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The targeted diagnosis and effective treatments of chronic skin wounds remain a healthcare burden, requiring the development of sensors for real-time monitoring of wound healing activity. Herein, we describe an adaptable method for the fabrication of carbon ultramicroelectrode arrays (CUAs) on flexible substrates with the goal to utilize this sensor as a wearable device to monitor chronic wounds. As a proof-of-concept study, we demonstrate the electrochemical detection of three electroactive analytes as biomarkers for wound healing state in simulated wound media on flexible CUAs. Notably, to follow pathogenic responses, we characterize analytical figures of merit for identification and monitoring of bacterial warfare toxin pyocyanin (PYO) secreted by the opportunistic human pathogen Pseudomonas aeruginosa . We also demonstrate the detection of uric acid (UA) and nitric oxide (NO • ), which are signaling molecules indicative of wound healing and immune responses, respectively. The electrochemically determined limit of detection (LOD) and linear dynamic range (LDR) for PYO, UA, and NO • fall within the clinically relevant concentrations. Additionally, we demonstrate the successful use of flexible CUAs for quantitative, electrochemical detection of PYO from P. aeruginosa strains and cellular NO • from immune cells in the wound matrix. Moreover, we present an electrochemical examination of the interaction between PYO and NO • , providing insight into pathogen-host responses. Finally, the effects of the antimicrobial agent, silver (Ag + ), on P. aeruginosa PYO production rates are investigated on flexible CUAs. Our electrochemical results show that the addition of Ag + to P. aeruginosa in wound simulant decreases PYO secretion rates.

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdO x /PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl 4 2- ions and a nanostructured film of electropolymerized PEDOT. Spectroscopic and electrochemical characterization indicate the presence of mixed-valence Pd species as-deposited (19 ± 7 at% Pd 0 , 64 ± 3 at% Pd 2+ , and 18 ± 4 at% Pd 4+ by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd 0 /α-PdO x active species in alkaline electrolyte and furthermore in the presence of oxygen. The elucidation of the Pd speciation as-deposited and in solution provides insight into the mechanism of electroless deposition in neutral aqueous conditions and the electrocatalytically active species during oxygen reduction in alkaline electrolyte. The PdO x /PEDOT film catalyses 4e - oxygen reduction ( n = 3.97) in alkaline electrolyte at low overpotential (0.98 V vs. RHE, onset potential), with mass- and surface area-based specific activities competitive with, or superior to, commercial 20% Pt/C and state-of-the-art Pd- and PEDOT-based nanostructured catalysts. The high activity of the nanostructured hybrid PdO x /PEDOT film is attributed to effective dispersion of accessible, stable Pd active sites in the PEDOT matrix., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Carbon-coated α-MnO 2 nanowires (C-MnO 2 NWs) were prepared from α-MnO 2 NWs by a two-step sucrose coating and pyrolysis method. This method resulted in the formation of a thin, porous, low mass-percentage amorphous carbon coating (<5 nm, ≤1.2 wt % C) on the nanowire with an increase in single-nanowire electronic conductivity of roughly 5 orders of magnitude (α-MnO 2 , 3.2 × 10 -6 S cm -1 ; C-MnO 2 , 0.52 S cm -1 ) and an increase in surface Mn 3+ (average oxidation state: α-MnO 2 , 3.88; C-MnO 2 , 3.66) while suppressing a phase change to Mn 3 O 4 at high temperature. The enhanced physical and electronic properties of the C-MnO 2 NWs-enriched surface Mn 3+ and high conductivity-are manifested in the electrocatalytic activity toward the oxygen reduction reaction (ORR), where a 13-fold increase in specific activity (α-MnO 2 , 0.13 A m -2 ; C-MnO 2 , 1.70 A m -2 ) and 6-fold decrease in charge transfer resistance (α-MnO 2 , 6.2 kΩ; C-MnO 2 , 0.9 kΩ) were observed relative to the precursor α-MnO 2 NWs. The C-MnO 2 NWs, composed of ∼99 wt % MnO 2 and ∼1 wt % carbon coating, also demonstrated an ORR onset potential within 20 mV of commercial 20% Pt/C and a chronoamperometric current/stability equal to or greater than 20% Pt/C at high overpotential (0.4 V vs RHE) and high temperature (60 °C) with no additional conductive carbon.

