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9 pages, 1940 KiB

Open AccessCommunication

Electrochemical Detection of Microplastics in Water Using Ultramicroelectrodes

by Changhui Lee, Sangwon Han and Jun Hui Park

Chemosensors 2024, 12(12), 278; https://doi.org/10.3390/chemosensors12120278 - 23 Dec 2024

Cited by 5 | Viewed by 2256

Herein, a method for detecting microplastics in water using single-entity electrochemistry is presented, with a focus on the interaction between microplastics in aqueous solution and the surface of an ultramicroelectrode (UME). Polystyrene and polypropylene, two commonly used plastics that were ground and dispersed [...] Read more.

Herein, a method for detecting microplastics in water using single-entity electrochemistry is presented, with a focus on the interaction between microplastics in aqueous solution and the surface of an ultramicroelectrode (UME). Polystyrene and polypropylene, two commonly used plastics that were ground and dispersed in aqueous solution, served as the detection target materials. The collisional contact of microplastics with the UME was transduced into a discernible signal. To detect microplastics in solution using an UME, redox species (e.g., ferrocyanide) were continuously oxidized at the electrode, and the resulting steady-state current was monitored. Collisional contact followed by adsorption of microplastics on the UME disturbed the diffusional flux of redox species, resulting in an immediate change in the steady-state current. Detection sensitivity was further enhanced by optimizing the electrolyte composition to induce a migration effect. COMSOL Multiphysics simulations were employed to analyze the magnitude of the current changes as a function of microplastic size. The size distribution obtained from the simulations closely matched measurements from dynamic light scattering (DLS). Full article

(This article belongs to the Section Electrochemical Devices and Sensors)

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11 pages, 4513 KiB

Open AccessArticle

Superior Single-Entity Electrochemistry Performance of Capping Agent-Free Gold Nanoparticles Compared to Citrate-Capped Gold Nanoparticles

by Dain Heo, Ki Jun Kim and Seong Jung Kwon

Nanomaterials 2024, 14(17), 1399; https://doi.org/10.3390/nano14171399 - 28 Aug 2024

Cited by 1 | Viewed by 1314

Abstract

In observing the electrocatalytic current of nanoparticles (NPs) using single-entity electrochemistry (SEE), the surface state of the NPs significantly influences the SEE signal. This study investigates the influence of capping agents on the electrocatalytic properties of gold (Au) NPs using SEE. Two inner-sphere [...] Read more.

In observing the electrocatalytic current of nanoparticles (NPs) using single-entity electrochemistry (SEE), the surface state of the NPs significantly influences the SEE signal. This study investigates the influence of capping agents on the electrocatalytic properties of gold (Au) NPs using SEE. Two inner-sphere reactions, hydrazine oxidation and glucose oxidation, were chosen to explore the SEE characteristics of Au NPs based on the capping agent presence. The results revealed that “capping agent-free” Au NPs exhibited signal magnitudes and frequencies consistent with theoretical expectations, indicating superior stability and catalytic performance in electrolyte solutions. In contrast, citrate-capped Au NPs showed signals varying depending on the applied potential, with larger magnitudes and lower frequencies than expected, likely due to an aggregation of NPs. This study suggests that capping agents play a crucial role in the catalytic performance and stability of Au NPs in SEE. By demonstrating that minimizing capping agent presence can enhance effectiveness in SEE, it provides insights into the future applications of NPs, particularly highlighting their potential as nanocatalysts in energy conversion reactions and environmental applications. Full article

(This article belongs to the Special Issue Novel Ways of Developing Bio- and Electrochemical Sensors with Nanomaterials)

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12 pages, 2620 KiB

Open AccessArticle

Electrochemical Characterization of Neurotransmitters in a Single Submicron Droplet

by Heekyung Park and Jun Hui Park

Biosensors 2024, 14(2), 102; https://doi.org/10.3390/bios14020102 - 17 Feb 2024

Viewed by 2086

Abstract

Single-entity electrochemistry, which employs electrolysis during the collision of single particles on ultramicroelectrodes, has witnessed significant advancements in recent years, enabling the observation and characterization of individual particles. Information on a single aqueous droplet (e.g., size) can also be studied based on the [...] Read more.

