there are many related reviews [16–20]. Therefore, we only selected the following
topics to make some comments: sensing metal ions through coordination and
sensing biomolecules through indicator displacement assay (IDA) or tandem assay
and the surfaces. Many metal ions and inorganic anions play important roles
in human growth and development. Additionally, there are some ions that can
harm health and induce diseases. Recently, the sensing and recognition of these
ions have been a significant goal in the field of chemical sensors. By simple
modification, calixarenes can be used to sense and detect various cations (e.g., alkali
and alkaline earth metal cations, lead, transition metal cations, rare-earth metal
cations, and organic cations) or anions (e.g., some bio-anions) [19]. Recently,
Karakurt et al. designed the “switch-on” fluorescence sensor for the determination
of Hg
2+ ion based on the perylene bisimide derivative containing calix[4]arene
units (PB-CX[4]) (Fig. 4) [21]. In the mixed solvent of DMF and water, the PBCX[4] sensor had a very high selectivity and sensitivity to Hg
2+ ions due to the
fluorescent switch-on signal generated by the photoinduced electron transfer (PET)
effect. According to the results of the JOB experiment, it was found that PB-CX[4]
formed a 1:2 complex with Hg
2+ . The association constant of PB-CX[4] with Hg
2+
was determined to be 1.66 Â 10
9 M
À2 , and the detection limit was 5.56 Â 10
À7 M.
Finally, PB-CX[4] was applied to imaging Hg
2+ in human colon cancer cell lines by
confocal fluorescence microscopy, which has potential bio-application value. M.
Yilmaz and co-workers also completed a similar work and synthesized two kinds of
water-soluble fluorescent calixarenes for sensing and imaging Hg
2+ in living cells
[22]. The complexation with Hg
2+ would result in fluorescence quenching due to the
PET process. The resulting LODs were 1.14 Â 10
À5 and 3.42 Â 10
À5 M. These
nontoxic sensors were then used to sense and image Hg
2+ in the SW-620 cell line,
and excellent results were observed.
A distinctive feature of calixarenes is that they tend to quench fluorescence after
complexation with fluorescent dyes. The mechanism is generally considered to be
the PET effect [23]. The calixarene skeleton is constructed by base-catalyzed
condensation of 4-substituted phenols with formaldehyde. As a rule, the electronrich hydroxyl- or alkoxyl-substituted aryl rings are prone to act as electron donors
toward excited states, which lead to fluorescence quenching upon binding of fluorescent dyes. In fluorescence detection technology, the fluorescence signal from
“off” to “on” is a more reliable signal conditioning means. A variety of “switchon” fluorescence sensing supramolecular systems have been developed based on the
quenching fluorescence property and applied to the detection of tumor markers and
other diagnostically significant biological analytes. These fluorescence detection
systems are based primarily on the principle of IDA (Fig. 5a): When the calixarenes
and dyes act as sensing pairs, the fluorescence of the dyes is in a quenched state; after
the analytes are added to the sensing system, the analytes replace dyes by binding to
the calixarenes, and the dyes recover their own fluorescence. Whether the sensing
system is suitable for detecting analytes depends mainly on the sensitivity and
selectivity of the system. To improve sensitivity, the dye should have a high
fluorescence quantum yield and maximum quenching fluorescence after being
encapsulated by calixarene; to minimize interference from nontarget species, the
8 Supramolecular Medicine of Diverse Calixarene Derivatives
207
topics to make some comments: sensing metal ions through coordination and
sensing biomolecules through indicator displacement assay (IDA) or tandem assay
and the surfaces. Many metal ions and inorganic anions play important roles
in human growth and development. Additionally, there are some ions that can
harm health and induce diseases. Recently, the sensing and recognition of these
ions have been a significant goal in the field of chemical sensors. By simple
modification, calixarenes can be used to sense and detect various cations (e.g., alkali
and alkaline earth metal cations, lead, transition metal cations, rare-earth metal
cations, and organic cations) or anions (e.g., some bio-anions) [19]. Recently,
Karakurt et al. designed the “switch-on” fluorescence sensor for the determination
of Hg
2+ ion based on the perylene bisimide derivative containing calix[4]arene
units (PB-CX[4]) (Fig. 4) [21]. In the mixed solvent of DMF and water, the PBCX[4] sensor had a very high selectivity and sensitivity to Hg
2+ ions due to the
fluorescent switch-on signal generated by the photoinduced electron transfer (PET)
effect. According to the results of the JOB experiment, it was found that PB-CX[4]
formed a 1:2 complex with Hg
2+ . The association constant of PB-CX[4] with Hg
2+
was determined to be 1.66 Â 10
9 M
À2 , and the detection limit was 5.56 Â 10
À7 M.
Finally, PB-CX[4] was applied to imaging Hg
2+ in human colon cancer cell lines by
confocal fluorescence microscopy, which has potential bio-application value. M.
Yilmaz and co-workers also completed a similar work and synthesized two kinds of
water-soluble fluorescent calixarenes for sensing and imaging Hg
2+ in living cells
[22]. The complexation with Hg
2+ would result in fluorescence quenching due to the
PET process. The resulting LODs were 1.14 Â 10
À5 and 3.42 Â 10
À5 M. These
nontoxic sensors were then used to sense and image Hg
2+ in the SW-620 cell line,
and excellent results were observed.
A distinctive feature of calixarenes is that they tend to quench fluorescence after
complexation with fluorescent dyes. The mechanism is generally considered to be
the PET effect [23]. The calixarene skeleton is constructed by base-catalyzed
condensation of 4-substituted phenols with formaldehyde. As a rule, the electronrich hydroxyl- or alkoxyl-substituted aryl rings are prone to act as electron donors
toward excited states, which lead to fluorescence quenching upon binding of fluorescent dyes. In fluorescence detection technology, the fluorescence signal from
“off” to “on” is a more reliable signal conditioning means. A variety of “switchon” fluorescence sensing supramolecular systems have been developed based on the
quenching fluorescence property and applied to the detection of tumor markers and
other diagnostically significant biological analytes. These fluorescence detection
systems are based primarily on the principle of IDA (Fig. 5a): When the calixarenes
and dyes act as sensing pairs, the fluorescence of the dyes is in a quenched state; after
the analytes are added to the sensing system, the analytes replace dyes by binding to
the calixarenes, and the dyes recover their own fluorescence. Whether the sensing
system is suitable for detecting analytes depends mainly on the sensitivity and
selectivity of the system. To improve sensitivity, the dye should have a high
fluorescence quantum yield and maximum quenching fluorescence after being
encapsulated by calixarene; to minimize interference from nontarget species, the
8 Supramolecular Medicine of Diverse Calixarene Derivatives
207