Fabrication and Characterization of a Dual Submicrometer-Sized Electrode

Considerations for dual barrel electrode fabrication and experimentation

New electrochemical probes offer the opportunity to investigate new systems. A dual barrel electrode can be laser pulled to produce micron-sized platinum disk electrodes. Here, we detail several important considerations for both the fabrication process and for experimental implimentation of the probe. We provide parameters for a Sutter P-2000 laser puller, methods for optical and electrochemical characterization, tips for how to successfully bevel the microelectrodes, and how salt concentrations and electrostatic discharge affect the voltammetry. This paper serves as a guide for how to successfully implement dual barrel electrodes from fabrication to experimentation.

Membraneless Ionic Liquid Droplet Nanoprobe for Oxygen Sensing and Gas Phase Scanning Electrochemical Microscopy

A novel membraneless oxygen sensing nanoprobe was developed based on a hanging drop ionic liquid electrochemical cell. An ultrasmall (<500 nm) working electrode and small volume electrochemical cell allowed for an impressively low detection limit of ∼13 ppm and a response time less than 100 ms, which is unusually fast for an electrochemical gas sensor. The oxygen sensor was stable for hours of operation and, owing to the membraneless design, was easily regenerable when fouled. The pulled capillary form factor of the nanoprobe was found compatible with scanning probe techniques, the demonstration of which was made by application as a tip electrode in gas phase scanning electrochemical microscopy (SECM). In the SECM experiments, the oxygen nanoprobe exhibited micrometer scale spatial resolution with ease. This unique probe design developed here may potentially be engineered into versatile sensors for various volatile molecules other than oxygen, such as those pertinent to hazard analysis and biomedical diagnosis.

Electrochemiluminescence Based on a Dual Carbon Ultramicroelectrode with Confined Steady-State Annihilation

Developing novel microelectronic devices for electrochemical measurements and electrochemiluminescence (ECL) study is of great importance. Herein, we fabricated a submicrometer-sized dual carbon electrode (DCE) and investigated its annihilation ECL behavior under steady-state conditions for the first time. The oxidation and reduction of the model luminophore, [Ru(bpy)₃]²⁺, occurred separately at the two sides of the DCE, and the electrogenerated ions then diffused to the gap between the two electrodes to generate the excited-state intermediate [Ru(bpy)₃]^2+* and ECL emission. Compared with other types of two-electrode systems, the prepared DCE possesses a smaller total size and an ultrasmall interelectrode distance of 60 nm or less, which could result in a shorter diffusion time and an amplified ECL signal without the purification of the solvent and supporting electrolytes. On the basis of the constructed ECL microscopic platform, we successfully obtained a stable and confined ECL signal in the vicinity of the electrode tip. Furthermore, a two-dimensional finite element method simulation of this model system was performed to quantitively analyze the concentration profiles of the electrogenerated species around the tip of the DCE and predict the concentrations of [Ru(bpy)₃]^2+* with various gap distances. The simulation results also proved that the higher concentrations of [Ru(bpy)₃]^2+* could be achieved with a smaller distance with a possible amplification factor of 6 (compared with the concentration when the gap distance is greater than 300 nm). This work provides an experimental model for further improvement of ECL efficiency and broadens the availability for annihilation ECL applications in small confined spaces.

Integrated multi-ISE arrays with improved sensitivity, accuracy and precision

Increasing use of ion-selective electrodes (ISEs) in the biological and environmental fields has generated demand for high-sensitivity ISEs. However, improving the sensitivities of ISEs remains a challenge because of the limit of the Nernstian slope (59.2/n mV). Here, we present a universal ion detection method using an electronic integrated multi-electrode system (EIMES) that bypasses the Nernstian slope limit of 59.2/n mV, thereby enabling substantial enhancement of the sensitivity of ISEs. The results reveal that the response slope is greatly increased from 57.2 to 1711.3 mV, 57.3 to 564.7 mV and 57.7 to 576.2 mV by electronic integrated 30 Cl⁻ electrodes, 10 F⁻ electrodes and 10 glass pH electrodes, respectively. Thus, a tiny change in the ion concentration can be monitored, and correspondingly, the accuracy and precision are substantially improved. The EIMES is suited for all types of potentiometric sensors and may pave the way for monitoring of various ions with high accuracy and precision because of its high sensitivity.

Recent advances in the development and application of nanoelectrodes

Nanoelectrodes have key advantages compared to electrodes of conventional size and are the tool of choice for numerous applications in both fundamental electrochemistry research and bioelectrochemical analysis. This Minireview summarizes recent advances in the development, characterization, and use of nanoelectrodes in nanoscale electroanalytical chemistry. Methods of nanoelectrode preparation include laser-pulled glass-sealed metal nanoelectrodes, mass-produced nanoelectrodes, carbon nanotube based and carbon-filled nanopipettes, and tunneling nanoelectrodes. Several new topics of their recent application are covered, which include the use of nanoelectrodes for electrochemical imaging at ultrahigh spatial resolution, imaging with nanoelectrodes and nanopipettes, electrochemical analysis of single cells, single enzymes, and single nanoparticles, and the use of nanoelectrodes to understand single nanobubbles.

Preparation, electrochemical responses and sensing application of Au disk nanoelectrodes down to 5 nm

Single Au nano-disk nanoelectrodes with the radii down to 5 nm have been prepared, which can be used to measure ferritin molecules in the amount of ∼3900 molecules or 6.1 zmol.

Fabrication, characterization, and functionalization of dual carbon electrodes as probes for scanning electrochemical microscopy (SECM)

Dual carbon electrodes (DCEs) are quickly, easily, and cheaply fabricated by depositing pyrolytic carbon into a quartz theta nanopipet. The size of DCEs can be controlled by adjusting the pulling parameters used to make the nanopipet. When operated in generation/collection (G/C) mode, the small separation between the electrodes leads to reasonable collection efficiencies of ca. 30%. A three-dimensional finite element method (FEM) simulation is developed to predict the current response of these electrodes as a means of estimating the probe geometry. Voltammetric measurements at individual electrodes combined with generation/collection measurements provide a reasonable guide to the electrode size. DCEs are employed in a scanning electrochemical microscopy (SECM) configuration, and their use for both approach curves and imaging is considered. G/C approach curve measurements are shown to be particularly sensitive to the nature of the substrate, with insulating surfaces leading to enhanced collection efficiencies, whereas conducting surfaces lead to a decrease of collection efficiency. As a proof-of-concept, DCEs are further used to locally generate an artificial electron acceptor and to follow the flux of this species and its reduced form during photosynthesis at isolated thylakoid membranes. In addition, 2-dimensional images of a single thylakoid membrane are reported and analyzed to demonstrate the high sensitivity of G/C measurements to localized surface processes. It is finally shown that individual nanometer-size electrodes can be functionalized through the selective deposition of platinum on one of the two electrodes in a DCE while leaving the other one unmodified. This provides an indication of the future versatility of this type of probe for nanoscale measurements and imaging.