Encapsulation of Hemin in Metal-Organic Frameworks for Catalyzing the Chemiluminescence Reaction of the H2O2-Luminol System and Detecting Glucose in the Neutral Condition

A non-enzymatic electrochemical biosensor based on Au@PBA(Ni-Fe):MoS2 nanocubes for stable and sensitive detection of hydrogen peroxide released from living cells

Hydrogen peroxide (H2O2) is the main product of enzymatic reactions and plays an important role in biological processes. The detection of H2O2 inside organisms or cells is critical. Here, we report a nickel-iron Prussian blue analogue nanocube doped with molybdenum disulfide and Au nanoparticles (Au@PBA(Ni-Fe):MoS2) as an electrochemical sensing material for the stable detection of H2O2 in neutral solutions for a long time. First, the Prussian blue analogue (PBA(Ni-Fe)) is synthesized by a simple charge-assembly technology, and then etched into PBA(Ni-Fe):MoS2 hollow nanocubes by a high-temperature hydrothermal reaction. Finally, Au nanoparticles are reduced inside the PBA(Ni-Fe):MoS2in situ to generate Au@PBA(Ni-Fe):MoS2 nanocubes. Ni-doping enhances the nanocube's stability in neutral solutions; as a result, the sensor can maintain a stable current response towards H2O2 reduction for more than 1 h. The sensing material can meet the needs of a long-time test. The introduction of Au enhances the electron transfer efficiency, which endows the sensor with good reduction ability for H2O2 at 0 V over a wide linear range (0.5-200 μM and 210-3000 μM) and with a low detection limit (0.23 μM (S/N = 3)), which fulfills the requirements for the detection of H2O2 in a biological system. The sensor can sense H2O2 released from cells stimulated by ascorbic acid. Au@PBA(Ni-Fe):MoS2 provides good guidance for the future development of efficient biosensors to be applied in cell biology.

Boric-acid-modified Fe3O4@PDA@UiO-66 for enrichment and detection of glucose by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Herein, boric-acid-modified multifunctional Zr-based metal-organic frameworks (denoted as Fe₃O₄@PDA@B-UiO-66) were synthesized by hydrothermal reaction and surface modification. Compared to traditional matrix, Fe₃O₄@PDA@B-UiO-66 has the advantages of high ionization efficiency, high surface area, low matrix background, porous structure, and numerous boric-acid-active sites. By combining matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), Fe₃O₄@PDA@B-UiO-66 was used as an adsorbent and matrix for enrichment and detection of glucose, based on a specific reaction between boric acid and glucose. The limit of detection was 58.5 nM. The proposed method provides a simple and efficient approach for the sensitive and quantitative detection of glucose in complex samples based on MALDI-TOF MS. Design and synthesis of boric-acid-modified multifunctional magnetic metal-organic frameworks (designated as Fe₃O₄@PDA@B-UiO-66) applied as adsorbent and matrix for the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of glucose in complex biosamples.

MOF-Derived Bimetallic CoFe-PBA Composites as Highly Selective and Sensitive Electrochemical Sensors for Hydrogen Peroxide and Nonenzymatic Glucose in Human Serum