Transparent carbon ultramicroelectrode arrays (T-CUAs) were made using a previously reported facile fabrication method (Duay et al. Anal. Chem. 2015, 87, 10109). Two modifications introduced to the T-CUAs were examined for their analytical response to nitric oxide (NO • ). The first modification was the application of a cellulose acetate (CA) gas permeable membrane. Its selectivity to NO • was extensively characterized via chronoamperometry, electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). The thickness of the CA membrane was determined to be 100 nm and 88 ± 15 nm using AFM and EIS, respectively. Furthermore, the partition and diffusion coefficients of NO • within the CA membrane were determined to be 0.0500 and 2.44 × 10 -13 m 2 /s using EIS measurements. The second modification to the 1.54T-CUA was the introduction of chitosan and gold nanoparticles (CS/GNPs) to enhance its catalytic activity, sensitivity, and limit of detection (LOD) to NO • . Square wave voltammetry was used to quantify the NO • concentration at the CA membrane covered 1.54T-CUA with and without CS/GNPs; the LODs were determined to be 0.2 ± 0.1 and 0.44 ± 0.02 μM (S/N = 3), with sensitivities of 9 ± 9 and 1.2 ± 0.4 nA/μM, respectively. Our results indicate that this modification to the arrays results in a significant catalytic enhancement to the electrochemical oxidation of NO • . Hence, these electrodes allow for the in situ mechanistic and kinetic characterization of electrochemical reactions with high electroanalytical sensitivity.

A high-resolution in situ spectroelectrochemical optical diffraction experiment has been developed to understand the volume expansion/contraction process of amorphous silicon (a-Si) thin-film anodes. Electrodes consisting of 1D transmissive gratings of silicon have been produced through photolithographic methods. After glovebox assembly in a home-built Teflon cell, monitoring of the diffraction efficiency of these gratings during the lithiation/delithiation process is performed using an optical microscope equipped with a Bertrand lens. When the diffraction efficiency along with optical constants obtained from in situ spectroscopic ellipsometry is utilized, volume changes of the active materials can be deduced. Unlike transmission electron microscopy and atomic force microscopy characterization methods of observing silicon's volume expansion, this experiment allows for real-time monitoring of the volume change at charge/discharge cycles greater than just the first few along with an experimental environment that directly mimics that of a real battery. This technique shows promising results that provide needed insight into understanding the lithium alloying reaction and subsequent induced capacity fade during the cycling of alloying anodes in lithium-ion batteries.

Opaque and transparent carbon ultramicro- to nanoelectrode arrays were made using a previously reported facile versatile fabrication method (Duay et al. Anal. Chem. 2014, 86, 11528). First, opaque carbon ultramicroelectrode arrays (CUAs) were characterized for their analytical response to hydrogen peroxide (H2O2) oxidation using cyclic voltammetry. The alumina blocking layer was found to contribute to the noise and thus had undesirable effects on the array's limit of detection (LOD) for H2O2 at fast scan rates. Nonetheless, at slower scan rates (ν ≤ 250 mV s(-1)), the LODs for H2O2 for both opaque (O-CUAs) and transparent arrays (T-CUAs) were found to be lower than previously reported levels for array-based UMEs. LODs as low as 35 nM H2O2 are obtained for T-CUA at a 2.5 mV s(-1) scan rate. Furthermore, the transparent arrays were analyzed for their spectroelectrochemical response during the oxidation/reduction of ferrocenemethanol. Results showed very good correlation between the optical and electrochemical response for ferrocenemethanol at a UV wavelength of 254 nm. Thus, these electrodes allow for the in situ mechanistic and kinetic characterization of heterogeneous electrochemical and intermediate homogeneous chemical reactions with high electroanalytical sensitivity, low detection limits, and wide dynamic range.

