Info

Biomolecule

Hydrophobic Interactions

Covalent Coupling

Hetero-Bifunctional Linker

X, Y = -SH, -COOH, NH2, -OH NP - Nanoparticle Biomolecule = peptide, proteins, nucleic acid, carbohydrates

Figure 4.2. Procedures for solubilizing nanoparticles in water solution and for conjugation to biological molecules. See insert for color representation of this figure.

Figure 4.3. Schematic illustration of strategies for delivering nanoparticle probes into living cells. See insert for color representation of this figure.

In contrast to permeabilization-mediated delivery, carrier-mediated delivery relies on receptor mediated endocytosis. A classic example is the delivery of transferrin-conjugated QDs via transferrin-receptor-mediated endocytosis (Chan and Nie, 1998; Derfus et al., and Weissleder, 2004). Note that receptor-mediated endocytosis takes place in less than 30 min at 37°C, and it is suppressed and nanoparticles are not delivered into the cell at 4°C. When cell-penetrating peptides such as HIV-TAT peptide are used, the nanoparticles are able to escape the endosomal compartment and enter the nucleus or retain function for intracellular staining of actin filaments (Agrawal et al., 2003). The mechanism of HIV-TAT-peptide-mediated delivery is still a matter of debate, but recent research has shown that macropinocytosis (Wadia et al., 2004) and endocytosis followed by initial ionic interaction (Vives, 2003; Vives et al., 2003) are important steps in tat-peptide-mediated delivery. A major problem with this approach is that the nanoparticles are delivered as aggregates and may not be available for target binding. Physical delivery methods include microinjection and electroporation. In microinjection, nanoparticles are delivered into a cell using a micro needle, but this procedure is time-consuming (one cell at a time) and requires considerable training and skills. Electroporation was explored by Defrus et al. and has been found to result in nanoparticle aggregation (Derfus et al., 2004b). At present, a perfect method is still not available for delivery and targeting of nanoparticle probes inside living cells. This area will require considerable research effort in the next few years.

Figure 4.4. Optical properties of semiconductor QDs. (a) Absorption and fluorescence spectra of a 3.5-nm CdSeQD. [Reprinted from Murray et al. (1993), with permission of American Chemical Society.] (b) Photostability of QDs compared with Texas Red. [Reprinted from Gao et al. (2005) in Current Opinion in Biotechnology.] (c,d) Size tunable emission properties of CdSe QDs. [Reprinted from Smith and Nie, Analyst 129:672-7 (2004) and Chan et al. (2002) in Current Opinion in Biotechnology.] See insert for color representation of parts (c) and (d) of this figure.

Figure 4.4. Optical properties of semiconductor QDs. (a) Absorption and fluorescence spectra of a 3.5-nm CdSeQD. [Reprinted from Murray et al. (1993), with permission of American Chemical Society.] (b) Photostability of QDs compared with Texas Red. [Reprinted from Gao et al. (2005) in Current Opinion in Biotechnology.] (c,d) Size tunable emission properties of CdSe QDs. [Reprinted from Smith and Nie, Analyst 129:672-7 (2004) and Chan et al. (2002) in Current Opinion in Biotechnology.] See insert for color representation of parts (c) and (d) of this figure.

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