Chemistry Reference
In-Depth Information
of the porogen from the polymer matrix during the exothermic polymerization
process. One key is to slow the rate of the polymerization process in order to allow
the mechanical stresses to dissipate. For example, a MAA/EGDMA imprinted
polymer membrane, imprinted with 9-ethyladenine, was prepared between two
glass plates for the selective transport of nucleosides (MathewKrotz and Shea
1996). A nonvolatile porogen, dimethylformamide, was utilized during the polymeri-
zation, which resulted in a homogeneous optical transparent membrane. These mem-
branes exhibited good stability and mechanical strength, as well as good selectivity.
The imprinted membrane facilitated the transport of adenosine in a methanol/chloro-
form (6:94, v/v) solution with an adenosine/guanosine selectivity factor of 3.4. In a
second example, a propranolol imprinted polymer film was prepared through spin
coating by Schmidt et al. (2004). The prepolymerization mixture was spin coated
on a surface and then polymerized by UV initiation to form a solid polymer film.
This process used a combination of a polymeric porogen, poly(vinyl acetate), and
a low volatility solvent, diethylene glycol dimethyl ether, to prevent cracking of
the film during the spin-coating and polymerization steps. The thickness and porosity
of the films could be controlled by varying the concentration of the polymer porogen.
This MIP film retained the high capacity and selectivity for propranolol that was
demonstrated using the traditional MIP monoliths.
Electrochemical Polymerizations.
Electropolymerization is considered to be
one of the most direct methods for interfacing the MIP with a transducer surface
(Ulyanova et al. 2006). An early electrosynthesized MIP was prepared in 1989 by
Lapkowski's group for the electrochemical detection of adenosine triphosphate
(Boyle et al. 1989). An MIP-based quartz crystal microbalance (QCM) sensor was
also developed by electropolymerization of poly(o-phenylenediamine) onto the
conducting surface of a QCM in the presence of a neutral template, glucose
(Malitesta et al. 1999). The first MIP-based capacitive sensor was prepared by elec-
trochemical polymerization (Panasyuk et al. 1999). The MIP multilayer was prepared
by electropolymerizing phenol on gold electrodes with phenylalanine as the template
molecule. This capacitive sensor displayed selectivity for phenylanaline over other
compounds such as amino acids and phenol (Fig. 15.5). Although electropoly-
merization can deposit the recognition element directly on the transducer surface,
the requirement of electrochemically active monomers and polymers has limited
its utility.
15.4.3. Self-Assembled Monolayers
The self-assembly of an imprinted layer on the surface of a transducer was realized
through the adsorption of the template on gold, SiO
2
, or InO
2
surfaces followed by
treatment with an alkylthiol or organosilane (Hirsch et al. 2003). The first example
of this type of sensor was reported in 1987 by Tabushi and coworkers (1987).
Octadecylchlorosilane was chemisorbed in the presence of n-hexadecane onto tin
dioxide or silicon dioxide for electrochemical detection of phylloquinone, menaqui-
none,
topopherol, cholesterol, and adamantane. Another MIP-based sensor was
