Cobalt Nanoparticles and Atomic Sites in Nitrogen-Doped Carbon Frameworks for Highly Sensitive Sensing of Hydrogen Peroxide

Rational construction of porous cobalt nanoparticle integrated nitrogen doped hollow carbon nanostructures for peptide agonist exendin-4 biosensing

In this study, we designed a point-of-care (POC) testing electrochemical biosensor using an integrated biosensing assay based on hollow-like nitrogen-doped carbon nanostructures combined with cobalt nanoparticles (Co@HNCNs, Co3O4@HNCNs, and CoP@HNCNs). These are functionalized with Anti-Exendin-4 Antibodies (Anti-Ex-4-Abs) and Bovine Serum Albumin (BSA) to create sensitive probes (Co@HNCNs/Anti-Ex-4-Abs/BSA, Co3O4@HNCNs/Anti-Ex-4-Abs/BSA, and CoP@HNCNs/Anti-Ex-4-Abs/BSA) for the ultrasensitive detection of exendin-4 (Ex-4), a peptide agonist used in the treatment of type 2 diabetes mellitus (T2DM). Among the cobalt-based carbon nanostructures, the Co3O4@HNCNs/Anti-Ex-4-Abs/BSA nanoprobe demonstrated superior ability to specifically recognize Ex-4. This was indicated by a significant decrease in the chronoamperometric (CA) i-t current response, facilitating low-level detection of Ex-4. The nanoprobe was capable of detecting Ex-4 concentrations ranging from 1.0 to 90.0 pM, with a sensitivity of 0.60 μA/pM and a limit of detection (LOD) of 0.46 pM (S/N = 3). Furthermore, the Co3O4@HNCNs/Anti-Ex-4-Abs/BSA nanoprobes demonstrated the ability to detect nanomolar levels of Ex-4 in blood serum and urine samples, achieving satisfactory recovery rates of 96-104%. The proposed electrostatic interaction chemistry approach establishes a remarkable platform for constructing a peptide agonist biosensor that is effective for detecting Ex-4 in real human serum and urine samples.

A review of nanomaterials for biosensing applications

A biosensor is a device that reacts with the analyte to be analyzed, detects its concentration, and generates readable information, which plays an important role in medical diagnosis, detection of physiological indicators, and disease prevention. Nanomaterials have received increasing attention in the fabrication and improvement of biosensors due to their unique physicochemical and optical properties. In this paper, the properties of nanomaterials such as the size effect, optical and electrical properties, and their advantages in the field of biosensing are briefly summarized, and the application of nanomaterials can effectively improve the sensitivity and reduce the detection limit of biosensors. The advantages of commonly used nanomaterials such as gold nanoparticles (AuNPs), carbon nanotubes (CNTs), quantum dots (QDs), graphene, and magnetic nanobeads for biosensor applications are also reviewed. Besides, the two main types of biosensors using nanomaterials involved in their construction and their working principles are described, and the toxicity and biocompatibility of nanomaterials and the future direction of nanomaterial biosensors are discussed.

High power density output and durability of microbial fuel cells enabled by dispersed cobalt nanoparticles on nitrogen-doped carbon as the cathode electrocatalyst

To endow microbial fuel cells (MFCs) with low cost, long-term stability and high-power output, a novel cobalt-based cathode electrocatalyst (Nano-Co@NC) is synthesized from a polygonal metal-organic framework ZIF-67. After calcining the resultant ZIF-67, the as-synthesized Nano-Co@NC is characteristic of cobalt nanoparticles (Nano-Co) embedded in nitrogen-doped carbon (NC) that inherits the morphology of ZIF-67 with a large surface area. The Nano-Co particles that are highly dispersed and firmly fixed on NC not only ensure electrocatalytic activity of Nano-Co@NC toward the oxygen reduction reaction on the cathode, but also inhibit the growth of non-electrogenic bacteria on the anode. Consequently, the MFC using Nano-Co@NC as the cathode electrocatalyst demonstrates excellent performance, delivering a comparable initial power density and exhibiting far better durability than that using Pt/C (20 wt%) as the cathode electrocatalyst. The low cost and the excellent performance of Nano-Co@NC make it promising for MFCs to be used in practice.

