7 research outputs found
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 ā¼100. 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 ā¼10 fg/mL, while it
was ā¼100 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
Photoelectrochemical and Impedance Spectroscopic Analysis of Amorphous Si for Light-Guided Electrodeposition and Hydrogen Evolution Reaction
For
more efficient photoelectrochemical water splitting, there is a dilemma
that a photoelectrode needs both light absorption and electrocatalytic
faradaic reaction. One of the promising strategies is to deposit a
pattern of electrocatalysts onto a semiconductor surface, leaving
sufficient bare surface for light absorption while minimizing concentration
overpotential as well as resistive loss at the ultramicroelectrodes
for faradaic reaction. This scheme can be successfully realized by
āmasklessā direct photoelectrochemical patterning of
electrocatalyst onto an SiO<sub><i>x</i></sub>/amorphous
Si (a-Si) surface by the light-guided electrodeposition technique.
Electrochemical impedance spectroscopy at various pHs tells us much
about how it works. The surface states at the SiO<sub><i>x</i></sub>/a-Si interface can mediate the photogenerated electrons for
hydrogen evolution, whereas electroactive species in the solution
undergo outer-sphere electron transfer, taking electrons tunneling
across the SiO<sub><i>x</i></sub> layer from the conduction
band. In addition to previously reported long-distance lateral electron
transport behavior at a patterned catalyst/SiO<sub><i>x</i></sub>/a-Si interface, the charging process of the surface states
plays a crucial role in proton reduction, leading to deeper understanding
of the operation mechanisms for photoelectrochemical water splitting
In-Channel Electrochemical Detection in the Middle of Microchannel under High Electric Field
We propose a new method for performing in-channel electrochemical
detection under a high electric field using a polyelectrolytic gel
salt bridge (PGSB) integrated in the middle of the electrophoretic
separation channel. The finely tuned placement of a gold working electrode
and the PGSB on an equipotential surface in the microchannel provided
highly sensitive electrochemical detection without any deterioration
in the separation efficiency or interference of the applied electric
field. To assess the working principle, the open circuit potentials
between gold working electrodes and the reference electrode at varying
distances were measured in the microchannel under electrophoretic
fields using an electrically isolated potentiostat. In addition, āin-channelā
cyclic voltammetry confirmed the feasibility of electrochemical detection
under various strengths of electric fields (ā¼400 V/cm). Effective
separation on a microchip equipped with a PGSB under high electric
fields was demonstrated for the electrochemical detection of biological
compounds such as dopamine and catechol. The proposed āin-channelā
electrochemical detection under a high electric field enables wider
electrochemical detection applications in microchip electrophoresis
Nonfaradaic Nanoporous Electrochemistry for Conductometry at High Electrolyte Concentration
Nanoporous electrified surfaces create
a unique nonfaradaic electrochemical
behavior that is sensitively influenced by pore size, morphology,
ionic strength, and electric field modulation. Here, we report the
contributions of ion concentration and applied ac frequency to the
electrode impedance through an electrical double layer overlap and
ion transport along the nanopores. Nanoporous Pt with uniform pore
size and geometry (L<sub>2</sub>-ePt) responded more sensitively to
conductivity changes in aqueous solutions than Pt black with poor
uniformity despite similar real surface areas and enabled the previously
difficult quantitative conductometry measurements at high electrolyte
concentrations. The nanopores of L<sub>2</sub>-ePt were more effective
in reducing the electrode impedance and exhibited superior linear
responses to not only flat Pt but also Pt black, leading to successful
conductometric detection in ion chromatography without ion suppressors
and at high ionic strengths
Miniaturized Reverse Electrodialysis-Powered Biosensor Using Electrochemiluminescence on Bipolar Electrode
We
suggest an electrochemiluminescence (ECL)-sensing platform driven
by ecofriendly, disposable, and miniaturized reverse electrodialysis
(RED) patches as an electric power source. The flexible RED patches
composed of ion-exchange membranes (IEMs) can produce voltage required
for ECL sensing by simply choosing the appropriate number of IEMs
and the ratio of salt concentrations. We integrate the RED patch with
a bipolar electrode on the microfluidic chip to demonstrate the proof-of-concept,
i.e., glucose detection in the range of 0.5ā10 mM by observing
ECL emissions with naked eyes. The miniaturized RED-powered biosensing
system is widely applicable for electrochemical-sensing platforms.
This is expected to be a solution for practical availability of battery-free
electrochemical sensors for disease diagnosis in developing countries
On-Site Formation of Functional Dopaminergic Presynaptic Terminals on Neuroligin-2-Modified Gold-Coated Microspheres
Advancements in neural interface
technologies have enabled the
direct connection of neurons and electronics, facilitating chemical
communication between neural systems and external devices. One promising
approach is a synaptogenesis-involving method, which offers an opportunity
for synaptic signaling between these systems. Janus synapses, one
type of synaptic interface utilizing synaptic cell adhesion molecules
for interface construction, possess unique features that enable the
determination of location, direction of signal flow, and types of
neurotransmitters involved, promoting directional and multifaceted
communication. This study presents the first successful establishment
of a Janus synapse between dopaminergic (DA) neurons and abiotic substrates
by using a neuroligin-2 (NLG2)-mediated synapse-inducing method. NLG2
immobilized on gold-coated microspheres can induce synaptogenesis
upon contact with spatially isolated DA axons. The induced DA Janus
synapses exhibit stable synaptic activities comparable to that of
native synapses over time, suggesting their suitability for application
in neural interfaces. By calling for DA presynaptic organizations,
the NLG2-immobilized abiotic substrate is a promising tool for the
on-site detection of synaptic dopamine release
Modulation of Quinone PCET Reaction by Ca<sup>2+</sup> Ion Captured by Calix[4]quinone in Water
CalixĀ[4]Āarene-triacid-monoquinone
(CTAQ), a quinone-containing
water-soluble ionophore, was utilized to investigate how proton-coupled
electron transfer (PCET) reactions of quinones were influenced by
redox-inactive metal ions in aqueous environment. This ionophoric
quinone derivative captured a Ca<sup>2+</sup> ion that drastically
altered the voltammetric behavior of quinone, showing a characteristic
response to pH and unique redox wave separation. Spectroelectrochemistry
verified significant stabilization of the semiquinone, and electrocatalytic
currents were observed in the presence of Ca<sup>2+</sup>-free CTAQ.
Using digital simulation of cyclic voltammograms to clarify how the
thermodynamic properties of quinones were altered, a simple scheme
was proposed that successfully accounted for all the observations.
The change induced by Ca<sup>2+</sup> complexation was explained on
the basis of the combined effects of the electrostatic influence of
the captured metal ion and hydrogen bonding of water molecules with
the support of DFT calculation