The use of nanoparticles in electroanalysis: a review

Optimisation Study of Co Deposition on Chars from MAP of Waste Tyres as Green Electrodes in ORR for Alkaline Fuel Cells

Oxygen Reduction Reaction (ORR) catalysts, from waste automobile tyres obtained from Microwave assisted pyrolysis (MAP), were enriched with Co and Cu using the simple treatments sonochemical and electrochemical deposition. Catalytic activity was evaluated through onset potential and number of exchanged electrons measurements. Electrochemical data demonstrate an improvement in catalytic activity of the electrochemical modified char with Co. Char electrodes enriched with Co show a maximum positive shift of 40 mV with respect to raw char electrodes with a number of exchanged electrons per O2 molecule close to 4 (as for Pt) for the best sample. This corresponds to a reduction of the production of unwanted oxygen peroxide from 23% for raw char to 1%. Sample structure evolution before and after electrochemical deposition and electro-catalysis was investigated by scanning transmission electron microscopy and XPS. Such electrochemical treatments open new possibilities of refining waste chars and finding an economic alternative to noble metals-based catalysts for alkaline fuel cells.

Disposable and Low-Cost Electrode Based on Graphene Paper-Nafion-Bi Nanostructures for Ultra-Trace Determination of Pb(II) and Cd(II)

There is a huge demand for rapid, reliable and low-cost methods for the analysis of heavy metals in drinking water, particularly in the range of sub-part per billion (ppb). In the present work, we describe the preparation, characterization and analytical performance of the disposable sensor to be employed in Square Wave Anodic Stripping Voltammetry (SWASV) for ultra-trace simultaneous determination of cadmium and lead. The electrode consists of graphene paper-perfluorosulfonic ionomer-bismuth nano-composite material. The electrode preparation implies a key step aimed to enhance the Bi3+ adsorption into nafion film, prior to the bismuth electro-deposition. Finely dispersed bismuth nanoparticles embedded in the ionomer film are obtained. The electrode was characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Electrochemical Impedance Spectroscopy (EIS). The electrode shows a linear response in the 5-100 ppb range, a time-stability tested up to almost three months, and detection limits up to 0.1 ppb for both Pb2+ and Cd2+. The electrode preparation method is simple and low in cost and the obtained analytical performance is very competitive with the state of art for the SWASV determination of Pb2+ and Cd2+ in solution.

Open-tubular Capillary Electrochromatography with Janus Structured Au-Fe3O4 Nanoparticles Coating as Stationary Phase

A novel Au-Fe₃O₄ nanoparticles-based capillary column was fabricated by magnetic approach for open-tubular capillary electrochromatography (OT-CEC). The bifunctional dumbbell-like Janus Au-Fe₃O₄ nanoparticles (Au-Fe₃O₄ NPs) were prepared through a hydrothermal synthesis strategy, and the morphology was characterized by transmission electron microscopy (TEM). Multilayers Au-Fe₃O₄ NPs were easily coated onto the inner surface of silica capillary by an external magnetic field to generate an Au-Fe₃O₄ NPs-based column. Compared with a bare capillary, the modified surface exhibited more stable and suppressed electroosmotic mobility. The column showed good separation efficiency for neutral analytes in the OT-CEC separation mode, with theoretical plate numbers of up to 79705 per meter for naphthalene. The successful separation of dihydroxy benzene isomers and proteins demonstrated that the column exhibits a reasonable separation performance. The reproducibility of the Au-Fe₃O₄ NPs capillary was studied, with relative standard deviations (RSD) for day-to-day and column-to-column less than 1 and 1.75%, respectively.

