Avocado oil, coconut oil, walnut oil as true oil phase for ion transfer at nanoscale liquid/liquid interfaces

Dual-channel nano-carbon-liquid/liquid junction electrodes for multi-modal analysis: redox-active (dopamine) and non-redox-active (acetylcholine)

We present here a dual-channel nanoelectrode to detect both redox-active and non-redox-active analytes. The dual-channel nanoelectrode was developed from theta nanopipette. We developed one channel of the theta nanopipette to be a carbon nanoelectrode and the other channel to be a nano interface between two immiscible electrolyte solutions (nanoITIES) electrode, producing a nano-carbon-ITIES platform. The carbon nanoelectrode channel was developed by carbon deposition via pyrolysis followed by focused ion beam milling to measure redox-active analytes. The nanoITIES electrode channel was developed to detect non-redox-active analytes. The nano-carbon-ITIES electrodes were characterized using electrochemistry, scanning electron microscopy and transmission electron microscopy. Dopamine (a redox-active analyte) and acetylcholine (a non-redox-active analyte) were measured on the dual-channel nano-carbon-ITIES platform using the carbon nanoelectrode and the nanoITIES electrode, respectively. Using cyclic voltammetry, the diffusion-limited current of dopamine and acetylcholine detection on the nano-carbon-ITIES electrode increased linearly with increasing their concentrations. Using chronoamperometry (current versus time), we showed that the nano-carbon-ITIES electrode detected acetylcholine and dopamine at the same time. The introduced first-ever dual-functional nano-carbon-ITIES electrodes expand the current literature in multi-channel electrodes for multi-purpose analysis, which is an emerging area of research. Developing the analytical capability for the simultaneous detection of acetylcholine and dopamine is a critical step towards understanding diseases and disorders where both dopamine and acetylcholine are involved.

Electroanalytical applications of ITIES - A review

Over the last decades, the interface between two immiscible electrolyte solutions (ITIES) attracted considerable attention of the scientific community due to their vast applications, such as extraction, catalysis, partition studies and sensing. The aim of this Review is to highlight the potential of electrochemistry at the ITIES for analytical purposes, focusing on ITIES-based sensors for detection and quantification of chemically and biologically relevant (bio)molecules. We start by addressing the evolution of ITIES in terms of number of publications over the years along with an overview of their main applications (Chapter 1). Then, we provide a general historical perspective about pioneer voltammetric studies at water/oil systems (Chapter 2). After that, we discuss the most impacting improvements on ITIES sensing systems from both perspectives, set-up design (interface stabilization and miniaturization, selection of the organic solvent, etc.) and optimization of experimental conditions to improve selectivity and sensitivity (Chapter 3). In Chapter 4, we discuss the analytical applications of ITIES for electrochemical sensing of several types of analytes, including drugs, pesticides, proteins, among others. Finally, we highlight the present achievements of ITIES as analytical tool and provide future challenges and perspectives for this technology (Chapter 5).

Nanoelectrochemistry at liquid/liquid interfaces for analytical, biological, and material applications

Herein, we feature our recent efforts toward the development and application of nanoelectrochemistry at liquid/liquid interfaces, which are also known as interfaces between two immiscible electrolyte solutions (ITIES). Nanopipets, nanopores, and nanoemulsions are developed to create the nanoscale ITIES for the quantitative electrochemical measurement of ion transfer, electron transfer, and molecular transport across the interface. The nanoscale ITIES serves as an electrochemical nanosensor to enable the selective detection of various ions and molecules as well as high-resolution chemical imaging based on scanning electrochemical microscopy. The powerful nanoelectroanalytical methods will be useful for biological and material applications as illustrated by in situ studies of solid-state nanopores, nuclear pore complexes, living bacteria, and advanced nanoemulsions. These studies provide unprecedented insights into the chemical reactivity of important biological and material systems even at the single nanostructure level.

Oil-in-Water emulsions stabilized by alumina nanoparticles with organic electrolytes: Fate of particles

HYPOTHESIS

Oil-in-dispersion emulsions can be stabilized by like charged particles and surfactant. Surfactant adsorbs at the oil-water interface to reduce the interfacial tension and endow the interface with charge, while particles remain dispersed in the aqueous phase to provide electrostatic repulsion between droplets and particles. Can weakly surface-active organic electrolytes adsorb at the oil-water interface and behave like surfactants in stabilizing oil-in-dispersion emulsions with like charged particles?

EXPERIMENTS

Symmetrical organic electrolytes, tetraalkylammonium bromides (R₄NBr), with either no or very low interfacial activity endowing oil droplets with charge were combined with alumina nanoparticles to stabilize emulsions. The effect of R chain length (varying from methyl to butyl) on the type and stability of emulsions was investigated.

FINDINGS

Mixtures of high concentrations of short chain R₄NBr salts (R = methyl or ethyl) and alumina particles stabilise oil-in-water Pickering emulsions, whereas longer chain (R = propyl or butyl) analogues stabilize oil-in-dispersion emulsions assisted by alumina particles. Tetrapropylammonium and tetrabutylammonium cations adsorb at the oil-water interface reducing the interfacial tension and endowing the interface with charge. The stability of the oil-in-dispersion emulsions is dominated by the electrostatic repulsion between the droplets and between droplets and particles in the continuous aqueous phase.

