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This Article reports methods to deposit iridium oxide nanoparticles (IrOx NPs) onto flexible materials for charge storage and the stable charge–discharge mechanism. In this work, IrOx NPs were elec...

In this Article, we report a coulometric sensing platform that is capable of sensing analytes on a working electrode and providing a visual readout of the analyte concentration on a silver (Ag) band counter electrode in a microchannel. The display mechanism relies on the electro-oxidation of metallic Ag as a complementary reaction to the sensing reduction reaction. The Ag band counter electrode is arranged longitudinally in a microchannel while the frontal tip of the band electrode directly faces a gold (Au) working electrode, which lies across the microchannel. The Ag oxidation always occurs at the band electrode's tip region that faces the working electrode due to the Ohmic potential drop across the solution in the microchannel. The decrement of the Ag electrode, which is clearly measurable with the naked eye, correlates linearly with an analyte concentration (e.g., 0.1-2.5 mM p-benzoquinone) and with an analyte feeding rate (i.e., a sample solution flow rate of 1.0-75.0 μL min(-1)). The platform design is also effective for a model analyte of horseradish peroxidase (HRP)-avidin in the dynamic range of 0.1-3.0 μg mL(-1).

In this presentation, we report a battery-powered distance-based electrochemical sensor that can be operated without the need for laboratory-based instruments. This sensing platform can effectively convert an electrochemical current from a sensing reaction to a visual signal that is identifiable as the length of the silver band electrode (Ag BE). As presently configured, the electrochemical sensing reaction occurs when the working electrode triggers the electro-oxidation of the Ag on the Ag BE, which causes the Ag BE to shorten due to oxidation. The key advantage of this new sensor is that it can be operated using a two-electrode system, which allows this sensing platform to operate using only two AA batteries as the power source. We suggest this approach as a conceptual pathway that can lead to instrument-free distance-based electrochemical sensor design.

Here we report a battery-powered distance-based electrochemical sensor that can be operated without the need for laboratory-based instruments. This sensing platform can effectively convert an electrochemical current from a sensing reaction to a visual signal that is identifiable as the length of the silver band electrode (Ag BE). As presently configured, the electrochemical sensing reaction occurs when the working electrode triggers the electro-oxidation of the Ag on the Ag BE, which causes the Ag BE to shorten due to oxidation. Previously, we demonstrated that the resultant length of the Ag BE directly correlates with electrochemical species in analyte solution using a three-electrode system Oh and Chow (2016). Compared to our previously reported distance-based electrochemical sensor, the key advantage of this new sensor is that it can be operated using a two-electrode system, which allows this sensing platform to operate using only two AA batteries as the power source. We suggest this approach as a conceptual pathway that can lead to instrument-free distance-based electrochemical sensor design.

This article describes an electrochemical method to remove bacterial biofilm from a stainless steel (SS) surface using a potential pulse/reverse pulse technique. This technique employs a periodic waveform that consists of anodic and cathodic pulses. The pulses can effectively strip a thin layer of metal off the SS surface, along with the adherent biofilm, in a saline solution. Not only can the pulses effectively remove biofilm from the SS surface, but they also regenerate the original mirror-like shiny surface. The importance of this electrochemical biofilm removal method is its wide applicability for any types of biofilms. That is, instead of directly removing the biofilm, it removes a very thin layer of the metal under the biofilm. Thus, the removal process is independent to the nature of the biofilms. Furthermore, this electrochemical biofilm removal method is rapid (less than 30 s of potential pulse time) and does not require hazardous chemicals.

Research into electrochemical sensing in paper devices has increased dramatically in the past few years because electrochemical methods allow sensitive, selective, and quantitative detection once incorporated into paper devices. This article provides a mini-review on recent advances in electrochemical paper-based analytical devices (PADs) that have been reported within the past 36 months. Specifically, this review discusses the recently reported PAD formats that have been successfully adapted into electrochemical sensing devices employing classic electrochemical concepts and methods. The electrochemical techniques coupled to those PADs include cyclic voltammetry, amperometry, coulometry, and potentiometry. The electrochemical systems employed by those PADs involve microelectrodes, convective mass transfer, surface-modified electrodes, flow injection, signal amplification, ion-selective electrodes, and ion-exchange membranes, respectively. This mini-review discusses general aspects of the aforementioned methods and the resulting electrochemical PADs.

