Biomedical Engineering Reference
In-Depth Information
Noncovalent interactions suf er from inherent nonspecii city. In addi-
tion, there is still the possibility of denaturation of the protein on the sur-
face. A potential solution to this issue is through conjugation of His-tagged
protein to NP surface via nickel as an intermediate. In this case, control of
NP-protein stoichiometry is also possible [52-53].
11.4.2 Nanoporous Materials
As indicated above, one important issue in the construction of a bio-
sensor is the immobilization of enzymes and proteins with retained or
enhanced activities and lifetimes. Unlike NA, proteins are susceptible
to loss of activity upon immobilization on surfaces or conjugation to
other species due to the unfolding processes. h us, information on the
conformation, orientation, and speciic activity of conjugated proteins
is of paramount importance for the development and optimization of
highly speciic and sensitive nanodevices. Control over orientation of
protein immobilizations and conjugations to nanomaterials, far from
their active site, are attractive topics in protein chemistry, and much
research is directed towards the bioconjugation of proteins to nanoma-
terials at a predetermined site on the protein surface.
According to theoretical calculations, maximum stability of a protein
can be fuli lled by the adsorption or the entrapment within spherical cages
whose diameters are 2-6 times that of the dimension of the native molecule.
h e dimensions of most biomolecules are in the range of a few nanometers.
h us, NPG with tunable pore size and dimension in the range of up to a
few tens of nanometers provides an ideal environment for immobilization
and encapsulation of biomolecules. h e microstructure of the NPG coni nes
enzymes and proteins, while providing sui cient freedom for the biomol-
ecules to retain their natural bioactivity or even enhance it [54]. h is spe-
cialty puts NPG in the list of a new generation of advanced materials, and
the widespread application of NPG in biosensing stems from its exceptional
character.
11.4.2.1 Enzyme-Modii ed NPG-Based Biosensors
Many research groups have used the outstanding characteristics of NPGs
for immobilization of enzymes [54, 55]. Enzymes can either be directly
physisorbed onto the NPG or covalently linked at er i rst modifying the
NPG with a self-assembled monolayer [56]. Based on the unique physical
and chemical characteristics of NPG, Qiu
et al.
[6] obtained NPG by deal-
loying Ag from Au/Ag alloy and constructed an electrochemical biosensor
