13 research outputs found
Altered Spatial Resolution of Scanning Electrochemical Microscopy Induced by Multifunctional Dual-Barrel Microelectrodes
The nonuniform diffusion
profile to the edge of many multifunctional
microelectrodes has the potential to give rise to distortions in its
imaging capability, reducing the spatial accuracy of the techniques
they are used in. In this work, numerical simulations are used to
predict these distortions for dual-barrel electrodes used in the combined
feedback/generationācollection mode of scanning electrochemical
microscopy imaging a model substrate. The sensitivity of this distortion
to tipāsubstrate distance, electrolyte composition, and size
and shape of a reactive substrate feature are discussed
High-Speed Scanning Electrochemical Microscopy Method for Substrate Kinetic Determination: Application to Live Cell Imaging in Human Cancer
Scanning
electrochemical microscopy (SECM) is increasingly applied
to study and image live cells. Quantitative analyses of biological
systems, however, still remain challenging. In the presented study,
single human adenocarcinoma cervical cancer cells are electrochemically
investigated by means of SECM. The target cellās electrochemical
response is observed over time under the influence of green tea catechins
(GTC), which are suggested to offer chemopreventive and therapeutic
effects on cancer. The electrochemical response of living target cells
is measured experimentally and quantified in an apparent heterogeneous
rate constant by using a numerical model, based on forced convection
during high speed SECM imaging. The beneficial effect of GTC on cancer
cells could be confirmed by SECM, and the presented study shows an
alternative approach toward unraveling the mechanisms involved during
inhibition of carcinogenesis
Forced Convection during Feedback Approach Curve Measurements in Scanning Electrochemical Microscopy: Maximal Displacement Velocity with a Microdisk
In scanning electrochemical microscopy (SECM), an approach
curve performed in feedback mode involves the downward displacement
of a microelectrode toward a substrate while applying a bias to detect
dissolved electroactive species at a diffusion-limited rate. The resulting
measured current is said to be at steady state. In order to reduce
the required measurement time, the approach velocity can be increased.
In this paper, we investigate experimentally and theoretically the
combination of diffusion and convection processes related to a moving
microdisk electrode during feedback approaches. Transient modeling
and numerical simulations with moving boundaries are performed, and
the results are compared to the experimental approach curves obtained
in aqueous solution. The geometry and misalignment of the microelectrode
influence the experimental approach curves recorded at high approach
velocities. The effects are discussed through the decomposition of
the current into transient diffusional, radial convectional, and axial
convectional contributions. Finally a ready-to-use expression is provided
to rapidly evaluate the maximal approach velocity for steady state
measurements as a function of the microelectrode geometry and the
physical properties of the media. This expression holds for the more
restrictive case of negative feedback as well as other modes, such
as SECM approach curves performed at substrates displaying first order
kinetics
High-Speed Scanning Electrochemical Microscopy Method for Substrate Kinetic Determination: Method and Theory
Scanning
electrochemical microscopy (SECM) allows imaging and analysis
of a variety of biological samples, such as living cells. Up to now,
it still remains a challenge to successfully decouple signals related
to topography and reactivity. Furthermore, such delicate samples require
careful adjustment of experimental parameters, such as scan velocity.
The present study proposes a method to extract a substrateās
kinetic rate by numerical modeling and experimental high speed constant
height SECM imaging. This is especially useful for the determination
of substrates with unknown surface reaction kinetics and large topographical
features. To make this approach applicable to soft cell samples, which
cannot be imaged at high velocity, a nonlinear fit strategy is presented
to obtain kinetic rate values also under slow scan velocity conditions
Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy
Scanning electrochemical cell microscopy is a useful
technique
for determining variations in corrosion behavior across a surface.
However, the numerous options for experimental parameters and little
understanding of their effect on the corroding system render comparisons
of results between studies difficult. Herein, we explore changes in
corrosion behavior of two martensitic stainless steels, a cast CA6NM
and a wrought S41500, as a result of the chosen experimental parameters,
including scan rate, approach potential, surface oil immersion, and
tip aperture diameter. The study demonstrates that these experimental
parameters can be controlled to probe oxide passivation kinetics and
single pitting events by changing the surface state and cathodic currents.
We measured the pitting and repassivation kinetics of a single pit
and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points
were measured within 17 h of experimental time on the stainless steel
samples, allowing statistical averages of corrosion and pitting values.
