9 Aptamers for the Diagnosis of Malign Tumors
251
mismatched base pairs, these two subunits can exist alone without the target. The
target VEGF could bind with Apt 1 and Apt 2 to form the target/aptamer complex
with duplex DNA region, and trigger the enzyme-assisted target-recycling signal
amplification to generate a positive fluorescence signal. And the employment of GO
could effectively reduce the background signal and improved high sensitivity with
the LOD as 1 pM [64] (Fig. 9.5c).
With the continuous efforts and increased species of cancer-related protein
biomarker aptamers, the possibility to develop suitable fluorescence probe-assisted
aptasensors can lend more impetus to improve this technique for clinic applications.
Moreover, an aptamer-based fluorescence analysis platform can be combined with
novel luminescent nanomaterials and various nanocarriers, providing the basis for
synergistic therapeutic strategies.
9.3.2.3 Colorimetric-Based Platform
Colorimetric assays employ the reagents that offer a measurable color change relative to the amount of the analyte. Benefit from the convenient operation, visualized results, the colorimetric assays are widely used in several biochemical tests,
as well as the structure of the aptamer-based platform. For example, Yang’s group
developed a label-free colorimetric aptasensor for thrombin detection, utilizing the
peroxidase mimicking the activity of DNA-templated Ag/Pt bimetallic nanoclusters
(DNA–Ag/Pt NCs) to improving the sensitivity [65]. In another study, the colorimetric biosensing system was established for cancer-related gene sensing based on
the amplification of a DNA molecular machine, containing a primer-contained polymerization template (PTT) and a primer-locked hairpin probe (HP). In the presence
of the target K-ras gene, the DNA machine was formed with the help of polymerase.
Then, the nicking endonuclease assisted the formation of aptamer/hemin duplex and
HRP-mimicking DNAzyme to amplify the signal. This proposed assay exhibited a
linear range as 0.01–150 nM, with the LOD of 10 pM [66].
9.4 Tumor Cells Analysis
Cancers are formed through the accumulation of multiple mutations within the
malignant cells, leading to the uncontrolled cells growth with the help of independent synthesis or overexpression of certain enzymes or growth factors. Thus, tumor
cells are important cancer biomarkers for disease diagnosis. Circulating tumor cells
(CTCs) are a type of cancer cells circulating in peripheral blood, which are derived
from primary or metastatic tumors and leading to new fatal metastasis. Therefore,
CTCs are the main reason for cancer-caused death, and to some extent revealing the
mechanism of cancer development and metastasis [67, 68]. Capture and detection of
CTCs can be used as a liquid biopsy of several tumors, offering the opportunity for
early diagnosis of cancers, earlier analysis of recurrence and therapeutic efficacy, and
251
mismatched base pairs, these two subunits can exist alone without the target. The
target VEGF could bind with Apt 1 and Apt 2 to form the target/aptamer complex
with duplex DNA region, and trigger the enzyme-assisted target-recycling signal
amplification to generate a positive fluorescence signal. And the employment of GO
could effectively reduce the background signal and improved high sensitivity with
the LOD as 1 pM [64] (Fig. 9.5c).
With the continuous efforts and increased species of cancer-related protein
biomarker aptamers, the possibility to develop suitable fluorescence probe-assisted
aptasensors can lend more impetus to improve this technique for clinic applications.
Moreover, an aptamer-based fluorescence analysis platform can be combined with
novel luminescent nanomaterials and various nanocarriers, providing the basis for
synergistic therapeutic strategies.
9.3.2.3 Colorimetric-Based Platform
Colorimetric assays employ the reagents that offer a measurable color change relative to the amount of the analyte. Benefit from the convenient operation, visualized results, the colorimetric assays are widely used in several biochemical tests,
as well as the structure of the aptamer-based platform. For example, Yang’s group
developed a label-free colorimetric aptasensor for thrombin detection, utilizing the
peroxidase mimicking the activity of DNA-templated Ag/Pt bimetallic nanoclusters
(DNA–Ag/Pt NCs) to improving the sensitivity [65]. In another study, the colorimetric biosensing system was established for cancer-related gene sensing based on
the amplification of a DNA molecular machine, containing a primer-contained polymerization template (PTT) and a primer-locked hairpin probe (HP). In the presence
of the target K-ras gene, the DNA machine was formed with the help of polymerase.
Then, the nicking endonuclease assisted the formation of aptamer/hemin duplex and
HRP-mimicking DNAzyme to amplify the signal. This proposed assay exhibited a
linear range as 0.01–150 nM, with the LOD of 10 pM [66].
9.4 Tumor Cells Analysis
Cancers are formed through the accumulation of multiple mutations within the
malignant cells, leading to the uncontrolled cells growth with the help of independent synthesis or overexpression of certain enzymes or growth factors. Thus, tumor
cells are important cancer biomarkers for disease diagnosis. Circulating tumor cells
(CTCs) are a type of cancer cells circulating in peripheral blood, which are derived
from primary or metastatic tumors and leading to new fatal metastasis. Therefore,
CTCs are the main reason for cancer-caused death, and to some extent revealing the
mechanism of cancer development and metastasis [67, 68]. Capture and detection of
CTCs can be used as a liquid biopsy of several tumors, offering the opportunity for
early diagnosis of cancers, earlier analysis of recurrence and therapeutic efficacy, and