Hydrothermal and plasma nitrided electrospun carbon nanofibers for amperometric sensing of hydrogen peroxide

Synthesis, surface modifications, and biomedical applications of carbon nanofibers: Electrospun vs vapor-grown carbon nanofibers

Engineered nanostructures are materials with promising properties, enabled by precise design and fabrication, as well as size-dependent effects. Biomedical applications of nanomaterials in disease-specific prevention, diagnosis, treatment, and recovery monitoring require precise, specific, and sophisticated approaches to yield effective and long-lasting favorable outcomes for patients. In this regard, carbon nanofibers (CNFs) have been indentified due to their interesting properties, such as good mechanical strength, high electrical conductivity, and desirable morphological features. Broadly speaking, CNFs can be categorized as vapor-grown carbon nanofibers (VGCNFs) and carbonized CNFs (e.g., electrospun CNFs), which have distinct microstructure, morphologies, and physicochemical properties. In addition to their physicochemical properties, VGCNFs and electrospun CNFs have distinct performances in biomedicine and have their own pros and cons. Indeed, several review papers in the literature have summarized and discussed the different types of CNFs and their performances in the industrial, energy, and composites areas. Crucially however, there is room for a comprehensive review paper dealing with CNFs from a biomedical point of view. The present work therefore, explored various types of CNFs, their fabrication and surface modification methods, and their applications in the different branches of biomedical engineering.

Synthesis, Catalytic Properties and Application in Biosensorics of Nanozymes and Electronanocatalysts: A Review

The current review is devoted to nanozymes, i.e., nanostructured artificial enzymes which mimic the catalytic properties of natural enzymes. Use of the term "nanozyme" in the literature as indicating an enzyme is not always justified. For example, it is used inappropriately for nanomaterials bound with electrodes that possess catalytic activity only when applying an electric potential. If the enzyme-like activity of such a material is not proven in solution (without applying the potential), such a catalyst should be named an "electronanocatalyst", not a nanozyme. This paper presents a review of the classification of the nanozymes, their advantages vs. natural enzymes, and potential practical applications. Special attention is paid to nanozyme synthesis methods (hydrothermal and solvothermal, chemical reduction, sol-gel method, co-precipitation, polymerization/polycondensation, electrochemical deposition). The catalytic performance of nanozymes is characterized, a critical point of view on catalytic parameters of nanozymes described in scientific papers is presented and typical mistakes are analyzed. The central part of the review relates to characterization of nanozymes which mimic natural enzymes with analytical importance ("nanoperoxidase", "nanooxidases", "nanolaccase") and their use in the construction of electro-chemical (bio)sensors ("nanosensors").

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.

Screen-Printed Soft-Nitrided Carbon Electrodes for Detection of Hydrogen Peroxide

Nitrogen-doped carbon materials have garnered much interest due to their electrocatalytic activity towards important reactions such as the reduction of hydrogen peroxide. N-doped carbon materials are typically prepared and deposited on solid conductive supports, which can sometimes involve time-consuming, complex, and/or costly procedures. Here, nitrogen-doped screen-printed carbon electrodes (N-SPCEs) were fabricated directly from a lab-formulated ink composed of graphite that was modified with surface nitrogen groups by a simple soft nitriding technique. N-SPCEs prepared from inexpensive starting materials (graphite powder and urea) demonstrated good electrocatalytic activity towards hydrogen peroxide reduction. Amperometric detection of H₂O₂ using N-SPCEs with an applied potential of −0.4 V (vs. Ag/AgCl) exhibited good reproducibility and stability as well as a reasonable limit of detection (2.5 µM) and wide linear range (0.020 to 5.3 mM).

A disposable electrochemical sensor based on electrospinning of molecularly imprinted nanohybrid films for highly sensitive determination of the organotin acaricide cyhexatin

Nanofibrous polyporous membranes imprinted with cyhexatin (CYT) were formed via the ordered distribution of the imprints in electrospun nanofibers. The MIPs have a high mass transfer rate and enhanced adsorption capacity. In addition, a printed carbon electrode with enhanced sensitivity was developed via electrochemical fabrication of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs). The molecularly imprinted sensor exhibits excellent selectivity and sensitivity for CYT. The structure and morphology of the nanohybrid films were characterized by using scanning electron microscopy, atomic force microscopy and chronoamperometry. The sensing performances were evaluated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy by using hexacyanoferrate(IV) as an electrochemical probe. The electrode, best operated at a working potential of around 0.16 V (vs. Ag/AgCl), has a linear response in the 1-800 ng mL^-1 CYT concentration range and a detection limit of 0.17 ng mL^-1 (at S/N = 3). The sensor demonstrated satisfactory recoveries when applied to the determination of CYT in spiked pear samples. Graphical abstract Schematic presentation of the electrochemical sensor for detection of CYT.

Development of highly sensitive H2O2 redox sensor from electrodeposited tellurium nanoparticles using ionic liquid

A new, non-enzymatic, low-cost sensor based on tellurium nanoparticles (TeNPs) for the analytical determination of H₂O₂ has been proposed. An economically viable electrochemical technique was employed for the synthesis of TeNPs based non-enzymatic H₂O₂ sensor. Thin films of TeNPs were successfully electrodeposited on fluorine-doped tin oxide (FTO) substrate using [BMIM][Ac] ionic liquid at 90 °C. The effect of deposition potential on the morphology, phase formation, and electrochemical characterisation of nanostructured Te films has been studied. Field emission scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy were employed to characterize the nanostructured Te films on FTO surface. The electro-catalytic performance of the proposed TeNPs/FTO sensor has been studied by cyclic voltammetry (CV) and chronoamperometry (CA) in phosphate buffer (Argon saturated) in the absence and presence of H₂O₂. TeNPs/FTO fabricated at applied potential of -1.40 V showed an excellent electro-catalytic activity towards H₂O₂ reduction. The proposed TeNPs/FTO sensor shows an excellent sensitivity of 757 µA mM^-1 cm^-2. The sensor possess good selectivity and stability with an excellent amperometric response time of about 5 s. The present study also demonstrates that TeNPs/FTO is a promising sensing material suitable for determination of H₂O₂ in practical samples.

Carbon-dot wrapped ZnO nanoparticle-based photoelectrochemical sensor for selective monitoring of H2O2 released from cancer cells

This study reports on a simple approach for the fabrication of an electrode modified with biocompatible C-dot wrapped ZnO nanoparticles for selective photoelectrochemical monitoring of H₂O₂ released from living cells. The biocompatibility of the ZnO nanoparticles was confirmed through in-vitro cellular testing using the MTT assay on Huh7 cell lines. The ZnO nanoparticles wrapped with dopamine-derived C-dots possess numerous catalytically active sites, excessive surface defects, good electrical conductivity, and efficient separation ability of photo-induced electrons and holes. These properties offer highly sensitive and selective non-enzymatic photo-electrochemical monitoring of H₂O₂ released from HeLa cells after stimulation with N-formylmethionyl-leucyl-phenylalanine. The sensor has a wide linear range (20-800 nM), low detection limit (2.4 nM), and reliable reproducibility, this implying its suitability for biological and biomedical applications. Graphical abstract Schematic of the fabrication of ZnO nanoparticles by using a plant extract as a reducing agent. Wrapping of ZnO with C-dots enhances the photoelectrocatalytic efficacy. Sensitive and selective photoelectrochemical monitoring of H₂O₂ released from cancer cells is demonstrated.

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.