A facile synthesis of FeS/Fe3C nanoparticles highly dispersed on in situ grown N-doped CNTs as cathode electrocatalysts for microbial fuel cells

A novel composite of iron sulfide, iron carbide and nitrogen carbides (Nano-FeS/Fe3C@NCNTs) as a cathode electrocatalyst for microbial fuel cells (MFCs) is synthesized by a one-pot solid state reaction, which yields a unique configuration of FeS/Fe3C nanoparticles highly dispersed on in situ grown nitrogen-doped carbon nanotubes (NCNTs). The highly dispersed FeS/Fe3C nanoparticles possess large active sites, while the NCNTs provide an electronically conductive network. Consequently, the resultant Nano-FeS/Fe3C@NCNTs exhibit excellent electrocatalytic activity towards the oxygen reduction reaction (ORR), with a half-wave potential close to that of Pt/C (about 0.88 V vs. RHE), and enable MFCs to deliver a power density of 1.28 W m-2 after two weeks' operation, which is higher than that of MFCs with Pt/C as the cathode electrocatalyst (1.02 W m-2). Theoretical calculations and experimental data demonstrate that there is a synergistic effect between Fe3C and FeS in Nano-FeS/Fe3C@NCNTs. Fe3C presents a strong attraction and electron-donating tendency to oxygen molecules, serving as the main active component, while FeS reduces charge transfer resistance by transferring electrons to Fe3C, synergistically improving the kinetics of the ORR and power density of MFCs.

Synthesis of Graphene Oxide-Coupled CoNi Bimetallic MOF Nanocomposites for the Simultaneous Analysis of Catechol and Hydroquinone

Herein, a three-dimensional flower-like cobalt-nickel bimetallic metal-organic framework (CoNi-MOF) coupled with two-dimensional graphene oxide (GO) nanocomposites was successfully synthesized for the selective and simultaneous electrochemical determination of catechol (CC) and hydroquinone (HQ). The three-dimensional flower-like structure of the CoNi-MOF/GO nanocomposite has a multilayer structure and a large surface area, which greatly improves its electrocatalytic activity towards CC and HQ. Differential pulse voltammetry (DPV) results showed that the peak-to-peak separation of CC (0.223 V) and HQ (0.120 V) was 103 mV at a CoNi-MOF/GO modified glassy carbon electrode (CoNi-MOF/GO/GCE), suggesting that the proposed modified electrode can selectively and simultaneously determine them. Under optimal conditions, the CoNi-MOF/GO/GCE showed an excellent analytical performance for the simultaneous determination of CC and HQ, including a wide linear range (0.1-100 μM), low detection limit (0.04 μM for HQ and 0.03 μM for CC) and high anti-interference ability. As expected, the developed modified electrode has been used to analyze CC and HQ in river water, with acceptable results.

Defect Engineering To Tailor Metal Vacancies in 2D Conductive Metal-Organic Frameworks: An Example in Electrochemical Sensing

Two-dimensional conductive metal-organic frameworks (2D conductive MOFs) with π-d conjugations exhibit high electrical conductivity and diverse coordination structures, making them constitute a desirable platform for new electronic devices. Defects are inevitable in the self-assembly process of 2D conductive MOFs. Arguably, defect engineering that deliberately manipulates defects demonstrates great potential to enhance the electrocatalytic activity of this family of novel materials. Herein, a facile and universal defect engineering strategy is proposed and demonstrated for metal vacancy regulation of metal benzenehexathiolato (BHT) coordination polymer films. Controllable metal vacancies can be produced by simply tuning the proton concentration during the confined self-assembly process at the liquid-liquid interface. This facile but universal defect design strategy has been proven to be effective in a class of materials including Cu-BHT, Ni-BHT, and Ag-BHT for physicochemical regulation. To further demonstrate the feasibility and practicality in electrochemical applications, the elaborately fabricated Cu-BHT films with abundant Cu vacancies deliver competitive performance in electrocatalytic sensing of H₂O₂. Mechanistic analysis revealed that the Cu vacancies act as effective active sites for adsorption and reduction of H₂O₂, and the tuned electronic structure boosts the electrocatalytic reaction. The developed advanced sensing platform confirms the excellent commercial potential of Cu-BHT sensors for H₂O₂. The findings provide insights into the molecular structure design of 2D conducting MOFs by defect engineering and demonstrate the commercial potential of Cu-BHT electrochemical sensors.

