Light-Addressable Electrodes for Dynamic and Flexible Addressing of Biological Systems and Electrochemical Reactions.

In this review article, we are going to present an overview on possible applications of light-addressable electrodes (LAE) as actuator/manipulation devices besides classical electrode structures. For LAEs, the electrode material consists of a semiconductor. Illumination with a light source with the appropiate wavelength leads to the generation of electron-hole pairs which can be utilized for further photoelectrochemical reaction. Due to recent progress in light-projection technologies, highly dynamic and flexible illumination patterns can be generated, opening new possibilities for light-addressable electrodes. A short introduction on semiconductor-electrolyte interfaces with light stimulation is given together with electrode-design approaches. Towards applications, the stimulation of cells with different electrode materials and fabrication designs is explained, followed by analyte-manipulation strategies and spatially resolved photoelectrochemical deposition of different material types.

Electrodeposition of Ginseng/Polyaniline Encapsulated Poly(lactic-co-glycolic Acid) Microcapsule Coating on Stainless Steel 316L at Different Deposition Parameters.

Electrodeposition is commonly used to deposit ceramic or metal coating on metallic implants. Its utilization in depositing polymer microcapsule coating is currently being explored. However, there is no encapsulation of drug within polymer microcapsules that will enhance its chemical and biological properties. Therefore, in this study, ginseng which is known for its multiple therapeutic effects was encapsulated inside biodegradable poly(lactic-co-glycolic acid) (PLGA) microcapsules to be coated on pre-treated medical grade stainless steel 316L (SS316L) using an electrodeposition technique. Polyaniline (PANI) was incorporated within the microcapsules to drive the formation of microcapsule coating. The electrodeposition was performed at different current densities (1-3 mA) and different deposition times (20-60 s). The chemical composition, morphology and wettability of the microcapsule coatings were characterized through attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and contact angle analyses. The changes of electrolyte colors, before and after the electrodeposition were also observed. The addition of PANI has formed low wettability and uniform microcapsule coatings at 2 mA current density and 40 s deposition time. Reduction in the current density or deposition time caused less attachment of microcapsule coatings with high wettability records. While prolonging either one parameter has led to debris formation and melted microcapsules with non-uniform wettability measurements. The color of electrolytes was also changed from milky white to dark yellow when the current density and deposition time increased. The application of tolerable current density and deposition time is crucial to obtain a uniform microcapsule coating, projecting a controlled release of encapsulated drug.

Electrodeposition-based rapid bioprinting of 3D-designed hydrogels with a pin art device.

Three-dimensional (3D) designed hydrogels are receiving considerable attention for use in tissue engineering. Herein, we present a novel method for bioprinting 3D hydrogels by electrodeposition with a pin art device. The device consists of a metal substrate and an array of electrode pins that can slide independently. To fabricate a 3D-hydrogel, pins are pushed from the rear with a 3D object to generate a 3D extruded-pin relief of the object; the extruded pins are then inserted into a chitosan/gelatin hydrogel. Due to H+ consumption at these pins, which collectively act as a cathode, the protonated amino groups of the chitosan become deprotonated, which results in the electrodeposition of the chitosan bound to the gelatin onto the extruded pins. The untreated hydrogel is removed by heating to provide the 3D-designed chitosan/gelatin hydrogel. As a proof of concept, hydrogels of various shapes were fabricated. In addition, cells were successfully cultured in a hydrogel, highlighting its biocompatibility. This method is useful for constructing 3D artificial tissue consisting of hydrogels and cells.

Low Conductive Electrodeposited Poly(2,5-dimethoxyaniline) as a Key Material in a Double Lateral Heterojunction, for Sub-ppm Ammonia Sensing in Humid Atmosphere.

We present a new device called a double lateral heterojunction (DLH) as an ammonia sensor in humid atmosphere. It combines polyaniline derivatives in their poor conducting state with a highly conductive molecular material, lutetium bisphthalocyanine, LuPc2. Polyaniline and poly(2,5-dimethoxyaniline) are electrodeposited on ITO interdigitated electrodes, leading to an original device that can be obtained only by electrochemistry and not by other solution processing techniques. Both polymers lead to highly conducting materials that require a neutralization step before their coverage by LuPc2. While the device based on polyaniline shows ohmic behavior, the nonlinear I- V characteristics of the poly(2,5-dimethoxyaniline)-based DLH prove the existence of energy barriers at the interfaces, as demonstrated by impedance spectroscopy. It exhibits a particularly interesting sensitivity to ammonia, at room temperature and in a broad relative humidity range. Thanks to its higher energy barriers, the poly(2,5-dimethoxyaniline)/LuPc2 DLH is the most sensitive device with a limit of detection of 320 ppb. This work paves the way for the use of substituted polyanilines in conductometric sensors not only in the field of air quality monitoring but also in the field of health diagnosis by measurement in human breath.

