Topics in Current Chemistry (2020) 378:12
1 3
character of the physical interactions, variations in pH [122], temperature [123]
or polarity of the medium [124] may promote the desorption of the immobilized
component.
For electrostatic adsorption, the conjugation of biomolecules to NPs relies on
the attraction due to opposite charges in both species. The surface of NPs can be
engineered to have a specific charge in order to promote the interaction with biomolecules. For example, the reversible immobilization of trypsin has been reported
through the direct immobilization of the enzyme via the electrostatic interactions
between the positively charged trypsin and the negatively charged citric acid coating
Fe 3 O 4 NPs [125].
The adsorption of proteins onto inorganic supports, such as noble metal and
metal oxide NPs, and the influence of electrostatic interactions in the conjugation,
have been described in several reports [126–128]. These interactions have proved to
be particularly useful in the assembly of plasmid deoxyribonucleic acid (DNA) onto
the surface of MNPs. Bioconjugation is promoted by the strong interaction between
the negative charge associated with the phosphate backbone of most nucleic acids
and the positively charged Fe 3 O 4 NPs coated with a layer of silicon dioxide [129].
This effect may be achieved with other ligands possessing amino groups, such as
(3-aminopropyl)triethoxysilane (APTES), chitosan and tris(hydroxymethyl)aminomethane (Tris) [130]. Despite the simplicity and efficiency of this strategy of conjugation, it is highly sensitive to the pH and the ionic strength of the medium [131].
On the other hand, hydrophobic interactions are commonly used to adsorb hydrophobic drugs onto nanometric supports. In this case, the surface of the NPs is modified with hydrophobic molecules to allow the absorption of the drugs, which are
then triggered and released inside cells when the coatings of the NPs are degraded.
Wu et al. [132] described the synthesis of Janus nanoparticles comprised of Au
nanorods and a polydivinylbenzene (PDVB) matrix, as a promising biomedical
material for cancer treatment. The hydrophobic components of PDVB were used
as carriers of curcumin for chemotherapy. This anticancer drug was loaded into the
Janus nanoparticles due to strong hydrophobic interactions between curcumin and
PDVB. The UV–Vis extinction of Janus NPs in the near infrared region also makes
them an ideal candidate for photothermal therapy, guaranteeing significant decrease
of cell viability, migration, and invasion as a result of combined chemo- and photothermal-effects [132].
5.2 Supramolecular Conjugation
Supramolecular conjugation is based on the molecular recognition between a
ligand and a receptor, in which both the ligand and the receptor accommodate
each other in a dynamic process based on chemical complementarity, without
the actual formation of covalent bonds. When NPs are involved, the receptor is
generally located at the surface of the NP, and immobilization occurs by means
of a reaction via host–guest self-assembly [133]. Supramolecular interactions are
also reversible, but possess the advantage of directing the orientation of biomolecules, which is the main advantage of the supramolecular strategy as compared to
106
Reprinted from the journal
1 3
character of the physical interactions, variations in pH [122], temperature [123]
or polarity of the medium [124] may promote the desorption of the immobilized
component.
For electrostatic adsorption, the conjugation of biomolecules to NPs relies on
the attraction due to opposite charges in both species. The surface of NPs can be
engineered to have a specific charge in order to promote the interaction with biomolecules. For example, the reversible immobilization of trypsin has been reported
through the direct immobilization of the enzyme via the electrostatic interactions
between the positively charged trypsin and the negatively charged citric acid coating
Fe 3 O 4 NPs [125].
The adsorption of proteins onto inorganic supports, such as noble metal and
metal oxide NPs, and the influence of electrostatic interactions in the conjugation,
have been described in several reports [126–128]. These interactions have proved to
be particularly useful in the assembly of plasmid deoxyribonucleic acid (DNA) onto
the surface of MNPs. Bioconjugation is promoted by the strong interaction between
the negative charge associated with the phosphate backbone of most nucleic acids
and the positively charged Fe 3 O 4 NPs coated with a layer of silicon dioxide [129].
This effect may be achieved with other ligands possessing amino groups, such as
(3-aminopropyl)triethoxysilane (APTES), chitosan and tris(hydroxymethyl)aminomethane (Tris) [130]. Despite the simplicity and efficiency of this strategy of conjugation, it is highly sensitive to the pH and the ionic strength of the medium [131].
On the other hand, hydrophobic interactions are commonly used to adsorb hydrophobic drugs onto nanometric supports. In this case, the surface of the NPs is modified with hydrophobic molecules to allow the absorption of the drugs, which are
then triggered and released inside cells when the coatings of the NPs are degraded.
Wu et al. [132] described the synthesis of Janus nanoparticles comprised of Au
nanorods and a polydivinylbenzene (PDVB) matrix, as a promising biomedical
material for cancer treatment. The hydrophobic components of PDVB were used
as carriers of curcumin for chemotherapy. This anticancer drug was loaded into the
Janus nanoparticles due to strong hydrophobic interactions between curcumin and
PDVB. The UV–Vis extinction of Janus NPs in the near infrared region also makes
them an ideal candidate for photothermal therapy, guaranteeing significant decrease
of cell viability, migration, and invasion as a result of combined chemo- and photothermal-effects [132].
5.2 Supramolecular Conjugation
Supramolecular conjugation is based on the molecular recognition between a
ligand and a receptor, in which both the ligand and the receptor accommodate
each other in a dynamic process based on chemical complementarity, without
the actual formation of covalent bonds. When NPs are involved, the receptor is
generally located at the surface of the NP, and immobilization occurs by means
of a reaction via host–guest self-assembly [133]. Supramolecular interactions are
also reversible, but possess the advantage of directing the orientation of biomolecules, which is the main advantage of the supramolecular strategy as compared to
106
Reprinted from the journal