Nanostructured, high-surface-area carbon electrodes have large electrochemical double-layer capacitances compared to smooth-surfaced electrodes because of their enhanced internal surface areas, e.g., several hundred m2g–1. In the present work, we demonstrate that the electrical capacitance of carbon “nanofoams”, both in commercially available forms and as prepared by the authors, can be significantly enhanced by the insertion into their pores of small Au nanoparticles (∼2 nm diameter core) to whose surfaces are bonded ferrocenyl-hexane thiolate ligands (SC6Fc) (>40 per nanoparticle). The enhanced capacitive behavior of the modified nanoporous carbon (in CH3CN or CH2Cl2 with 1.0 or 2.0 M Bu4NPF6 as the supporting electrolyte) is clearly seen in their cyclic voltammetric responses and is attributed to a combination of the ferrocene redox-capacity and the double-layer capacity of the intercalated nanoparticles. Footprint-normalized, volume-normalized, and gravimetric-normalized integral capacitances of 0.28 ...

The electronic conductivity of films of iridium oxide (IrO(x)) composed of ca. 2 nm nanoparticles (NPs) is strongly dependent on the film oxidation state. The Ir(IV)O(x) NPs can be electrochemically converted to several oxidation states, ranging from Ir(III) to Ir(V) oxides. The NP films exhibit a very high apparent conductivity, e.g., 10(-2) S cm(-1), when the NPs are in the oxidized +4/+5 state. When the film is fully reduced to its Ir(III) state, the apparent conductivity falls to 10(-6) S cm(-1).

Here we report a simple design philosophy, based on the principles of bipolar electrochemistry, for the operation of microelectrochemical integrated circuits. The inputs for these systems are simple voltage sources, but because they do not require much power they could be activated by chemical or biological reactions. Device output is an optical signal arising from electrogenerated chemiluminescence. Individual microelectrochemical logic gates are described first, and then multiple logic circuits are integrated into a single microfluidic channel to yield an integrated circuit that can perform parallel logic functions. AND, OR, NOR, and NAND gates are described. Eventually, systems such as those described here could provide on-chip data processing functions for lab-on-a-chip devices.

In this paper, we report a new electroanalytical technique we call snapshot voltammetry. This method combines the properties of bipolar electrodes with electrogenerated chemiluminescence (ECL) to provide a means for recording optical voltammograms in a single micrograph. In essence, the information in a snapshot voltammogram is contained in the spatial domain rather than in the time domain, which is the case for conventional voltammetry. The use of a triangle-shaped bipolar electrode stabilizes the interfacial potential difference along its length. Basic electrochemical parameters extracted from snapshot voltammograms are in good agreement with those obtained by conventional voltammetry. Although not explicitly demonstrated in this paper, this method offers the possibility of using arrays of bipolar electrodes to obtain numerous snapshot voltammograms simultaneously.

Bipolar electrodes are potentially useful for a variety of sensing applications, but their implementation has been hampered by an inability to easily monitor the current through such electrodes. However, current can be indirectly determined using electrogenerated chemiluminescence (ECL) as a reporting mechanism. This paper provides a detailed theoretical analysis of ECL reporting at bipolar electrodes. In addition, experiments are described that confirm the theory. Finally, we correlate ECL intensity directly to current through the use of split bipolar electrodes. The results indicate that the lowest current that can be indirectly detected through ECL reporting is ∼32 μA/cm2, which corresponds to a reporting sensitivity of ∼7200 counts/nA in the present experimental system.

Sol–gel films doped with fluorescein (FL) and phenol red (PR) dyes were evaluated for their responses to ammonia gas. In a steady state, the sensors respond to the gas-phase ammonia evolved from ammonium hydroxide solutions in the range of 5 × 10−6 to 0.05 M for FL-doped gels, and 10−4 to 1 M for PR-doped gels. The sensors have high selectivity for ammonia against larger amines and moderate selectivity against methyl and ethylamines. The FL-gel exhibits rapid and reproducible response to dry NH3 gas samples of 9–50 ppm, while PR-gel is insensitive to ammonia in this low concentration range. The life-times of the sensors are over a year.

