photobleaching, long lifetimes, and high quantum yields, QDs have been widely
used as fluorescence probes in analytical chemistry, biology, and medicine. For
application of QDs in sensor or in biological imaging, the QDs must be dispersible
in aqueous solution and luminous with higher fluorescence efficiency. Thus, the
synthesis and application of water-soluble QDs with controlled size and surface
functionality should be explored and developed [77]. Cyclodextrins (CDs), as a
representative supermolecule host, can form a size-modulated host-guest inclusion
complex in the cavity and provide an external selectivity tuned by the functionalities
on the rim. The CDs can be used as an ideal functional molecule to improve the
solubility, stability, and biocompatibility of QDs. The combination of the luminescence properties of QDs and the molecular recognition ability of CDs has provided
highly sensitive and selective sensing platforms for various targets. In this part, we
focus on the recent advances in the construction of CD-functionalized QDs and their
applications in molecular recognition [78, 79].
15.4.1 CD-Functionalized QDs as an Achiral Recognition Sensing
Platforms
Luminescence sensing that uses conjugates of QDs with CDs constitutes an emerging and widely explored area of general ion or molecular recognition research
[80–84]. Li et al. reported a kind of CD-modified CdSe/ZnS QDs, which have
been prepared by using ultrasonic irradiation of a mixture of TOPO-coated CdSe/
ZnS QDs and α-, β-, or γ-CD in anhydrous ethanol [80]. A host-guest interaction
between TOPO ligand and CD resulted in the CD coating on the surface of QDs.
Furthermore, the CD-modified CdSe/ZnS QDs have been explored to detect the
phenol isomers by quenching fluorescence intensity. The quenching luminescence of
the CD-coated QDs was attributed to the fact that the phenol molecules entered the
cavity of the coating CD and competed with the TOPO to form an inclusion
complex. Specifically, it was found that the luminescence of α-CD or β-CD-modified
QDs can be quenched by all of the phenols, but only a little effect on γ-CD-modified
QDs.
Li et al. prepared a kind of CD-CdSe QDs by directly replacing the oleic acid
(Ole) on the CdSe QDs surface with β-CD in an alkaline aqueous solution [81]. CDs
are modified on QDs’ surface via covalent binding, and the resulted β-CD-CdSe QDs
exhibited high photoluminescence efficiency and stability in the water environment.
Moreover, the several transition-metal ions (Ag
+
, Hg
2+ , Co
2+ , Zn
2+ ) have efficiently
quenched the restored fluorescence of β-CD-CdSe QDs. The results demonstrated
the potential utility of β-CD-CdSe QDs for the detection of these ions with wide
linear range.
Another sensing system based on β-CD and CdSe/ZnS QDs was developed for
determination of ascorbic acid [82]. In this case, the fluorescence of the QDs was
quenched by the oxidized ascorbic acid. Moreover, the β-CD-CuInS 2 QDs have
attracted attention as a new class of sensor for detection of adenosine-5-triphosphate
(ATP) [83]. A slight enhancement of fluorescence emission from β-CD-CuInS 2 QDs
440
W. Liang and S. Shuang
used as fluorescence probes in analytical chemistry, biology, and medicine. For
application of QDs in sensor or in biological imaging, the QDs must be dispersible
in aqueous solution and luminous with higher fluorescence efficiency. Thus, the
synthesis and application of water-soluble QDs with controlled size and surface
functionality should be explored and developed [77]. Cyclodextrins (CDs), as a
representative supermolecule host, can form a size-modulated host-guest inclusion
complex in the cavity and provide an external selectivity tuned by the functionalities
on the rim. The CDs can be used as an ideal functional molecule to improve the
solubility, stability, and biocompatibility of QDs. The combination of the luminescence properties of QDs and the molecular recognition ability of CDs has provided
highly sensitive and selective sensing platforms for various targets. In this part, we
focus on the recent advances in the construction of CD-functionalized QDs and their
applications in molecular recognition [78, 79].
15.4.1 CD-Functionalized QDs as an Achiral Recognition Sensing
Platforms
Luminescence sensing that uses conjugates of QDs with CDs constitutes an emerging and widely explored area of general ion or molecular recognition research
[80–84]. Li et al. reported a kind of CD-modified CdSe/ZnS QDs, which have
been prepared by using ultrasonic irradiation of a mixture of TOPO-coated CdSe/
ZnS QDs and α-, β-, or γ-CD in anhydrous ethanol [80]. A host-guest interaction
between TOPO ligand and CD resulted in the CD coating on the surface of QDs.
Furthermore, the CD-modified CdSe/ZnS QDs have been explored to detect the
phenol isomers by quenching fluorescence intensity. The quenching luminescence of
the CD-coated QDs was attributed to the fact that the phenol molecules entered the
cavity of the coating CD and competed with the TOPO to form an inclusion
complex. Specifically, it was found that the luminescence of α-CD or β-CD-modified
QDs can be quenched by all of the phenols, but only a little effect on γ-CD-modified
QDs.
Li et al. prepared a kind of CD-CdSe QDs by directly replacing the oleic acid
(Ole) on the CdSe QDs surface with β-CD in an alkaline aqueous solution [81]. CDs
are modified on QDs’ surface via covalent binding, and the resulted β-CD-CdSe QDs
exhibited high photoluminescence efficiency and stability in the water environment.
Moreover, the several transition-metal ions (Ag
+
, Hg
2+ , Co
2+ , Zn
2+ ) have efficiently
quenched the restored fluorescence of β-CD-CdSe QDs. The results demonstrated
the potential utility of β-CD-CdSe QDs for the detection of these ions with wide
linear range.
Another sensing system based on β-CD and CdSe/ZnS QDs was developed for
determination of ascorbic acid [82]. In this case, the fluorescence of the QDs was
quenched by the oxidized ascorbic acid. Moreover, the β-CD-CuInS 2 QDs have
attracted attention as a new class of sensor for detection of adenosine-5-triphosphate
(ATP) [83]. A slight enhancement of fluorescence emission from β-CD-CuInS 2 QDs
440
W. Liang and S. Shuang