Interaction between Amorphous Zirconia Nanoparticles and Graphite: Electrochemical Applications for Gallic Acid Sensing Using Carbon Paste Electrodes in Wine

Amorphous zirconium oxide nanoparticles (ZrO₂) have been used for the first time, to modify carbon paste electrode (CPE) and used as a sensor for the electrochemical determination of gallic acid (GA). The voltammetric results of the ZrO₂ nanoparticles-modified CPE showed efficient electrochemical oxidation of gallic acid, with a significantly enhanced peak current from 261 µA ± 3 to about 451 µA ± 1. The modified surface of the electrode and the synthesised zirconia nanoparticles were characterised by scanning electrode microscopy (SEM), Energy-dispersive x-ray spectroscopy (EDXA), X-ray powdered diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Meanwhile, the electrochemical behaviour of GA on the surface of the modified electrode was studied using differential pulse voltammetry (DPV), showing a sensitivity of the electrode for GA determination, within a concentration range of 1 × 10⁻⁶ mol L⁻¹ to 1 × 10⁻³ mol L⁻¹ with a correlation coefficient of R² of 0.9945 and a limit of detection of 1.24 × 10⁻⁷ mol L⁻¹ (S/N = 3). The proposed ZrO₂ nanoparticles modified CPE was successfully used for the determination of GA in red and white wine, with concentrations of 0.103 mmol L⁻¹ and 0.049 mmol L⁻¹ respectively.

Phenosafranin-Based Colorimetric-Sensing Platform for Nitrite Detection Enabled by Griess Assay

A facile and effective colorimetric-sensing platform based on the diazotization of phenosafranin for the detection of NO 2 - under acidic conditions using the Griess assay is presented. Diazotization of commercial phenosafranin produces a color change from purplish to blue, which enables colorimetric quantitative detection of NO 2 - . Optimal detection conditions were obtained at a phenosafranin concentration of 0.25 mM, HCl concentration of 0.4 M, and reaction time of 20 min. Under the optimized detection conditions, an excellent linearity range from 0 to 20 μM was obtained with a detection limit of 0.22 μM. Favorable reproducibility and selectivity of the colorimetric sensing platform toward NO 2 - were also verified. In addition, testing spiked ham sausage, bacon, and sprouts samples demonstrated its excellent practicability. The presented colorimetric sensing platform is a promising candidate for the detection of NO 2 - in real applications.

Operando Studies of the Electrochemical Dissolution of Silver Nanoparticles in Nitrate Solutions Observed With Hyperspectral Dark-Field Microscopy

Since nanoparticles are frequently used in commercial applications, there is a huge demand to obtain deeper insights into processes at the nanoscale. Especially, catalysis, chemical and electrochemical reaction dynamics are still poorly understood. Thus, simultaneous and coupled opto-and spectro-electrochemical dark-field microscopy is used to study in situ and operando the electrochemically driven dissolution mechanism of single silver nanoparticles in the presence of nitrate ions as non-complexing counter-ions, herein. Hyperspectral imaging is used to probe the intrinsic localized surface plasmon resonance of individual silver nanospheres before, during and after their electrochemical oxidation on a transparent indium tin oxide (ITO) electrode. Furthermore, optical video imaging was performed for additional information. Based on the complete loss of spectral information and intensity, a dissolution of the particles during the reaction was concluded. This way it is revealed that the dissolution of individual particles proceeds over several seconds, indicating a hindrance by the nitrate ions. Only electrochemical analysis does not provide this insight as the measured current does not allow distinguishing between successive fast dissolution of one particle after another or slow dissolution of several particles in a concerted manner. For comparison, experiments were performed in the presence of chloride ions. It was observed that the silver chloride formation is an instantaneous process. Thus, it is possible to study and define the reaction dynamics on the single nanoparticle level in various electrochemical systems and electrolyte solutions. Accordingly, operando opto- and spectro-electrochemical studies allow us to conclude, that the oxidation of silver to solvated silver cations is a kinetically slow process, while the oxidation to silver chloride is fast. We propose this approach as a new method to study electrocatalyst materials, their transformation and degradation under operando conditions.

