<p>Zein is a major storage protein of corn, with unique
amphiphilic film forming properties. It is insoluble in water, but soluble in
70% ethanol and acetic acid, and has been declared ‘generally recognized as
safe’ (GRAS) by the FDA. Due to new advances in food nanotechnology, zein is
being investigated for various applications such as biodegradable packaging,
oral delivery of proteins and peptides, scaffold for tissue engineering, as
well as biodegradable sensor platforms. The time consuming and highly
complicated methods for toxin and allergen analysis in the food industry
necessitates the need for a rapid, selective, compact and easy-to-use method of
detection for analytes. In the scope of this dissertation, we investigated the
feasibility of functional zein nanocomposite films and formation of a zein
nanocomposite sensor assembly for rapid and highly selective electrochemical
measurements of food toxins and allergens. Fabrication of a zein based
electrochemical amperometric sensor assembly was studied, first through the
comparison of various zein film characteristics changes with the application of
Laponite®, graphene oxide and carbon nanotube nanoparticles, followed by a
proof-of-concept study by detecting the gluten allergen protein gliadin. </p>
<p>To mechanistically study the functional zein nanocomposite
films, Laponite®, a silica nanoparticle, was added in the presence of 70%
ethanol solvent and oleic acid plasticizer. The films were studied using
various characterization techniques like transmission electron microscopy
(TEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy
(AFM), thermogravimetric analysis (TGA), differential scanning calorimetry
(DSC), water contact angle measurements etc. Through Si-N bond formation
between Laponite® and zein, fabricated zein nanocomposite films showed increase
in surface hydrophobicity, water vapor barrier properties, tensile strength and
Young’s modulus. Graphene oxide (GO), a carbon nanoparticle, was also
incorporated into zein through the solvent casting process. Uniform dispersion
of GO nanoparticles within zein matrix were confirmed up to 1% GO loading, and
covalent and hydrogen bonding mechanisms were proposed. Similar to
zein-Laponite® (Z-LAP) nanocomposites, zein-GO (Z-GO) showed increase in
hydrophobic tendencies, rougher surface and a 300% improvement in Young’s
modulus and 180% improvement in tensile strength at only 3% GO loading. Both
nanoparticles increased tensile strength, thermal stability and water vapor
barrier property of the films, indicating a potential for food packaging as an
alternative application for the nanocomposite films.</p>
Finally,
the research focused on the fabrication of an electrochemical amperometric sensor,
capable of detecting the protein gliadin, which is responsible for the allergic
reaction with people having celiac disease. Novel biodegradable coatings made
from zein nanocomposites: zein-graphene oxide, zein-Laponite® and
zein-multiwalled carbon nanotubes (Z-CNT) using drop casting technique were
tested for fabricating the electrochemical sensors using cyclic voltammetry
(CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry
(SWV) techniques. As Z-CNT produced the strongest signals compared to other
nanomaterials, the active tip of the electrochemical sensor was functionalized
through a sequence of layer by layer deposition of Z-CNT nanocomposite,
antibody and target analyte. Here, Z-CNT acts as a natural linker molecule with
large number of functional groups, that causes immobilization of capture
antibody and target, to ensure high sensor performance. Both CV curves and SWV
curves indicated successful sequential immobilization of gliadin antibody onto
the Z-CNT coated electrode. The Z-CNT biosensor was successfully able to give
CV signals for gliadin toxins for as low as 0.5 ppm and was highly specific for
gliadin in the presence of other interfering molecules, and remained stable
over a 30-day period. The low-cost, thin, conductive zein films offered a
promising alternative for protein immobilization platforms used in sensors and
can be extended to other matrices in biosensors as well as other functional
film applications
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11323367 |
| Date | 10 December 2019 |
| Creators | Tahrima Binte Rouf (8085995) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Design_and_Mechanistic_Understanding_of_Zein_Nanocomposite_Films_and_Their_Implementation_in_an_Amperometric_Biosensor_for_Detection_of_Gliadin/11323367 |
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