9 Aptamers for the Diagnosis of Malign Tumors
267
Colorimetric-based assays are easy operation without precise equipment,
presenting visual results in a short time. Therefore, many colorimetric-based assays
have been developed for exosome detection [156]. A multiplexed colorimetric sensor
was fabricated based on the modification of AuNPs with a panel of aptamers for
the detection of ubiquitous or putative exosome surface proteins. The complexation of aptamers with the AuNPs could protect them from aggregation. In the presence of exosomes, the specific and much stronger interaction between aptamers and
exosomes would replace the aptamers-AuNPs binding, leading to the aggregation
of AuNPs and visible color change of solution [162] (Fig. 9.10b). Another colorimetric and visible sensor was established employing the s-SWCNTs (single-walled
carbon nanotubes) as a platform for the immobilization of the aptamer targeting
CD63, a ubiquitous exosome marker. The aptamer-functionalized s-SWCNTs act as
an enhanced peroxidase-mimic nanozyme for TMB (3,3’,5,5’-tetramethylbenzidine)
oxidization, leading to a deep blue color change in the solution. The appearance of
exosomes attracts the aptamers to leave the surface of s-SWCNTs, reducing the
nanozyme activity and resulting in a visible and measurable color change. The LOD
of this sensor was 5.2×10
5 exosomes/mL [163].
Electrochemical-based aptasensors have also been developed for exosomes
sensing. For example, the aptamer-based electrochemical sensor for tetraspanin
CD63 detection was developed based on the competition between redox-labeled
complementary DNA strand and the target exosomes for the aptamers immobilized
onto the gold electrode [164]. In another work, a label-free DPV aptasensor was established for the liver cancer HepG2 cells and exosomes detection. Combing with the
DNA nano-tetrahedron (NTH) structure and aptamers, this NTH-based aptasensor
could detect the hepatocellular exosomes with 100-fold higher sensitivity compared
to the single-stranded aptamer-based sensor, proving the proof-of-concept for tumorderived exosomes quantification [165] (Fig. 9.10c). The traditional single-stranded
DNA molecules always suffer from easily non-specifically aggregation on the electrode interface. Compared to this, DNA NTH structure exhibits mechanical rigidity,
structural stability, as well as excellent specific orientation, due to the pyramid-like
high-organizational formation united with six edges and four triangle faces, offering
reduced interfacial entanglement and segregation [166]. Based on the SERS technique, an ultrasensitive aptasensor was established for simultaneous detection of three
types of cancer-derived exosomes. Three different aptamers, as CEA, HER2, and
PSMA aptamers, (targeting T84 colorectal, SKBR3 breast cancer cells, and LNCaP
prostate cancer cells, respectively) were immobilized on the surface of AuNPs. Using
magnetic beads as the capture substrate, the added exosomes can induce the formation
of aptamer-immuno-complex and archive the LOD of 73, 32, and 203 exosomes/mL
for T84, SKBR3, and LNCaP, respectively [167] (Fig. 9.10d).
267
Colorimetric-based assays are easy operation without precise equipment,
presenting visual results in a short time. Therefore, many colorimetric-based assays
have been developed for exosome detection [156]. A multiplexed colorimetric sensor
was fabricated based on the modification of AuNPs with a panel of aptamers for
the detection of ubiquitous or putative exosome surface proteins. The complexation of aptamers with the AuNPs could protect them from aggregation. In the presence of exosomes, the specific and much stronger interaction between aptamers and
exosomes would replace the aptamers-AuNPs binding, leading to the aggregation
of AuNPs and visible color change of solution [162] (Fig. 9.10b). Another colorimetric and visible sensor was established employing the s-SWCNTs (single-walled
carbon nanotubes) as a platform for the immobilization of the aptamer targeting
CD63, a ubiquitous exosome marker. The aptamer-functionalized s-SWCNTs act as
an enhanced peroxidase-mimic nanozyme for TMB (3,3’,5,5’-tetramethylbenzidine)
oxidization, leading to a deep blue color change in the solution. The appearance of
exosomes attracts the aptamers to leave the surface of s-SWCNTs, reducing the
nanozyme activity and resulting in a visible and measurable color change. The LOD
of this sensor was 5.2×10
5 exosomes/mL [163].
Electrochemical-based aptasensors have also been developed for exosomes
sensing. For example, the aptamer-based electrochemical sensor for tetraspanin
CD63 detection was developed based on the competition between redox-labeled
complementary DNA strand and the target exosomes for the aptamers immobilized
onto the gold electrode [164]. In another work, a label-free DPV aptasensor was established for the liver cancer HepG2 cells and exosomes detection. Combing with the
DNA nano-tetrahedron (NTH) structure and aptamers, this NTH-based aptasensor
could detect the hepatocellular exosomes with 100-fold higher sensitivity compared
to the single-stranded aptamer-based sensor, proving the proof-of-concept for tumorderived exosomes quantification [165] (Fig. 9.10c). The traditional single-stranded
DNA molecules always suffer from easily non-specifically aggregation on the electrode interface. Compared to this, DNA NTH structure exhibits mechanical rigidity,
structural stability, as well as excellent specific orientation, due to the pyramid-like
high-organizational formation united with six edges and four triangle faces, offering
reduced interfacial entanglement and segregation [166]. Based on the SERS technique, an ultrasensitive aptasensor was established for simultaneous detection of three
types of cancer-derived exosomes. Three different aptamers, as CEA, HER2, and
PSMA aptamers, (targeting T84 colorectal, SKBR3 breast cancer cells, and LNCaP
prostate cancer cells, respectively) were immobilized on the surface of AuNPs. Using
magnetic beads as the capture substrate, the added exosomes can induce the formation
of aptamer-immuno-complex and archive the LOD of 73, 32, and 203 exosomes/mL
for T84, SKBR3, and LNCaP, respectively [167] (Fig. 9.10d).