Development of graphene oxide/calcium phosphate coating by pulse electrodeposition on anodized titanium: Biocorrosion and mechanical behavior.

In this work, graphene oxide (GO) reinforcement was used to improve the strength and fracture toughness of the calcium phosphate (CaP) coating applied on the anodized titanium using pulse electrodeposition. Based on the results, the CaP coating consisted of mixed phases of octa-calcium phosphate (OCP), dicalcium phosphate dehydrate (DCPD) and hydroxyapatite (HAp); however, compositing of this coating with GO caused deposition of the pure HAp phase. Moreover, the nanohardness and Young's modulus of the CaP-GO coating increased over 52% and 41%, respectively, as compared to those measured for the GO-free coating. An improvement of about 16% in the adhesion strength of the CaP coating composited with GO to the anodized titanium was also arisen from improving integrity, crystallinity and decreasing the Young's modulus mismatch of this coating with titanium substrate. Finally, uniformity in the microstructure and more biostability of the CaP-GO coating led to its better protection against the corrosion of anodized titanium.

Pencil-Drawing Skin-Mountable Micro-Supercapacitors.

In this study, integrated plaster-like micro-supercapacitors based on medical adhesive tapes are fabricated by a simple pencil drawing process combined with a mild solution deposition of MnO2 . These solid micro-supercapacitors not only exhibit excellent stretchability, flexibility, and biocompatibility, but also possess outstanding electrochemical performances, such as exceptional rate capability and cycling stability. Hence they may act as skin-mountable and thin-film energy storage devices of high efficiency to power miniaturized and wearable electronic devices.

Hydrogel electrodeposition based on bipolar electrochemistry.

Bipolar electrochemistry has attracted great interest for applications based on sensing, electrografting, and electrodeposition, because the technique enables electrochemical reactions to be induced at multiple bipolar electrodes (BPEs) with only a single power supply. However, there are only a few reports on the biofabrication of hydrogels using BPEs. In this study, we applied bipolar electrochemistry to achieve the electrodeposition of calcium-alginate hydrogels at specified target areas, which is possible because of the use of water electrolysis to obtain acidification at the anodic pole. This scheme was used to successfully fabricate an array of hydrogel deposits at a BPE array. In addition, hydrogels were successfully fabricated either at only the target BPEs or only the target areas of BPEs by repositioning the driving electrodes. Furthermore, a hydrogel was drawn on a large BPE as a canvas by using small driving electrodes. As a demonstration of the electrodeposited hydrogels for bioapplications, mammal cells were cultured in the hydrogels. Because the amount and shape of the hydrogel deposits can be controlled by using the bipolar system, the system we developed can be used for biosensors and cell culture platforms.

Hybrid 3D printing and electrodeposition approach for controllable 3D alginate hydrogel formation.

Calcium alginate hydrogels are widely used as biocompatible materials in a substantial number of biomedical applications. This paper reports on a hybrid 3D printing and electrodeposition approach for forming 3D calcium alginate hydrogels in a controllable manner. Firstly, a specific 3D hydrogel printing system is developed by integrating a customized ejection syringe with a conventional 3D printer. Then, a mixed solution of sodium alginate and CaCO3 nanoparticles is filled into the syringe and can be continuously ejected out of the syringe nozzle onto a conductive substrate. When applying a DC voltage (∼5 V) between the substrate (anode) and the nozzle (cathode), the Ca2+ released from the CaCO3 particles can crosslink the alginate to form calcium alginate hydrogel on the substrate. To elucidate the gel formation mechanism and better control the gel growth, we can further establish and verify a gel growth model by considering several key parameters, i.e., applied voltage and deposition time. The experimental results indicate that the alginate hydrogel of various 3D structures can be formed by controlling the movement of the 3D printer. A cell viability test is conducted and shows that the encapsulated cells in the gel can maintain a high survival rate (∼99% right after gel formation). This research establishes a reliable method for the controllable formation of 3D calcium alginate hydrogel, exhibiting great potential for use in basic biology and applied biomedical engineering.

