252
Q. Lv et al.
individual anti-cancer drugs chosen [69]. However, the CTCs sensing methods have
to possess high sensitivity and selectivity, because of their rare counts in the complex
blood samples [70]. Many analysis approaches have been successfully constructed for
CTCs identification and detection. For instance, the first CTC analysis test, so-called
CellSearch has been proved by the U.S. Food and Drug Administration (FDA). This
test method bases on immunomagnetic enrichment by binding the specific surface
molecule EpCAM of tumor cells with antibodies. Until now, the CellSearch is the
only CTC sensing device with FDA clearance and widely used in clinical [71].
Cancer cells could be captured by identifying the over-expressed abnormal
proteins or glycans on the cell surface using the targeting elements such as lectin,
antibody, and aptamer. Aptamers can be used in sufficiently sensitive diagnosis assays
for the detection and capture of circulating tumor cells, as well as for the followed
release of viable cancer cells. Aptamer-based functional large DNA networks have
been applied for cancer cells capture, and then nuclease treatment could recover the
cells [72]. Similarly, the aptamers immobilized on the surface of silicon nanowires
(SiNWs) could achieve a capture rate of 95% and a recovery efficiency of 94%
for circulating lung cancer cells [73]. In another work, the anti-EGFP aptamerfunctionalized glass beads were used to establish the Hele-Shaw device for efficiently
isolating cancer cells from the cellular mixture. The complementary sequence of the
capture aptamers was used for cell release operation [74]. Therefore, these aptamerbased approaches can facilitate the recovery of the viable cancer cells only under
mild conditions, but the natural nucleases-containing biological samples (as blood)
can’t be tasted directly due to the aptamer degradation.
9.4.1 Electrochemical Cytosensors
Many electrochemical devices (EC)have been exploited for cancer cells detection, including amperometry, voltammetry, and impedance biosensors [75], electrochemiluminescence cytosensors (ECL) [76], as well as photoelectrochemical
sensors (PEC), depended on the electrochemical signal changes. These electrochemical cytosensors have some unique advantages like rapid response, non-destructive,
easy operation, and miniaturization. The combination of EC techniques with the
tumor cells-targeting aptamers approves great potential for constructing cancer diagnosis platforms [77, 78]. The aptamer-based EC cytosensors can fall into several
categories according to their configuration like aptamer-target cells (direct-type),
capture elements-target cells-signaling element (sandwich-type), and some other
approaches. For the detection sensitivity improvement, a variety of nanomaterials
have been utilized for recognition elements immobilization or electrochemical reaction catalysis, in order to accelerate signal transduction and amplify the signals
[79].
For the direct-type EC sensors, the establishment of a bio-recognition interface
on the electrodes is very important, which can monitor the target cell-capture event
and convert it to readable EC signals. The aptamer probes are usually immobilized
Q. Lv et al.
individual anti-cancer drugs chosen [69]. However, the CTCs sensing methods have
to possess high sensitivity and selectivity, because of their rare counts in the complex
blood samples [70]. Many analysis approaches have been successfully constructed for
CTCs identification and detection. For instance, the first CTC analysis test, so-called
CellSearch has been proved by the U.S. Food and Drug Administration (FDA). This
test method bases on immunomagnetic enrichment by binding the specific surface
molecule EpCAM of tumor cells with antibodies. Until now, the CellSearch is the
only CTC sensing device with FDA clearance and widely used in clinical [71].
Cancer cells could be captured by identifying the over-expressed abnormal
proteins or glycans on the cell surface using the targeting elements such as lectin,
antibody, and aptamer. Aptamers can be used in sufficiently sensitive diagnosis assays
for the detection and capture of circulating tumor cells, as well as for the followed
release of viable cancer cells. Aptamer-based functional large DNA networks have
been applied for cancer cells capture, and then nuclease treatment could recover the
cells [72]. Similarly, the aptamers immobilized on the surface of silicon nanowires
(SiNWs) could achieve a capture rate of 95% and a recovery efficiency of 94%
for circulating lung cancer cells [73]. In another work, the anti-EGFP aptamerfunctionalized glass beads were used to establish the Hele-Shaw device for efficiently
isolating cancer cells from the cellular mixture. The complementary sequence of the
capture aptamers was used for cell release operation [74]. Therefore, these aptamerbased approaches can facilitate the recovery of the viable cancer cells only under
mild conditions, but the natural nucleases-containing biological samples (as blood)
can’t be tasted directly due to the aptamer degradation.
9.4.1 Electrochemical Cytosensors
Many electrochemical devices (EC)have been exploited for cancer cells detection, including amperometry, voltammetry, and impedance biosensors [75], electrochemiluminescence cytosensors (ECL) [76], as well as photoelectrochemical
sensors (PEC), depended on the electrochemical signal changes. These electrochemical cytosensors have some unique advantages like rapid response, non-destructive,
easy operation, and miniaturization. The combination of EC techniques with the
tumor cells-targeting aptamers approves great potential for constructing cancer diagnosis platforms [77, 78]. The aptamer-based EC cytosensors can fall into several
categories according to their configuration like aptamer-target cells (direct-type),
capture elements-target cells-signaling element (sandwich-type), and some other
approaches. For the detection sensitivity improvement, a variety of nanomaterials
have been utilized for recognition elements immobilization or electrochemical reaction catalysis, in order to accelerate signal transduction and amplify the signals
[79].
For the direct-type EC sensors, the establishment of a bio-recognition interface
on the electrodes is very important, which can monitor the target cell-capture event
and convert it to readable EC signals. The aptamer probes are usually immobilized