Medical Design Briefs - June 2021 - 16

Next-Gen POC Diagnostics
Fig. 2 - Desktop potentiostat (left) from the 1990s and handheld potentiostat (right) from 2020. (Left photo courtesy of University of Rostock - Institute
for Electronic Appliances and Circuits)
tiostat is required (see Figure 2). A po -
tentiostat uses three electrodes and a
feedback loop to control the potential
and measure the current flowing at just
one of these electrodes, the working
electrode. The potential will be measured
to a fixed reference point and thus
a lot of information about the event happening
at the working electrode can be
gathered.
Why not just two electrodes? One reason
is that the potential of the working
electrode cannot be measures against a
fixed point when there are only two electrodes.
Imagine a two-electrode system
that consists of the already mentioned
working electrode, and the electrode,
whose potential should be the fixed reference
point, is the reference electrode.
In this case, a certain potential is
applied between these electrodes and an
electrochemical reaction happens at the
Technique Working principle
Cyclic
Voltammetry
Square Wave
Voltammetry
Linear potential ramps,
current recorded
Potential pulses superimposed
on a linear ramp, current
difference between right
before the pulse and the end
of the pulse
Open Circuit
Potentiometry
Electrochemical
Impedance
Spectroscopy
Zero current, potential is
measured
AC potential applied,
impedance and phase shift
from AC current calculated
working electrode, but since the circuit
needs to be closed and current needs to
flow, a reaction that is inverse to the
reaction at the working electrode must
occur; that is, if an oxidation occurs at
the working electrode, a reduction must
take place at the reference electrode. If
a current flows at a constant potential,
an electrochemical reaction must happen
according to Faraday's law.
The change of the solution surrounding
the reference electrode, due to a
flowing current, leads to a change of the
potential that is supposed to be the fixed
reference point. But the current flow
cannot be limited through the reference
electrode (RE), because all limitations
should be caused by the desired process
to investigate; that is, the process at the
working electrode (WE).
The solution for this problem is a
third electrode. At this counter elecAdvantages
Shape
often
characteristic, fast,
quantitative signal
Sensitive, overcomes
diffusion limitation,
quantitative signal
Noninvasive,
quantitative signal
Very interfacesensitive,
label-free
detection
Application areas
Fundamental research,
characterization
Quantitative
measurements
Corrosion research,
ion-selective electrodes
Coatings, corrosion,
battery research,
label-free biosensors
Table 1. Different electrochemical techniques enable precise potential control and current measurement
for the detection of many substances.
16
Cov
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ToC
trode (CE), also known as auxiliary electrode,
the counter-reaction to the working
electrode's reactions takes place.
The current is flowing between the
working and the counter electrode. The
potential is controlled between the
working electrode and reference electrode.
The potential between the counter
electrode and reference electrode is
adjusted in such a way that the current
flowing through the working electrode
at a certain potential between working
and reference electrode is satisfied.
This technology allows the use of
many different electrochemical techniques
like cyclic voltammetry, square
wave voltammetry, open circuit potential
measurements, etc. (see Table 1). The
precise potential control and current
measurement allow the detection of
many substances. This has led to many
lab-based quantitative measurements. It
is not always possible to wait for a laboratory
or to ship samples. On-site POC
measurements, especially during the
pandemic, have become very important.
Electroanalysis, the detection of substances
by electrochemistry, offers many
options to quantitatively determine different
substances and species, but for
many years potentiostats were lab bound
(see Figure 3). Now the newest generation
of compact potentiostats offered by
PalmSens, for example, with expertise in
instrument design, including hardware,
firmware, and software offer potentiostat
systems with high precision, portability,
programmability, and low cost.
The compact and ready-to-use potentiostats
like the Sensit Smart, are capable
Medical Design Briefs, June 2021
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Medical Design Briefs - June 2021

Table of Contents for the Digital Edition of Medical Design Briefs - June 2021

Medical Design Briefs - June 2021 - Intro
Medical Design Briefs - June 2021 - Cov4
Medical Design Briefs - June 2021 - Cov1a
Medical Design Briefs - June 2021 - Cov1b
Medical Design Briefs - June 2021 - Cov1
Medical Design Briefs - June 2021 - Cov2
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Medical Design Briefs - June 2021 - Cov3
Medical Design Briefs - June 2021 - CovIV
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