Biomedical Engineering Reference
In-Depth Information
Fig. 4.8
(
a
) Schematic of adenosine-induced assembly of split fluorescent aptamers on liposome
surface. (
b
) If immobilized on silica nanoparticles, the aptamers cannot diffuse or assemble in the
presence of adenosine. Fluorescence spectra for split aptamer immobilized on fluid DOPC (
c
)or
on silica (
d
) upon titration with adenosine (Reproduced from Ref. [
61
] by permission of the Royal
Society of Chemistry)
endocytosis [
59
]. Using such a dynamic assembly mechanism, numerous proteins
and metabolites can be detected by the cell. Due to the complexity of membrane
proteins, studying their assembly remains difficult [
60
]. In addition, analytical
applications related to the ligand mobility have been rarely explored. By splitting an
aptamer into two halves and attaching both ends to the liposome surface containing a
fluorophore (FAM and TMR) on each split aptamer, a biomimetic sensor is produced
(Fig.
4.8
a). In the presence of the target analyte adenosine, the two aptamer halves
assemble into the binding structure to quench the donor FAM fluorescence because
of the nearby TMR acceptor [
61
]. As shown in Fig.
4.8
c, the FAM fluorescence
was quenched by
50% in the presence of 2-mM adenosine, and the signal change
was instantaneous. A detection limit of 60-
M adenosine was obtained using this
sensor. For comparison, the same split aptamer system was immobilized on a silica
nanoparticle (Fig.
4.8
b), where no fluorescence signal change was observed upon
addition of adenosine (Fig.
4.8
d).
4.9
Biomedical Applications
Targeted drug delivery can increase drug efficacy and reduce toxicity. Currently
15 liposome-based drugs are either commercially available or in phase III clinical
studies [
62
]. For targeting purposes, a corresponding antibody is often used for
cellular receptor recognition. However, antibodies have poor stability and are
susceptible to denaturation. They are also immunogenic with large batch-to-batch
Search WWH ::
Custom Search