330
Y. Cheng and H. Jin
In 2019, Wu group [42] fabricated a kind of electrochemical sensor based on
aptamer, which can be used for real-time monitoring of insulin release in vitro. The
sensor uses a guanine-rich aptamer modified by redox markers to recognize insulin
specifically. The aptamer can fold into a G-quadruplex. The insulin sensor may also
be used to monitor insulin secretion by β cells in the pancreas [43]. LOD of this
insulin sensor can be as low as 20 nM.
11.2.4 25-HydroxyvitaminD3 Related Aptamers
Vitamin D is an essential metabolite in the human body. Under the human epidermis,
vitamin D precursors are converted to vitamin D in blood vessels by vitamin D binding
protein (DBP) and stored in a semi-activated state of 25-hydroxy vitamin D3. When
vitamin D is needed in human tissues, this semi-activated form of vitamin D enters
the tissue and converts it into a fully activated state, which is 1,25-hydroxy vitamin
D3 [44]. More than 50% of people in the world suffer a lack of vitamin D [45]. When
people are deficient in vitamin D, they are at increased risk for rheumatoid arthritis,
metabolic syndrome, cancer, and cardiovascular disease. Almost every tissue in the
human body has the receptors of the 25-hydroxy vitamin D3, which is a suitable target
for detecting vitamin D levels in human body. Traditionally, researchers have used
commercial antibody kits to detect 25-hydroxy vitamin D3. However, considering the
short shelf life, high cost, and rigorous storage conditions of antibody kits, researchers
have to find new methods of detection.
In 2017 [23], Bang Hyun Lee screened a 25-hydroxy vitamin D3 aptamer by a
target molecule immobilization-free GO-SELEX method (Fig. 11.4). This aptamer,
named VDBA14, can bind to 25-hydroxy vitamin D3 with high specificity and
affinity(KD 11 nM). Based on the AuNPs-based colorimetric assay, the VDBA14
aptasensor has a dynamic range from 0.19 to 25 μM. The color change can be identifiable at 1.56 μM in the naked eye, the ultimate detectable limit for vitamin D was
1 μM in normal binding buffer, and 12 μM in spiked human serum samples. To
detect 25-hydroxy vitamin D3 in vitro, VDBA14 provides a lower detection limit, a
more informative analytical window, and better selectivity.
Alsager et al. [46] reported a modified method based on AuNPs to overcome the
major limitation of colorimetric aptasensors, i.e., the residual binding between the
aptamer and AuNPs. The author eliminates residual binding between the aptamer
and the surface of the nanogold particles by simply centrifugation and resuspension
of the mixture solution after target recognition. This method enhances the detection
limit of VDBA14 aptasensor having at least fourfold improvement compared to its
original performance, with a 1-nM level of detection, a wide dynamic range, robust
operation, and high selectivity. The accuracy of the aptasensor was further validated
in the human blood sample, and the result was consistent with the result obtained
from HPLC.
Y. Cheng and H. Jin
In 2019, Wu group [42] fabricated a kind of electrochemical sensor based on
aptamer, which can be used for real-time monitoring of insulin release in vitro. The
sensor uses a guanine-rich aptamer modified by redox markers to recognize insulin
specifically. The aptamer can fold into a G-quadruplex. The insulin sensor may also
be used to monitor insulin secretion by β cells in the pancreas [43]. LOD of this
insulin sensor can be as low as 20 nM.
11.2.4 25-HydroxyvitaminD3 Related Aptamers
Vitamin D is an essential metabolite in the human body. Under the human epidermis,
vitamin D precursors are converted to vitamin D in blood vessels by vitamin D binding
protein (DBP) and stored in a semi-activated state of 25-hydroxy vitamin D3. When
vitamin D is needed in human tissues, this semi-activated form of vitamin D enters
the tissue and converts it into a fully activated state, which is 1,25-hydroxy vitamin
D3 [44]. More than 50% of people in the world suffer a lack of vitamin D [45]. When
people are deficient in vitamin D, they are at increased risk for rheumatoid arthritis,
metabolic syndrome, cancer, and cardiovascular disease. Almost every tissue in the
human body has the receptors of the 25-hydroxy vitamin D3, which is a suitable target
for detecting vitamin D levels in human body. Traditionally, researchers have used
commercial antibody kits to detect 25-hydroxy vitamin D3. However, considering the
short shelf life, high cost, and rigorous storage conditions of antibody kits, researchers
have to find new methods of detection.
In 2017 [23], Bang Hyun Lee screened a 25-hydroxy vitamin D3 aptamer by a
target molecule immobilization-free GO-SELEX method (Fig. 11.4). This aptamer,
named VDBA14, can bind to 25-hydroxy vitamin D3 with high specificity and
affinity(KD 11 nM). Based on the AuNPs-based colorimetric assay, the VDBA14
aptasensor has a dynamic range from 0.19 to 25 μM. The color change can be identifiable at 1.56 μM in the naked eye, the ultimate detectable limit for vitamin D was
1 μM in normal binding buffer, and 12 μM in spiked human serum samples. To
detect 25-hydroxy vitamin D3 in vitro, VDBA14 provides a lower detection limit, a
more informative analytical window, and better selectivity.
Alsager et al. [46] reported a modified method based on AuNPs to overcome the
major limitation of colorimetric aptasensors, i.e., the residual binding between the
aptamer and AuNPs. The author eliminates residual binding between the aptamer
and the surface of the nanogold particles by simply centrifugation and resuspension
of the mixture solution after target recognition. This method enhances the detection
limit of VDBA14 aptasensor having at least fourfold improvement compared to its
original performance, with a 1-nM level of detection, a wide dynamic range, robust
operation, and high selectivity. The accuracy of the aptasensor was further validated
in the human blood sample, and the result was consistent with the result obtained
from HPLC.