Single-entity electrochemistry, which employs electrolysis during the collision of single particles on ultramicroelectrodes, has witnessed significant advancements in recent years, enabling the observation and characterization of individual particles. Information on a single aqueous droplet (e.g., size) can also be studied based on the redox species contained therein. Dopamine, a redox-active neurotransmitter, is usually present in intracellular vesicles. Similarly, in the current study, the electrochemical properties of neurotransmitters in submicron droplets were investigated. Because dopamine oxidation is accompanied by proton transfer, unique electrochemical properties of dopamine were observed in the droplet. We also investigated the electrochemical properties of the adsorbed droplets containing DA and the detection of oxidized dopamine by the recollision phenomenon. Full article

(This article belongs to the Special Issue Biosensing Based on Electrochemical Analysis)

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14 pages, 3055 KiB

Open AccessArticle

Single-Entity Electrochemistry in the Agarose Hydrogel: Observation of Enhanced Signal Uniformity and Signal-to-Noise Ratio

by Jaedo Na, Kyungsoon Park and Seong Jung Kwon

Gels 2023, 9(7), 537; https://doi.org/10.3390/gels9070537 - 2 Jul 2023

Cited by 2 | Viewed by 2020

Abstract

For the first time, single-entity electrochemistry (SEE) was demonstrated in a hydrogel matrix. SEE involves the investigation of the electrochemical characteristics of individual nanoparticles (NPs) by observing the signal generated when a single NP, suspended in an aqueous solution, collides with an electrode [...] Read more.

For the first time, single-entity electrochemistry (SEE) was demonstrated in a hydrogel matrix. SEE involves the investigation of the electrochemical characteristics of individual nanoparticles (NPs) by observing the signal generated when a single NP, suspended in an aqueous solution, collides with an electrode and triggers catalytic reactions. Challenges associated with SEE in electrolyte-containing solutions such as signal variation due to NP aggregation and noise fluctuation caused by convection phenomena can be addressed by employing a hydrogel matrix. The polymeric hydrogel matrix acts as a molecular sieve, effectively filtering out unexpected signals generated by aggregated NPs, resulting in more uniform signal observations compared to the case in a solution. Additionally, the hydrogel environment can reduce the background current fluctuations caused by natural convection and other factors such as impurities, facilitating easier signal analysis. Specifically, we performed SEE of platinum (Pt) NPs for hydrazine oxidation within the agarose hydrogel to observe the electrocatalytic reaction at a single NP level. The consistent porous structure of the agarose hydrogel leads to differential diffusion rates between individual NPs and reactants, resulting in variations in signal magnitude, shape, and frequency. The changes in the signal were analyzed in response to gel concentration variations. Full article

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9 pages, 1843 KiB

Open AccessCommunication

Electrochemical Analysis of Attoliter Water Droplets in Organic Solutions through Partitioning Equilibrium

by Hyeongkwon Moon and Jun Hui Park

Sensors 2023, 23(4), 2157; https://doi.org/10.3390/s23042157 - 14 Feb 2023

Cited by 2 | Viewed by 2181

Abstract

Herein, we report the electrochemical monitoring of attoliters of water droplets in an organic medium by the electrolysis of an extracted redox species from the continuous phase upon collisional events on an ultramicroelectrode. To obtain information about a redox-free water droplet in an [...] Read more.

Herein, we report the electrochemical monitoring of attoliters of water droplets in an organic medium by the electrolysis of an extracted redox species from the continuous phase upon collisional events on an ultramicroelectrode. To obtain information about a redox-free water droplet in an organic solvent, redox species with certain concentrations need to be contained inside it. The redox species inside the droplet were delivered by a partitioning equilibrium between the organic phase and the water droplets. The mass transfer of the redox species from the surrounding organic phase to the droplet is very fast because of the radial diffusion, which resultantly establishes the equilibrium. Upon the collisional contact between the droplet and the electrode, the extracted redox species in the water droplets were selectively electrolyzed, even though the redox species in the organic continuous phase remained unreacted because of the different solvent environments. The electrolysis of the redox species in the droplets, where the concentration is determined by the equilibrium constant of the redox species in water/oil, can be used to estimate the size of single water droplets in an organic solution. Full article

(This article belongs to the Special Issue Electrochemical Sensors for Analytical Applications)

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12 pages, 2747 KiB

Open AccessCommunication

Single Co₃O₄ Nanocubes Electrocatalyzing the Oxygen Evolution Reaction: Nano-Impact Insights into Intrinsic Activity and Support Effects

by Zhibin Liu, Manuel Corva, Hatem M. A. Amin, Niclas Blanc, Julia Linnemann and Kristina Tschulik

Int. J. Mol. Sci. 2021, 22(23), 13137; https://doi.org/10.3390/ijms222313137 - 4 Dec 2021

Cited by 38 | Viewed by 4691

Abstract

Single-entity electrochemistry allows for assessing electrocatalytic activities of individual material entities such as nanoparticles (NPs). Thus, it becomes possible to consider intrinsic electrochemical properties of nanocatalysts when researching how activity relates to physical and structural material properties. Conversely, conventional electrochemical techniques provide a [...] Read more.