Application of TiO2-Cu Composites in Photocatalytic Degradation Different Pollutants and Hydrogen Production

In the present work, copper nanoparticles were deposited onto the surface of two different commercial titanias (Evonik Aeroxide P25 and Aldrich anatase). During the synthesis, the concentration of copper was systematically varied (0.5%, 1.0%, 1.5%, 5.0%, and 10 wt.%) to optimize the composite-composition. The photocatalytic activity was evaluated under UV-light, using methyl orange and Rhodamine B as model and ketoprofen as real pollutant. For the hydrogen production capacity, oxalic acid was used as the sacrificial agent. The morpho-structural properties were investigated by using XRD (X-ray diffraction), TEM (Transmission Electron Microscopy) DRS (Diffuse Reflectance Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and SEM-EDX methods (Scanning Electron Microscopy-Energy Dispersive X-ray Analysis). Increasing the copper concentration enhanced the photocatalytic activity for methyl orange degradation in the case of Aldrich anatase-based composites. When the P25-based composites were considered, there was no correlation between the Cu concentration and the activity; but, independently of the base photocatalyst, the composites containing 10% Cu were the best performing materials. Contrarily, for the ketoprofen degradation, increasing the copper concentration deteriorated the photoactivity. For both Aldrich anatase and P25, the best photocatalytic activity was shown by the composites containing 0.5% Cu. For the degradation of Rhodamine B solution, 1.5% of copper nanoparticles was the most suitable. When the hydrogen production capacity was evaluated, the P25-based composites showed higher performance (produced more hydrogen) than the Aldrich anatase-based ones. It was found that Cu was present in four different forms, including belloite (Cu(OH)Cl), metallic Cu, and presumably amorphous Cu(I)- and Cu(II)-based compounds, which were easily convertible among themselves during the photocatalytic processes.

Carbon and graphene quantum dots: a review on syntheses, characterization, biological and sensing applications for neurotransmitter determination

Neuro-transmitters have been considered to be essential biochemical molecules, which monitor physiological and behavioral function in the peripheral and central nervous systems. Thus, it is of high pharmaceutical and biological significance to analyze neuro-transmitters in the biological samples. So far, researchers have devised a lot of techniques for assaying these samples. It has been found that electro-chemical sensors possess features of robustness, selectivity, and sensitivity as well as real-time measurement. Graphene quantum dots (GQDs) and carbon QDs (CQDs) are considered some of the most promising carbon-based nanomaterials at the forefront of this research area. This is due to their characteristics including lower toxicity, higher solubility in various solvents, great electronic features, strong chemical inertness, high specific surface areas, plenty of edge sites for functionalization, and versatility, in addition to their ability to be modified via absorbent surface chemicals and the addition of modifiers or nano-materials. Hence in the present review, the synthesis methods of GQDs and CQDs has been summarized and their characterization methods also been analyzed. The applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, such as biological imaging, drug/gene delivery, antibacterial and antioxidant activity, photoluminescence sensors, electrochemiluminescence sensors and electrochemical sensors, have also been discussed. This study then covers sensing features of key neurotransmitters, including dopamine, tyrosine, epinephrine, norepinephrine, serotonin and acetylcholine. Hence, issues and challenges of the GQDs and CQDs were analyzed for their further development.

Carbon and graphene quantum dots for biological and sensing applications of neurotransmitters.

All-electrochemical synthesis of a three-dimensional mesoporous polymeric g-C3N4/PANI/CdO nanocomposite and its application as a novel sensor for the simultaneous determination of epinephrine, paracetamol, mefenamic acid, and ciprofloxacin

mpg-C₃N₄/PANI/CdO nanocomposite was electrochemically synthesized and used for simultaneous determination of EPI, PAR, MFA, and CIP. Also, HOMO and LUMO eigenvalues of the EPI, PAR, MFA and CIP molecules have been evaluated using the DFT method.

Application of nanotechnology based-biosensors in analysis of wine compounds and control of wine quality and safety: A critical review

Nanotechnology is one of the most promising future technologies for the food industry. Some of its applications have already been introduced in analytical techniques and food packaging technologies. This review summarizes existing knowledge about the implementation of nanotechnology in wine laboratory procedures. The focus is mainly on recent advancements in the design and development of nanomaterial-based sensors for wine compounds analysis and assessing wine safety. Nanotechnological approaches could be useful in the wine production process, to simplify wine analysis methods, and to improve the quality and safety of the final product.

