VS4 Nanodendrites with Narrow Bandgaps in Activating Dissolved Oxygen for Boosted Chemiluminescence and Hemin Detection by Unexpected Quenching

Chemiluminescence (CL)-based analytical methods utilize luminophores that need to be activated with an oxidizing agent to trigger CL emission. Despite its susceptibility to decomposition when exposed to external light or trace metals, hydrogen peroxide (H2O2) has been widely used to develop chemiluminescent methods due to the limited number of suitable alternatives for activating chemiluminescent luminophores. Also, analytical methods based on the well-known luminol/H2O2 CL system have low sensitivity. Dissolved oxygen (DO) is a naturally abundant and environmentally benign alternative oxidant for luminol and other CL luminophores. However, DO alone is inactive and needs an efficient catalyst or a coreaction accelerator for its activation. Because of the narrow bandgap of VS4 (ca. 1.12 eV), it can facilitate fast electron-transfer kinetics with an acceptor molecule such as DO. Here, we introduce vanadium tetrasulfide (VS4) to boost CL for the first time. Under the optimized conditions, VS4 nanodendrite catalyzes the generation of reactive oxygen species by activating DO which subsequently reacts with luminol to generate intense CL. It enhances the CL intensity of luminol/DO by about 10,000 times. Surprisingly, hemin remarkably quenches the generated CL of luminol/DO/VS4 nanodendrites, which is completely opposite to its typical enhancement of luminol CL. Based on the remarkable concentration-dependent quenching of the luminol/DO/VS4 nanodendrite CL by hemin, we have developed a sensitive CL method that can selectively detect hemin in the linear concentration range of 1-250 nM and achieved a limit of detection of 0.11 nM. The practical utility of the developed method was demonstrated by the determination of hemin in a pharmaceutical drug for the treatment of acute intermittent porphyria and in human serum. This study demonstrates that VS4 holds great promise in analytical method development.

In Situ Exfoliation Growth Strategy Realizing Controlled Synthesis of 3D to 2D MOF Materials as High-Performance Electrochemical Biosensors

Two-dimensional (2D) metal-organic framework (MOF) nanosheets with large surface area, ultrathin thickness, and highly accessible active sites have attracted great research attention. Developing efficient approaches to realize the controllable synthesis of well-defined 2D MOFs with a specific composition and morphology is critical. However, it is still a significant challenge to construct thin and uniform 2D MOF nanosheets and resolve the reagglomeration as well as poor stability of target 2D MOF products. Here, an "in situ exfoliation growth" strategy is proposed, where a one-step synthetic process can realize the successful fabrication of PBA/MIL-53(NiFe)/NF nanosheets on the surface of nickel foam (NF) via in situ conversion and exfoliation growth strategies. The PBA/MIL-53(NiFe)/NF nanosheets combine the individual advantages of MOFs, Prussian blue analogues (PBAs), and 2D materials. As expected, the resulting PBA/MIL-53(NiFe)/NF as a glucose electrode exhibits an extremely high sensitivity of 25.74 mA mM-1 cm-2 in a very wide concentration range of 180 nM to 4.8 μM. The present exciting work provides a simple and effective strategy for the construction of high-performance nonenzymatic glucose electrochemical biosensors.

Bimetallic CuFe Prussian blue analogue cubes enhanced luminol chemiluminesence and its application

In this paper, bimetallic CuFe Prussian blue analogue (CuFe PBA) was discovered to have oxidase-like activity. Luminol can be oxidized under alkaline conditions without adding other oxidants. The chemiluminescence (CL) intensity produced is more than 1000 times that of the original luminol-NaOH system. Thus, a novel luminol-NaOH-CuFe PBA CL sensor was constructed. The CL intensity of the system would drastically decrease with the addition of uric acid (UA), it served as the foundation for the creation of an enzyme-free CL sensor for the determination of UA. The CL signal intensity of the system showed a linear connection with the square of the UA concentration in the range of 0.25 to 0.45 mmol·L-1, and the limits of detection was 0.10 mmol·L-1. This system could be used to construct an efficient CL sensor for the detection of UA in human serum.

Recent Advances in Nanomaterial-Based Chemiluminescence Probes for Biosensing and Imaging of Reactive Oxygen Species

Reactive oxygen species (ROS) play important roles in organisms and are closely related to various physiological and pathological processes. Due to the short lifetime and easy transformation of ROS, the determination of ROS content in biosystem has always been a challenging task. Chemiluminescence (CL) analysis has been widely used in the detection of ROS due to its advantages of high sensitivity, good selectivity and no background signal, among which nanomaterial-related CL probes are rapidly developing. In this review, the roles of nanomaterials in CL systems are summarized, mainly including their roles as catalysts, emitters, and carriers. The nanomaterial-based CL probes for biosensing and bioimaging of ROS developed in the past five years are reviewed. We expect that this review will provide guidance for the design and development of nanomaterial-based CL probes and facilitate the wider application of CL analysis in ROS sensing and imaging in biological systems.