A wide range of metal oxides have been studied as pseudocapitors, with the goal of achieving higher power than traditional batteries and higher energy than traditional capacitors. However, most metal oxides have relatively low conductivity, and the few exceptions, like RuO2, are prohibitively expensive. Mixed metal oxides provided an opportunity to incorporate small amounts of expensive materials to enhance the performance of a less expensive, poorer performing material. Here, by homogeneously co-depositing a small amount of energy dense and conductive RuO2 into MnO2 nanowires, we demonstrate an improvement in specific capacitance. Importantly, we also demonstrate that this improvement is not primarily provided by redox activity of RuO2, but rather by improvement of the composite conductivity. A series of RuO2-MnO2 composite nanowires with different RuO2 loading percentages have been synthesized by performing co-electrodeposition in a porous alumina template. The structure of these RuO2-MnO2 nanowires is characterized by TEM and SEM. EDS mapping shows that RuO2 is well distributed in MnO2 matrix nanowires. The chemical constituents and the phase of these composite nanowires are confirmed by X-ray photoelectron and Raman spectroscopy. The amount of RuO2 is controlled by varying the concentrations of RuCl3 and MnAc2 in the deposition solution. The precise masses of MnO2 and RuO2 are determined by ICP-AES elemental analysis. MnO2 nanowires with 6.70 wt% RuO2 demonstrate a specific capacitance of 302 F g(-1) at 20 mV s(-1), compared to 210 F g(-1) for pristine MnO2 nanowires. Investigation of the RuO2 loading amount effect was conducted by electrochemical impedance spectroscopy (EIS) and deconvolution of capacitances, using methods previously reported by both Dunn and Transsiti. The RuO2-MnO2 nanowires studied here demonstrate a simple, straighforward method to overcome the intrinsically poor conductivity of MnO2, and clarify the source of RuO2's contribution to the improved performance.

Magnesium batteries have been considered to be one of the promising beyond lithium ion technologies due to magnesium's abundance, safety, and high volumetric capacity. However, very few materials show reversible performance as a cathode in magnesium ion systems. We present herein the best reported cycling performances of MnO2 as a magnesium battery cathode material. We show that the previously reported poor Mg(2+) insertion/deinsertion capacities in MnO2 can be greatly improved by synthesizing self-standing nanowires and introducing a small amount of water molecules into the electrolyte. Electrochemical and elemental analysis results revealed that the magnitude of Mg(2+) insertion into MnO2 highly depends on the ratio between water molecules and Mg(2+) ions present in the electrolyte and the highest Mg(2+) insertion capacity was observed at a ratio of 6H2O/Mg(2+) in the electrolyte. We demonstrate for the first time, that MnO2 nanowire electrode can be "activated" for Mg(2+) insertion/deinsertion by cycling in water containing electrolyte resulting in enhanced reversible Mg(2+) insertion/deinsertion even with the absence of water molecules. The MnO2 nanowire electrode cycled in dry Mg electrolyte after activation in water-containing electrolyte showed an initial capacity of 120 mA h g(-1) at a rate of 0.4 C and maintained 72% of its initial capacity after 100 cycles.

The voltammetric response for nano- to micrometer-sized electrode arrays are represented by two major regimes: a sigmoidal shaped i-v response for arrays acting as individual electrodes in parallel and peak-shaped i-v response for arrays acting as an ensemble in concert. Here, we present a facile and versatile technique to fabricate ultramicro- to nanoelectrode arrays using atomic layer deposition of insulating Al2O3 on conductive carbon films masked by 1.54, 11, or 90-μm-diameter polystyrene spheres (PSS). The ratio between the interelectrode distance and the electrode radii of the electrode arrays is a predictable function of the PSS radius used in fabrication, resulting in electrode arrays with a tunable voltammetric response. Arrays are characterized utilizing cyclic voltammetry and electrochemical impedance spectroscopy, which provides the critical scan rate, νcrit, the scan rate at which the radial diffusion layers of the individual electrodes overlap and appear as a single linear diffusion layer. Thus, below ν(crit), the electrode has a peak-shaped i-v response associated with semi-infinite linear diffusion, whereas above this critical scan rate, the i-v response is sigmoidal as a result of hemispherical radial diffusion. Results indicate that the critical scan rates are 6.6, 1.0, and 0.01 V/s for the 1.54, 11, and 90 μm PSS prepared electrode arrays, respectively.

