Biomedical Engineering Reference
In-Depth Information
required to achieve electrical signals. Labeling or tagging is dei ned as the
usage of additional chemicals other than the receptors to obtain an output
signal at the transducer. A typical example of labeling is using dyes with
nucleic acid probes to produce l uorescence.
Unfortunately, the use of labels or dyes, also create artifacts in the output
response. Removing the necessity of tagging allow researchers to conduct
biological, physiological, and pharmacological analyses under conditions
that more closely mimic those found in a living organism with
in vitro
assays. Elimination of reagents or cell engineering, also simplii es both
assay development and sensor fabrication. In drug discovery research for
example, label-free assays can developed for biological target validation,
pathway deconvolution, receptor panning, agonist trai cking, as well as
ligand-bias and orphan target assay development, among others. Label-free
analysis has also gained popularity due to the success of pathway analysis-
based drug discovery, which focuses on understanding interdependencies
among biological pathways. h e usage other methods such as electrical or
chemical signals instead of dyeing, allows scientists to gain more under-
standing on cell behavior and how they communicate with each other.
8.3 Electrochemical Biosensors
Electrochemical biosensors convert biochemical events into electrical sig-
nals. When a biological sample is placed on the sensor, the sensor should
be able to produce an electrical signal, which corresponds to the concen-
tration of the sample. Electrical signals are produced due to the transfer
of electrons at the solid-liquid interface of the sensor. Depending on the
experimental setup, dif erent forms of electrical signals can be obtained
such as voltage (potentiometry), current (amperometry) and impedance
(impedance spectroscopy).
In brief, potentiometry involves the measurement of voltage in the bio-
sensor or electrochemical cell, when no current is applied. Measured volt-
age should be proportional to the concentration of the analyte under test.
h e typical equation relating voltage or potential, E in the presence of an
ion a, and an interfering species, b can be described using the Nernst equa-
tion set out as
Equation 8.1
below:
RT
(
)
0
EE
=−
log
aKa
+
(8.1)
a
a b
,
b
Fx
