Myoglobin immobilized on mesoporous carbon foam in a hydrogel (selep) dispersant for voltammetric sensing of hydrogen peroxide

Dual-functional marine algal carbon-based materials with highly efficient dye removal and disinfection control

The design and simple, green preparation of dual-functional materials for the decontamination of both hazardous dyes and pathogenic microorganisms from wastewater remain challenging currently. Herein, a promising marine algal carbon-based material (named C-SA/SP) with both highly efficient dye adsorptive and antibacterial properties was fabricated based on the incorporation of sodium alginate and a low dose of silver phosphate via a facile and eco-friendly approach. The structure, removal of malachite green (MG) and congo red (CR), and their antibacterial performance were studied, and the adsorption mechanism was further interpreted by the statistical physics models, besides the classic models. The results show that the maximum simulated adsorption capacity for MG reached 2798.27 mg/g, and its minimal inhibit concentration for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was 0.4 mg/mL and 0.2 mg/mL, respectively. The mechanistic study suggests that silver phosphate exerted the effects of catalytic carbon formation and pore formation, while reducing the electronegativity of the material as well, thus improving its dye adsorptive performance. Moreover, the MG adsorption onto C-SA/SP showed vertical orientation and a multi-molecular way, and its adsorption sites were involved in the adsorption process with the increase of temperature. Overall, the study indicates that the as-made dual-functional materials have good applied prospects for water remediation.

Biorecognition of hydrogen peroxide using a novel electrochemical platform designed with Glossoscolex paulistus giant hemoglobin

The giant extracellular hemoglobin of the annelid Glossoscolex paulistus (HbGp; 3.6 MDa) is a valuable and underexplored supramolecular hemoprotein system for the biorecognition of reactive oxygen species. In this work, an efficient and simple electrochemical platform was designed for analyzing H₂O₂, using HbGp covalently immobilized on Nafion®-modified glassy carbon electrode, named as HbGp/Nafion/GCE. Voltammetric and spectroscopic studies revealed the importance of prior modification of the electrodic support with the conducting polymer to obtain satisfactory hemoglobin electroactivity, as well as a biocompatible microenvironment for its immobilization. In terms of biological activity, it was observed a greater reactivity of the biomolecule in acidic medium, enabling the detection of the analyte by a quasi-reversible mechanism, whose kinetics was limited by analyte diffusion. In the presence of H₂O₂, the native structure of hemoglobin (oxy-HbGp (Fe²⁺)) oxidizes to ferryl-HbGp (Fe⁴⁺) and this redox reaction can be monitored on HbGp/Nafion/GCE with a detection limit of 8.5 × 10^‒7  mol L^-1. In addition to high sensitivity, the electrochemical biosensor also provided reproducible, consistent, and accurate measurements. The electroanalytical method showed an appropriate performance to quantify different levels of H₂O₂ in milk samples, proving the potential of HbGp/Nafion/GCE for this purpose.

ZIF-67 MOF-derived Co nanoparticles supported on N-doped carbon skeletons for the amperometric determination of hydrogen peroxide

ZIF-67-derived Co nanoparticles supported on N-doped carbon skeletons have been prepared from melamine foam (Co-NPs/NCs) for non-enzymatic electrochemical H₂O₂ detection. The synthesis of Co-NPs/NCs was demonstrated via calcination treatment using melamine foam (MF) and ZIF-67 as precursors. The experimental results show that Co-NPs/NCs composites exhibit eminent catalytic activity toward specific determination of H₂O₂ with high selectivity and sensitivity (252.43 and 203.88 μA mM^-1 cm^-2), low LOD (0.12 μM), and wide linear ranges (10-2080 and 2080-11,800 μM). The excellent performance might be ascribed to the synergetic effects of MOF and N-doped carbon skeletons. The carbon skeletons serve as a conductive bridge and provide a large specific surface area, which can facilitate electron transfer and well disperse nanoparticles. This non-enzymatic electrochemical sensor based on Co-NPs/NCs can successfully detect H₂O₂ secreted by living cells, indicating its great potential in the early diagnosis and pathological exploration of disease.

A glassy carbon electrode modified with a nanocomposite prepared from Pd/Al layered double hydroxide and carboxymethyl cellulose for voltammetric sensing of hydrogen peroxide

A Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated using carboxymethyl cellulose as a green substrate via co-precipitation method. The synthesized nanocomposite was characterized using different methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy, and electrochemical techniques. A glassy carbon electrode (GCE) was then modified with the suspended composite to obtain an electrochemical sensor for hydrogen peroxide (H₂O₂). The voltammetric (cathodic) current of the modified GCE was measured at -380 mV (vs. Ag/AgCl), at the scan rate of 50 mV.s^-1. Results show a linear dynamic range of 1 to 120 μM, and a 0.3 µM limit of detection (at S/N = 3). Intraday and interday relative standard deviations are in the ranges of 4.9-5.4% and 6.8-7.3%, respectively. The sensor was applied for the determination of H₂O₂ in basil extracts, milk, and spiked river water samples. The recoveries are between 96.60 and 102.30%. Graphical abstractA Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated via co-precipitation method and was characterized using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy and electrochemical techniques. CMC@Pd/Al-LDH was used to fabricate H₂O₂ electrochemical sensor.