Peroxymonosulfate Activation on Synergistically Enhanced Single-Atom Co/Co@C for Boosted Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative

Tris(bipyridine) ruthenium(II)-based luminophores have been well developed in the area of electrochemiluminescence, while their applications in chemiluminescence (CL) are rarely studied due to the poor luminous efficiency and complicated CL reaction. Herein, a novel tris(bipyridine) ruthenium(II)-based ternary CL system is proposed by introducing cobalt single atoms integrated with graphene-encapsulated cobalt nanoparticles (Co SAs/Co@C) and peroxymonosulfate (PMS) as advanced coreaction accelerator and promising coreactant, respectively. On the basis of the experimental results and density functional theory calculations, it is concluded that Co@C can synergistically modulate the adsorption behavior of PMS on Co SAs and then efficiently activate PMS to produce massive singlet oxygen for remarkable CL emission. Under the optimum conditions, the as-prepared CL biosensor exhibits a good linear range, excellent sensitivity, and selectivity, holding great potential for the practical detection of prostate-specific antigen in human serum.

Mesoporous Ti0.5Cr0.5N for trace H2S detection with excellent long-term stability

Efficient, accurate and reliable detection and monitoring of H₂S is of significance in a wide range of areas: industrial production, medical diagnosis, environmental monitoring, and health screening. However the rapid corrosion of commercial platinum-on-carbon (Pt/C) sensing electrodes in the presence of H₂S presents a fundamental challenge for fuel cell gas sensors. Herein we report a solution to the issue through the design of a sensing electrode, which is based on Pt supported on mesoporous titanium chromium nitrides (Pt/Ti_0.5Cr_0.5N). Its desirable characteristics are due to its high electrochemical stability and strong metal-support interactions. The Pt/Ti_0.5Cr_0.5N-based sensors exhibit a much smaller attenuation (1.3%) in response to H₂S than Pt/C-sensor (40%), after 2 months sensing test. Furthermore, the Pt/Ti_0.5Cr_0.5N-based sensors exhibit negligible cross response to other interfering gases compared with hydrogen sulfide. Results of density functional theory calculation also verify the excellent long-term stability and selectivity of the gas sensor. Our work hence points to a new sensing electrode system that offers a combination of high performance and stability for fuel-cell gas sensors.

Hydrolysis of Organophosphorus Agents Catalyzed by Cobalt Nanoparticles Supported on Three-Dimensional Nitrogen-Doped Graphene

Catalytic chemical degradations and many other methodologies have been explored for the removal and/or degradation of organophosphorus agents (OPs) that are often used as pesticides, nerve agents, and plasticizers. To explore more efficient and recyclable catalysts for the removal and/or degradation of OPs, we fabricate the composites of cobalt nanoparticles and three-dimensional nitrogen-doped graphene (Co/3DNG). We demonstrate that OPs can be hydrolyzed efficiently at ambient temperature by the Co/3DNG. Because of the unique structural and chemical properties of the supporting matrix 3DNG and active species Co-N, the catalytic activities of Co/3DNG composites are much higher than those of bare 3DNG, Co nanoparticles, or the Co nanoparticles physically mixed with 3DNG. We conclude that in the Co/3DNG composites, the interaction between 3DNG and Co stabilizes and distributes well the Co nanoparticles and affords the active catalytic species Co-N.

