Controlling Gold Morphology Using Electrodeposition for the Preparation of Electrochemical Aptamer-Based Sensors.

Nanostructuring of gold surfaces to enhance electroactive surface area has proven to significantly enhance the performance of electrochemical aptamer-based (E-AB) sensors, particularly for electrodes on the microscale. Unlike for sensors fabricated on polished gold surfaces, predicting the behavior of E-AB sensors on surfaces with varied gold morphologies becomes more intricate due to the effects of surface roughness and the shapes and sizes of surface features on supporting a self-assembled monolayer. In this study, we explored the impact of gold morphology characteristics on sensor performance, evaluating parameters such as signal change in response to the addition of the target analyte, aptamer probe packing density, and continuous sensing ability.

Scanning ion conductance microscopy revealed cisplatin-induced morphological changes related to apoptosis in single adenocarcinoma cells.

The studies of drug-induced apoptosis play a vital role in the identification of potential drugs that could treat diseases such as cancer. Alterations in the native morphology of cancer cells following treatment with anticancer drugs serve as one of the indicators that reveal drug efficacy. Various techniques such as optical microscopy, electron microscopy (EM), and atomic force microscopy (AFM) have been used to map the three dimensional (3D) morphological changes in cells induced with drugs.

Electrocatalytic activity and surface oxide reconstruction of bimetallic iron-cobalt nanocarbide electrocatalysts for the oxygen evolution reaction.

For renewable energy technology to become ubiquitous, it is imperative to develop efficient oxygen evolution reaction (OER) electrocatalysts, which is challenging due to the kinetically and thermodynamically unfavorable OER mechanism. Transition metal carbides (TMCs) have recently been investigated as desirable OER pre-catalysts, but the ability to tune electrocatalytic performance of bimetallic catalysts and understand their transformation under electrochemical oxidation requires further study. In an effort to understand the tunable TMC material properties for enhancing electrocatalytic activity, we synthesized bimetallic FeCo nanocarbides with a complex mixture of FeCo carbide crystal phases.

Selective Aptamer Modification of Au Surfaces in a Microelectrode Sensor Array for Simultaneous Detection of Multiple Analytes.

Aptamers have been employed as the biorecognition element in electrochemical aptamer-based (E-AB) biosensors, for the detection of a diverse range of analyte molecules, on electrodes with sizescales ranging from a few microns to several millimeters. Simultaneous detection of multiple different analytes requires the selective modification of multiple electrode surfaces with different aptamers. This process is typically achieved by incubating separate macroscale electrodes in a solution with the desired aptamer, which is unsuitable for microelectrode arrays in which the electrodes are closely spaced.

Design and Synthesis of Kekulè and Non-Kekulè Diradicaloids via the Radical Periannulation Strategy: The Power of Seven Clar's Sextets.

This work introduces an approach to uncoupling electrons via maximum utilization of localized aromatic units, i.e., the Clar's π-sextets.

A Single Source, Scalable Route for Direct Isolation of Earth-Abundant Nanometal Carbide Water-Splitting Electrocatalysts.

Single-phase MCs (M = Fe, Co, and Ni) were prepared by solvothermal conversion of Prussian blue single source precursors. The single source precursor is prepared in water, and the conversion process is carried out in alkylamines at reaction temperatures above 200 °C. The reaction is scalable using a commercial source of Fe-PB.

Creation of an unexpected plane of enhanced covalency in cerium(III) and berkelium(III) terpyridyl complexes.

Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating Bk with 4'-(4-nitrophenyl)-2,2':6',2"-terpyridine (terpy*), a ligand with a large dipole.

Repetitive drug releases from light-activatable micron-sized liposomes.

In this work, a novel light activatable micron-sized liposomal drug carrier that has a unique capability to release drug repetitively in proportion to the cycle number of short irradiation (5 s) of near-infrared (NIR) pulsed laser is reported. We synthesized methotrexate (MTX)-loaded liposomes based on a modified reverse-phase evaporation method. Gold nanorods (AuNR) were attached to the liposomal surfaces, enabling the liposomes to release drug under short NIR irradiation via the photothermal effect.

