6 Quantum Dots and Quantum Rods
Nanocrystals with semiconducting metals are broadly referred as quantum dots (QDs).
QDs are known to exhibit unique optical properties, such as broad absorption, sizedependent photoluminescence with high quantum efficiency, long-term photostability, and low photobleaching. QDs have been synthesized from various
combinations of metals to provide selected photoluminescence properties [2]. Due
to their inherent photoluminescence properties, QDs coated with glycan units have
been used in several biomedical applications, especially as luminescent labels in
animal and cell imaging studies and as a fluorescent probes for studying carbohydrate–protein interactions [90–92]. Although the semiconducting metals are generally
toxic in nature, their toxicity can be reduced significantly by coating with hydrophilic
glycan monolayers for their use in vivo. In this section, we describe a few recent
applications of glyco-QDs that have been used as imaging agents, nanosensors, and
drug delivery vehicles. Nishimura and coworkers demonstrated the synthesis of
multifunctionalized glyco-QDs with various sugars and studied their in vivo imaging
applications [93]. QDs (CdSe/ZnS or CDSeTe/CdS) have been functionalized with
phosphorylcholine derivative 72 in combination with amine functionalized thiol 73,
which was subsequently used for the incorporation of glycans (74–80) (Fig. 13).
Further enzymatic modifications of the GlcNAc-QDs 76 afforded the more complex
functionalized oligosaccharides (81–84) at the surface of the nano-objects. The formation of glyco-functionalized QDs was confirmed by MALDI-ToF MS (matrixassisted laser desorption/ionization time-of-flight mass spectrometry) analysis. In vivo
near-infrared fluorescence imaging studies in mice demonstrated the stability and the
non-fouling nature of the glyco-QDs. Most of the glycan-functionalized QDs shown in
Fig. 13 (74–79, 81 and 83), except for sialylated oligosaccharides, accumulated rapidly
in the liver after 5–10 min of tail vein injection in mice and the fluorescence of the QDs
was almost quenched over 1 h in most cases, indicating the degradation of glyco-QDs.
On the other hand, glyco-QDs having terminal sialic acid residues (82 and 84)
exhibited long-term stability in the body 2 h after injection, without noticeable
accumulation into the liver, and were distributed among various tissues. The study
emphasized the influence of the neighboring sugar group on the in vivo characteristics
of GNPs, such as stability and organ-specific distribution and consequently on targetspecific drug delivery applications. Live animal imaging studies for the Lewis Xfunctionalized nano-objects 83 were conducted for the first time.
Ragusa and coworkers studied the cellular uptake and in vitro drug release abilities
of glyco-quantum rods (QRs) (85 and 86) functionalized with lactose and dopamine
(Fig. 14) [94]. In addition, the fluorescent QRs were used as nanosensors in protein
interaction studies. The galactoside ligands were introduced via reductive amination of
reducing lactose to an amine-functionalized QR, whereas the dopamine drug was
installed through ester bonds with the hydroxyl groups of the galactose. The bioavailability of the galactose groups of the QRs was verified in a protein binding study with
Ricinus communis (RCA 120 ) lectin. After the lectin binding, the quenching of
photoluminescence properties of QRs 85 and 86 were observed. Although the
320
N. Kottari et al.
Nanocrystals with semiconducting metals are broadly referred as quantum dots (QDs).
QDs are known to exhibit unique optical properties, such as broad absorption, sizedependent photoluminescence with high quantum efficiency, long-term photostability, and low photobleaching. QDs have been synthesized from various
combinations of metals to provide selected photoluminescence properties [2]. Due
to their inherent photoluminescence properties, QDs coated with glycan units have
been used in several biomedical applications, especially as luminescent labels in
animal and cell imaging studies and as a fluorescent probes for studying carbohydrate–protein interactions [90–92]. Although the semiconducting metals are generally
toxic in nature, their toxicity can be reduced significantly by coating with hydrophilic
glycan monolayers for their use in vivo. In this section, we describe a few recent
applications of glyco-QDs that have been used as imaging agents, nanosensors, and
drug delivery vehicles. Nishimura and coworkers demonstrated the synthesis of
multifunctionalized glyco-QDs with various sugars and studied their in vivo imaging
applications [93]. QDs (CdSe/ZnS or CDSeTe/CdS) have been functionalized with
phosphorylcholine derivative 72 in combination with amine functionalized thiol 73,
which was subsequently used for the incorporation of glycans (74–80) (Fig. 13).
Further enzymatic modifications of the GlcNAc-QDs 76 afforded the more complex
functionalized oligosaccharides (81–84) at the surface of the nano-objects. The formation of glyco-functionalized QDs was confirmed by MALDI-ToF MS (matrixassisted laser desorption/ionization time-of-flight mass spectrometry) analysis. In vivo
near-infrared fluorescence imaging studies in mice demonstrated the stability and the
non-fouling nature of the glyco-QDs. Most of the glycan-functionalized QDs shown in
Fig. 13 (74–79, 81 and 83), except for sialylated oligosaccharides, accumulated rapidly
in the liver after 5–10 min of tail vein injection in mice and the fluorescence of the QDs
was almost quenched over 1 h in most cases, indicating the degradation of glyco-QDs.
On the other hand, glyco-QDs having terminal sialic acid residues (82 and 84)
exhibited long-term stability in the body 2 h after injection, without noticeable
accumulation into the liver, and were distributed among various tissues. The study
emphasized the influence of the neighboring sugar group on the in vivo characteristics
of GNPs, such as stability and organ-specific distribution and consequently on targetspecific drug delivery applications. Live animal imaging studies for the Lewis Xfunctionalized nano-objects 83 were conducted for the first time.
Ragusa and coworkers studied the cellular uptake and in vitro drug release abilities
of glyco-quantum rods (QRs) (85 and 86) functionalized with lactose and dopamine
(Fig. 14) [94]. In addition, the fluorescent QRs were used as nanosensors in protein
interaction studies. The galactoside ligands were introduced via reductive amination of
reducing lactose to an amine-functionalized QR, whereas the dopamine drug was
installed through ester bonds with the hydroxyl groups of the galactose. The bioavailability of the galactose groups of the QRs was verified in a protein binding study with
Ricinus communis (RCA 120 ) lectin. After the lectin binding, the quenching of
photoluminescence properties of QRs 85 and 86 were observed. Although the
320
N. Kottari et al.