Cantilever Nanobiosensor Functionalized with Tyrosinase for Detection of Estrone and β-estradiol in Water

This work aimed to develop cantilever nanobiosensor functionalized with tyrosinase enzyme to detect 17β-estradiol and estrone hormones. In this system, the tyrosinase enzyme was covalently immobilized by self-assembled monolayer onto the cantilever sensor surface. It was possible to verify that the high hormone concentration investigated resulted in high voltage response. The nanobiosensor presented a distinction between the concentrations evaluated and was verified sensitivities of 0.497 and 0.101 V/μg, limit of detection of 0.1 and 0.4 ng/L for the hormones 17β-estradiol and estrone, respectively. The device showed good reversibility and during 30 days of storage maintained about 99% of the original signal. The cantilever nanobiosensor applied in different water samples (ultrapure, river, tap, and mineral) showed good performance, so could be readily extended toward the on-site monitoring of the other trace small molecular pollutants in environmental water matrices.

One-step electrodeposition of AuNi nanodendrite arrays as photoelectrochemical biosensors for glucose and hydrogen peroxide detection

A novel nonsemiconductor photoelectrochemical biosensor was first constructed using the unique plasmonic AuNi nanodendrite arrays. The AuNi nanodendrite arrays were rapidly prepared by a one-step electrodeposition method using the porous anodic aluminum templates. Owing to its hierarchical structure with abundant active sites, the synergistic catalytic of Au and Ni can be better exploited. These plasmonic AuNi nanodendrite arrays display exceptional photoelectrocatalytic activities for glucose oxidation and hydrogen peroxide reduction reaction under visible light illumination. Specifically, the detection sensitivity for glucose (3.7277 mA mM^-1 cm^-2) under illumination is about 3.3 folds improvement than in the dark (1.1287 mA mM^-1 cm^-2), together with high accuracy and low detection limit of 3 μM. The markedly enhanced performance of AuNi nanodendrite arrays can be attributed to its hierarchical structure with abundant active sites and plasmonic effect of Au with strong absorption band in visible region. Such a newly developed method via the facile and low-cost route is of great significance in designing the plasmon-aided photoelectrochemical biosensors.

CoPtx/γ-Al2O3 bimetallic nanoalloys as promising catalysts for hydrazine electrooxidation

Stable bimetallic catalysts composed of CoPtx/γ-Al2O3 (x = Pt/Co molar ratio) were synthesized by wet impregnation method followed by calcination and the H2 reduction. The powders were characterized using XRD, AAS, BET, SEM, EDX, TPR, and TPO techniques. The prepared catalysts were drop casted on the glassy carbon electrode (GCE) and catalytic performance was examined for hydrazine electrooxidation in alkaline medium via cyclic voltammetry (CV). All the compositions in CoPtx/γ-Al2O3 series showed high responses towards hydrazine electrooxidation, however; high activity of CoPt0.034/γ-Al2O3 catalyst inferred it as a best material with an anodic peak current (iP) response of 200 μA at 0.86 V. The prominent electrochemical (EC) responses for this composition are attributed to better accessible surface area resulting in a fast electron transfer. The CoPtx/γ-Al2O3 catalysts are reported as the robust and superior prospective materials for extensive electroanalytical and catalytic studies.

Synthesis and Catalytic Properties of Modified Electrodes by Pulsed Electrodeposition of Pt/PANI Nanocomposite

In this study, the modification of glassy carbon electrodes by potentiostatic pulsed deposition of platinum nanoparticles and potentiostatic pulsed polymerization of polyaniline nanofibers was investigated. During the preparation of the nano-composite materials, the control of the potentiostatic pulsed deposition and potentiostatic pulsed polymerization parameters, such as pulse potential, pulse width time, duty cycle, and platinum precursor concentration allowed the optimization of the size, shape, and distribution of the deposited Pt nanoparticles. It is noteworthy that the polymerization method, cyclic voltammetry method, or potentiostatic pulsed polymerization method show an important effect in the morphology of the deposited polyaniline (PANI) film. The obtained modified electrodes, with highly uniform and well dispersed platinum nanoparticles, exhibit good electrocatalytic properties towards methanol oxidation.