One-Step Electrodeposition of NiCo2 S4 Nanosheets on Patterned Platinum Electrodes for Non-Enzymatic Glucose Sensing.

The preparation of NiCo2 S4 (NCS) nanosheets on photolithographically patterned platinum electrodes by electrodeposition was explored. The as-prepared nanosheets were systematically characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. The NCS-modified Pt electrode was used as a non-enzymatic glucose sensor. The sensor response exhibited two linear regions in glucose concentration, with a limit of detection of 1.2 µm. The sensors showed that the as-prepared NCS nanosheets have excellent electrocatalytic activity towards glucose with long stability, good reproducibility, and excellent anti-interference properties, and thus, this material holds promise for the development of a practical glucose sensor.

Optimizing the recovery of copper from electroplating rinse bath solution by hollow fiber membrane.

This study aimed to recover and remove copper from industrial model wastewater solution by non-dispersive solvent extraction (NDSX). Two mathematical models were developed to simulate the performance of an integrated extraction-stripping process, based on the use of hollow fiber contactors using the response surface method. The models allow one to predict the time dependent efficiencies of the two phases involved in individual extraction or stripping processes. The optimal recovery efficiency parameters were determined as 227 g/L of H2SO4 concentration, 1.22 feed/strip ratio, 450 mL/min flow rate (115.9 cm/min. flow velocity) and 15 volume % LIX 84-I concentration in 270 min by central composite design (CCD). At these optimum conditions, the experimental value of recovery efficiency was 95.88%, which was in close agreement with the 97.75% efficiency value predicted by the model. At the end of the process, almost all the copper in the model wastewater solution was removed and recovered as CuSO4.5H2O salt, which can be reused in the copper electroplating industry.

Electroaddressing of ZnS quantum dots by codeposition with chitosan to construct fluorescent and patterned device surface.

Electroaddressing is an attractive method for triggering assembly of stimuli-responsive biopolymers with exquisite spatiotemporal control, and it also offers a controllable means to concurrently assemble biological materials and nanoparticles for a diverse range of applications. Here, we demonstrate a novel method to construct fluorescent and patterned device surfaces by electroaddressing of quantum dots (QDs)/chitosan composite. First, the surfaces of ZnS QDs/chitosan composite on the electrodes are built by electrodeposition method. It is shown that the deposited surface displays clear fluorescence under UV light, and the fluorescence intensity of the surface can be controlled by electrodeposition conditions (e.g., deposition time). Furthermore, a variety of fluorescent patterns can be constructed by employing electrodes or substrates with various shapes. Specifically, taking advantage of the spatiotemporal selectivity of electroaddressing and the pH-responsive property of chitosan, we construct diverse fluorescent patterns by electroaddressing QDs/chitosan composite at the localized region. It is also found that the fluorescent patterns of QDs/chitosan composite have reproducibility. Thus, this work presents a convenient, versatile, and controllable method to construct fluorescent and patterned device surface by electroaddressing, which has promising applications in photoluminescence device, fluorescent and patterned coating, and nanocomposite biodevice.

Electrosprayed core-shell solid dispersions of acyclovir fabricated using an epoxy-coated concentric spray head.

A novel structural solid dispersion (SD) taking the form of core-shell microparticles for poorly water-soluble drugs is reported for the first time. Using polyvinylpyrrolidone (PVP) as a hydrophilic polymer matrix, the SDs were fabricated using coaxial electrospraying (characterized by an epoxy-coated concentric spray head), although the core fluids were unprocessable using one-fluid electrospraying. Through manipulating the flow rates of the core drug-loaded solutions, two types of core-shell microparticles with tunable drug contents were prepared. They had average diameters of 1.36±0.67 and 1.74±0.58 µm, and were essentially a combination of nanocomposites with the active ingredient acyclovir (ACY) distributed in the inner core, and the sweeter sucralose and transmembrane enhancer sodium dodecyl sulfate localized in the outer shell. Differential scanning calorimetry and X-ray diffraction results demonstrated that ACY, sodium dodecyl sulfate, and sucralose were well distributed in the PVP matrix in an amorphous state because of favorable second-order interactions. In vitro dissolution and permeation studies showed that the core-shell microparticle SDs rapidly freed ACY within 1 minute and promoted nearly eightfold increases in permeation rate across the sublingual mucosa compared with raw ACY powders.

