Electrochemical aptasensors provide a highly sensitive and selective methodology. Since only a few target analytes exhibit redox properties, an aptamer probe is
usually created by attachment of electroactive labels, such as methylene blue,
ferrocene, or similar [40]. Additionally, molecular beacons consist of a dual-label
molecule which adopts two or more conformations [41]. After target recognition,
molecular beacons change their conformation producing a signal change which is
detectable. In fact, electrochemical beacons (e-beacons) have been explored by Radi
et al. Therein, a bifunctional derivative of the thrombin-binding aptamer is used with
a redox-active moiety. The ferrocene-labeled aptamer with thiol functionality
was bound to a polycrystalline gold electrode surface. The results showed a linear
response of the ferrocene oxidation signal to the increase in the thrombin
concentration [42].
Nonetheless, optical devices are most widely developed and available in the
market place [8]. A molecular beacon fluorescence resonance energy transfer
(FRET) phenomenon is the most commonly used strategy and will be described in
Sect. 3.1.
Aptamer-linked immobilized sorbent assay (ALISA), flow cytometry,
microfluidics, precipitation, and magnetic nanomaterials are technologies that have
also been adapted to aptasensors [43].
In brief, the use of aptamers as a diagnostic tool is developed by diverse
methodologies, applicable to diverse targets, with growing market place products
and sensitive, specific, robust, and affordable results.
2.3 In Vivo Aptamer Diagnostics
The successful use of probes for in vivo applications requires additional characteristics, to assure the effectiveness and a safety profile. A molecular imaging probe
needs to reduce the pharmacological effects to biological systems and processes to a
minimal level [10]. Principally, assurance profiles and overcoming biological barriers present a challenge [44]. Thus, a probe with clinical translation potential is
expected to exhibit the following properties.
Non-immunogenic and Nontoxic Both aspects provide the biological assurance
profile for an in vivo probe. Probes for in vivo applications are treated as a particular
class of pharmaceutical, and world pharmaceutical regulations are applied. Although
a diagnostic probe allows the observation of pathology, it has no pharmacological
effect and is administered in a very small amount. In addition, the absence of
immunogenicity and toxicity of aptamers results in the biological assurance profile
for the development of an in vivo probe [7].
High In Vivo Stability This is a huge challenge due to numerous enzymes in serum
and tissue, which may degrade the probe. Probes have to overcome this first
biological barrier to reach the target at a sufficient concentration. Since endo- and
exonucleases are abundant in biological fluids, several modifications of nucleotides
148
V. Calzada
usually created by attachment of electroactive labels, such as methylene blue,
ferrocene, or similar [40]. Additionally, molecular beacons consist of a dual-label
molecule which adopts two or more conformations [41]. After target recognition,
molecular beacons change their conformation producing a signal change which is
detectable. In fact, electrochemical beacons (e-beacons) have been explored by Radi
et al. Therein, a bifunctional derivative of the thrombin-binding aptamer is used with
a redox-active moiety. The ferrocene-labeled aptamer with thiol functionality
was bound to a polycrystalline gold electrode surface. The results showed a linear
response of the ferrocene oxidation signal to the increase in the thrombin
concentration [42].
Nonetheless, optical devices are most widely developed and available in the
market place [8]. A molecular beacon fluorescence resonance energy transfer
(FRET) phenomenon is the most commonly used strategy and will be described in
Sect. 3.1.
Aptamer-linked immobilized sorbent assay (ALISA), flow cytometry,
microfluidics, precipitation, and magnetic nanomaterials are technologies that have
also been adapted to aptasensors [43].
In brief, the use of aptamers as a diagnostic tool is developed by diverse
methodologies, applicable to diverse targets, with growing market place products
and sensitive, specific, robust, and affordable results.
2.3 In Vivo Aptamer Diagnostics
The successful use of probes for in vivo applications requires additional characteristics, to assure the effectiveness and a safety profile. A molecular imaging probe
needs to reduce the pharmacological effects to biological systems and processes to a
minimal level [10]. Principally, assurance profiles and overcoming biological barriers present a challenge [44]. Thus, a probe with clinical translation potential is
expected to exhibit the following properties.
Non-immunogenic and Nontoxic Both aspects provide the biological assurance
profile for an in vivo probe. Probes for in vivo applications are treated as a particular
class of pharmaceutical, and world pharmaceutical regulations are applied. Although
a diagnostic probe allows the observation of pathology, it has no pharmacological
effect and is administered in a very small amount. In addition, the absence of
immunogenicity and toxicity of aptamers results in the biological assurance profile
for the development of an in vivo probe [7].
High In Vivo Stability This is a huge challenge due to numerous enzymes in serum
and tissue, which may degrade the probe. Probes have to overcome this first
biological barrier to reach the target at a sufficient concentration. Since endo- and
exonucleases are abundant in biological fluids, several modifications of nucleotides
148
V. Calzada