attach onto the surface of radionanomaterials. For example, sortase A was used to
functionalize the surface of different protein-derived nanomaterials for catalysis,
sensing, or imaging applications [38]. More recently, this method was used to
produce a nano-vaccine platform by effective antigen coupling onto virus
nanoparticles [39]. To date, there is only very limited report using this surface
modification strategy for radionanomaterials. One example is that furin was used to
control the condensation and self-assembly of a benzothiazole-derived nanoparticle
and facilitate the incorporation of
18 F onto the surface of this nanoparticle [40].
When we use chemical reaction to modify radionanomaterial surface, the choice
of agents and reaction condition should be very careful. The basic rules should
include: (1) the structural integrity of radionanomaterials should be mostly maintained post reaction (including the property and quantity of loaded isotopes inside),
(2) the reaction should be fast, efficient, and environment friendly, (3) separation of
the resultant modified radionanomaterials from the reactants should be relatively
simple, and (4) the obtained surface-modified radionanomaterial should be sufficiently biocompatible.
10.2.2 Physical Interaction
Surface modification from physical interactions between nanomaterials and decorating molecules has several advantages. First, these methods usually can maintain
the physiochemical and structural properties of original nanomaterials to a better
extent compared with chemical reaction methods. Also, the overall stability of
modified nanomaterials from these methods is adequate for most biomedical
applications. In addition, some biomolecules (e.g. nucleic acids) can be loaded
effectively onto nanomaterial surface without tedious chemical reaction/purification
and can also be unloaded at the desired location afterwards [41].
10.2.2.1 Ligand Exchange/Replacement
Utilization of molecules which can replace the initial surface coating during the
synthesis has been a well-accepted approach for surface modification of inorganic
radionanomaterials [42]. Usually small hydrodynamic size can be maintained using
this strategy. For example, up-conversional nanoparticles (UCNPs) are usually
obtained with oleic acid (OA) as the ‘capping’ agent, while OA can be further
exchanged by a diversity of hydrophilic molecules [43]. These replacement ligand
molecules are composed by two portions—anchoring part which has strong affinity
for nanomaterial surface [e.g. thiols/disulfides/amines/phosphines for noble metal
nanoparticles or quantum dots (QD)], and stability/functional part which can
bestow the nanomaterial with satisfactory colloidal stability as well as provide
functionalization site for attachment of other molecules [44]. The stability/
functional part can also determine the molecular adsorption in vivo.
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functionalize the surface of different protein-derived nanomaterials for catalysis,
sensing, or imaging applications [38]. More recently, this method was used to
produce a nano-vaccine platform by effective antigen coupling onto virus
nanoparticles [39]. To date, there is only very limited report using this surface
modification strategy for radionanomaterials. One example is that furin was used to
control the condensation and self-assembly of a benzothiazole-derived nanoparticle
and facilitate the incorporation of
18 F onto the surface of this nanoparticle [40].
When we use chemical reaction to modify radionanomaterial surface, the choice
of agents and reaction condition should be very careful. The basic rules should
include: (1) the structural integrity of radionanomaterials should be mostly maintained post reaction (including the property and quantity of loaded isotopes inside),
(2) the reaction should be fast, efficient, and environment friendly, (3) separation of
the resultant modified radionanomaterials from the reactants should be relatively
simple, and (4) the obtained surface-modified radionanomaterial should be sufficiently biocompatible.
10.2.2 Physical Interaction
Surface modification from physical interactions between nanomaterials and decorating molecules has several advantages. First, these methods usually can maintain
the physiochemical and structural properties of original nanomaterials to a better
extent compared with chemical reaction methods. Also, the overall stability of
modified nanomaterials from these methods is adequate for most biomedical
applications. In addition, some biomolecules (e.g. nucleic acids) can be loaded
effectively onto nanomaterial surface without tedious chemical reaction/purification
and can also be unloaded at the desired location afterwards [41].
10.2.2.1 Ligand Exchange/Replacement
Utilization of molecules which can replace the initial surface coating during the
synthesis has been a well-accepted approach for surface modification of inorganic
radionanomaterials [42]. Usually small hydrodynamic size can be maintained using
this strategy. For example, up-conversional nanoparticles (UCNPs) are usually
obtained with oleic acid (OA) as the ‘capping’ agent, while OA can be further
exchanged by a diversity of hydrophilic molecules [43]. These replacement ligand
molecules are composed by two portions—anchoring part which has strong affinity
for nanomaterial surface [e.g. thiols/disulfides/amines/phosphines for noble metal
nanoparticles or quantum dots (QD)], and stability/functional part which can
bestow the nanomaterial with satisfactory colloidal stability as well as provide
functionalization site for attachment of other molecules [44]. The stability/
functional part can also determine the molecular adsorption in vivo.
190
D. Chen and H. Hong