

Ni-hemin metal-organic framework with highly efficient peroxidase catalytic activity: toward colorimetric cancer cell detection and targeted therapeutics

Background

Given the great benefits of artificial enzymes, a simple approach is proposed via assembling of Ni²⁺ with hemin for synthesis of Ni-hemin metal–organic-frameworks (Ni-hemin MOFs) mimic enzyme. The formation of the Ni-hemin MOFs was verified by scanning electron microscopy, Transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Energy-dispersive X-ray spectroscopy and UV–vis absorption spectroscopy. This novel nanocomposite exhibited surprising peroxidase like activity monitored by catalytic oxidation of a typical peroxidase substrate, 3,3,5,5′-tetramethylbenzidine, in the presence of H₂O₂. By using folic acid conjugated MOF nanocomposite as a recognition element, we develop a colorimetric assay for the direct detection of cancer cells.

Results

The proposed sensor presented high sensitivity and selectivity for the detection of human breast cancer cells (MCF-7) and Human Caucasian gastric adenocarcinoma. By measuring UV–vis absorbance response, a wide detection range from 50 to 10⁵ cells/mL with a detection limit as low as 10 cells/mLwas reached for MCF-7 cells. We further discuss therapeutics efficiency of Ni-hemin MOFs in the presence of H₂O₂ and ascorbic acid. Peroxidase-mimic Ni-hemin MOFs as reactive oxygen species which could damage MCF-7 cancer cells, however for normal cells (human embryonic kidney HEK 293 cells) killing effect was negligible.

Conclusions

Based on these behaviors, the developed method offers a fast, easy and cheap assay for the interest in future diagnostic and treatment application.

Hemin immobilized into metal-organic frameworks as an electrochemical biosensor for 2,4,6-trichlorophenol

Hemin immobilized into copper-based metal-organic frameworks was successfully prepared and used as a new electrode material for sensitive electrochemical biosensing. X-ray diffraction patterns, Fourier transform infrared spectra, scanning electron microscopy, UV-vis absorption spectroscopy, and cyclic voltammetry were used to characterize the resultant composites. Due to the interaction between the copper atom groups and hemin, the constrained environment in Cu-MOF-74 acts as a matrix to avoid the dimerization of enzyme molecules and retain its biological activity. The hemin/Cu-MOF composites demonstrated enhanced electrocatalytical activity and high stability towards the oxidation of 2,4,6-trichlorophenol. Under optimum experimental conditions, the sensor showed a wide linear relationship over the range of 0.01-9 μmol L^-1 with a detection limit (3σ) of 0.005 μmol L^-1. The relative standard deviations were 4.6% and 3.5% for five repeated measurements of 0.5 and 5 μmol L^-1 2,4,6-trichlorophenol, respectively. The detection platforms for 2,4,6-trichlorophenol developed here not only indicate that hemin/Cu-MOF-74 possesses intrinsic biological reactivity, but also enable further work to be conducted towards the application of enzyme-containing metal-organic frameworks in electrochemical biosensors.

A novel biosensor based on ball-flower-like Cu-hemin MOF grown on elastic carbon foam for trichlorfon detection

In this study, ball-flower-like Cu-hemin MOFs microstructures supported by flexible three-dimensional (3D) nitrogen-containing melamine carbon foam composites (denoted as Cu-H MOFs/NECF) were constructed. They were used for the immobilization of acetylcholinesterase (AChE) to detect trichlorfon, a widely applicable organophosphorus pesticide (OP). The formation of Cu-H MOFs/NECF was confirmed by scanning electron microscopy, X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The results indicated that ball-flower-like Cu-hemin MOF microstructures were evenly grown on the fibers of 3D-NECF via a simple room temperature mixing method, which could greatly increase the effective surface area. The Cu-H MOFs/NECF composites also overcome the disadvantages of carbon foam materials such as too large pore diameters that always lead to the stacking of the protease and poor conductivity. Moreover, the composites contain nitrogen elements not only from melamine but also from hemin, which is bound to greatly increase the biocompatibility. The composites were directly used to immobilize a large number of AChE to prepare integrated AChE/Cu-H MOFs/NECF electrodes. Simultaneously, the integrated electrode showed better performance for trichlorfon detection. The sensor exhibited good stability and toughness, wide linear range (0.25–20 ng mL⁻¹) and low detection limit (0.082 ng mL⁻¹). Hence, the AChE/Cu-H MOFs/NECF trichlorfon sensor could be a valuable platform for the pesticide residues field testing.

The Cu-hemin MOFs/nitrogen-doped elastic carbon foam (Cu-hemin MOFs/NECF) composite structure was constructed as the supporting matrix to load acetylcholinesterase (AChE) for preparing pesticide biosensors.