The fabrication of two-dimensional (2D) metal-organic frameworks (MOFs) and Prussian blue analogues (PBAs) combines the advantages of 2D materials, MOFs and PBAs, resolving the poor electronic conductivity and slow diffusion of MOF materials for electrochemical applications. In this work, 2D leaflike zeolitic imidazolate frameworks (Co-ZIF and Fe-ZIF) as sacrificial templates are in situ converted into PBAs, realizing the successful fabrication of PBA/ZIF nanocomposites on nickel foam (NF), namely, CoCo-PBA/Co-ZIF/NF, FeFe-PBA/Fe-ZIF/NF, CoFe-PBA/Co-ZIF/NF, and Fe/CoCo-PBA/Co-ZIF/NF. Such fabrication can effectively reduce transfer resistance and greatly enhance electron- and mass-transfer efficiency due to the electrochemically active PBA particles and NF substrate. These fabricated electrodes as multifunctional sensors achieve highly selective and sensitive glucose and H₂O₂ biosensing with a very wide detective linear range, extremely low limit of detection (LOD), and good stability. Among them, CoFe-PBA/Co-ZIF/NF exhibits the best sensing performance with a very wide linear range from 1.4 μM to 1.5 mM, a high sensitivity of 5270 μA mM^-1 cm^-2, a low LOD of 0.02 μM (S/N = 3), and remarkable stability and selectivity toward glucose. What is more, it can realize excellent detection of glucose in human serum, demonstrating its practical applications. Furthermore, this material as a multifunctional electrochemical sensor also manifests superior detection performance against hydrogen peroxide with a wide linear range of 0.2-6.0 mM, a high sensitivity of 196 μA mM^-1 cm^-2, and a low limit of detection of 1.08 nM (S/N = 3). The sensing mechanism for enhanced performance for glucose and H₂O₂ is discussed and proved by experiments in detail.

A capillary-based fluorimetric platform for the evaluation of glucose in blood using gold nanoclusters and glucose oxidase in the ZIF-8 matrix

A capillary-based fluorimetric analysis method was developed for probing glucose (Glu) in blood using Glu oxidase-anchored gold nanoclusters (GOD-AuNCs) and the ZIF-8 matrix. AuNCs were attached with GOD to be further encapsulated into the ZIF-8 matrix through the protein-mediated formation route. The resulting GOD-AuNCs@ZIF-8 nanocomposites could present the AuNC-improved catalysis of GOD and ZIF-8-improved environmental stability. The ZIF-8-enhanced fluorescence intensity of AuNCs could also be expected. Moreover, a capillary-based fluorometric platform was constructed for sensing Glu by coating the capillaries first with GOD-AuNCs and then the ZIF-8 matrix. Herein, Glu was introduced through the self-driven sampling to trigger the GOD-catalyzed production of hydrogen peroxide, which could induce the fluorescence quenching rationally depending on the Glu concentrations. The developed fluorimetric method could allow for the rapid and simple detection of Glu with the concentrations linearly ranging from 5.0 μM to 2.5 mM. Besides, the feasibility of practical applications was demonstrated by the evaluation of Glu in blood showing the recoveries of 96.2%-103.4%. Importantly, the proposed design of the capillary-based fluorimetric platform by the synergetic combination of catalysis-specific recognition and fluorescence signaling may open a new door toward extensive applications in the biological sensing, catalysis, and imaging fields.

In Situ Formed Catalytic Interface for Boosting Chemiluminescence

Designing the catalytic interface that preferentially attracts reactants is highly desirable for amplifying chemiluminescence (CL) emission. Herein, to boost the generation of reactive oxygen species (ROS) from dissolved O₂ molecule, flower-like cobalt hydroxide (f-Co(OH)₂) based catalytic interface with hierarchical and porous architecture were in situ created in the coexistence of BSA and Co²⁺. Benefiting from the oxidase-like catalysis capability and the unique microstructure of f-Co(OH)₂, ROS was efficiently produced. Meanwhile, the capping ligands of BSA endowed the interface with the capability of enriching functionality through the interaction between BSA and luminol. 100-fold CL enhancement was achieved using the as-prepared catalytic interface compared with the classical luminol-Co²⁺ or luminol-BSA system. Moreover, the proposed catalytic amplification mechanism could be extended to the different proteins such as lysozyme, protamine, thrombin, papain. Based on the quenching effect on CL, a sensitive sensing platform was constructed for the determination of ascorbic acid with satisfied results. Our finding provided a novel "all-in-one" route to design the catalytic interface for amplifying CL emission.

