Artificial bioaffinity elements
The biological component of a biosensor is considered the
most costly and weakest part of the design. For example, antibodies are produced in tissue culture or animals and are
expensive. Moreover, developing selective antibodies can
take a year or more due to the multiple steps incurred. As
with other biological recognition agents, the fragility also reduces the shelf-life of the sensor and necessitates special storage such as refrigeration. Therefore, there has been strong
interest in developing artificial or synthetic affinity agents as
a substitute for those of biological origins. The most promising artificial receptors are aptamers and molecularimprinted
polymers, both of which have found utility in sensor designs
for analytes of interest to the food sector (Ju et al., 2011).
Ofspecific relevanceis the relativelynew technique ofsurface
imprinting onto paramagnetic nanobeads using Atom Transfer Radical Polymerization (ATRP). Here the surface of ferric
oxide nanobeads are functionalized with 2-bromoisobutyryl
that acts as an anchor point (initiator) to elongating polymer.
The template, monomer and cross-linking agent are added
along with the initiator (e.g. CuCl2). Unlike traditional MIP
synthesis, the elongation of the growing polymer proceeds
in a controlled and ordered manner. Upon completion of the
polymerization process the template is removed leaving voids
with the affinity for the target (Salian & Byrne, 2013). To date
model proteins such as lysozyme, BSA and myoglobin have
been imprinted but this has now been extended to other biological targets such as Tobacco Mosaic Virus (Sun, 2013;
Fig. 2). By grafting the imprinted polymer onto the surface
of paramagnetic beads it is possible to concentrate the target
by applying a magnetic field.