Effect of Laser Irradiation on Reversibility and Drug Release of Light-Activatable Drug-Encapsulated Liposomes.

Although several studies have demonstrated repetitive drug release using light-activatable liposomes, inconsistent drug release at each activation limits widespread usage. Here, we report reversible plasmonic material-coated encapsulated liposomes for proportional controlled delivery of methotrexate (MTX), which is a common drug for cancer and autoimmune diseases, using repetitive laser irradiation. Our results suggest a proportional increase in total drug release after repetitive laser irradiation.

Electrochromic, Closed-Bipolar Electrodes Employing Aptamer-Based Recognition for Direct Colorimetric Sensing Visualization.

In this paper, we adapt the electrochemical, aptamer-based (E-AB) sensor platform to develop colorimetric aptamer-based sensors using a closed-bipolar electrode (C-BPE) system. The C-BPE E-AB sensors provide quantitative detection of target molecules based on the rate of color change of an electrochromic Prussian blue (PB) thin-film indicator electrode. The C-BPE cathode, or sensing electrode, is modified with a redox-labeled aptamer that binds to a specific target.

Rapid Two-Millisecond Interrogation of Electrochemical, Aptamer-Based Sensor Response Using Intermittent Pulse Amperometry.

In this manuscript, we employ the technique intermittent pulse amperometry (IPA) to interrogate equilibrium and kinetic target binding to the surface of electrochemical, aptamer-based (E-AB) sensors, achieving as fast as 2 ms time resolution. E-AB sensors comprise an electrode surface modified with a flexible nucleic acid aptamer tethered at the 3'-terminus with a redox-active molecule. The introduction of a target changes the conformation and flexibility of the nucleic acid, which alters the charge transfer rate of the appended redox molecule.

Quantitative Framework for Stochastic Nanopore Sensors Using Multiple Channels.

Membrane protein channels employed as stochastic sensors offer large signal-to-noise ratios and high specificity in single molecule binding measurements. Stochastic events in a single ion channel system can be measured using current-time traces, which are straightforward to analyze. Signals arising from measurement using multiple ion channels are more complicated to interpret.

Comparison of fast electron transfer kinetics at platinum, gold, glassy carbon and diamond electrodes using Fourier-transformed AC voltammetry and scanning electrochemical microscopy.

Heterogeneous electron transfer (ET) processes at electrode/electrolyte interfaces are of fundamental and applied importance and are extensively studied by a range of electrochemical techniques, all of which have various attributes but also limitations. The present study focuses on the one-electron oxidation of tetrathiafulvalene (TTF) and reduction of tetracyanoquinodimethane (TCNQ) in acetonitrile solution by two powerful electrochemical techniques: Fourier-transformed large amplitude alternating current voltammetry (FTACV); and scanning electrochemical microscopy (SECM), both of which are supported by detailed theoretical models. At conventional Pt, Au and glassy carbon (GC) electrode materials, the apparent (overall) charge transfer kinetic values determined by FTACV give standard ET rate constants, k, that are fast and close to the reversible limit.

Electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH): comparison of highly oriented pyrolytic graphite (HOPG) and polycrystalline boron-doped diamond (pBDD) electrodes.

The electro-oxidation of nicotinamide adenine dinucleotide (NADH) is studied at bare surfaces of highly oriented pyrolytic graphite (HOPG) and semi-metallic polycrystalline boron-doped diamond (pBDD). A comparison of these two carbon electrode materials is interesting because they possess broadly similar densities of electronic states that are much lower than most metal electrodes, but graphite has carbon sp-hybridization, while in diamond the carbon is sp-hybridised, with resulting major differences in bulk structure and surface termination. Using cyclic voltammetry (CV), it is shown that NADH oxidation is facile at HOPG surfaces but the reaction products tend to strongly adsorb, which causes rapid deactivation of the electrode activity.