Bimetallic CuCo2 S4 Nanozymes with Enhanced Peroxidase Activity at Neutral pH for Combating Burn Infections

Peroxidase-mimicking nanozymes that can generate toxic hydroxyl radicals (^. OH) hold great promise as antibacterial alternatives. However, most of them display optimal performance under strongly acidic conditions (pH 3-4), and are thus not feasible for many medical uses, including burn infections with a wound pH close to neutral. Herein, we report a copper-based nanozyme (CuCo₂ S₄ ) that exhibits intrinsic peroxidase-like activity and can convert H₂ O₂ into ^. OH at neutral pH. In particular, bimetallic CuCo₂ S₄ nanoparticles (NPs) exhibited enhanced peroxidase-like activity and antibacterial capacity, superior to that of the corresponding monometallic CuS and CoS NPs. The CuCo₂ S₄ nanozymes possessed excellent ability to kill various bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, this CuCo₂ S₄ nanozymes could effectively disrupt MRSA biofilms in vitro and accelerate MRSA-infected burn healing in vivo. This work provides a new peroxidase mimic to combat bacteria in neutral pH milieu and this CuCo₂ S₄ nanozyme could be a promising antibacterial agent for the treatment of burn infections.

A chemiluminescence assay for determination of lysozyme based on the use of magnetic alginate-aptamer composition and hemin@HKUST-1

Lysozyme aptamer-functionalized magnetic alginate hydrogel was prepared for separation and enrichment of lysozyme. Luminol-labeled aptamer was used as a signal tag, and the signal tag was adsorbed on magnetic carboxylated carbon nanotubes based on the π-interaction. When lysozyme was added, the aptamer specifically binds to the lysozyme, causing the signal tag to detach from the magnetic carboxylated carbon nanotubes. When the aptamer/lysozyme complex bound to the complementary single strand of aptamer on the hemin@HKUST-1, lysozyme was released. The released lysozyme can be recombined with the signal tag adsorbed on the magnetic carboxylated carbon nanotube, allowing more signal tag to be dispersed into the solution. Determination of lysozyme was achieved by releasing the luminol-labeled aptamer to generate a chemiluminescence signal at a wavelength of 425 nm. It was proved by experiments that the synthesized hemin@HKUST-1 had a strong catalytic effect on the luminol-NaOH-H₂O₂ system. The chemiluminescence signal was increased nearly 100 times. The complementary pairing allowed the luminol to be immobilized on the surface of hemin@HKUST-1. The generation and consumption of short-lived reactive oxygen species were concentrated on the surface of the MOFs, which improves the chemiluminescence efficiency. The introduction of hemin@HKUST-1 and DNA solved the defects of chemiluminescence analysis. The chemiluminescence assay was able to detect lysozyme with linear range of 1.05 × 10^-6 U∙mg^-1 (6.00 × 10^-13 mol∙L^-1)-1.25 × 10^-2 U∙mg^-1 (7.14 × 10^-9 mol∙L^-1); the detection limit was 3.50 × 10^-7 U∙mg^-1 (2.00 × 10^-13 mol∙L^-1) (R² = 0.99). The recovery of lysozyme in spiked saliva samples was 97.4-102.8%. Graphical abstract Schematic presentation of chemiluminescence assay. Lysozyme (Lys) was captured by aptamer-modified magnetic sodium alginate (M-Alg-Apt); Glycine (pH = 2) as eluent for Lys. Luminol-modified Apt (Apt-luminol) as signal tag; magnetic carbon nanotubes (MCNTs) as adsorption matrix; cDNA was complementary to Apt; hemin@HKUST-1 as catalyst.

Trimetallic PdCuAu Nanoparticles for Temperature Sensing and Fluorescence Detection of H 2 O 2 and Glucose

The design of palladium-based nanostructures has good prospects in various applications. This paper reports a simple one-step synthesis method of PdCuAu nanoparticles (PdCuAu NPs) prepared directly in aqueous solution. PdCuAu NPs have attracted much attention owing to their unique synergistic electronic effect, optical and catalytic performance. As temperature sensor, PdCuAu NPs are sensitive to the fluorescence intensity change in the temperature range of 4-95°C, which is due to its unique optical properties. The prepared PdCuAu NPs have excellent catalytic performance for peroxidase-like enzymes. It can catalyze TMB rapidly in the presence of hydrogen peroxide and oxidize it to visible blue product (oxTMB). Based on its unique peroxidase-like properties, this study used PdCuAu NPs colorimetric platform detection of hydrogen peroxide and glucose. The linear ranges of hydrogen peroxide and glucose were 0.1-300 μM and 0.5-500 μM, respectively, and the detection limits (LOD) were 5 and 25 nM, respectively. This simple and rapid method provides a good prospect for the detection of H2O2 and glucose in practical applications.

