Redox Cycling in Nanopore-Confined Recessed Dual-Ring Electrode Arrays

A redox cycling geometry based on an array of nanopore-confined recessed dual-ring electrodes (RDREs) has been devised to amplify electrochemical signals and enhance the sensitivity of electroanalytical measurements. The RDRE arrays were fabricated using layer-by-layer deposition followed by focused ion beam milling. A characteristic feature of the nanoscale dual-ring geometry is that electrochemical reactions occurring at the bottom-ring electrode can be tuned by modulating the potential at the top-ring electrode. Thus, the resulting device was operated in generator–collector mode by holding the top-ring electrodes at a constant potential and performing cyclic voltammetry by sweeping the bottom-ring potential in aqueous Fe­(CN)₆^3–/4–. The enhanced (∼23×) limiting current, achieved by cycling the redox couple between top- and bottom-ring electrodes with high collection efficiency, was compared with that obtained in the absence of self-induced redox cycling (SIRC). Measured shifts in Fe­(CN)₆^3–/4– concentration distributions were found to be in excellent agreement with finite-element simulations. The SIRC effect in the RDRE array was also characterized by electrochemical experiments before and after oxygen plasma treatment. The plasma-treated RDRE array exhibited a significant signal amplification, with the faradaic current being augmented by a factor of ∼65 as a result of efficient redox cycling of electroactive species in the nanopores. The amplification factor of the devices was optimized by controlling the interpore distance, with larger pore density arrays exhibiting larger amplification factors

Electrochemical Signal Amplification for Immunosensor Based on 3D Interdigitated Array Electrodes

We devised an electrochemical redox cycling based on three-dimensional interdigitated array (3D IDA) electrodes for signal amplification to enhance the sensitivity of chip-based immunosensors. The 3D IDA consists of two closely spaced parallel indium tin oxide (ITO) electrodes that are positioned not only on the bottom but also the ceiling, facing each other along a microfluidic channel. We investigated the signal intensities from various geometric configurations: Open-2D IDA, Closed-2D IDA, and 3D IDA through electrochemical experiments and finite-element simulations. The 3D IDA among the four different systems exhibited the greatest signal amplification resulting from efficient redox cycling of electroactive species confined in the microchannel so that the faradaic current was augmented by a factor of ∼100. We exploited the enhanced sensitivity of the 3D IDA to build up a chronocoulometric immunosensing platform based on the sandwich enzyme-linked immunosorbent assay (ELISA) protocol. The mouse IgGs on the 3D IDA showed much lower detection limits than on the Closed-2D IDA. The detection limit for mouse IgG measured using the 3D IDA was ∼10 fg/mL, while it was ∼100 fg/mL for the Closed-2D IDA. Moreover, the proposed immunosensor system with the 3D IDA successfully worked for clinical analysis as shown by the sensitive detection of cardiac troponin I in human serum down to 100 fg/mL

Addressable Direct-Write Nanoscale Filament Formation and Dissolution by Nanoparticle-Mediated Bipolar Electrochemistry

Nanoscale conductive filaments, usually associated with resistive memory or memristor technology, may also be used for chemical sensing and nanophotonic applications; however, realistic implementation of the technology requires precise knowledge of the conditions that control the formation and dissolution of filaments. Here we describe and characterize an addressable direct-write nanoelectrochemical approach to achieve repeatable formation/dissolution of Ag filaments across a ∼100 nm poly­(ethylene oxide) (PEO) film containing either Ag⁺ alone or Ag⁺ together with 50 nm Ag-nanoparticles acting as bipolar electrodes. Using a conductive AFM tip, formation occurs when the PEO film is subjected to a forward bias, and dissolution occurs under reverse bias. Formation–dissolution kinetics were studied for three film compositions: Ag|PEO-Ag⁺, Ag|poly­(ethylene glycol) monolayer-PEO-Ag⁺, and Ag|poly­(ethylene glycol) monolayer-PEO-Ag⁺/Ag-nanoparticle. Statistical analysis shows that the distribution of formation times exhibits Gaussian behavior, and the fastest average initial formation time occurs for the Ag|PEO-Ag⁺ system. In contrast, formation in the presence of Ag nanoparticles likely proceeds by a noncontact bipolar electrochemical mechanism, exhibiting the slowest initial filament formation. Dissolution times are log-normal for all three systems, and repeated reformation of filaments from previously formed structures is characterized by rapid regrowth. The direct-write bipolar electrochemical deposition/dissolution strategy developed here presents an approach to reconfigurable, noncontact <i>in situ</i> wiring of nanoparticle arraysthereby enabling applications where actively controlled connectivity of nanoparticle arrays is used to manipulate nanoelectronic and nanophotonic behavior. The system further allows for facile manipulation of experimental conditions while simultaneously characterizing surface conditions and filament formation/dissolution kinetics

Baseline characteristics of study patients.

<p>Baseline characteristics of study patients.</p

Subjective discomfort assessed by visual analogue scale.

<p>Subjective discomfort assessed by visual analogue scale.</p

Baseline characteristics of study patients.

<p>Baseline characteristics of study patients.</p

Study devices.

<p>(A) Both rotatory compression device and hemostasis pad were used for the patients in the study group. (B) After placing the hemostasis pad over the puncture site, the rotatory compression device was applied.</p

The primary endpoint, time to hemostasis of the study and control groups.

<p>The primary endpoint, time to hemostasis of the study and control groups.</p