Biomedical Engineering Reference
In-Depth Information
nonlinearity of response; cross-sensitivity; and off-set and signal drift. More efforts need
to be devoted to these aspects and integrated silicon-based biochip design is an area of
active and ongoing research. Alternative approaches such as nanoparticle technologies are
therefore being considered. Nanoparticles have been prepared using not only silicon, but
also gold, carbon, and ferromagnetic particles. Nanoparticles provide the advantages of
the inorganic material as well as very high surface to volume ratios.
In a recent study, a water-soluble gold nanoparticles/polyaniline nanocomposite has
been reported (48). The particles were prepared using 3-aminophenylboronic acid (3-
APBA) as reductive and protective reagent. Poly(vinyl alcohol) (PVA) was used as dis-
perser based on the covalent bond interaction between the boronic acid and diol group.
The particle size was found to be a function of the concentration of PVA. The nanocom-
posite particles were found to detect glucose based on the competitive reaction of 3-APBA
and PVA, and that of 3-APBA.
In an alternative approach, Chinnayelka and McShane (49) present a design of biosen-
sors based on “smart” hollow microspheres. These spheres were prepared using a layer-
by-layer approach by self-assembly of Con A/dextran into multilayer films, followed by
polymer multilayers. First dissolvable resin microparticles were coated with fluorescein
isothiocyanate (FITC)-dextran
tetramethylrhodamine isothiocyanate (TRITC)-Con A
multilayers. Next polyelectrolyte multilayers were added, and the core particles were then
dissolved to yield hollow capsules. For biosensing, as glucose was added to the matrix,
FITC-dextran was displaced by TRITC-labeled Con A. The basic transduction principle
was the change in resonance energy transfer efficiency from FITC to TRITC.
7.2
Stimuli-Responsive Materials
Stimuli-responsive materials (StRMs) respond in a controlled and often reversible fashion
to changes in the environment such as ionic strength, pH, and temperature, nature of the
solvent, or light. The materials may respond by changing shape, polarity, charge, solubil-
ity, or viscosity. StRMs are finding extensive applications in drug delivery, biosensors,
actuators, bioseparations, or other areas. The applications and characteristics of StRMs
have previously been reviewed (50,51). Here only some aspects of this very popular area
of research are presented with the focus on biosensor applications.
7.2.1
pH-Sensitive Materials
Materials that are pH sensitive contain ionizable functional groups in which charge is gen-
erated in response to pH. This causes electrostatic repulsion and corresponding swelling
of the material. Examples include natural materials such as the polysaccharides chitosan,
alginate, and K -carrageenan, which respond to changes in pH, Ca 2 , and K , respectively
(52). Synthetic polymers or gels that are pH sensitive include polyethyleneimine, poly-
lysine, and poly- N , N -dimethyl aminoethyl methacrylamide, polyacrylic acid, and
polymethacrylic acid (PMAA). Other pH-sensitive materials include PMAA and PEG
copolymers (53), poly(acrylic acid-co-octyl acrylate) (54), poly(methacrylic acid-co-
ethacrylic acid) P(MA-co-EA) (55), 4-amino- N -(4, 6-dimethyl-2-pyrimidinyl) benzene sul-
fonamide- N , N -dimethylacrylamide (56), and poly- N -acryloyl- N -propylpiperazine
(PNANP) (57).
A genetically engineered silk-elastin-like protein-based copolymer (SELP) with an
amino acid repeat sequence of [(GVGVP)(4)GKGVP(GVGVP)(3)(GAGAGS)(4)](12) also
Search WWH ::




Custom Search