Intensive and Persistent Chemiluminescence System Based on Nano-/Bioenzymes with Local Tandem Catalysis and Surface Diffusion

A chemiluminescence (CL) system with long persistent and intensive emission is essential for accurate CL quantitative analysis and imaging assay. However, with most known CL systems being flash-type, it is still a great challenge to develop long-lasting CL systems. Here, by combining an iron porphyrin metal-organic frameworks (FePorMOFs) based peroxidase mimic with natural glucose oxidase (GOx), an intensive and persistent CL system is presented on the basis of local tandem catalysis and surface diffusion of the nano-/bioenzymes (FePorMOF/GOx). FePorMOF synthesized by iron porphyrin linker and zirconium ion node possesses high peroxidase catalytic activity and stability. Using luminol and glucose as substrate, the FePorMOF/GOx CL system can produce intensive CL emission containing a plateau period of 7.5 h. The strong CL signal is due to the local tandem generation and reaction of H₂O₂ by GOx and FePorMOF, which avoids the diffusion-limited kinetics and leads to a high catalytic efficiency of the nano-/bioenzymes. On the other hand, the long persistent CL emission is attributed mainly to the enzymatic reaction-controlled H₂O₂ supply and surface diffusion-controlled CL reaction. The proposed CL system is explored for CL imaging sensing of glucose and homogeneous immunoassay of α-fetoprotein. The nano-/bioenzymes CL system exhibits intensive and long constant CL emission in physiological condition, showing promising applications in real-time bioassay and bioimaging.

Enhancing hydrogel-based long-lasting chemiluminescence by a platinum-metal organic framework and its application in array detection of pesticides and d-amino acids

Organophosphorus pesticides (OPs) are harmful to people's health and d-amino acids (d-AAs) in the human body are closely related to various diseases. So, detection of OPs in foods and d-AAs in serum is important for food safety and clinical diagnosis. Herein, a long-lasting chemiluminescence (CL) imaging sensor was constructed for the detection of OPs and d-AAs. The method was based on N-(4-aminobutyl)-N-ethylisoluminol/Co2+/chitosan (ABEI/Co2+/CS) hydrogels, where metal organic framework materials (MOF-Pt) were selected as catalysts to improve the sensitivity greatly. Under the catalysis of acetylcholinesterase (AChE) and choline oxidase (CHO), H2O2 was produced by using acetylcholine chloride (ACh) as a substrate, which was sensitive to the proposed CL system. OPs inhibited the activity of AChE and decreased the production of H2O2, reducing CL intensity. The linear range of the method for chlorpyrifos was 0.5 ng mL-1-1.0 μg mL-1, with a limit of detection (LOD) of 0.21 ng mL-1. Seventeen kinds of OPs can be visually and simultaneously discerned by the CL imager. On the other hand, d-AAs were catalyzed and oxidized by d-α-amino oxidase (DAAO) to produce H2O2. Thus, d-Ala in serum was used as a model to be detected by the proposed method. The linear range for d-Ala was 1.0 μM-10 mM, with an LOD of 0.12 μM.

