84
such as acrylonitrile. In contrast, LAMs have a double bond adjacent to an oxygen
(vinyl acetate), nitrogen (N-vinylpyrrolidone), halogen (vinyl chloride) or sulfur
((4-bromophenyl)(vinyl)sulfane) lone pairs or saturated carbons (Moad 2017).
MAMs are typically polymerized with dithiobenzoate or trithiocarbonate RAFT
agents, while less active CTAs are used for highly reactive propagating radicals
provided by LAMs (Hill et al. 2015). RAFT polymerization is considered as one of
the most appropriate techniques for developing MIPs so far. It favors the creation
of binding sites with much more homogeneous structures than FRP, thus obtaining materials whose behavior resembles to monoclonal antibodies. The first works
devoted to MIPs and RAFT polymerization were focused on surface imprinting,
using an azo initiator (Titirici and Sellergren 2006) or a RAFT agent (Lu et al.
2007) previously immobilized on the surface of silica particles. Sellergren’s group
was the first to report this approach, which allowed to obtain MIP thin films on preformed silica particles. The materials developed under these conditions presented
a faster mass transfer than others prepared with conventional methods. Due to the
potential benefits related to MIPs developed by RAFT technology, it was also used
to develop imprinted materials, such as microparticles as sorbents for the treatment
of samples (Pan et al. 2009; Xu et al. 2011b), films for solid-phase microextraction
(Hu et al. 2012), magnetic NPs (Gonzato et al. 2011) and monolithic columns (Liu
et al. 2008), all of them showing improved performance compared to traditional
MIPs. Specifically, monolithic MIPs proved to have a macro-pore size distribution and a large specific surface area, which are key factors for developing columns with remarkable efficiency. To be applicable to biologic samples, subsequent
work on monolithic columns focused on the development of restricted access MIPs,
which presented the ability to exclude proteins (Li et al. 2013). This was possible
by the ability of RAFT polymerization to restart (as well as other CRP methods) at
any time. In order to clearly demonstrate the effect of CRP, Gonzato et al. (2014)
compared the performance of MIPs synthesized under FRP and RAFT polymerization, concluding that RAFT led to acrylic and methacrylic bulk MIPs having higher
affinity than FRP, even at low degree of crosslinking. These results were consistent
with other published articles (Turson et al. 2009; Cormack and Mehamod 2013).
Halhalli and Sellergren (2015) also reported a very interesting work, claiming that
the greater affinity, binding site accessibility and capacity shown by most MIPs prepared by CRP could be attributed to the different porous structure obtained in CRP
and FRP. Unlike CRP, FRP led to polymers with a wide distribution of pores and
low swelling tendency, with many poorly accessible binding sites, which resulted
in a lower capacity.
In recent years, the use of RAFT polymerization in imprinting technology continues its unique expansion. New RAFT approaches are emerging which contribute
to MIP synthesis under milder conditions to improve its bioapplicability. In this
sense, imprinted polymers have been developed, e.g. using photo-induced RAFT
polymerization by visible light (photo-induced electron transfer-reversible additionfragmentation chain transfer, PET-RAFT) (Zhu et al. 2017; Cai et al. 2019), or thiolepoxy coupling chemistry (a versatile ‘click’ reaction) (Ma et al. 2019).
A. Gómez-Caballero et al.
such as acrylonitrile. In contrast, LAMs have a double bond adjacent to an oxygen
(vinyl acetate), nitrogen (N-vinylpyrrolidone), halogen (vinyl chloride) or sulfur
((4-bromophenyl)(vinyl)sulfane) lone pairs or saturated carbons (Moad 2017).
MAMs are typically polymerized with dithiobenzoate or trithiocarbonate RAFT
agents, while less active CTAs are used for highly reactive propagating radicals
provided by LAMs (Hill et al. 2015). RAFT polymerization is considered as one of
the most appropriate techniques for developing MIPs so far. It favors the creation
of binding sites with much more homogeneous structures than FRP, thus obtaining materials whose behavior resembles to monoclonal antibodies. The first works
devoted to MIPs and RAFT polymerization were focused on surface imprinting,
using an azo initiator (Titirici and Sellergren 2006) or a RAFT agent (Lu et al.
2007) previously immobilized on the surface of silica particles. Sellergren’s group
was the first to report this approach, which allowed to obtain MIP thin films on preformed silica particles. The materials developed under these conditions presented
a faster mass transfer than others prepared with conventional methods. Due to the
potential benefits related to MIPs developed by RAFT technology, it was also used
to develop imprinted materials, such as microparticles as sorbents for the treatment
of samples (Pan et al. 2009; Xu et al. 2011b), films for solid-phase microextraction
(Hu et al. 2012), magnetic NPs (Gonzato et al. 2011) and monolithic columns (Liu
et al. 2008), all of them showing improved performance compared to traditional
MIPs. Specifically, monolithic MIPs proved to have a macro-pore size distribution and a large specific surface area, which are key factors for developing columns with remarkable efficiency. To be applicable to biologic samples, subsequent
work on monolithic columns focused on the development of restricted access MIPs,
which presented the ability to exclude proteins (Li et al. 2013). This was possible
by the ability of RAFT polymerization to restart (as well as other CRP methods) at
any time. In order to clearly demonstrate the effect of CRP, Gonzato et al. (2014)
compared the performance of MIPs synthesized under FRP and RAFT polymerization, concluding that RAFT led to acrylic and methacrylic bulk MIPs having higher
affinity than FRP, even at low degree of crosslinking. These results were consistent
with other published articles (Turson et al. 2009; Cormack and Mehamod 2013).
Halhalli and Sellergren (2015) also reported a very interesting work, claiming that
the greater affinity, binding site accessibility and capacity shown by most MIPs prepared by CRP could be attributed to the different porous structure obtained in CRP
and FRP. Unlike CRP, FRP led to polymers with a wide distribution of pores and
low swelling tendency, with many poorly accessible binding sites, which resulted
in a lower capacity.
In recent years, the use of RAFT polymerization in imprinting technology continues its unique expansion. New RAFT approaches are emerging which contribute
to MIP synthesis under milder conditions to improve its bioapplicability. In this
sense, imprinted polymers have been developed, e.g. using photo-induced RAFT
polymerization by visible light (photo-induced electron transfer-reversible additionfragmentation chain transfer, PET-RAFT) (Zhu et al. 2017; Cai et al. 2019), or thiolepoxy coupling chemistry (a versatile ‘click’ reaction) (Ma et al. 2019).
A. Gómez-Caballero et al.