MnO2 as a material for supercapacitors is generally predicted to insert only one cation per unit cell. However, it is shown here to reversibly insert more than one cation in an organic electrolyte; however, in an aqueous electrolyte, the insertion ion is actually shown to be a combination of protons and cations.

A redox exchange mechanism between potassium perruthenate (KRuO4) and the functional groups of selected polymers is used here to induce RuO2 into and onto conductive polymer nanowires by simply soaking the polymer nanowire arrays in KRuO4 solution. Conductive polymer nanowire arrays of polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT) were studied in this work. SEM and TEM results show that the RuO2 material was distributed differently in the PPY and PEDOT nanowire matrices. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were used to confirm the dispersion and formation of RuO2 materials in these polymer nanowires. Cyclic voltammetry and galvanostatic charge-discharge experiments were used to characterize their electrochemical performance. RuO2-polymer samples prepared with a 6 min soaking time in 10 mM KRuO4 solution show a high specific capacitance of 371 F g(-1) and 500 F g(-1) for PEDOT-based and PPY-based composite nanowires, respectively. This is attributed to the high exposure area of the conductive RuO2 and the good conductivity of the polymer matrix. This work demonstrates a simple method to synthesize heterogeneous polymer based-materials through the redox reaction between conductive polymers and high oxidation state transition metal oxide ions. Different heterogeneous nanocomposites were obtained depending on the polymer properties, and high energy storage performance of the metal oxides can be achieved within these heterogeneous nanostructures.

A review of electrochemically synthesized nanomaterials with different controllable architectures for electrochemical energy storage devices is shown. It is demonstrated that these nano-architectures can be created either by electrodeposition or by the electrochemical transformation of materials. Electrochemical synthesis is presented here as it provides intimate contact between the electrode and current collector and also promotes an electronic pathway for all materials to be connected to the circuit. Although still in their infancy, electrosynthesized nano-architectures show promise to be used in future electrochemical energy storage devices as utilization of this method bypasses the need for bulky conductive additives and electrochemically inactive binders. Furthermore, electrochemical transformations can be used to create additional architectural features or change the chemical make-up of the electrode. This review is meant to show the creativity of current science when it comes to these nano-architectured electrodes. It is organized by technique used for synthesis including hard template, soft template, and template-free synthesis along with electrochemical transformation techniques.

Hierarchical nanostructures have generated great interest in the energy, materials, and chemical sciences due to the synergic properties of their composite architectures. Herein, a hierarchical MnO₂ nanofibril/nanowire array is successfully synthesized. The structure consists of a conformal layer of MnO₂ nanofibrils evenly distributed on the surface of the individual MnO₂ nanowires. The synthetic mechanism of this hierarchical structure is characterized by electrochemical measurements, Raman spectroscopy, EELS, and electron microscopy. This material was then investigated at slow scan rates for its charge storage mechanisms in different solvents. In aqueous electrolyte, the nanofibrils show a capacitance almost purely dedicated to double-layer and surface adsorption processes, while in an acetonitrile electrolyte, the nanofibrils' capacitance comes mainly from a cation insertion process. This material was also tested at high scan rates in aqueous solution for its practical supercapacitor capabilities. The material shows a large capacitance of 298 F/g at 50 mV/s and 174 F/g at 250 mV/s. It also maintains 85.2% of its capacitance after 1000 cycles. The material also displays easily controllable parameters such as nanowire length, nanowire diameter, and amount of nanofibril material which is shown here to affect the capacitance dramatically.