Electrochemical and electrophoretic deposition of enzymes: principles, differences and application in miniaturized biosensor and biofuel cell electrodes.

Recent advances in nano-biotechnology have made it possible to realize a great variety of enzyme electrodes suitable for sensing and energy applications. In coating miniaturized electrodes with enzymes, there is no doubt that most of the available deposition processes suffer from the difficulty in depositing uniform and reproducible coatings of the active enzyme on the miniature transducer element. This mini-review highlights the promising prospects of two techniques, electrochemical deposition (ECD) and electrophoretic deposition (EPD), in enzyme immobilization onto miniaturized electrodes and their use as biosensors and biofuel cells. The main differences between ECD and EPD are described and highlighted in the sense to make it clear to the reader that both techniques employ electric fields to deposit enzyme but the conditions from which each process is achieved and hence the mechanisms are quite different. Many aspects dealing with deposition of enzyme under ECD and EPD are considered including surface charge of enzyme, its migration under the applied electric field and its precipitation on the electrode. Still all issues discussed in this mini-review are generic and need to be followed in the future by extensive theoretical and experimental research analysis. Finally, the advantages of ECD and EPD in fabrication of miniature biosensor and biofuel cell electrodes are described and discussed.

Hybrid helical magnetic microrobots obtained by 3D template-assisted electrodeposition.

Hybrid helical magnetic microrobots are achieved by sequential electrodeposition of a CoNi alloy and PPy inside a photoresist template patterned by 3D laser lithography. A controlled actuation of the microrobots by a rotating magnetic field is demonstrated in a fluidic environment.

Study on effect of plasma surface treatments for diamond deposition by DC arc plasmatron.

To improve the thermal conductivity and wear resistance of ceramic materials in the field of renewable energy technologies, diamond coating by plasma processing has been carried out in recent years. This study's goal is to improve diamond deposition on Al2O3 ceramic substrates by plasma surface treatments. Before diamond deposition was carried out in a vacuum, plasma surface treatments using Ar gas were conducted to improve conditions for deposition. We also conducted plasma processing for diamond deposition on Al2O3 ceramic substrates using a DC arc Plasmatron. The Al2O3 ceramic substrates with diamond film (5 x 15 mm2), were investigated by SEM (Scanning Electron Microscopy), AFM (Atomic Force Microscopy) and XRD (X-ray Diffractometer). Then, the C-H stretching of synthetic diamond films by FTIR (Fourier Transform Infrared Spectroscopy) was studied. We identified nanocrystalline diamond films on the Al2O3 ceramic substrates. The results showed us that the deposition rate of diamond films was 2.3 microm/h after plasma surface treatments. Comparing the above result with untreated ceramic substrates, the deposition rate improved with the surface roughness of the deposited diamond films.

Large-scale fabrication of 2-D nanoporous graphene using a thin anodic aluminum oxide etching mask.

A large-scale nanoporous graphene (NPG) fabrication method via a thin anodic aluminum oxide (AAO) etching mask is presented in this paper. A thin AAO film is successfully transferred onto a hydrophobic graphene surface under no external force. The AAO film is completely stacked on the graphene due to the van der Waals force. The neck width of the NPG can be controlled ranging from 10 nm to 30 nm with different AAO pore widening times. Extension of the NPG structure is demonstrated on a centimeter scale up to 2 cm2. AAO and NPG structures are characterized using optical microscopy (OM), Raman spectroscopy and field-emission scanning electron microscopy (FE-SEM). A field effect transistor (FET) is realized by using NPG. Its electrical characteristics turn out to be different from that of pristine graphene, which is due to the periodic nanostructures. The proposed fabrication method could be adapted to a future graphene-based nano device.

Capillary electrophoresis as a production tool for asymmetric microhybrids.