An imprinted polymeric matrix containing DNA for electrochemical sensing of 2,4-dichlorophenoxyacetic acid

The authors describe an electrochemical method for the determination of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). It is based on the use of a molecularly imprinted polymer (MIP) and of dsDNA as a bio-specific substance. The modified electrode was prepared by electropolymerization of ortho-phenylenediamine (oPD) in the presence of DNA and of 2,4-D (the template). The imprinted MIP was placed on a pencil graphite electrode (PGE) modified with chitosan and multiwalled carbon nanotubes (MWCNTs). The template was removed with 0.4 M NaOH. The interaction of DNA with 2,4-D leads to its adsorption on the electrode, and this increases the sensitivity and selectivity of the method. After rebinding 2,4-D, the decrease in the peak current of oxidation of iron(II) acting as an electrochemical redox probe was measured by differential pulse voltammetry (DPV). The current, typically measured at around 0.5 V, increases linearly in the 0.01 to 10 pM 2,4-D concentration range, and the detection limit is 4.0 fM. The method is highly selective for 2,4-D. The modified electrode was applied to quantify 2,4-D in spiked environmental water and soil samples and gave absolute recoveries varying from 91.5 to 109.0%. Graphical abstractSchematic representation of the fabrication of an electrochemical sensor for determination of 2,4-dichlorophenoxyacetic acid (2,4-D). Initially, the electrode was modified with chitosan and MWCNTs and then a composite was formed on it consisting of ortho-phenylenediamine (oPD), DNA and 2,4-D.

Ultrathin Phthalocyanine-Conjugated Polymer Nanosheet-Based Electrochemical Platform for Accurately Detecting H2O2 in Real Time

As a vital biological mediator and a widely used industrial oxidant, the accurate detection of hydrogen peroxide (H₂O₂) is of significance for both academic purpose and practical applications. Herein, we report a novel approach for the development of a high-performance electrochemical H₂O₂ sensor constructed by iron phthalocyanine (FePc)-based diyne-linked conjugated polymeric nanosheets (NSs), FePc-CP NSs. The FePc-CP NSs were delaminated from the bulk material via a defect- and disorder-induced synthetic strategy. By the quasi-Langmuir-Shäfer method, the prepared FePc-CP NSs were self-assembled into multilayer films with controllable thickness on electrodes. Owing to the highly exposed active centers on the surfaces, the FePc-CP NS film-modified electrodes exhibited excellent H₂O₂ determination performance with a wide linear detection range (0.1-1000 μM), a short response time (the response current approached the maximum value within 0.1 s), a low limit of detection (0.017 μM), and excellent sensitivity (97 μA cm^-2 mM^-1), which are comparable to the best results reported so far for electrochemical H₂O₂ sensors. In addition, the fabricated electrochemical H₂O₂ sensor also displayed satisfactory stability, reproducibility, and selectivity. Furthermore, the obtained FePc-CP NS film sensor can be applied in real-time monitoring of H₂O₂ in commercial orange juice and beer as well as H₂O₂ secreted from A549 live cells, revealing its application potential toward the accurate detection of H₂O₂ in real-sample analysis.

Defect and Additional Active Sites on the Basal Plane of Manganese-Doped Molybdenum Diselenide for Effective Enzyme Immobilization: In Vitro and in Vivo Real-Time Analyses of Hydrogen Peroxide Sensing

The defect engineering makes the new concepts and designs to further enhance the electrocatalytic activity of layered structures. In this work, we demonstrated the synthesis of Mn-doped MoSe₂ and reported the resultant defective sites. Subsequently, the MnMoSe₂ was developed as a new type of electrocatalyst for electrochemical biosensors. The formation of defect/distortion and effective immobilization of myoglobin (Mb) were evidently confirmed by using the transmission electron microscopy and UV-vis spectroscopy analyses, respectively. The result of electrochemical impedance spectroscopy analysis reveals that the Mn doping not only helps  to enzyme immobilization but also enhances the electronic conductivity of layered material.  Owing to the multiple signal amplification strategies, the proposed Mb-immobilized MnMoSe₂ (Mb@MnMoSe₂) exhibited an ultralow detection limit (0.004 μM) and a higher sensitivity (222.78 μA μM^-1 cm^-2) of H₂O₂. In real-sample analysis, the Mb@MnMoSe₂ showed a feasible recovery range of H₂O₂ detection in human serum (95.6-102.1%), urine (101.2-102.3%), and rain water (100.7-102.1%) samples. On the other hand, an in vivo study using HaCaT (7.1 × 10⁵/mL) and RAW 264.7 (1 × 10⁶/mL) living cells showed the feasible current responses of 0.096 and 0.085 μA, respectively. Finally, the Mn doping gives a new opportunity to fabricate a promising electrocatalyst for H₂O₂ biosensing.

Nitrogen-rich core-shell structured particles consisting of carbonized zeolitic imidazolate frameworks and reduced graphene oxide for amperometric determination of hydrogen peroxide

Core-shell structured particles were prepared from carbonized zeolitic imidazolate frameworks (ZIFs) and reduced graphene oxide (rGO). The particles possess a nitrogen content of up to 10.6%. The loss of nitrogen from the ZIF is avoided by utilizing the reduction and agglomeration of graphene oxide with suitable size (>2 μm) during pyrolysis. The resulting carbonized ZIF@rGO particles were deposited on a glassy carbon electrode to give an amperometric sensor for H₂O₂, typically operated at a voltage of -0.4 V (vs. Ag/AgCl). The sensor has a wide detection range (from 5 × 10^-6 to 2 × 10^-2 M), a 3.3 μM (S/N = 3) detection limit and a 0.272 μA·μM^-1·cm^-2 sensitivity, much higher than that of directly carbonized ZIFs. The sensor material was also deposited on a screen-printed electrode to explore the possibility of application. Graphical abstract Nitrogen doped carbon (NC) derived from carbonized zeolitic imidazolate frameworks is limited because of low nitrogen content. Here, nitrogen-rich NC@reduced graphene oxide (rGO) core-shell structured particles are described. The NC@rGO particles show distinctly better H₂O₂ detection performance than NC.