A study of spatially coupled bipolar electrochemistry on the sub-micrometer scale: colloidal particles on surfaces and cylinders in nuclear-track etched membranes

Fabrication of silver nanoparticles-deposited fabrics as a potential candidate for the development of reusable facemasks and evaluation of their performance

Recently, wearing facemasks in public has been raised due to the coronavirus disease 2019 epidemic worldwide. However, the performance and effectiveness of many existing products have raised significant concerns among people and professionals. Therefore, greater attempts have been focused recently to increase the efficacy of these products scientifically and industrially. In this respect, doping or impregnating facemask fabrics with metallic substances or nanoparticles like silver nanoparticles has been proposed. So, in the present study, we aimed to sonochemically coat silver nanoparticles on the non-woven Spunbond substrates at different sonication times and concentrations to develop antibacterial and antiviral facemask. The coated substrates were characterized using Field Emission Scanning Electron Microscope, Energy Dispersive X-Ray, X-ray diffraction, and Thermogravimetry analysis. The amount of silver released from the coated substrates was measured by atomic absorption spectroscopy. The filtration efficiency, pressure drop, and electrical conductivity of the coated samples were also investigated. The antibacterial activity of fabrics was evaluated against Escherichia coli and Staphylococcus aureus. Cellular viability of samples assessed by MTT and brine shrimp lethality tests. The results revealed that the higher sonication times and precursor concentrations result in a higher and more stable coating, larger particle size, wider particle size distribution, and lower content of released silver. Coated fabrics also revealed enhanced filtration efficiency (against nanosize particles), desired pressure drop, and antibacterial activity without significant cytotoxicity toward HEK 293 cells and Artemia nauplii. As a result, the coated fabrics could find potential applications in the development of facemasks for protection against different pathogenic entities.

Bipolar Electrochemistry - A Powerful Tool for Micro/Nano-Electrochemistry

The understanding of areas for "classical" electrochemistry (including catalysis, electrolysis and sensing) and bio-electrochemistry at the micro/nanoscale are focus on the continued performance facilitations or the exploration of new features. In the recent 20 years, a different mode for driving electrochemistry has been proposed, which is called as bipolar electrochemistry (BPE). BPE has garnered attention owing to the interesting properties: (i) its wireless nature facilitates electrochemical sensing and high throughput analysis; (ii) the gradient potential distribution on the electrodes surface is a useful tool for preparing gradient surfaces and materials. These permit BPE to be used for modification and analytical applications on a micro/nanoscale surface. This review aims to introduce the principle and classification of BPE and BPE at micro/nanoscale; sort out its applications in electrocatalysis, electrosynthesis, electrophoresis, power supply and so on; explain the confined BPE and summarize its analytical application for single entities (single cells, single particles and single molecules), and discuss finally the important direction of micro/nanoscale BPE.

Antifungal Properties of Pure Silver Films with Nanoparticles Induced by Pulsed-Laser Dewetting Process

Silver particles were prepared by dewetting Ag films coated on glass using a fiber laser. The size of the particles was controlled in the range of 92 nm–1.2 μm by adjusting the thickness of the Ag film. The structural properties and surface roughness of the particles were evaluated by means of scanning electron microscopy. In addition, the antifungal activity of the Ag particles was examined using spore suspensions of Colletotrichum gloeosporioides. It is shown that particles with a size of 1.2 μm achieved 100% inhibition of conidia growth of C. gloeosporioides after a contact time of just 5 min. Furthermore, the smaller particles also achieved good antifungal activity given a longer contact time. Similar results were observed for spore germination and pathogenicity tests performed on mango fruit and leaves. Overall, the results confirm that Ag particles have an excellent antifungal effect on C. gloeosporioides.

Two-Step Bipolar Electrochemistry: Generation of Composition Gradient and Visual Screening of Electrocatalytic Activity

Bipolar electrochemistry (BE) is employed for both creating electrocatalysts composition gradient and visual screening of the prepared composition on a single substrate in just two experiment runs. In a series of proof-of-principle experiments, we demonstrate gradient electrodeposition of Ni-Cu using BE; then the electrocatalytic activity of the prepared composition gradient toward the hydrogen evolution reaction (HER) is visually screened in the BE system using array of BPEs. Moreover, the morphology and the chemical composition of the Ni-Cu gradient are screened along the length of the bipolar electrode (BPE). By measuring the potential gradient over the BPE, it is also demonstrated that by controlling the concentration of the metals precursor and the supporting electrolyte, the length of the bipolar electrodeposited gradient can be controlled.