Colorimetric determination of tetrabromobisphenol A based on enzyme-mimicking activity and molecular recognition of metal-organic framework-based molecularly imprinted polymers

A sol-gel method is presented to synthesize molecularly imprinted polymers (MIPs) composed with a copper-based metal-organic framework (referred to as MIP/HKUST-1) on a paper support to selectively recognize tetrabromobisphenol A (TBBPA). The imprinting factor is 7.6 and the maximum adsorption capacity is 187.3 mg g^-1. This is much better than data for other MIPs. The degradation of TBBPA is introduced in the procedure. Due to the selective recognition by the MIP, the enzyme-mimicking properties of HKUST-1 under the MIP layer became weak due to the decrease of residue imprinted cavities. And adsorbed TBBPA can be degraded under consumption of hydrogen peroxide (H₂O₂). The combined effect of H₂O₂ and HKUST-1 cause the coloration caused by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine to become less distinct. This amplification strategy is used for the ultrasensitive and highly selective colorimetric determination of TBBPA. The gray intensity is proportional to the logarithm concentration of TBBPA in the range of 0.01-10 ng g^-1. The limit of detection is as low as 3 pg g^-1, and the blank intensities caused by TBBPA analogues are <1% of that caused by TBBPA at the same concentration, this implying excellent selectivity. The spiked recoveries ranged from 94.4 to 106.6% with relative standard deviation values that were no more than 8.6%. Other features include low costs, rapid response, easy operation and on-site testing. Graphical abstractSchematic representation of colorimetric determination of tetrabromobisphenol A (TBBPA) by paper-based metal-organic framework-based molecularly imprinted polymers (MIP/HKUST-1 composites) using 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate.

A point-of-care diagnostics logic detector based on glucose oxidase immobilized lanthanide functionalized metal-organic frameworks

In this work, a novel lanthanide functionalized metal organic framework enzyme (L-MOF-enzyme) composite has been first prepared via a surface attachment strategy between Eu³⁺@UMOF and glucose oxidase (GOx). Here, the Eu³⁺@UMOF can be used as a support for GOx immobilization and also a responsive fluorescent center towards glucose (Glu). The resulting material not only exhibits fascinating luminescence properties based on the ⁵D₀→⁷F₂ transition of Eu³⁺ and the catalytic performance of enzymes, but also some advantages of MOF-enzyme composites, including better stability, and great fluorescence selectivity and sensitivity towards Glu (detection limit = 0.2 μM). Besides, the composite exhibited an excellent selectivity and sensitivity towards Glu in serum and urine under room temperature and neutral conditions, which breaks the limitation of specific catalytic conditions of enzymes. Taking all the advantages of the L-MOF-enzyme composite, a point-of care (POC) diagnostics logic detector which can be used for the fluorescence detection of Glu in urine is designed. From the three outputs of the logic detector (L, M and H), we can intuitively realize the self-diagnosis of the three ranges of Glu concentrations that act as the inputs of the detector (0.1 μM-10 μM, 10 μM-10 mM, >10 mM) by the naked eye. The logic detector allows us, especially diabetics, to instantly detect glucose levels in the urine without going to the hospital for complicated inspections. This is the first attempt using L-MOFs combined with GOx to construct a POC diagnostics logic detector for fluorescence detection of Glu.

DNA-scaffold copper nanoclusters integrated into a cerium(III)-triggered Fenton-like reaction for the fluorometric and colorimetric enzymatic determination of glucose

A fluorometric and colorimetric method are described for the determination of hydrogen peroxide and glucose by integrating copper nanoclusters (CuNCs) into a Fenton-like reaction. The mechanism mainly depends on the fast formation of long-strand DNA-templated CuNCs with strong red fluorescence (with excitation/emission maxima at 340/640 nm) in the absence of H₂O₂. The DNA can be cleaved into short-oligonucleotide fragments by hydroxy radicals as formed in the Ce(III)-triggered Fenton-like reaction in the presence of H₂O₂. As a result, short-strand DNA loses the ability as a template for the formation of CuNCs. This leads to a decrease of fluorescence. The colorimetric assay, in turn, is based on the oxidation of colorless Ce(III) ions to the distinctly yellow Ce(IV) ions (with an absorption maximum at 400 nm) by H₂O₂. Compared with those assays based on the use of enzyme mimics, this method does not require any chromogenic substrates such as ABTS and TMB. Based on the dual-signal readout platform, we successfully achieved the detection of H₂O₂ and glucose. LODs are as low as 0.266 μM and 2.92 μM. The methods were applied to the sensitive determination of glucose by using glucose oxidase (GOx) which catalyzes the oxidization of glucose to produce H₂O₂. The practical application was demonstrated by determination of glucose in human serum, with apparent recoveries of 98.4-101.9% and 99.1-105.6%, respectively. The concentration of glucose ranges from 1 to 500 μM and 50 to 600 μM based on the dual-signal readout platform, respectively. This fluorometric and colorimetric dual-mode strategy will pave a new avenue for constructing effective assays for H₂O₂-related analytes in biochemical and clinical applications. Graphical abstractSchematic representation of a fluorometric and colorimetric dual-readout strategy for the sensitive determination of hydrogen peroxide and glucose. The assay has been designed by integrating copper nanoclusters into a Ce(III)-triggered Fenton-like reaction.