Hotspots analysis and perspectives of Prussian blue analogues (PBAs) in environment and energy in recent 20 years by CiteSpace

Prussian blue analogs (PBAs), a type of metal-organic frameworks (MOFs), have attracted much attention because of their large specific surface area, high porosity, easy synthesis, and low cost. This paper presents the first review of PBAs by applying the bibliometric visualization software CiteSpace. The co-occurrence, co-citation, and clustering analysis of 2214 articles in the Web of Science database on the topic of "Prussian blue analogs" over the past 20 years were performed. The results provide a comprehensive overview of the evolution of the research hotspots for this material, and most importantly, it is identified that the research hotspots and trends for PBAs materials are concentrated in the environmental and energy fields. For example, the material is used as an adsorbent or catalyst to reduce pollutants, produce clean energy, or for energy storage applications such as batteries or supercapacitors. Finally, some outlooks are provided on the future research trends of this material in the environmental and energy fields, presenting the challenges faced by this material. For instance, the conductivity and corrosion resistance of the material needs to be improved and secondary contamination should be decreased or even avoided. It is believed that this paper would provide a comprehensive, systematic, and dynamic overview of the research of PBAs, and promote the future research of PBAs in the fields of environment and energy.

Bimetallic FeMn@C derived from Prussian blue analogue as efficient nanozyme for glucose detection

In recent decades, nanomaterial-based artificial enzymes called nanozymes have received more and more attention and have been applied in biological, chemical, medical, and other fields. In this work, bimetallic FeMn@C was synthesized by calcination from the Prussian blue analogue. The synthesized bimetallic FeMn@C exhibits efficient peroxidase-like activity. The effect of Mn doping amount, catalytic kinetics, and mechanism of FeMn@C nanozyme was further studied in detail. The results show that the peroxidase-like activity of bimetallic FeMn@C is nearly 16 times higher than that of single-metal Fe@C. The peroxidase-like activity of FeMn@C originates from its production of radicals. Compared with natural enzymes, FeMn@C nanozyme has a better affinity for the substrates. Besides, FeMn@C nanozyme has better stability than natural enzymes. Because of its strong magnetism, FeMn@C nanozyme can be recycled easily and exhibits excellent recycling performance. Based on the good affinity of FeMn@C for H₂O₂, a rapid and selective colorimetric assay for glucose detection is constructed, with a wide linear range of 0.01-0.75 mM and low detection limit of 4.28 µM. This sensor has been successfully applied to the determination of glucose in fruit juice, showing good selectivity and accuracy. The synthesis of bimetallic FeMn@C provides a feasible way to design nanozymes with excellent catalytic activity, high stability, and easy separation.

Tuning nanozyme property of Co@NC via V doping to construct colorimetric sensor array for quantifying and discriminating antioxidant phenolic compounds

Through V₂O₅ etching of ZIF-67 and subsequent pyrolysis in an argon flow, the V doped Co@NC (V/Co@NC) with mixed-valence Co(II)/Co(III) and V(III)/V(IV) was successfully obtained. V doping plays an important role in regulating the enzyme-like activity of Co@NC. Specifically, the Co@NC has both oxidase-like activity and peroxidase-mimic activity, while the V/Co@NC possesses the specific oxidase-like activity. Benefiting from the elevated Co²⁺ level due to electrons transfer from the reduced V(III) to Co³⁺ and recyclable redox reactions between the Co(III)/Co(II) and V(IV)/V(III) couples, the V/Co@NC displays 4-fold increase in the oxidase-like activity, smaller K_m (0.18 mM) and larger V_max (4.01 × 10^-8 M s^-1) toward TMB relative to Co@NC. The origin of V/Co@NC as oxidase mimic is likely attributed to the generation of ¹O₂ and •OH. Different phenolic compounds (PC), like gallic acid, kaempferol, caffeic acid, quercetin, and catechin, have distinct antioxidant capacity, showing a differential inhibiting effect on the V/Co@NC-TMB system. The different PC antioxidants in the V/Co@NC-TMB system lead to unique decrease in the absorbance at 652 nm (A₆₅₂), resulting in a unique absorbance signal response mode. By choosing different combinations of A₆₅₂ signals at various time points, multichannel information can be extracted from a single nanozyme for pattern recognition. Based on this, a colorimetric array sensing platform for the identification of PC is established successfully. Furthermore, the constructed sensor array can be used for quantifying and discriminating multiple PC antioxidants.