This work will open new avenues for fine-tuning various corrosion
aspects at the microscale, thereby contributing to a deeper understanding
of the corrosion processes and mechanisms of diverse materials
Modular Flow-Through Platform for Spectroelectrochemical Analysis
A new
type of flow platform for electrochemical and spectroelectrochemical
measurements is presented. Finite element method simulations confirm
that the hydrodynamic profile within the device is not turbulent and
provides an analytical platform for the investigation of homogeneous
kinetics, radical lifetimes, and reaction mechanisms. The modular
āplug and playā configuration of the platform allows
one to carry out electrochemistry and spectroscopy individually or
simultaneously. Specific demonstrations of electroanalytical measurements
using the flow system platform includes voltammetric analysis of organometallic
compounds and quantitative analysis of ascorbic acid in commercial
orange juice samples. Combined spectroelectrochemical demonstrations
include electrochemical luminescence of ruthenium compounds and ligand
exchange reactions of iron complexes using UVāvis spectroscopy
Electrogenerated Chemiluminescence of Iridium-Containing ROMP Block Copolymer and Self-Assembled Micelles
The electrochemical properties and
electrogenerated chemiluminescence
(ECL) of an IrĀ(ppy)<sub>2</sub>(bpy)<sup>+</sup>-containing ROMP monomer,
block copolymer (containing IrĀ(ppy)<sub>2</sub>(bpy)<sup>+</sup> complexes,
PEG chains, and butyl moieties), and self-assembled micelles were
investigated. Following polymerization of the iridium complex, we
observed multiple oxidation peaks for the block copolymer in cyclic
voltammograms (CV) and differential pulse voltammograms (DPV), suggesting
the presence of multiple environments for the iridium complexes along
the polymer backbone. The ECL signals from monomer <b>1</b> and
polymer <b>2</b> were reproducible over continuous CV cycles
and stable over prolonged potential biases, demonstrating their robustness
toward ECL-based detection. Comparison of the ECL signal of the block
copolymer, containing multiple iridium complexes attached to the backbone,
and the monomeric complex showed enhanced signals for the polymer.
In fact, formation and reopening of the self-assembled micelles allowed
recovery of the polymer and near complete retention of its original
ECL intensity
Fabrication of Carbon, Gold, Platinum, Silver, and Mercury Ultramicroelectrodes with Controlled Geometry
A simple,
fast, and reproducible method for the fabrication of
disk ultramicroelectrodes (UMEs) with controlled geometry is reported.
The use of prepulled soda-lime glass capillaries allows one to bypass
the irreproducible torch-sealing and experimentally challenging tip-sharpening
steps used in conventional fabrication protocols. A micron-sized electroactive
wire is sealed inside this capillary producing UMEs with a highly
reproducible geometry. Total fabrication time (1 h) and experimental
difficulty are significantly reduced. Disk UMEs with various diameters
and cores were fabricated, including carbon fiber (7 and 11 Ī¼m),
gold (10 and 25 Ī¼m), platinum (10 and 25 Ī¼m), silver (25
Ī¼m), and mercury (25 Ī¼m). The ratio of the insulating
sheath to the electroactive core of the UMEs was 2.5ā3.6. Silver
UMEs were also used to produce a Ag/AgCl microreference electrode.
This general fabrication method can readily be applied to other electroactive
cores and could allow any research group to produce high quality disk
UMEs, which are a prerequisite for quantitative scanning electrochemical
microscopy
Determination of the Relationship between Expression and Functional Activity of Multidrug Resistance-Associated Protein 1 using Scanning Electrochemical Microscopy
Cancer cells can
develop multidrug resistance (MDR) after prolonged
exposure to chemotherapeutic drugs, which is a severe impediment to
successful treatment. MDR is typically associated with transmembrane
proteins mediating efflux of administered drugs, thereby keeping their
intracellular concentration below the threshold required to kill cells.
Although expression assays based on flow cytometry and immunostaining
have shown that multidrug resistance-associated protein 1 (MRP1) is
prevalent in many cancer types, the functional activity of this efflux
pump is more difficult to elucidate, especially at the single-cell
level. Herein, we report the measurement of MRP1 functional activity
in individual cancer cells using scanning electrochemical microscopy
(SECM). Cells were cultured onto plastic substrates containing selective
adhesion sites. Optical microscopy and SECM revealed that cells adapt
to the underlying surface, while MRP1 functional activity increases
once the dimensions of the adhesive islands become smaller than those
of the cell itself. Time-lapse SECM imaging revealed a suitable window
of 30 min to complete each measurement before the cell undergoes blebbing,
which is associated with a considerable increase in functional activity.
Distinct cell populations were produced by performing a doxorubicin
drug challenge on two parental cell lines (e.g., wild-type HeLa cells
and MRP1-overexpressing HeLa-R cells). Expression and functional activity
of MRP1 were determined using flow cytometry and SECM, and our findings
show that these parameters do not directly correlate. This suggests
that functional activity may represent a powerful indicator of a cancer
cellās response to chemotherapeutic treatment and should improve
our understanding of efflux mechanisms based on MRP1
Influence of Edge Effects on Local Corrosion Rate of Magnesium Alloy/Mild Steel Galvanic Couple
The effect of the insulator-mixed-material edge on the
galvanic
corrosion rate of magnesium alloy (AE44)āmild steel (MS) couple
is experimentally studied using scanning vibrating electrode technique
(SVET), profilometry, and classical electrochemistry. The local and
average corrosion rates estimated from the experimental depth of anodic
attack profile of AE44-MS couple are validated by 2D and 3D corrosion
numerical models. Our study demonstrates experimentally and theoretically
that the presence of the insulator edge increases the local current
density, which enhances the corrosion rate. The extent of the local
corrosion rate enhancement and its effect on the overall corrosion
rate of the mixed material is discussed and depends on the mixed materialās
geometry and the edge type