Metal-Organic Framework Loaded by Rhodamine B As a Novel Chemiluminescence System for the Paper-Based Analytical Devices and Its Application for Total Phenolic Content Determination in Food Samples

Herein, a novel paper-based chemiluminescence (CL) device has been reported for the estimation of total phenolic content of food samples. The CL system implemented on the paper was based on a hydrogen peroxide (H₂O₂)-rhodamine b (RhoB)-cobalt metal organic framework (CoMOF) reaction. It was found that the reaction of H₂O₂ with RhoB molecules, loaded into the nanopores of CoMOF (R@CoMOF), can produce an intensive CL emission. The experiments on the paper indicated that in the presence of CoMOF, the CL emission was greatly increased. In addition to this strong catalyzing effect, application of CoMOF on the paper improved the stability of the CL system for several days. As a useful analytical application for the obtained paper-based CL device (PCD), it was examined for the detection of phenolic antioxidants. It was observed that the addition of 5 μL of phenolic compounds (PC) on the paper containing the CL reagents can remarkably decrease the CL intensity. This effect was applied to design a simple analytical assay for PC. After the optimization process, the best sensitivity was obtained for gallic acid, quercetin, catechin, kaempferol, and caffeic acid with detection limits of 0.98, 1.36, 1.48, 1.81, and 2.55 ng mL^-1, respectively. The relative standard deviations (RSD%) were also less than 5%. This study is the first report on the practical application of PCD using a nanomaterial assisted CL reaction. It is simple, portable, and low-cost and consumes a very low amount of reagents and sample solution. The device was successfully applied in the investigation of total antioxidant capacity of molasses and honey samples.

Water-soluble Hemin-mPEG-enhanced Luminol Chemiluminescence for Sensitive Detection of Hydrogen Peroxide and Glucose

In the present study, we synthesized a water-soluble substance (Hemin-mPEG) at room temperature by using hemin and poly(ethylene glycol) methyl ether (mPEG). It was found that the Hemin-mPEG maintained the excellent catalytic activity inherited from hemin, and was first used to catalyze a luminol-H₂O₂ chemiluminescence (CL) system to generate an intense and slow CL signal. The results of a mechanism research showed that the presence of Hemin-mPEG could promote the production of oxygen-relative radicals from H₂O₂ and dissolved oxygen in solution. Based on this mechanism, an ultra-sensitive, cheap and simply practical sensor for detecting glucose and H₂O₂ was developed. Under the most optimal experimental conditions, H₂O₂ and glucose detection results exhibited a good linear range from 0.002 to 3 μM and from 0.02 to 4 μM, respectively, and the detection limits were 1.8 and 10 nM, respectively. This approach has been successfully used to detect glucose in actual biological samples, and achieved good results.