Flexible electronics such as wearable electronic clothing, paper-like electronic devices, and flexible biomedical diagnostic devices are expected to be commercialized in the near future. Flexible energy storage will be needed to power these devices. Supercapacitor devices based on freestanding nanowire arrays are promising high power sources for these flexible electronics. Electrodes for these supercapacitor devices consisting of heterogeneous coaxial nanowires of poly (3,4-ethylenedioxythiophene) (PEDOT)-shell and MnO(2)-core materials have been shown in a half cell system to have improved capacitance and rate capabilities when compared to their pure nanomaterials; however, their performance in a full cell system has not been fully investigated. Herein, these coaxial nanowires are tested in both a symmetric and an asymmetric (utilizing a PEDOT nanowire anode) full cell configuration in the aspect of charge storage, charge rate, and flexibility without using any carbon additives and polymer binders. It is found that the asymmetric cell outperforms the symmetric cell in terms of energy density, rate capability, and cycle ability. The asymmetric device's electrode materials display an energy density of 9.8 Wh/kg even at a high power density of 850 W kg(-1). This device is highly flexible and shows fast charging and discharging while still maintaining 86% of its energy density even under a highly flexed state. The total device is shown to have a total capacitance of 0.26 F at a maximum voltage of 1.7 V, which is capable of providing enough energy to power small portable devices.

MnO(2)/TiN nanotubes are fabricated using facile deposition techniques to maximize the surface area of the electroactive material for use in electrochemical capacitors. Atomic layer deposition is used to deposit conformal nanotubes within an anodic aluminium oxide template. After template removal, the inner and outer surfaces of the TiN nanotubes are exposed for electrochemical deposition of manganese oxide. Electron microscopy shows that the MnO(2) is deposited on both the inside and outside of TiN nanotubes, forming the MnO(2)/TiN nanotubes. Cyclic voltammetry and galvanostatic charge-discharge curves are used to characterize the electrochemical properties of the MnO(2)/TiN nanotubes. Due to the close proximity of MnO(2) with the highly conductive TiN as well as the overall high surface area, the nanotubes show very high specific capacitance (662 F g(-1) reported at 45 A g(-1)) as a supercapacitor electrode material. The highly conductive and mechanically stable TiN greatly enhances the flow of electrons to the MnO(2) material, while the high aspect ratio nanostructure of TiN creates a large surface area for short diffusion paths for cations thus improving high power. Combining the favourable structural, electrical and energy properties of MnO(2) and TiN into one system allows for a promising electrode material for supercapacitors., (This journal is © the Owner Societies 2011)

The formation mechanism of a coaxial manganese oxide/poly(3,4-ethylenedioxythiophene) (MnO(2)/PEDOT) nanowire is elucidated herein by performing electrodeposition of MnO(2) and PEDOT on Au-sputtered nanoelectrodes with different shapes (ring and flat-top, respectively) within the 200 nm diameter pores of an anodized aluminum oxide (AAO) template. It is found that PEDOT prefers to grow on the sharp edge of the ring-shaped electrode, while MnO(2) is more likely to deposit on the flat-top electrode due to its smooth surface. The formation of coaxial nanowires is shown to be a result of simultaneous growth of core MnO(2) and shell PEDOT by an analysis of the current density resulting from electrochemical deposition. Furthermore, the structures of the MnO(2)/PEDOT coaxial nanowires were studied for their application as supercapacitors by modifying their coelectrodeposition potential. A potential of 0.70 V is found to be the most favorable condition for synthesis of MnO(2)/PEDOT coaxial nanowires, resulting in a high specific capacitance of 270 F/g. Additionally, other heterogeneous MnO(2)/PEDOT nanostructures are produced, such as nanowires consisting of MnO(2) nanodomes with PEDOT crowns as well as segmented MnO(2)/PEDOT nanowires. This is accomplished by simply adjusting the parameters of the electrochemical deposition. Finally, in smaller diameter (50 nm) AAO channels, MnO(2) and PEDOT are found to be partially assembled into coaxial nanowires due to the alternative depletion of Mn(II) ions and EDOT monomers in the smaller diameter pores.