Magnetic-field-induced self-assembly of FeCo/CoFe2O4 core/shell nanoparticles with tunable collective magnetic properties

Self-assembly of nanoparticles into ordered patterns is a novel approach to build up new consolidated materials with desired collective physical properties. Herein, nanoparticle assemblies of composition-modulated bimagnetic nanoparticles have been produced via slow evaporation of their colloidal suspension in the absence or presence of magnetic fields. The assemblies obtained in the presence of the magnetic fields exhibit oriented nanoparticle chains in face-centered cubic superlattice structures, compared with the hexagonal closed-packed superlattice obtained without the magnetic field. The oriented structure has an alignment of the easy magnetization axis along the chains. This alignment leads to enhanced intra-superlattice interactions. As a result, the field-induced assembly displays collective magnetic properties with significantly enhanced magnetic anisotropy, remanent magnetization and coercivity. It is also found that the bimagnetic FeCo/CoFe2O4 core/shell nanostructure enhances the intra-particle interaction and thus is beneficial for the growth of oriented assembly of nanoparticles. Furthermore, the collective magnetic behavior is evidenced by the observation of a superferromagnetic-like magnetization relaxation in the ac-susceptibility curves.

Paper-based Chemiluminescence Device with Co-Fe Nanocubes for Sensitive Detection of Caffeic Acid

In this work, a new chemiluminescence (CL) system of Co-Fe prussian blue analogs nanocubes (Co-Fe PBA NCs) that can catalyze luminol to produce strong CL in the absence of H₂O₂ was established. Co-Fe PBA NCs have the property of oxidase-like activity, and it can catalyze the generation of active oxygen radicals in a dissolved oxygen system. Since caffeic acid (CA) can remove reactive oxygen species in the system, a sensitive detection method for CA on a paper-based chip was developed. Under the optimal conditions, this method showed a good linear response to CA in the range of 10 - 800 ng mL^-1 with a limit of 3 ng mL^-1. The proposed method had been used for the determination of CA in tea samples. The results may open a new avenue for the catalytic property on luminol CL system without extra oxidants.

Synergetic enhancement of electrochemical H2O2 detection in a nitrogen-doped carbon encapsulated FeCo alloy architecture

The development of Earth-abundant metal-based non-enzymatic electrodes with ultralow metal loadings for the efficient detection of hydrogen peroxide (H₂O₂) is highly desirable. We report here a remarkable three-dimensional nitrogen-doped porous carbon (NPC) encapsulated Earth-abundant metal architecture, i.e., NPC encapsulating FeCo alloy nanoparticles toward highly efficient electrochemical H₂O₂ detection. Specifically, an Fe_0.06Co_0.04@NPC-950 modified electrode can show excellent electrochemical performance for non-enzymatic H₂O₂ sensing in neutral media, with a wide linear range of 0.004 to 8 mM, a high sensitivity of 794 μA mA^-1 cm^-2 and a low limit of detection (LOD) of 0.13 μM, outperforming most of the reported non-noble metal electrocatalysts. Meanwhile, the fabricated Fe_0.06Co_0.04@NPC-950 modified electrode is capable of real-time monitoring of H₂O₂ in commercial orange juice, milk and serum, revealing its application potential toward the accurate detection of H₂O₂ in real-sample analysis. This electrode also has high selectivity, long-term stability and good reproducibility. Its excellent performance is correlated with the synergetic catalysis of the FeCo alloy, nitrogen-rich NPC with a large specific surface area (SSA) and the core-shell structure protecting the active sites from corrosion. This study offers an efficient pathway for developing high-performance and Earth-abundant catalysts toward electrochemical H₂O₂ detection.

Hierarchical Magnetic Network Constructed by CoFe Nanoparticles Suspended Within "Tubes on Rods" Matrix Toward Enhanced Microwave Absorption