Characterization of Nanopipettes.

Nanopipettes are widely used in electrochemical and analytical techniques as tools for sizing, sequencing, sensing, delivery, and imaging. For all of these applications, the response of a nanopipette is strongly affected by its geometry and surface chemistry. As the size of nanopipettes becomes smaller, precise geometric characterization is increasingly important, especially if nanopipette probes are to be used for quantitative studies and analysis.

Versatile Polymer-Free Graphene Transfer Method and Applications.

A new method for transferring chemical vapor deposition (CVD)-grown monolayer graphene to a variety of substrates is described. The method makes use of an organic/aqueous biphasic configuration, avoiding the use of any polymeric materials that can cause severe contamination problems. The graphene-coated copper foil sample (on which graphene was grown) sits at the interface between hexane and an aqueous etching solution of ammonium persulfate to remove the copper.

Time-Resolved Detection and Analysis of Single Nanoparticle Electrocatalytic Impacts.

There is considerable interest in understanding the interaction and activity of single entities, such as (electro)catalytic nanoparticles (NPs), with (electrode) surfaces. Through the use of a high bandwidth, high signal/noise measurement system, NP impacts on an electrode surface are detected and analyzed in unprecedented detail, revealing considerable new mechanistic information on the process. Taking the electrocatalytic oxidation of H2O2 at ruthenium oxide (RuOx) NPs as an example, the rise time of current-time transients for NP impacts is consistent with a hydrodynamic trapping model for the arrival of a NP with a distance-dependent NP diffusion-coefficient.

Hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM) as a new local dissolution kinetic probe: application to salicylic acid dissolution in aqueous solution.

Dissolution kinetics of the (110) face of salicylic acid in aqueous solution is determined by hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM) using a 2.5 μm diameter platinum ultramicroelectrode (UME). The method operates by translating the probe UME towards the surface at a series of positions across the crystal and inducing dissolution the reduction of protons to hydrogen, which titrates the weak acid and promotes the dissolution reaction, but only when the UME is close to the crystal.

Quad-barrel multifunctional electrochemical and ion conductance probe for voltammetric analysis and imaging.

The fabrication and use of a multifunctional electrochemical probe incorporating two independent carbon working electrodes and two electrolyte-filled barrels, equipped with quasi-reference counter electrodes (QRCEs), in the end of a tapered micrometer-scale pipet is described. This "quad-probe" (4-channel probe) was fabricated by depositing carbon pyrolytically into two diagonally opposite barrels of a laser-pulled quartz quadruple-barrelled pipet. After filling the open channels with electrolyte solution, a meniscus forms at the end of the probe and covers the two working electrodes.

Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces.

The nucleation and growth of metal nanoparticles (NPs) on surfaces is of considerable interest with regard to creating functional interfaces with myriad applications. Yet, key features of these processes remain elusive and are undergoing revision. Here, the mechanism of the electrodeposition of silver on basal plane highly oriented pyrolytic graphite (HOPG) is investigated as a model system at a wide range of length scales, spanning electrochemical measurements from the macroscale to the nanoscale using scanning electrochemical cell microscopy (SECCM), a pipette-based approach.

Hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM): visualizing interfacial reactions and fluxes from surfaces to bulk solution.

Hopping intermittent contact-scanning electrochemical microscopy (HIC-SECM) is introduced as a powerful new technique for the quantitative visualization of redox activity and concentration at and above a surface of interest. HIC-SECM combines a hopping imaging mode, in which data are acquired at a tip as a function of distance (z) from the surface, at a series of x, y pixels across the surface, using the principles of intermittent contact to provide a nonelectrochemical means of determining when the tip and the substrate come into contact. The implementation of HIC-SECM is described, and SECM feedback measurements in three-dimensional (3D) space over a gold band array are presented.