11 Hormone Aptamers in Endocrine-Related Diseases
323
In 2014, Alsager [11] group screened a second 75 mer estradiol aptamer (KD
25 nmol/L). The aptamer can tether with carboxylated polystyrene nanoparticles and
resolve the changing size of aptamer functionalized particles when target molecules
induce a more tightly folded aptamer conformation on the particle surface. These
methods are capable of detecting the presence of ~5 nM E2 in buffered water by
measuring changes in particle sizes. In 2015, Alsager et al. [12] further scissored
the 75 mer aptamer into the new 35 mer (Al-35) and 22-mer (Al-22) aptamers by
removed the flanking nucleotides on either side of the inner core sequence. The
specificity and selectivity of two short aptamers (KD14, 11 nmol/L) are significantly
better than 75 mer, and the detection sensitivity of estradiol is increased by 25 times.
In 2015, Spurti U. Akki group [13] screened the third estradiol aptamer 1 (84 mer)
and 2 (86 mer) (KD 0.6 μmol/L, 0.56 μmol/L), which also bind to progesterone,
testosterone, and androstenedione as well. The author showed that compared with
the previously produced DNA aptamers, the new aptamer recognized and bound
to estrone (E1), another estrogen steroid besides E2. In contrast, no binding was
detected for 17α-ethylenestradiol (EE) that is usually found as a contaminant in
natural waters. The researchers concluded that E2 aptamer binds well to E2 and the
structural analog E1, and the selectivity is 74 times higher than that of EE.
Vanschoenbeek et al. [14] obtained the fourth estradiol aptamers and two singlestranded DNA (KD 27 ~ 124 μmol/L, 0.9 ~ 6 μmol/L) through innovative screening
technology. These aptamers can recognize and bind different functional groups on the
steroid ring structure and have a high binding capacity for estrone and testosterone.
All abovementioned 17β-estradiol aptamer sequences were summarized in
Table 11.1, respectively.
Svobodová [15] team used three detection methods, microscalethermophoresis(MST), apta-PCR affinity assay (APAA), and surface plasmon resonance
(SPR), to determine the reported aptamers’ binding properties in terms of affinity
and specificity. The results showed that the estradiol aptamers screened by Alsager’s
team have a high affinity and binding specificity for estrogen, especially the truncated 35 mer and 22-mer aptamer only bind to estradiol but does not bind to other
analogs such as androgens, progesterone, and aldosterone. A structural comparison
of the aptamers revealed stem-loop structures as well as possible G-quadruplex
conformations and a three-way junction potentially involved in the target binding of
estradiol.
Kim et al. [16] developed an E2-targeted aptamer sensor based on the activatable
aptamer probe model system for sensitive 17β-estradiol determinations in bloodstains
specifically originating from females even at a dose as low as 20 pmol/μl. This
aptamer was only valid for blood samples from relatively young females; when
women enter menopausal statutes that accompany lower estradiol levels in the blood,
the sensor was not activated anymore. It indicates that enhancing the sensitivity of
the E2 aptasensor will be the challenge to meet the demand of detecting 17β-estradiol
at an ultra-trace level in human samples.
Huang et al. [17] constructed an aptasensor based on Ru complex and quantum
dots, this system employed Ru complex and quantum dots (QDs) as fluorescence
probes. E2 aptamer competes with QDs; when E2 aptamer was added, Ru complex
323
In 2014, Alsager [11] group screened a second 75 mer estradiol aptamer (KD
25 nmol/L). The aptamer can tether with carboxylated polystyrene nanoparticles and
resolve the changing size of aptamer functionalized particles when target molecules
induce a more tightly folded aptamer conformation on the particle surface. These
methods are capable of detecting the presence of ~5 nM E2 in buffered water by
measuring changes in particle sizes. In 2015, Alsager et al. [12] further scissored
the 75 mer aptamer into the new 35 mer (Al-35) and 22-mer (Al-22) aptamers by
removed the flanking nucleotides on either side of the inner core sequence. The
specificity and selectivity of two short aptamers (KD14, 11 nmol/L) are significantly
better than 75 mer, and the detection sensitivity of estradiol is increased by 25 times.
In 2015, Spurti U. Akki group [13] screened the third estradiol aptamer 1 (84 mer)
and 2 (86 mer) (KD 0.6 μmol/L, 0.56 μmol/L), which also bind to progesterone,
testosterone, and androstenedione as well. The author showed that compared with
the previously produced DNA aptamers, the new aptamer recognized and bound
to estrone (E1), another estrogen steroid besides E2. In contrast, no binding was
detected for 17α-ethylenestradiol (EE) that is usually found as a contaminant in
natural waters. The researchers concluded that E2 aptamer binds well to E2 and the
structural analog E1, and the selectivity is 74 times higher than that of EE.
Vanschoenbeek et al. [14] obtained the fourth estradiol aptamers and two singlestranded DNA (KD 27 ~ 124 μmol/L, 0.9 ~ 6 μmol/L) through innovative screening
technology. These aptamers can recognize and bind different functional groups on the
steroid ring structure and have a high binding capacity for estrone and testosterone.
All abovementioned 17β-estradiol aptamer sequences were summarized in
Table 11.1, respectively.
Svobodová [15] team used three detection methods, microscalethermophoresis(MST), apta-PCR affinity assay (APAA), and surface plasmon resonance
(SPR), to determine the reported aptamers’ binding properties in terms of affinity
and specificity. The results showed that the estradiol aptamers screened by Alsager’s
team have a high affinity and binding specificity for estrogen, especially the truncated 35 mer and 22-mer aptamer only bind to estradiol but does not bind to other
analogs such as androgens, progesterone, and aldosterone. A structural comparison
of the aptamers revealed stem-loop structures as well as possible G-quadruplex
conformations and a three-way junction potentially involved in the target binding of
estradiol.
Kim et al. [16] developed an E2-targeted aptamer sensor based on the activatable
aptamer probe model system for sensitive 17β-estradiol determinations in bloodstains
specifically originating from females even at a dose as low as 20 pmol/μl. This
aptamer was only valid for blood samples from relatively young females; when
women enter menopausal statutes that accompany lower estradiol levels in the blood,
the sensor was not activated anymore. It indicates that enhancing the sensitivity of
the E2 aptasensor will be the challenge to meet the demand of detecting 17β-estradiol
at an ultra-trace level in human samples.
Huang et al. [17] constructed an aptasensor based on Ru complex and quantum
dots, this system employed Ru complex and quantum dots (QDs) as fluorescence
probes. E2 aptamer competes with QDs; when E2 aptamer was added, Ru complex