9 Aptamers for the Diagnosis of Malign Tumors
255
moieties. The target cells have more than one recognition site, so that the cytosensor
can employ single or different types of aptamer or other recognition molecules for
one type of cells.
With the utilization of different designs for signal amplifications, sandwich-based
EC sensors can facilitate cancer cell detection. The enzyme-based signal amplification strategy usually employs the natural enzyme-labeled secondary recognition
units. For instance, the MUC1 aptamer functioned on the gold electrode surface for
MCF-7 cells identification, then the HRP-labeled aptamer was used for current signal
amplification. This cytosensor could detect MCF-7 cells in range of 10
2 –10
7 cells/mL
with the LOD of 100 cells/mL [91]. In contrast, the nanomaterial-based signal amplification strategy is employed to improve the detection sensitivity, just like catalysis
nanomaterials (nanozymes) [92]. For instance, Tabrizi’s group reported the flow
injection sandwich-type EC aptasensor for CCRF-CEM cells determination based
on the MWCNT-Pd nano nanocomposites-labeled catalytic aptamer. The target cells
were captured between the immobilized aptamer on the surface-functionalized electrode and the catalytic aptamer. Using the impedance and the voltammetry signals,
this aptasensor archived the detection linear range of 10–5.0 × 10
5 cells/mL with the
LOD of 8 cells/mL [88] (Fig. 9.6d). The same group fabricated another flow injection
sandwich-type EC aptasensor for adenocarcinoma gastric (ASG) cancer cell detection, by using the aptamer-modified Au@Ag nanoparticles for signal amplification
[93]. Another common strategy for signal amplification is that loading the nature
enzyme into the nanomaterials. Many enzyme-loaded multifunctional nanoprobes
have been employed for aptasensor fabrication, like the HRP-aptamer-AuNPs [94],
alkaline phosphatase (ALP) enzyme and concanavalin A (ConA)-coated AuNPs [95],
and hydroquinone (HQ)-HRP-aptamer/hemin/G-quadruplex aggregation [96].
9.4.2 Optical Aptasensors
The SPR technique has been employed in many types of cancer cells detections
with the help of several nanomaterials for signal amplification [97]. For instance, the
mucin-1 protein (MUC-1) aptamer-functionalized gold nanorods were employed for
constructing the SPR biosensor to detect MCF-7 breast cancer cells. The reported
LOD was 100 cells/mL [98]. Utilizing the specific aptamer immobilized gold
nanoparticles, the SPR signal was amplified to be able to detect 1 liver cancer cell
(SMCC-7721 cell) in 1 mL sample [99].
SERS technique could detect and image the cancer cells without the fluorescent molecular labels [56]. Tang et al reported an aptamer-based SERS nanoprobe
for metastatic breast cancer cells (MCF7) detection and imaging in mice blood. In
the work, the AS1411 and MUC1 aptamers were immobilized on the gold surface
through alkyne moieties. The change of SERS spectra reflects the number of target
cells, with the LOD of 5 cells/200 mL media [100]. Then a multiplex cocktail
of bio-orthogonal nanoprobes was developed for in vivo simultaneous detections
of several breast cancer phenotypes. This SERS biosensor used gold nanoflowers
255
moieties. The target cells have more than one recognition site, so that the cytosensor
can employ single or different types of aptamer or other recognition molecules for
one type of cells.
With the utilization of different designs for signal amplifications, sandwich-based
EC sensors can facilitate cancer cell detection. The enzyme-based signal amplification strategy usually employs the natural enzyme-labeled secondary recognition
units. For instance, the MUC1 aptamer functioned on the gold electrode surface for
MCF-7 cells identification, then the HRP-labeled aptamer was used for current signal
amplification. This cytosensor could detect MCF-7 cells in range of 10
2 –10
7 cells/mL
with the LOD of 100 cells/mL [91]. In contrast, the nanomaterial-based signal amplification strategy is employed to improve the detection sensitivity, just like catalysis
nanomaterials (nanozymes) [92]. For instance, Tabrizi’s group reported the flow
injection sandwich-type EC aptasensor for CCRF-CEM cells determination based
on the MWCNT-Pd nano nanocomposites-labeled catalytic aptamer. The target cells
were captured between the immobilized aptamer on the surface-functionalized electrode and the catalytic aptamer. Using the impedance and the voltammetry signals,
this aptasensor archived the detection linear range of 10–5.0 × 10
5 cells/mL with the
LOD of 8 cells/mL [88] (Fig. 9.6d). The same group fabricated another flow injection
sandwich-type EC aptasensor for adenocarcinoma gastric (ASG) cancer cell detection, by using the aptamer-modified Au@Ag nanoparticles for signal amplification
[93]. Another common strategy for signal amplification is that loading the nature
enzyme into the nanomaterials. Many enzyme-loaded multifunctional nanoprobes
have been employed for aptasensor fabrication, like the HRP-aptamer-AuNPs [94],
alkaline phosphatase (ALP) enzyme and concanavalin A (ConA)-coated AuNPs [95],
and hydroquinone (HQ)-HRP-aptamer/hemin/G-quadruplex aggregation [96].
9.4.2 Optical Aptasensors
The SPR technique has been employed in many types of cancer cells detections
with the help of several nanomaterials for signal amplification [97]. For instance, the
mucin-1 protein (MUC-1) aptamer-functionalized gold nanorods were employed for
constructing the SPR biosensor to detect MCF-7 breast cancer cells. The reported
LOD was 100 cells/mL [98]. Utilizing the specific aptamer immobilized gold
nanoparticles, the SPR signal was amplified to be able to detect 1 liver cancer cell
(SMCC-7721 cell) in 1 mL sample [99].
SERS technique could detect and image the cancer cells without the fluorescent molecular labels [56]. Tang et al reported an aptamer-based SERS nanoprobe
for metastatic breast cancer cells (MCF7) detection and imaging in mice blood. In
the work, the AS1411 and MUC1 aptamers were immobilized on the gold surface
through alkyne moieties. The change of SERS spectra reflects the number of target
cells, with the LOD of 5 cells/200 mL media [100]. Then a multiplex cocktail
of bio-orthogonal nanoprobes was developed for in vivo simultaneous detections
of several breast cancer phenotypes. This SERS biosensor used gold nanoflowers