Bipolar electrochemical method for dynamic in situ control of single metal nanowire growth

Fabrication plays a key role in determining the unique electrical, optical, and catalytic properties of metal nanowires. Here we present a bipolar electrochemical method for dynamically monitoring and controlling the rate of single metal nanowire growth in situ without a direct electrical connection. Solutions of a metal precursor and a reducing agent are placed on either side of a silica nanochannel, and a pair of electrodes is used to apply a tunable electric potential across the channel. Metal nanowire growth is initiated by chemical reduction when the two solutions meet and continues until the nanochannel is blocked by the formation of a short metal wire segment. Further growth is driven by a bipolar electrochemical mechanism which enables the reduction of metal precursor ions at one end of the nanowire and the oxidation of the reducing agent at the other. The growth rate is monitored in real time by simultaneously recording both the faradaic current and optical microscope video and can be adjusted accordingly by changing the applied electric potential. The resulting nanowire is solid, electrically insulated, and can be used as a bipolar nanoelectrode. This technique can be extended to other electrochemical systems, as well, and provides a confined reaction space for studying the dynamics of any process that can be optically or electrically monitored.

Self-movement of water droplet at the gradient nanostructure of Cu fabricated using bipolar electrochemistry

This Article reports on gradient electrodeposition of copper on the surface of a bipolar electrode (BPE). The formation mechanism of the as-fabricated gradient nanostructure is discussed, and the effects of time, potential, and concentration of CuSO4 solution on the morphology of the deposited structures are investigated. Scanning electron microscopy (SEM) is used to visualize the morphology of the deposited Cu at different positions of the BPE. By scanning from the cathodic pole to the midpoint of the BPE, three distinct structures are observed; (i) nanodendrites, (ii) nanodendrites in the vicinity of nanoparticles, and (iii) nanoparticles. The BPE surface was characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The contact angle measurement of a water droplet reveals a surface with gradient wettability. Modification of the as-electrodeposited Cu surface with 1-dodecanethiol provides self-movement of the water droplet.

Site Selective Electrodeposition of Metals and Conductive Polymer Nano-Structures on Isolated Carbon Nanopipes Using Electric Fields

We report the successful application of bipolar electrochemistry for depositing metals and conducting polymer nano-structures on isolated template-grown carbon nanopipes (CVD-CNP). Metals such as tin, cobalt and nickel were reduced electrochemically at the tips of isolated CVD- CNP from their chloride or nitrate salts. Polypyrrole dendrites could also be grown on both ends of selected CVD-CNP. The potential applications of thus encapsulated CVD-CNP in nano- fluidics and other areas will be discussed.

Depositing silver nanoparticles on/in a glass slide by the sonochemical method

A glass substrate was coated with silver by ultrasound irradiation. The structure and morphology of the nanoparticles in the deposited film were characterized using methods such as XRD, TEM, HR TEM, HRSEM, AFM, TOF-SIMS and optical spectroscopy. It was demonstrated that nucleation and the ensuing growth of the nanoparticles occurs in solution and is influenced by the concentration of the precursor, temperature and time of sonication. TOF-SIMS measurements revealed that silver nanoparticles passed through the glass interface and diffused within the glass substrate up to ∼60 nm. An analysis of the thermal effects accompanying the sonochemical cavitation of micro-bubbles in the solution near the solid surfaces shows that the collision of nanoparticles can lead to their melting and coalescence. Sonochemical deposition takes place layer by layer, so that the completion of the deposition of each layer of nanoparticles is followed by the sintering of adjacent particles and the formation of a close-packed layer. Using PVP as a stabilizing agent, a monolayer coating of silver nanoparticles on the glass surface was obtained. The coated glass demonstrated antibacterial activity.