Hierarchical magnetic-dielectric composites are promising functional materials with prospective applications in microwave absorption (MA) field. Herein, a three-dimension hierarchical "nanotubes on microrods," core-shell magnetic metal-carbon composite is rationally constructed for the first time via a fast metal-organic frameworks-based ligand exchange strategy followed by a carbonization treatment with melamine. Abundant magnetic CoFe nanoparticles are embedded within one-dimensional graphitized carbon/carbon nanotubes supported on micro-scale Mo₂N rod (Mo₂N@CoFe@C/CNT), constructing a special multi-dimension hierarchical MA material. Ligand exchange reaction is found to determine the formation of hierarchical magnetic-dielectric composite, which is assembled by dielectric Mo₂N as core and spatially dispersed CoFe nanoparticles within C/CNTs as shell. Mo₂N@CoFe@C/CNT composites exhibit superior MA performance with maximum reflection loss of - 53.5 dB at 2 mm thickness and show a broad effective absorption bandwidth of 5.0 GHz. The Mo₂N@CoFe@C/CNT composites hold the following advantages: (1) hierarchical core-shell structure offers plentiful of heterojunction interfaces and triggers interfacial polarization, (2) unique electronic migration/hop paths in the graphitized C/CNTs and Mo₂N rod facilitate conductive loss, (3) highly dispersed magnetic CoFe nanoparticles within "tubes on rods" matrix build multi-scale magnetic coupling network and reinforce magnetic response capability, confirmed by the off-axis electron holography.

The facile fabrication and high-performance sensing of glucose of sea-urchin-like CoFeLDH/PBA/NF heterojunction

The sea-urchin-like CoFeLDH/PBA/NF heterojunction was successfully synthesized, exhibiting excellent glucose sensing performance with ultra-high sensitivity, outstanding reproducibility, stability and selectivity.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.

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 novel alkaline phosphatase activity sensing strategy combining enhanced peroxidase-mimetic feature of sulfuration-engineered CoOx with electrostatic aggregation

Given alkaline phosphatase (ALP) takes part in the phosphorylation/dephosphorylation processes in the body, its activity is universally taken as an important indicator of many diseases, and thus developing reliable and efficient methods for ALP activity determination becomes quite important. Here, we propose a new sensing strategy for ALP activity by integrating the improved peroxidase-mimicking catalysis of sulfuration-engineered CoO_x with the hexametaphosphate ion (HMPi)-mediated electrostatic aggregation. After sulfuration engineering, the CoO_x composite coming from the pyrolysis of ZIF-67 exhibits enhanced peroxidase-mimetic catalytic ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to its oxide TMBox, offering a remarkable color change from colorless to mazarine; with the presence of HMPi, the rapid electrostatic assembly of negatively charged HMPi and positively charged TMBox leads to the aggregation of the latter, resulting in a color fading phenomenon; when ALP is added in advance to hydrolyze the HMPi mediator, the aggregation procedure is significantly suppressed, and such that the solution color can be recovered. Based on this principle, efficient determination of ALP activity was gained, giving a wide detection scope from 0.8 to 320 U/L and a detection limit as low as 0.38 U/L. Reliable analysis of the target in serum samples was also achieved, verifying the feasibility and practicability of our strategy in measuring ALP activity for clinical applications. Graphical abstract.

Functional nanostructure-loaded three-dimensional graphene foam as a non-enzymatic electrochemical sensor for reagentless glucose detection

Non-enzymatic and reagentless electrochemical sensors for convenient and sensitive detection of glucose are highly desirable for prevention, diagnosis and treatment of diabetes owing to their unique merits of simplicity and easy operation. Facile fabrication of a three-dimensional (3D) sensing interface with non-enzymatic recognition groups and an immobilized electrochemical probe remains challenge. Herein, a novel non-enzymatic electrochemical sensor was developed for the sensitive and reagentless detection of glucose by loading functional nanostructure on 3D graphene. Monolithic and macroporous 3D graphene (3DG) foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Prussian blue (PB) and gold nanoparticles (AuNPs) were first co-electrodeposited on 3DG (3DG/PB-AuNPs) as immobilized signal indicator and electron conductor. After a polydopamine (PDA) layer was introduced on 3DG/PB-AuNPs via facile self-polymerization of dopamine to stabilize internal PB probes and offer chemical reducibility, the second layer of AuNPs was in situ formed to assemble the recognition ligand, mercaptobenzoboric acid (MPBA). Owing to the high stability of PB and good affinity between MPBA and glucose, the non-enzymatic sensor was able to be used in reagentless detection of glucose with high selectivity, wide linear range (5 μM–65 μM) and low detection limit (1.5 μM). Furthermore, the sensor was used for the detection of glucose level in human serum samples.

A non-enzymatic electrochemical sensor was fabricated by loading functional nanostructure on three-dimensional graphene foam for reagentless detection of glucose with high sensitivity and stability.

A simple chemiluminescent aptasensor for the detection of α-fetoprotein based on iron-based metal organic frameworks

MIL-100 (Fe) was used to construct a chemiluminescent aptasensing platform based on the electrostatic adsorption of MIL-100 (Fe) and aptamers.