Electrostatic-Gated Kinetics of Rapid Ion Transfers at a Nano-liquid/Liquid Interface

Charge (ion and electron)-transfer reactions at a liquid/liquid interface are critical processes in many important biological and chemical systems. An ion-transfer (IT) process is usually very fast, making it difficult to accurately measure its kinetic parameters. Nano-liquid/liquid interfaces supported at nanopipettes are advantageous approaches to study the kinetics of such ultrafast IT processes due to their high mass transport rate. However, correct measurements of IT kinetic parameters at nanointerfaces supported at nanopipettes are inhibited by a lack of knowledge of the nanometer-sized interface geometry, influence of the electric double layer, wall charge polarity, etc. Herein, we propose a new electrochemical characterization equation for nanopipettes and make a suggestion on the shape of a nano-water/1,2-dichloroethane (nano-W/DCE) interface based on the characterization and calculation results. A theoretical model based on the Poisson-Nernst-Planck equation was applied to systematically study how the electric double layer influences the IT process of cations (TMA⁺, TEA⁺, TPrA⁺, ACh⁺) and anions (ClO₄^-, SCN^-, PF₆^-, BF₄^-) at the nano-W/DCE interface. The relationships between the wall charge conditions and distribution of concentration and potential inside the nanopipette revealed that the measured standard rate constant (k⁰) was enhanced when the polarity of the ionic species was opposite to the pipette wall charge and reduced when the same. This work lays the right foundation to obtain the kinetics at the nano-liquid/liquid interfaces.

Detection of Acetylcholine at Nanoscale NPOE/Water Liquid/Liquid Interface Electrodes

The interface between two immiscible electrolyte solutions (ITIES) has become a very powerful analytical platform for sensing a diverse range of chemicals (e.g., metal ions and neurotransmitters) with the advantage of being able to detect non-redox electroactive species. The ITIES is formed between organic and aqueous phases. Organic solvent identity is crucial to the detection characteristics of the ITIES [half-wave transfer potential (E_1/2), potential window range, limit of detection, transfer coefficient (α), standard heterogeneous ion-transfer rate constant (k⁰), etc.]. Here, we demonstrated, for the first time at the nanoscale, the detection characteristics of the NPOE/water ITIES. Linear detection of the diffusion-limited current at different concentrations of acetylcholine (ACh) was demonstrated with cyclic voltammetry (CV) and i-t amperometry. The E_1/2 of ACh transfer at the NPOE/water nanoITIES was -0.342 ± 0.009 V versus the E_1/2 of tetrabutylammonium (TBA⁺). The limit of detection of ACh at the NPOE/water nanoITIES was 37.1 ± 1.5 μM for an electrode with a radius of ∼127 nm. We also determined the ion-transfer kinetics parameters, α and k⁰, of TBA⁺ at the NPOE/water nanoITIES by fitting theoretical cyclic voltammograms to experimental voltammograms. This work lays the basis for future cellular studies using ACh detection at the nanoscale and for studies to detect other analytes. The NPOE/water ITIES offers a potential window distinct from that of the 1,2-dichloroethane (DCE)/water ITIES. This unique potential window would offer the ability to detect analytes that are not easily detected at the DCE/water ITIES.

Voltammetric study of cefotaxime at the macroscopic and miniaturized interface between two immiscible electrolyte solutions

The electrochemical behavior of cefotaxime (CTX⁺) was investigated at the polarized macro- and micro-interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry and alternating current voltammetry. Miniaturization was achieved with fused silica microcapillary tubing entrapped in a polymeric casing. Scanning electron microscopy (SEM) was employed for the fabricated LLI support characterization. Voltammetric investigation of CTX⁺ at macro- and μ-ITIES allowed the determination of many physicochemical parameters, such as formal Galvani potential of the ion transfer reaction (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta }_{org}^{aq}{\varPhi}^{\prime }$$\end{document}ΔorgaqΦ′), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G^{′aq → org}), and water-1,2-dichloroethane partition coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\log}{P}_{water/ DCE}^{CTX+}$$\end{document}logPwater/DCECTX+). Additionally, based on the results obtained the analytical parameters including voltammetric sensitivity, limits of detection and the limits of quantification (in micromolar range) were calculated. The applicability of the developed procedures was verified in spiked still mineral and tap water samples.

Avocado oil: Production and market demand, bioactive components, implications in health, and tendencies and potential uses

Avocado is a subtropical/tropical fruit with creamy texture, peculiar flavor, and high nutritional value. Due to its high oil content, a significant quantity of avocado fruit is used for the production of oil using different methods. Avocado oil is rich in lipid-soluble bioactive compounds, but their content depends on different factors. Several phytochemicals in the oil have been linked to prevention of cancer, age-related macular degeneration, and cardiovascular diseases and therefore have generated an increase in consumer demand for avocado oil. The aim of this review is to critically and systematically analyze the worldwide production and commercialization of avocado oil, its extraction methods, changes in its fat-soluble phytochemical content, health benefits, and new trends and applications. There is a lack of information on the production and commercialization of the different types of avocado oil, but there are abundant data on extraction methods using solvents, centrifugation-assisted aqueous extraction, mechanical extraction by cold pressing (varying concentration and type of enzymes, temperature and time of reaction, and dilution ratio), ultrasound-assisted extraction, and supercritical fluid to enhance the yield and quality of oil. Extensive information is available on the content of fatty acids, although it is limited on carotenoids and chlorophylls. The effect of avocado oil on cancer, diabetes, and cardiovascular diseases has been demonstrated through in vitro and animal studies, but not in humans. Avocado oil continues to be of interest to the food, pharmaceutical, and cosmetic industries and is also generating increased attention in other areas including structured lipids, nanotechnology, and environmental care.