another external stimulus that can be used to release genes from AuNPs. Kawano
et al. [19] showed that electroporation can be used to release the DNA from AuNPs
modified with mPEG-SH5000. Bimetallic NPs, made up of alloyed combination
of Au and Ag in the form of nanorods, have also been used for gene delivery [20].
Thus, metallic NPs offer an opportunity to remote-control gene delivery.
3.1.2 Magnetic NPs (Magnetofection)
Magnetic NPs (MNP) have recently gained great interest as non-viral carriers for
gene delivery [21]. In this system, DNA can be attached to MNPs (normally in
suspension) and introduced into the cell culture medium. The DNA–MNP
complexes (called “Magnetoplex”) are then focused to the target cells by applying
a high-field or high-gradient magnetic force produced by rare earth magnets (or
electromagnets) placed below the cell culture to increase the sedimentation of the
complex. Upon binding to the cell surface, the Magnetoplex can be taken up by
endocytosis and the DNA is released from the MNPs intracellularly. The transfection efficiency can be further increased by using an oscillating magnetic force
[22, 23] and MNP heating [24, 25]. The technique (called magnetofection)
promotes rapid transfection with increased gene delivery efficiency and, consequently, many static-field magnetofection systems are now available commercially.
The MNPs generally consist of superparamagnetic iron oxide NPs (SPION)
(magnetite, Fe 3 O 4 , or maghemite, Fe 2 O 3 ), which magnetize strongly under an
external magnetic field but retain no permanent magnetism upon removal of the
magnetic field at room temperature. This property prevents aggregation or
clumping and, thereby, helps in easy dispersal. However, SPION can readily
agglomerate to form large particles in aqueous solutions of ~pH 7. Thus, for use
as MNPs, they are either encapsulated within a polymer (PEG, poly-L-lactic acid) or
metallic (gold, silver) shell or are dispersed within a polymer matrix (silica,
polyvinyl alcohol, polyvinylpyrrolidone or dextran). Pre-coating of the MNPs
also makes them biostable, biodegradable and nontoxic. The shell or matrix can
be functionalized by attaching carboxyl groups, amines, biotin, streptavidin,
antibodies, etc. to promote uptake by the target cells, prevent aggregation and
increase transfection efficiency and reduce cytotoxicity. Several types of coating
agents have been used, including anionic surfactants (oleic acid, lauroyl
sarcosinate), nonionic water-soluble surfactant (Pluronic F-127), fluorinated surfactant (lithium 3-[2-(perfluoroalkyl) ethylthio]propionate), polymers (PEG, PLL,
poly(propyleneimine) dendrimers), carbohydrates (chitosan, heparan sulfate), silica
particles (MCM48), proteins (serum albumin, streptavidin), hydroxyapatite,
phospholipids, cationic cell-penetrating peptide (TAT peptide), non-activated
virus envelope (HVJ-E), transfection reagent (Lipofectamine 2000) and viruses
(adenovirus, retrovirus). See [23, 26] for a detailed review. These coating agents are
often used in conjunction with PEI, which not only binds with DNA to the MNPs
but also serves as a NP dispersant [27].
Nanoparticles for Gene Delivery into Stem Cells and Embryos
57
et al. [19] showed that electroporation can be used to release the DNA from AuNPs
modified with mPEG-SH5000. Bimetallic NPs, made up of alloyed combination
of Au and Ag in the form of nanorods, have also been used for gene delivery [20].
Thus, metallic NPs offer an opportunity to remote-control gene delivery.
3.1.2 Magnetic NPs (Magnetofection)
Magnetic NPs (MNP) have recently gained great interest as non-viral carriers for
gene delivery [21]. In this system, DNA can be attached to MNPs (normally in
suspension) and introduced into the cell culture medium. The DNA–MNP
complexes (called “Magnetoplex”) are then focused to the target cells by applying
a high-field or high-gradient magnetic force produced by rare earth magnets (or
electromagnets) placed below the cell culture to increase the sedimentation of the
complex. Upon binding to the cell surface, the Magnetoplex can be taken up by
endocytosis and the DNA is released from the MNPs intracellularly. The transfection efficiency can be further increased by using an oscillating magnetic force
[22, 23] and MNP heating [24, 25]. The technique (called magnetofection)
promotes rapid transfection with increased gene delivery efficiency and, consequently, many static-field magnetofection systems are now available commercially.
The MNPs generally consist of superparamagnetic iron oxide NPs (SPION)
(magnetite, Fe 3 O 4 , or maghemite, Fe 2 O 3 ), which magnetize strongly under an
external magnetic field but retain no permanent magnetism upon removal of the
magnetic field at room temperature. This property prevents aggregation or
clumping and, thereby, helps in easy dispersal. However, SPION can readily
agglomerate to form large particles in aqueous solutions of ~pH 7. Thus, for use
as MNPs, they are either encapsulated within a polymer (PEG, poly-L-lactic acid) or
metallic (gold, silver) shell or are dispersed within a polymer matrix (silica,
polyvinyl alcohol, polyvinylpyrrolidone or dextran). Pre-coating of the MNPs
also makes them biostable, biodegradable and nontoxic. The shell or matrix can
be functionalized by attaching carboxyl groups, amines, biotin, streptavidin,
antibodies, etc. to promote uptake by the target cells, prevent aggregation and
increase transfection efficiency and reduce cytotoxicity. Several types of coating
agents have been used, including anionic surfactants (oleic acid, lauroyl
sarcosinate), nonionic water-soluble surfactant (Pluronic F-127), fluorinated surfactant (lithium 3-[2-(perfluoroalkyl) ethylthio]propionate), polymers (PEG, PLL,
poly(propyleneimine) dendrimers), carbohydrates (chitosan, heparan sulfate), silica
particles (MCM48), proteins (serum albumin, streptavidin), hydroxyapatite,
phospholipids, cationic cell-penetrating peptide (TAT peptide), non-activated
virus envelope (HVJ-E), transfection reagent (Lipofectamine 2000) and viruses
(adenovirus, retrovirus). See [23, 26] for a detailed review. These coating agents are
often used in conjunction with PEI, which not only binds with DNA to the MNPs
but also serves as a NP dispersant [27].
Nanoparticles for Gene Delivery into Stem Cells and Embryos
57