A dye doped sol–gel for the sensing of hydrochloric acid in solution and/or gaseous phase is described. The sol–gel is obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS) in the presence of phenol red (PR) and further spin-coating onto glass slides. The sensitive response is based on an increase of the absorption band at 510 nm of phenol red entrapped in the sol–gel casting when exposed to HCl solution or gas, due to protonation of the dye. The detection limit of the sol–gel response to moisturized gaseous HCl is below 12 ppm, and its response to HCl in solution falls in the range of 0.01–6 M. The sol–gel coating has a response time of less than 40 s in steady-state, and life-time of more than a year. Weak acids such as acetic acid, benzoic acid, salicylate acid, citrate acid, and carbonic acid do not interfere the response. The responses in acid solutions are completely reversible. In the gaseous phase, response of HCl appears to be moisture sensitive.

Long lasting and fast response optical sensor for the detection of pH in the range of 6–12 is described. The sensor is fabricated by spin coating silica sol in the presence of phenol red (PR). The sol is in turn obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS). The performance of the sensor depends on the ratio of Ph-TriOES to TEOS. At the optimal composition, the sensor has a response time of less than 20 s, the response is completely reversible and its life-time is over 12 months.

Over the past decade, bipolar electrochemistry has emerged from relative obscurity to provide a promising new means for integrating electrochemistry into lab-on-a-chip systems. This article describes the fundamental operating principles of bipolar electrodes, as well as several interesting applications.

We report a microelectrochemical array composed of 1000 individual bipolar electrodes that are controlled with just two driving electrodes and a simple power supply. The system is configured so that faradaic processes occurring at the cathode end of each electrode are correlated to light emission via electrogenerated chemiluminescence (ECL) at the anode end. This makes it possible to read out the state of each electrode simultaneously. The significant advance is that the electrode array is fabricated on a glass microscope slide and is operated in a simple electrochemical cell. This eliminates the need for microfluidic channels, provides a fabrication route to arbitrarily large electrode arrays, and will make it possible to place sensing chemistries onto each electrode using a robotic spotter.

We report an electrochemical DNA microarray sensor whose function is controlled with just two wires regardless of the number of individual sensing electrodes. The bipolar sensing electrode is modified with probe DNA, and the anode end of each electrode is configured to emit light (electrogenerated chemiluminescence) upon hybridization of cDNA labeled with electrocatalytic (oxygen reduction) Pt nanoparticles at the cathode. The important finding is that DNA can be selectively detected at an array of three electrodes. In principle, however, this advance provides a means for controlling the potential of many electrodes using just two wires and then indirectly determining the current flowing through all of them simultaneously by correlating light emission to current.

Here we report a new type of sensing platform that is based on electrodissolution of a metallic bipolar electrode (BPE). When the target DNA binds to the capture probe at the cathodic pole of the BPE, it triggers the oxidation and dissolution of Ag metal present at the anodic pole. The loss of Ag is easily detectable with the naked eye or a magnifying glass and provides a permanent record of the electrochemical history of the electrode. More importantly, the decrease in the length of the BPE can be directly correlated to the number of electrons passing through the BPE and hence to the sensing reaction at the cathode.

We report a two-channel microelectrochemical sensor that communicates between separate sensing and reporting microchannels via one or more bipolar electrodes (BPEs). Depending on the contents of each microchannel and the voltage applied across the BPE, faradaic reactions may be activated simultaneously in both channels. As presently configured, one end of the BPE is designated as the sensing pole and the other as the reporting pole. When the sensing pole is activated by a target, electrogenerated chemiluminescence (ECL) is emitted at the reporting pole. Compared to previously reported single-channel BPE sensors, the key advantage of the multichannel architecture reported here is physical separation of the ECL reporting cocktail and the solution containing the target. This prevents chemical interference between the two channels.

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