Development of Au-Pd@UiO-66-on-ZIF-L/CC as a self-supported electrochemical sensor for in situ monitoring of cellular hydrogen peroxide

Integrating metal-organic frameworks (MOFs) of different components or structures together and exploiting them as electrochemical sensors for electrochemical sensing has aroused great interest. Furthermore, the incorporation of noble metals with MOFs is conducive to the improvement of catalytic performance. In this work, Pd@UiO-66-on-ZIF-L nanomaterials were successfully synthesised onto a self-supported flexible carbon cloth (Pd@UiO-66-on-ZIF-L/CC) through a novel strategy called MOF-on-MOF. Then, Au nanoparticles were electrodeposited onto Pd@UiO-66-on-ZIF-L/CC to obtain Au-Pd@UiO-66-on-ZIF-L/CC, which can serve as an excellent electrocatalyst for the reduction of hydrogen peroxide (H₂O₂). The obtained flower-like Pd@UiO-66-on-ZIF-L/CC hybrid MOF changes the structure of the monomeric MOF alone and adds more attachment sites. The synergy of the bimetals greatly improved the catalytic performance of the as-developed sensor. Electrochemical experiment results show that the proposed sensor based on Au-Pd@UiO-66-on-ZIF-L/CC has an extended linear range from 1 μM to 19.6 mM with a sensitivity of 390 μA mM^-1 cm^-2, and a low limit of detection (LOD) of 21.2 nM (S/N = 3). Moreover, it has good anti-interference, reproducibility, repeatability and excellent stability. Furthermore, the real-time in situ detection of H₂O₂ secreted from human adenocarcinomic alveolar basal epithelial cells (A549 cells) was achieved by culturing cells on Au-Pd@UiO-66-on-ZIF-L/CC, which indicates the potential of the sensor for applications in cancer pathology. Both the synthesis strategy and the sensor design provide new methods and ideas for the production of ultrasensitive H₂O₂ electrochemical sensors.

Active Site Engineering in CoP@NC/Graphene Heterostructures Enabling Enhanced Hydrogen Evolution

As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@NC/GR) are derived from a bimetallic metal-organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔG_H*) from -0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H₂SO₄ (or 125 mV in 1 M KOH) to 10 mA cm^-2, accelerated HER kinetics with a low Tafel slope of 47.5 mV dec^-1, and remarkable structural and HER stability.

Highly active catalyst using zeolitic imidazolate framework derived nano-polyhedron for the electro-oxidation of l-cysteine and amperometric sensing

Herein, N-doped porous carbon nano-polyhedron embedded with Co₃O₄ (Co₃O₄-NPCN) was reported for the electro-catalytic oxidation and amperometric detection of l-cysteine. Co₃O₄-NPCN was synthesized by the two-step redox calcination of zeolitic imidazolate framework (ZIF). Surface morphology characterization revealed that Co₃O₄-NPCN displayed a uniform size and rhombic dodecahedral shape. Structure and composition analysis found that Co₃O₄-NPCN was a N-doped carbon polyhedral matrix with hollow and porous structure, and Co₃O₄ nano-spheres were evenly distributed into the polyhedral matrix. Due to the hollow and porous structure, N-doped carbon matrix and embedded Co₃O₄ nano-spheres, Co₃O₄-NPCN performed a remarkable electro-catalysis towards the oxidation of l-cysteine at a very low potential of 0.10 V. A diffusion-controlled l-cysteine oxidation process was observed at Co₃O₄-NPCN prepared electrode. Accordingly, amperometric method was established for l-cysteine detection with a very fast current response in 2 s, wide linear range of 0.05 μM- 5.2 mM and low detection limit of 6.9 nM. Besides, notable selectivity, repeatability, reproducibility and long-term stability were also achieved. Moreover, Co₃O₄-NPCN sensor was successfully applied to the l-cysteine detection in human serum samples indicating the practical application of the as-developed sensor.

In situ hierarchical encapsulation of bimetallic selenides into honeycomb-like nitrogen doped porous carbon nanosheets for highly sensitive and selective guanosine detection