Cu-Doped Carbon Dots as Catalysts for the Chemiluminescence Detection of Glucose

Development of metal-doped carbon dots (CDs) to effectively modulate their electronic properties and surface chemical reactivities is still in its early stage. In this paper, a facile solid-phase synthesis strategy was developed to synthesize Cu-doped CDs (Cu-CDs) using citric acid as the carbon source and Cu(NO₃)₂·3H₂O as the dopant, respectively. The as-prepared Cu-CDs exhibited superior peroxidase-like activity to horseradish peroxidase and were stable under a wide range of pH and temperatures. Consequently, the Cu-CD-based chemiluminescence sensing was applied to sensitively detect glucose with a low detection limit of 0.32 μM, and the recoveries and the relative standard deviation of the serum sample are 87.2-112.2 and 8.16% (n = 6), respectively. Notably, the proposed chemiluminescence sensing was also successfully applied for label-free detection of glucose in complex biological samples, which envisioned its potential applications in clinical diagnosis and other analytical assays.

A new photoelectrochemical immunosensor for ultrasensitive assay of prion protein based on hemin-induced photocurrent direction switching

As a significant biomarker of prion diseases, ultrasensitive assay of infectious isoform of prion (PrP^Sc) is highly desirable for early diagnostics of prion diseases. Herein, taking normal cellular form of prion (PrP^C) as a model owing to a high risk of pathogenicity of PrP^Sc, a new photoelectrochemical immunosensor has been developed based on hemin-induced switching of photocurrent direction. In the presence of PrP^C, nitrogen-doped porous carbon-hemin polyhedra labeled with secondary antibody were introduced onto the CdS-chitosan (CS) nanoparticles-modified indium-tin oxide (ITO) electrode via the antigen-antibody specific recognition. Because of the matched energy level between CdS and hemin, the high-efficiency switch of photocurrent direction of the ITO/CdS-CS photoelectrode from anodic to cathodic photocurrent was observed even at very low concentration (0.4 aM) of PrP^C. Through changing the specific antibody, this method can be easily expanded to PrP^Sc assay. Such low detectable limit is very useful in the early diagnosis and screening of prion diseases. The developed method has also promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Enhancing Luminol Electrochemiluminescence by Combined Use of Cobalt-Based Metal Organic Frameworks and Silver Nanoparticles and Its Application in Ultrasensitive Detection of Cardiac Troponin I

Electrochemiluminescence (ECL) has emerged as one of the most important methods for in vitro diagnosis and detection, but it is still limited in sensitivity for ultrasensitive biodetections. Fast and ultrasensitive detection of biomolecules is critical, especially for the clinical detection of cardiac troponin I (cTnI) for cardiac infarction diagnosis. In this study, an effective tactic was developed to enhance ECL efficiency of the luminol system, by combined use of Co²⁺-based metal organic frameworks (MOF), zeolitic imidazolate frameworks (ZIF-67), and luminol-capped Ag nanoparticles (luminol-AgNPs). The integration leads to a pronounced ∼115-fold enhancement in luminol ECL. On the basis of this fascinating sensing platform, a robust label-free ECL immunosensor was constructed for ultrasensitive detection of cTnI, the main marker of myocardial infarction, with good stability and a detection limit as low as 0.58 fg mL^-1 (S/N = 3).

Engineering FeCo alloy@N-doped carbon layers by directly pyrolyzing Prussian blue analogue: new peroxidase mimetic for chemiluminescence glucose biosensing

Direct pyrolysis of a Prussian blue analogue produced FeCo@NC with high and stable peroxidase-like activity, which catalyzes luminol oxidation by H₂O₂ to generate strong CL emission, and this finding results in a new CL biosensor for glucose.

Selective and Sensitive Sensing of Hydrogen Peroxide by a Boronic Acid Functionalized Metal-Organic Framework and Its Application in Live-Cell Imaging

A new boronic acid functionalized Zr(IV) metal-organic framework having the capability of sensing H₂O₂ in live cells is reported. The Zr-MOF bears a UiO-66 structure and contains 2-boronobenzene-1,4-dicarboxylic acid (BDC-B(OH)₂) as a framework linker. The activated Zr-UiO-66-B(OH)₂ compound (called 1') is highly selective for the fluorogenic detection of H₂O₂ in HEPES buffer at pH 7.4, even in the presence of interfering ROS (ROS = reactive oxygen species) and other biologically relevant analytes. The fluorescent probe was found to display extraordinary sensitivity for H₂O₂ (detection limit 0.015 μM) in HEPES buffer, which represents a lower value in comparison to those of the MOF probes documented so far for sensing H₂O₂ using other analytical methods. Taking advantage of its high selectivity and sensitivity for H₂O₂ in HEPES buffer, the probe was successfully employed for the imaging of intracellular H₂O₂. Imaging studies with MDAMB-231 cells revealed the emergence of bright blue fluorescence after loading with probe 1' and subsequent treatment with H₂O₂ solution.