Graphene-derived nanomaterials as recognition elements for electrochemical determination of heavy metal ions: a review

This review (with 155 refs.) summarizes the progress made in the past few years in the field of electrochemical sensors based on graphene-derived materials for the determination of heavy metal ions. Following an introduction of this field and a discussion of the various kinds of modified graphenes including graphene oxide and reduced graphene oxide, the review covers graphene based electrodes modified (or doped) with (a) heteroatoms, (b) metal nanoparticles, (c) metal oxides, (d) small organic molecules, (e) polymers, and (f) ternary nanocomposites. Tables are provided that afford an overview of representative methods and materials for fabricating electrochemical sensors. Furthermore, sensing mechanisms are discussed. A concluding section presents new perspectives, opportunities and current challenges. Graphical Abstract Schematic illustration of electrochemical sensor for heavy metal ion sensing based on heteroatom-doped graphene, metal-modified graphene, metal-oxide-modified graphene, organically modified graphene, polymer-modified graphene, and ternary graphene based nanocomposites.

Microwave-Assisted Biogenic Synthesis of Metal-Decorated Reduced Graphene Oxide and their Electrochemical Properties

Herein we report a microwave assisted, fungal (Ganoderma lucidum) extract mediated synthesis of noble metal decorated reduced graphene oxide(r-GO). The carbon to oxygen ratio increased from 1.46 in GO to 2.72 in r-GO. The electron rate transfer capabilities of Pt, Pd, Ru, Pt-Pd and Pt- Ru decorated r- GO were tested in ferri-ferro coupling reaction. Excellent electrochemical behaviour were observed in their ability to oxidize hydrazine, reduce H2O2, as well as oxygen reduction in alkaline medium and hydrogen evolution in acidic medium. These reactions represent diverse applications in energy production, storage, electrochemical sensing and electro catalysis, thus the method presented here can be quite useful in diverse applications.

Silver Nanoparticles-Chitosan Composite Embedded Graphite Screen-Printed Electrodes as a Novel Electrochemical Platform in the Measurement of Trace Level Nitrite: Application to Milk Powder Samples

Background:

Nitrites can exert acute toxic effects in humans. It is widely used as a preservative in dairy and meat products. The nitrites form N-nitrosamines, which are potential carcinogens and cause detrimental health effects. Herein we report a disposable graphite screen-printed sensor developed using silver metal nano particle embedded chitosan composite in the quantification of nitrite at trace level.

Methods:

Conventional methods possess various limitations. Electrochemical methods provide an ideal platform for trace nitrite analysis. The prepared composite has been characterized by UV-Visible spectrometry, SEM, EDS and XRD techniques. The proposed sensor has been fabricated by using graphite screen-printed electrodes through drop coating of the composite material. The redox behavior and its application of the fabricated electrode have been studied using cyclic and anodic stripping voltammetric methods.

Results:

Graphite screen-printed electrodes after modification have been used to identify the electrocatalytic behavior of nitrite oxidation in an aqueous medium. All the parameters influencing the analytical signal have been optimized and incorporated in the recommended procedure. The proposed sensor has been used to measure the nitrite levels from commercially available milk powder samples and the results have been compared with the standard protocol. The results of the proposed sensor are in good agreement with the standard protocol.

Conclusion:

Ag metal nanoparticles have been embedded in chitosan matrix and used as a composite material in the chemical modification of graphite screen-printed electrodes. GSPEs are easy to fabricate. They provide wide linear working range i.e. 30 - 1140 µM of nitrite. The sensor is highly stable, reproducible and provides a very low detection limit of 1.84 µM. The method has been applied to measure trace level nitrite from milk powder samples.