An innovative electrochemical nanocomposite for the detection of guanosine (Gua) was proposed by in situ encapsulation of nickel-iron bimetallic selenides confined into honeycomb-like nitrogen doped porous carbon nanosheets, denoted as (Ni,Fe)Se₂/N-PCNs. The porous carbon nanosheets were prepared by utilizing nickel-iron layered double hydroxide (Ni-Fe LDH) as the substrate and zeolitic imidazolate frameworks (ZIF-67) nanocrystals as the sacrificial templates via hydrothermal synthesis, followed by a process of acid etching and pyrolysis selenylation. Interestingly, the nickel-ferric bimetallic selenides material (Ni,Fe)Se₂, is rarely fabricated successfully using selenylation treatment, which is a highly conductive and robust support to promote the electron transport. Meanwhile, the obtained (Ni,Fe)Se₂/N-PCNs have the favorable architectural features of both unique three-dimensional (3D) porous structural and hierarchical connectivity, which are expected to provide more active sites for electrochemical reactions and ease of electron, ion, and biomolecule penetration. Benefiting from the inherent virtues of its composition, together with unique structural advantages, the (Ni,Fe)Se₂/N-PCNs possess ideal sensing properties for guanosine detection with a low detection limit of 1.20 × 10^-8 M, a wide linear range of 5.30 × 10^-8 ~ 2.27 × 10^-4 M and a good stability. Superb selectivity for potential interfering species and superb recoveries in serum suggests its feasibility for practical applications.

Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H₂O₂ reduction and excellent sensing performance for the electrochemical detection of H₂O₂. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 μM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H₂O₂ in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

General and fast synthesis of graphene frameworks using sugars for high-performance hydrogen peroxide nonenzymatic electrochemical sensor

3D graphene frameworks (GFs) are fast and scalably synthesized via a general and facile method from the rich biomass of sugars with the aid of molten salts, using glucose as the prototype, to obtain an effective sensing platform for sensitive nonenzymatic hydrogen peroxide (H₂O₂) detection. The electroactive area of the GFs/GCE (0.1437 cm²) is obviously higher than that of bare GCE (0.0653 cm²). The GFs are found to exhibit remarkable electrocatalytic activity toward H₂O₂ reduction while avoiding enzyme loading. The electrochemical sensor for H₂O₂ based on GFs displays a low detection limit of 0.032 ± 0.005 μM (S/N = 3) at a working potential of - 0.55 V in 0.01 M N₂-saturated phosphate-buffered saline (PBS, pH = 7.4) by an amperometric method. The sensor has good selectivity over other compounds such as ascorbic acid, dopamine, uric acid, NaCl, citric acid, and glucose. Moreover, the sensor shows excellent reproducibility with a relative standard deviation of 3.7% and acceptable stability after 30 days of usage. Furthermore, it can detect H₂O₂ released from living tumorigenic cells in real time. Most importantly, it is demonstrated that such GFs can be obtained from a variety of sugars (sucrose, fructose, lactose, and maltose). This work may offer a new general avenue for the synthesis of 3D GFs and promote the development of electrochemical sensors. Graphical abstract We have reported a general and fast method to synthesize GFs from sugars (glucose, sucrose, fructose, lactose, and maltose) with the addition of molten Na₂CO₃ salt as a template. The developed GFs can be applied as excellent electrode materials for efficient electrochemical sensing of H₂O₂.

A robust Mn@FeNi-S/graphene oxide nanocomposite as a high-efficiency catalyst for the non-enzymatic electrochemical detection of hydrogen peroxide

Exploring high-efficiency, stable, and cost-effective electrocatalysts for electrochemical activities is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with manganese-doped FeNi-S encapsulated into graphene oxide (Mn@FeNi-S/GO) with unprecedented electrocatalytic activity was developed by simple one-step heat treatment followed by sonication. X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and N₂ sorption isotherm demonstrated the successful formation of Mn@FeNi-S/GO. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further confirmed the kinetic-favourable adsorption of hydrogen peroxide (H₂O₂) onto the surface sites of Mn@FeNi-S/GO. Additionally, the synergetic effects between Mn@FeNi-S and GO are regarded as significant contributors to an efficient electron transfer path, and they promote the capture of H₂O₂ in hybrid catalysts. Under an optimal condition, a biosensor-based Mn@FeNi-S/GO electrode exhibits a high sensitivity of 8.929 μA μM^-1 cm^-2 and a detection limit of 8.84 nM with a wide detection range for H₂O₂ and excellent selectivity; also, it is capable of online monitoring H₂O₂ derived from apple juice and human blood serum.