Biomedical Engineering Reference
In-Depth Information
An interesting strategy for protein recognition at the quartz crystal microbalance chip
surface by surface imprinting was reported by Ratner et al. [23]. Firstly, a layer of template
protein was absorbed onto a mica substrate. Disaccharides were then deposited onto the
protein molecule as a protective layer against denaturation and degradation. Subsequently,
radio-frequency glow discharge plasma was used to deposit hexafluoropropylene onto the
protein-disaccharide complexes. The outer surface of that film was attached to a glass
substrate by adhesion facilitating detachment of the mica substrate. Finally, the mica substrate
and template protein were removed from the hemispherically shaped binding pockets which
exhibited highly selective recognition for a variety of template proteins, including albumin,
immunoglobulin G, lysozyme, ribonuclease and streptavidin. The specificity of these surfaces
prepared with this kind of imprinting strategy is predominantly based on the shape selectivity
and hydrogen bonding interaction. This promising strategy certainly has potential for further
optimization exploiting different recognition chemistries for functional mapping of protein
surfaces. In addition, this strategy assumes that the conformation of the deposited protein
used as the template is similar to the free one in solution. Hayden et al. [59] produced
polymer receptors for the online monitoring of bioanalytes formed directly onto quartz crystal
microbalances using surface imprinting technique. The molded materials were capable of
enriching whole cells, viruses and enzymes on the sensor layer surface. Enzyme imprinted
polymer layers were also effective as nucleation site for the induction of protein
crystallization.
In another example of molecular imprinted polymers in which the recognition sites have
been confined to the surfaces, Tan et al. [51] successfully synthesized bovine serum albumin
surface-imprinted particles with a two-stage core-shell miniemulsion polymerization. The
imprinting strategy was based on the surface immobilization of template molecules with a
series of surface modification of the support beads. Actually, many surface-imprinted beads
have been successfully prepared with the core-shell polymerization method [60-62]. In one
notable work [63], cholesterol surface imprinted submicron beads were successfully
synthesized. The significance of this work is the application of a carbonate ester sacrificial
spacer which had been utilized in a molecular imprinting system through the conventional
bulk imprinting approach [64]. In this technique, the template cholesterol is covalently linked
to the functional monomer. After the removal of the template, rebinding of the template
molecule to the molecular imprinted polymer would only require noncovalent interactions.
So, this semicovalent strategy not only allows the creation of homogeneous binding sites with
covalent imprinting, but also takes advantage of the fast rebinding rate of noncovalent
adsorption. Also using core-shell emulsion polymerization, perez et al. [65] prepared surface
imprinted beads in the presence of polymerizable surfactant, pyridinium 12-(4-
vinylbenzyloxycarbonyl)dodecanesulfate and pyridinium 12-(cholesteryloxycarbon-
yloxy)dodeca nesulfate. Using the special surfactant, the template molecules could be
effectively constrained to the W/O phase boundary during the emulsion polymerization, thus
successfully creating hydrophobic binding sites for cholesterol on the imprinted bead
surfaces. Furthermore, the selectivity of the surface-imprinted beads was enhanced. In another
example, immobilizing the protein template at the surface of the beads, Bonini et al. [50]
reported the preparation of imprinted beads for the recognition of human serum albumin. The
recognition and binding of the imprinted beads was tested with a complex sample, human
serum and targeted removal of human serum albumin without a loss of the other protein
components was demonstrated.
