high ionic strength. Using the glycidyl methacrylate comonomer as a chemical
handle for chemoligation, BSA was coupled to the particles, which were then
used for immunoseparation of anti-BSA from serum. After incubation with the
serum, the particles were separated by flocculation [119]. Similarly, particles
that contained magnetite were used by this group for separation and
purification using a magnetic field to collect the particles [120].
Hydrogel nanoparticles have also been employed in a molecularly imprinted
polymer (MIP) scheme. The principle behind MIP is based on both shape and
molecular-recognition templating. When the polymerizatio n is carried out in
the presence of ‘‘template’’ molecules, it is envisioned that the polymer wi ll
rigidify around that template, forming a cavity that is optimized for binding of
that molecule. After the templates are removed, it is hoped that the cavity
retains that shape and is able to bind and detect that particular molecule or
similar molecules in a complex mixture. Ye et al. have synthesized hydrogel
nanoparticles in the presence of theophylline and 17b-estradiol. The sensing
molecules wer e dissolved in the mixture of methacrylic acid and trimethylol-
propane trimethacrylate and then polymerized either thermally or by UV
irradiation. In these studies, they used radioligand binding analysis to
determine the sensitivity and selectivity of analyte binding [121]. Competitive
binding experiments showed high selectivity for the analyte.
Daunert and coworkers in a recent report showed how biological process es
can be used to tailor the response of hydrogels [122]. A biological recognition
unit was incorporated into the hydrogel structure and conformational changes
in the unit, in response to external factors, resulted in volume changes in the
hydrogel. Calmodulin (CaM) is a protein that undergoes different con forma-
tional changes on binding with Ca
2+
(native to dumbbell-like), certain
peptides, or a certain class of drugs like phenothiazines (native to more
constricted). CaM was incorporated in the hydrogel by genetically engineering
the protein to have a cysteine residue at the C-terminus, which was furt her
conjugated to an allylamine in order to attain oriented immobilization of the
protein in the hydrogel network. For incorporating phenothiazine in the
polymer network, a derivative having polymerizable acrylate group was
synthesized. Free radical polymerization of the polymerizable protein and drug,
an acrylamide monomer, and cross-linker BIS resulted in the desired hydrogels.
The hydrogel showed reversible swelling that was dependent on the
concentration of Ca
2+
. On saturating the hydrogel with Ca
2+
, the resulting
conformational change in CaM and the phenothiazine binding site of CaM
became accessible to the immobilized drug, resulting in the increased cross-
linking and shrinkage of the hydrogel. The gel swelled on Ca
2+
removal,
resulting from the release of the drug derivative from the binding site and also
since the water uptake property of the polymer was changed due to
modification of the hydroph obic surface of the protein. The hydrogel also
showed response to phenothiazines. When the hydrogel was treated with free
phenothiazine (chlorpromazine), the hydrogel swelled due the competitive
binding of the free drug replacing the bound immobilized drug from the
binding site of the conjugated protein. These protein- and drug-mo dified
78 BIOMEDICAL NANOSTRUCTURES