90
Some authors have proposed the term pseudotemplate using a structural analogue of the template for imprinting. Gutierrez-Climente et al. (2017) proposed the
immobilization of a carboxylic derivative template on the surface of glass beads,
since the template itself did not contain any functional group capable of being linked
to the solid support. Once the pseudo-template was immobilized on glass beads, it
was used for NP synthesis using the solid-phase imprinting approach (GutierrezClimente et al. 2017).
Piletska et al. (2017) also explored the phenomenon of Oswald ripening in combination with the solid-phase approach for the preparation of commercial silica in
the presence of immobilized templates. Prepared silica NPs were evaluated by competitive assays, replacing the antibodies used in traditional immunoassays. They
also concluded that the Ostwald maturation could be considered as an alternative
approach to polycondensation and could be performed under physiological conditions. This could be considered to be determinant for biological templates such as
proteins, since these conditions ensure their native conformation (Piletska et al.
2017; Ekpenyong-Akiba et al. 2019).
So far, the solid-phase approach has shown a limitation related to the low specific
surface area of the solid support, which results in low yields of NPs. To overcome
this limitation, new processes related to the use of nanosized magnetic template carriers have been introduced. In this sense, Mahajan et al. (2019) reported an approach
integrating imprinted nanogels with magnetic carriers. The nanogels were synthesized by solid-phase synthesis and Fe 3 O 4 was chosen as the magnetic core. The
reported method provides considerably higher yield compared to the solid-phase
approach on glass beads (Mahajan et al. 2019). Similarly, Chen et al. (2017) proposed a new protocol for the immobilization of the template through a homogeneous route using a quartz chip as support.
Undoubtedly, solid-phase synthesis is a widely used technique for the production
of MIP NPs. However, so far only a few chemicals have been explored for template
immobilization. From this point of view, click chemistry could be more than an
attractive alternative to conventional template immobilization on the solid support
(Medina Rangel et al. 2019).
5.3.2.5 The Core-Shell Approach
The core-shell strategy is a method to obtain surface-imprinted NPs consisting of at
least two different parts: one is the particle nucleus or core, while the other is the
core coating known as the shell. The core can be made of different materials such as
carbon nanomaterials (Demir et al. 2018), Au and silver nanoclusters (Shahar et al.
2018), magnetic NPs (Hussain et al. 2016), quantum dots (Panagiotopoulou et al.
2016) or silica (Fernandes et al. 2017). Surface-imprinted core-shell NP-based
polymers have recognition sites distributed in a thin layer, and therefore, contribute
to faster mass transfer rate.
The molecularly imprinted core-shell particles can be prepared through different
polymerization strategies to obtain materials with complex structures and
controllable sizes. One of the most direct techniques for producing core-shell MIPs
A. Gómez-Caballero et al.
Some authors have proposed the term pseudotemplate using a structural analogue of the template for imprinting. Gutierrez-Climente et al. (2017) proposed the
immobilization of a carboxylic derivative template on the surface of glass beads,
since the template itself did not contain any functional group capable of being linked
to the solid support. Once the pseudo-template was immobilized on glass beads, it
was used for NP synthesis using the solid-phase imprinting approach (GutierrezClimente et al. 2017).
Piletska et al. (2017) also explored the phenomenon of Oswald ripening in combination with the solid-phase approach for the preparation of commercial silica in
the presence of immobilized templates. Prepared silica NPs were evaluated by competitive assays, replacing the antibodies used in traditional immunoassays. They
also concluded that the Ostwald maturation could be considered as an alternative
approach to polycondensation and could be performed under physiological conditions. This could be considered to be determinant for biological templates such as
proteins, since these conditions ensure their native conformation (Piletska et al.
2017; Ekpenyong-Akiba et al. 2019).
So far, the solid-phase approach has shown a limitation related to the low specific
surface area of the solid support, which results in low yields of NPs. To overcome
this limitation, new processes related to the use of nanosized magnetic template carriers have been introduced. In this sense, Mahajan et al. (2019) reported an approach
integrating imprinted nanogels with magnetic carriers. The nanogels were synthesized by solid-phase synthesis and Fe 3 O 4 was chosen as the magnetic core. The
reported method provides considerably higher yield compared to the solid-phase
approach on glass beads (Mahajan et al. 2019). Similarly, Chen et al. (2017) proposed a new protocol for the immobilization of the template through a homogeneous route using a quartz chip as support.
Undoubtedly, solid-phase synthesis is a widely used technique for the production
of MIP NPs. However, so far only a few chemicals have been explored for template
immobilization. From this point of view, click chemistry could be more than an
attractive alternative to conventional template immobilization on the solid support
(Medina Rangel et al. 2019).
5.3.2.5 The Core-Shell Approach
The core-shell strategy is a method to obtain surface-imprinted NPs consisting of at
least two different parts: one is the particle nucleus or core, while the other is the
core coating known as the shell. The core can be made of different materials such as
carbon nanomaterials (Demir et al. 2018), Au and silver nanoclusters (Shahar et al.
2018), magnetic NPs (Hussain et al. 2016), quantum dots (Panagiotopoulou et al.
2016) or silica (Fernandes et al. 2017). Surface-imprinted core-shell NP-based
polymers have recognition sites distributed in a thin layer, and therefore, contribute
to faster mass transfer rate.
The molecularly imprinted core-shell particles can be prepared through different
polymerization strategies to obtain materials with complex structures and
controllable sizes. One of the most direct techniques for producing core-shell MIPs
A. Gómez-Caballero et al.