Plastic Antibodies - Designing Receptors for the Next Generation of Biosensors - page 118

3.5 Separation

The most popular MIP formats used in separation are membranes and microparticles.
Nevertheless MIP NPs with high-surface area might offer advantages especially if
they can be integrated with membranes or fibers to improve their performance. The
first example of MIP NPs-containing composite membrane dates back to 2002
[ 108 ]. In this work Lehmann and coauthors prepared MIP NPs imprinted with
Boc- L -phenylalanine anilide using mini-emulsion polymerization and used them to
create composite membranes for enantiomeric separation. The authors, however,
did not study the separation performance of the created membrane, but only its
porosity and flow properties. Silvestri and coauthors prepared 174 nm MIP NPs
imprinted with THO and caffeine by precipitation polymerization, and embedded
them in poly(methyl methacrylate- co -acrylic acid) membranes using a solid-phase
inversion method [ 109 ]. The binding characteristics of the membranes were quite
good, with 40 times more THO bound to the MIP NP-based membrane compared to
membranes without nanoparticles. Moreover, they exhibited a selectivity factor for
THO versus caffeine of 10. The same authors later used this strategy to create
composite membranes containing MIP NPs for cholesterol [ 110 ]. All the
synthesized nanoparticles exhibited specific rebinding capacities for the template,
both in ethanol and in phosphate buffer. This trend was mirrored by the membranes
which possessed a specific binding capacity of 14 mg template g 1 of the composite
system. Chronakis and coauthors incorporated MIP NPs imprinted with E2 and
THO into composite nanofibers using the method of electrospinning [ 111 ]. MIP
NPs were synthesized using precipitation polymerization, suspended in a solution
of polyethylene terephthalate (PET) in dichloromethane and trifluoroacetic acid,
and electrospun forming regular nanofibers of about 150-300 nm in diameter
(Fig. 8 ).
The nanofibers produced in this way were able to accommodate up to 75% (w/w)
of nanoparticles, exhibiting excellent binding properties. The same authors later
incorporated NPs imprinted with propranolol into nanofibers prepared by
electrospinning and used them to specifically extract and concentrate propranolol
from spiked tap water samples [ 112 ]. The binding specificity was preserved even in
the presence of other

-blockers. Piperno and coauthors have used cross-linking of
PVA to create more stable and water-compatible electrospun nanofibers with
incorporated MIP NPs imprinted with dansyl- L -phenylalanine [ 113 ]. The 400 nm
MIP NPs were produced by precipitation polymerization. Electrospun cross-linked
fibers retained their recognition activity even after multiple adsorption/desorption
cycles, thus highlighting their stability and possibility to be used as solid-phase
extraction (SPE) media. Zhu and coauthors synthesized 400 nm core-shell silica
MIP nanoparticles by a sol-gel process that could be used directly in SPE
applications for extraction of bisphenol A [ 114 ]. MIP NPs had an adsorption
capacity 2.5-fold higher than non-imprinted particles, with very rapid rebinding
kinetics, probably due to the binding sites being located near the surface of the
particles. In addition, they recovered close to 100% of the template, even in the

b