The site selective electrodeposition of silver metal onto a conducting object such as carbon microtubes (CMTs) in an electrolytic solution could be achieved by means of bipolar electrochemistry. Two half reactions are simultaneously carried out at both extremities of the CMT, which act as a bipolar electrode. The thermodynamic threshold value of the process, which consists in metal electroreduction and concomitant water oxidation is directly related to the length of CMT. That is the reason why, when scaling down the methodology to microscale objects, electric fields in the range of tenths of kilovolts per meter are necessary. In that context, a CE apparatus provides a convenient experimental platform to achieve in a straightforward manner such experimental conditions. We exemplify this methodology with the efficient and quick electroreduction of Ag⁺ on CMTs from a low-concentration aqueous electrolytic solution during the migration across a fused capillary. CE allows applying safely a large enough electric field (typically ∼30 kV/m) for the successful modification of 15 to 20 µm-long substrates. The corresponding hybrid materials have been characterized by optical microscopy as well as SEM and energy-dispersive X-ray spectroscopy.

Simple, rapid and green one-step strategy to synthesis of graphene/carbon nanotubes/chitosan hybrid as solid-phase extraction for square-wave voltammetric detection of methyl parathion.

Simple, rapid, green and one-step electrodeposition strategy was first proposed to synthesis of graphene/carbon nanotubes/chitosan (GR/CNTs/CS) hybrid. The one-step electrodeposition approach for the construction of GR-based hybrid is green environmentally, which would not involve the chemical reduction of graphene oxide (GO) and therefore result in no further contamination. The whole procedure is simple and needs only several minutes. Combining the advantages of GR (large surface area, high conductivity and good adsorption ability), CNTs (high surface area, high enrichment capability and good adsorption ability) and CS (good adsorption and excellent film-forming ability), the obtained GR/CNTs/CS composite could be highly efficient to capture organophosphate pesticides (OPs) and used as solid phase extraction (SPE). The GR/CNTs/CS sensor is used for enzymeless detection of OPs, using methyl parathion (MP) as a model analyte. Significant redox response of MP on GR/CNTs/CS sensor is proved. The linear range is wide from 2.0ngmL(-1) to 500ngmL(-1), with a detection limit of 0.5ngmL(-1). Detection limit of the proposed sensor is much lower than those enzyme-based sensors and many other enzymeless sensors. Moreover, the proposed sensor exhibits high reproducibility, long-time storage stability and satisfactory anti-interference ability. This work provides a green and one-step route for the preparation of GR-based hybrid, and also offers a new promising protocol for OPs analysis.

Online in-tube microextractor coupled with UV-Vis spectrophotometer for bisphenol A detection.

A simple and high extraction efficiency online in-tube microextractor (ITME) was developed for bisphenol A (BPA) detection in water samples. The ITME was fabricated by a stepwise electrodeposition of polyaniline, polyethylene glycol and polydimethylsiloxane composite (CPANI) inside a silico-steel tube. The obtained ITME coupled with UV-Vis detection at 278 nm was investigated. By this method, the extraction and pre-concentration of BPA in water were carried out in a single step. Under optimum conditions, the system provided a linear dynamic range of 0.1 to 100 µM with a limit of detection of 20 nM (S/N ≥3). A single in-tube microextractor had a good stability of more than 60 consecutive injections for 10.0 µM BPA with a relative standard deviation of less than 4%. Moreover, a good tube-to-tube reproducibility and precision were obtained. The system was applied to detect BPA in water samples from six brands of baby bottles and the results showed good agreement with those obtained from the conventional GC-MS method. Acceptable percentage recoveries from the spiked water samples were obtained, ranging from 83-102% for this new method compared with 73-107% for the GC-MS standard method. This new in-tube CPANI microextractor provided an excellent extraction efficiency and a good reproducibility. In addition, it can also be easily applied for the analysis of other polar organic compounds contaminated in water sample.

Effect of solution conductivity and electrode shape on the deposition of carbon nanotubes from solution using dielectrophoresis.

Dielectrophoresis (DEP) is a popular technique for fabricating carbon nanotube (CNT) devices. The electric current passing through the solution during DEP creates a temperature gradient, which results in electrothermal fluid flow because of the presence of the electric field. CNT solutions prepared with various methods can have different conductivities and the motion of the solution because of the electrothermal phenomenon can affect the DEP deposition differently in each case. We investigated the effect of this movement in solutions with various levels of conductivity through experiments as well as numerical modeling. Our results show that electrothermal motion in the solution can alter the deposition pattern of the nanotubes drastically for high conductivity solutions, while DEP remains the dominant force when a low conductivity (surfactant-free) solution is used. The extent of effectiveness of each force is discussed in the various cases and the fluid movement model is investigated using two- and three-dimensional finite element simulations.