After the selection procedure, sequencing is performed, and the aptamers are
synthetized [28]. Based on multiple alignment and structural simulation software, it is
possible to predict different characteristics such as structural motifs, G-quadruplex, and
conserved sequences.
There are multiple post-SELEX reactions described, and fortunately, aptamers
are versatile enough to undergo diverse modifications [29]. For example, nowadays,
it is possible to introduce new chemical modifications to protect aptamers against
degradation or confer new functionalities.
Oligonucleotide composition exposes a variety of chemical groups and thus
enables the attachment of signaling agents. Likewise, signaling agents can enable
diverse chemical reactions or physical interaction with aptamers. Most frequently,
functionalities consist of the covalent incorporation of 5
0 or 3
0 groups, such as
amines and thiols, by phosphor chemistry reactions [30]. However, it must be
verified that post-SELEX modifications do not affect the initial characteristics of
the oligonucleotide sequence. Finally, the purification of the probe is very important.
The molecular weight and physicochemical properties of aptamers allow for the use
of molecular exclusion techniques or similar, which enable a complete isolation of
the probe.
2.2 Aptamer In Vitro Applications
Aptamer characteristics, as summarized above, make them ideal diagnostic reagents.
Accordingly, the number of applications continues to grow and is expected to make
great contributions to the biotechnology industry in the near future [31]. To date, a
high number of in vitro aptamer diagnostic applications have been reported [32].
The most developed application of diagnostic aptamers is in the field of biosensors (“aptasensors”), wherein the aptamers’ versatility allows for a wide array of
sensor formats.
Aptamers often recognize their targets by a mechanism in which they undergo
structural rearrangements [33] which can be used to transduce the binding event into
a measurable signal [34].
Surface plasmon resonance (SPR) is a modern analytical technique based on the
measured signal being caused by refractive index changes, due to the mass of a
compound in solution that interacts with a target immobilized at a liquid–solid
interface, in an evanescent wave field [35]. Recently, a SPR aptamer biosensor
was explored for the detection of a label-free toxin. These strategies have great
advantages in terms of rapidity and real-time sensing as well as sensitivity [36].
Otherwise, a variety of aptamer probes are used for biosensor development, such
as electrochemical sensors, surface-enhanced Raman spectroscopy (SERS), and
optical formats.
The SERS technology is based on the frequency shifts of Raman scattering and
can provide “fingerprint” information of the analytes’ chemical structure [37]. In this
sense, an aptamer sandwich methodology was developed for influenza virus
146
V. Calzada
synthetized [28]. Based on multiple alignment and structural simulation software, it is
possible to predict different characteristics such as structural motifs, G-quadruplex, and
conserved sequences.
There are multiple post-SELEX reactions described, and fortunately, aptamers
are versatile enough to undergo diverse modifications [29]. For example, nowadays,
it is possible to introduce new chemical modifications to protect aptamers against
degradation or confer new functionalities.
Oligonucleotide composition exposes a variety of chemical groups and thus
enables the attachment of signaling agents. Likewise, signaling agents can enable
diverse chemical reactions or physical interaction with aptamers. Most frequently,
functionalities consist of the covalent incorporation of 5
0 or 3
0 groups, such as
amines and thiols, by phosphor chemistry reactions [30]. However, it must be
verified that post-SELEX modifications do not affect the initial characteristics of
the oligonucleotide sequence. Finally, the purification of the probe is very important.
The molecular weight and physicochemical properties of aptamers allow for the use
of molecular exclusion techniques or similar, which enable a complete isolation of
the probe.
2.2 Aptamer In Vitro Applications
Aptamer characteristics, as summarized above, make them ideal diagnostic reagents.
Accordingly, the number of applications continues to grow and is expected to make
great contributions to the biotechnology industry in the near future [31]. To date, a
high number of in vitro aptamer diagnostic applications have been reported [32].
The most developed application of diagnostic aptamers is in the field of biosensors (“aptasensors”), wherein the aptamers’ versatility allows for a wide array of
sensor formats.
Aptamers often recognize their targets by a mechanism in which they undergo
structural rearrangements [33] which can be used to transduce the binding event into
a measurable signal [34].
Surface plasmon resonance (SPR) is a modern analytical technique based on the
measured signal being caused by refractive index changes, due to the mass of a
compound in solution that interacts with a target immobilized at a liquid–solid
interface, in an evanescent wave field [35]. Recently, a SPR aptamer biosensor
was explored for the detection of a label-free toxin. These strategies have great
advantages in terms of rapidity and real-time sensing as well as sensitivity [36].
Otherwise, a variety of aptamer probes are used for biosensor development, such
as electrochemical sensors, surface-enhanced Raman spectroscopy (SERS), and
optical formats.
The SERS technology is based on the frequency shifts of Raman scattering and
can provide “fingerprint” information of the analytes’ chemical structure [37]. In this
sense, an aptamer sandwich methodology was developed for influenza virus
146
V. Calzada