Simple One-Pot Preparation of a Rapid Response AIE Fluorescent Metal-Organic Framework

Luminogenic materials, particularly those that have turn-on response by sensing the analytes, are highly regarded as optical instruments, sensing material, fluorescent probes, etc. However, most of these materials are only usable in dilute form and often show the self-quenching effect at high concentrations. The use of light-emitting AIE-based materials (aggregation-induced emission) is the solution of this problem. The rigid structure of these active fluorescence ligands, which contains several aromatic rings attached to each other, does not lose its fluorescence properties by increasing the concentration. Unlike other AIE ligands, which have a complex or multistep synthetic route, here, we present a simple one-pot method for in situ synthesis of the AIE ligand and the metal-organic framework (MOF) contained therein. Presence of metal nodes having varied outer-shell electron configurations affects the fluorescence intensity of these materials and, thus, both high and low emissive "turn on" MOFs were readily acquired. Based on the possible interactions between the free nitrogens on the ligand and the phenolic compounds, the MOFs enable highly selective and sensitive detection of phenol derivatives in several seconds with low detection limits (less than 65 nM for 4-aminophenol and 120 nM for phenol) through turn-on emission fluorescence.

Cancer-Cell Imaging Using Copper-Doped Zeolite Imidazole Framework-8 Nanocrystals Exhibiting Oxidative Catalytic Activity

Copper-doped zeolite imidazole framework-8 (Cu/ZIF-8) was prepared and its peroxidase-like oxidative catalytic activity was examined with a demonstration of its applicability for cancer-cell imaging. Through simple solution chemistry at room temperature, Cu/ZIF-8 nanocrystals were produced that catalytically oxidized an organic substrate of o-phenylenediamine in the presence of H₂ O₂ . In a similar manner to peroxidase, the Cu/ZIF-8 nanocrystals oxidized the substrate through a ping-pong mechanism with an activation energy of 59.2 kJ mol^-1 . The doped Cu atoms functioned as active sites in which the active Cu intermediates were expected to be generated during the catalysis, whereas the undoped ZIF-8 did not show any oxidative activity. Cu/ZIF-8 nanocrystals exhibited low cell toxicity and displayed catalytic activity through interaction with H₂ O₂ among various reactive oxygen species in a cancer cell. This oxidative activity in vitro allowed cancer-cell imaging by exploiting the photoluminescence emitted from the oxidized product of o-phenylenediamine, which was insignificant in the absence of the Cu/ZIF-8 nanocrystals. The results of this study suggest that the Cu/ZIF-8 nanocrystal is a promising catalyst for the analysis of the microbiological systems.

Heterogeneous catalysis with encapsulated haem and other synthetic porphyrins: Harnessing the power of porphyrins for oxidation reactions

Encapsulated metalloporphyrins have been widely studied for their use as efficient heterogeneous catalysts, inspired by the known catalytic activity of porphyrins in haemoproteins. The oxidation of organic substrates by haemoproteins is one of the well-known roles of these proteins, in which the haem (ferriprotoporphyrin IX = FePPIX) cofactor is the centre of reactivity. While these porphyrins are highly efficient catalysts in the protein environment, once removed, they quickly lose their reactivity. It is for this reason that they have garnered much interest in the field of heterogeneous catalysis of oxidation reactions. This review details current research in the field, focusing on the application of encapsulated haem, and other synthetic metalloporphyrins, applied to oxidation reactions.