In order to fulfil the future requirements of electrochemical energy storage, such as high energy density at high power demands, heterogeneous nanostructured materials are currently studied as promising electrode materials due to their synergic properties, which arise from integrating multi-nanocomponents, each tailored to address a different demand (e.g., high energy density, high conductivity, and excellent mechanical stability). In this article, we discuss these heterogeneous nanomaterials based on their structural complexity: zero-dimensional (0-D) (e.g. core-shell nanoparticles), one-dimensional (1-D) (e.g. coaxial nanowires), two-dimensional (2-D) (e.g. graphene based composites), three-dimensional (3-D) (e.g. mesoporous carbon based composites) and the even more complex hierarchical 3-D nanostructured networks. This review tends to focus more on ordered arrays of 1-D heterogeneous nanomaterials due to their unique merits. Examples of different types of structures are listed and their advantages and disadvantages are compared. Finally a future 3-D heterogeneous nanostructure is proposed, which may set a goal toward developing ideal nano-architectured electrodes for future electrochemical energy storage devices.

MnO2 nanoparticle enriched poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires are fabricated by simply soaking the PEDOT nanowires in potassium permanganate (KMnO4) solution. The structures of these MnO2 nanoparticle enriched PEDOT nanowires are characterized by SEM and TEM, which show that the MnO2 nanoparticles have uniform sizes and are finely dispersed in the PEDOT matrix. The chemical constituents and bonding of these composite nanowires are characterized by energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and infrared spectroscopy, which indicate that the formation and dispersion of these MnO2 nanoparticles into the nanoscale pores of the PEDOT nanowires are most likely triggered by the reduction of KMnO4 via the redox exchange of permanganate ions with the functional group on PEDOT. Varying the concentrations of KMnO4 and the reaction time controls the loading amount and size of the MnO2 nanoparticles. Cyclic voltammetry and galvanostatic charge-discharge are used to characterize the electrochemical properties of these MnO2 nanoparticle loaded PEDOT nanowires. Due to their extremely high exposed surface area with nanosizes, the pristine MnO2 nanoparticles in these MnO2 nanoparticle enriched PEDOT nanowires show very high specific capacitance (410 F/g) as the supercapacitor electrode materials as well as high Li+ storage capacity (300 mAh/g) as cathode materials of Li ion battery, which boost the energy storage capacity of PEDOT nanowires to 4 times without causing excessive volume expansion in the polymer. The highly conductive and porous PEDOT matrix facilitates fast charge/discharge of the MnO2 nanoparticles and prevents them from agglomerating. These synergic properties enable the MnO2 nanoparticle enriched PEDOT nanowires to be promising electrode materials for supercapacitors and lithium ion batteries.

We report the synthesis of composite RuO(2)/poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes with high specific capacitance and fast charging/discharging capability as well as their potential application as electrode materials for a high-energy and high-power supercapacitor. RuO(2)/PEDOT nanotubes were synthesized in a porous alumina membrane by a step-wise electrochemical deposition method, and their structures were characterized using electron microscopy. Cyclic voltammetry was used to qualitatively characterize the capacitive properties of the composite RuO(2)/PEDOT nanotubes. Their specific capacitance, energy density and power density were evaluated by galvanostatic charge/discharge cycles at various current densities. The pseudocapacitance behavior of these composite nanotubes originates from ion diffusion during the simultaneous and parallel redox processes of RuO(2) and PEDOT. We show that the energy density (specific capacitance) of PEDOT nanotubes can be remarkably enhanced by electrodepositing RuO(2) into their porous walls and onto their rough internal surfaces. The flexible PEDOT prevents the RuO(2) from breaking and detaching from the current collector while the rigid RuO(2) keeps the PEDOT nanotubes from collapsing and aggregating. The composite RuO(2)/PEDOT nanotube can reach a high power density of 20 kW kg(-1) while maintaining 80% energy density (28 Wh kg(-1)) of its maximum value. This high power capability is attributed to the fast charge/discharge of nanotubular structures: hollow nanotubes allow counter-ions to readily penetrate into the composite material and access their internal surfaces, while a thin wall provides a short diffusion distance to facilitate ion transport. The high energy density originates from the RuO(2), which can store high electrical/electrochemical energy intrinsically. The high specific capacitance (1217 F g(-1)) which is contributed by the RuO(2) in the composite RuO(2)/PEDOT nanotube is realized because of the high specific surface area of the nanotubular structures. Such PEDOT/RuO(2) composite nanotube materials are an ideal candidate for the development of high-energy and high-power supercapacitors.