Single-entity electrochemistry allows for assessing electrocatalytic activities of individual material entities such as nanoparticles (NPs). Thus, it becomes possible to consider intrinsic electrochemical properties of nanocatalysts when researching how activity relates to physical and structural material properties. Conversely, conventional electrochemical techniques provide a normalized sum current referring to a huge ensemble of NPs constituting, along with additives (e.g., binders), a complete catalyst-coated electrode. Accordingly, recording electrocatalytic responses of single NPs avoids interferences of ensemble effects and reduces the complexity of electrocatalytic processes, thus enabling detailed description and modelling. Herein, we present insights into the oxygen evolution catalysis at individual cubic Co₃O₄ NPs impacting microelectrodes of different support materials. Simulating diffusion at supported nanocubes, measured step current signals can be analyzed, providing edge lengths, corresponding size distributions, and interference-free turnover frequencies. The provided nano-impact investigation of (electro-)catalyst-support effects contradicts assumptions on a low number of highly active sites. Full article

(This article belongs to the Collection Feature Papers in Materials Science)

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18 pages, 3827 KiB

Open AccessArticle

[2 × 2] Molecular Grids of Ni(II) and Zn(II) with Redox-Active 1,4-Pyrazine-Bis(thiosemicarbazone) Ligands

by Natalia Arefyeva, Aaron Sandleben, Alexander Krest, Ulrich Baumann, Mathias Schäfer, Maxim Kempf and Axel Klein

Inorganics 2018, 6(2), 51; https://doi.org/10.3390/inorganics6020051 - 21 May 2018

Cited by 9 | Viewed by 5607

Abstract

Tetranuclear complexes [M₄(L^R)₄] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H₂L [...] Read more.

Tetranuclear complexes [M₄(L^R)₄] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H₂L^R (1,4-pyrazine-2,5-bis(R-carbaldehyde-thiosemicarbazone); R = Me, Et, ⁱPr, or Ph). The complexes were characterised in solution by NMR, MS, IR, and UV-Vis absorption spectroscopy and (spectro)electrochemical methods. HR-MS spectra unequivocally reveal that the tetranuclear species are very stable in solution and any measurements represent these species. Only at higher temperatures (fragmentation in solution: MS and in the solid: TG-DTA) or upon the addition of protons (acidic UV-Vis titrations) can the tetrameric entities be decomposed. Single crystal XRD measurement remained preliminary. Rapid loss of co-crystallised solvent molecules within the [2 × 2] grid-type structures resulted in crystals of very poor quality, but the results were qualitatively in line with spectroscopy, electrochemistry, and quantum chemical (DFT) calculations. IR and NMR spectroscopy point clearly to a thiolate coordination of dianionic (deprotonated) ligands. The electrochemistry reveals four electronically coupled and reversible one-electron reductions centred largely at the pyrazine bridges. EPR and UV-Vis spectroelectrochemical measurements in combination with DFT calculation support the assignment. Full article

(This article belongs to the Special Issue First-Row Transition Metal Complexes)

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14 pages, 2716 KiB

Open AccessArticle

Synthesis and Characterisation of the Europium (III) Dimolybdo-Enneatungsto-Silicate Dimer, [Eu(α-SiW₉Mo₂O₃₉)₂]¹³⁻

by Loïc Parent, Pedro De Oliveira, Anne-Lucie Teillout, Anne Dolbecq, Mohamed Haouas, Emmanuel Cadot and Israël M. Mbomekallé

Inorganics 2015, 3(3), 341-354; https://doi.org/10.3390/inorganics3030341 - 13 Jul 2015

Cited by 8 | Viewed by 4885

Abstract

The chemistry of polyoxometalates (POMs) keeps drawing the attention of researchers, since they constitute a family of discrete molecular entities whose features may be easily modulated. Often considered soluble molecular oxide analogues, POMs possess enormous potential due to a myriad of choices concerning [...] Read more.

The chemistry of polyoxometalates (POMs) keeps drawing the attention of researchers, since they constitute a family of discrete molecular entities whose features may be easily modulated. Often considered soluble molecular oxide analogues, POMs possess enormous potential due to a myriad of choices concerning size, shape and chemical composition that may be tailored in order to fine-tune their physico-chemical properties. Thanks to the recent progress in single-crystal X ray diffraction, new POMs exhibiting diverse and unexpected structures have been regularly reported and described. We find it relevant to systematically analyse the different equilibria that govern the formation of POMs, in order to be able to establish reliable synthesis protocols leading to new molecules. In this context, we have been able to synthesise the Eu³⁺-containing silico-molybdo-tungstic dimer, [Eu(α-SiW₉Mo₂O₃₉)₂]¹³⁻. We describe the synthesis and characterisation of this new species by several physico-chemical methods, such as single-crystal X-ray diffraction, ¹⁸³W NMR and electrochemistry. Full article

(This article belongs to the Special Issue Polyoxometalates)

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