Development Of Electrochemical Biosensor Based On Nylon-6 Membrane
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Date
2019-07-01
Authors
Shaimi, Roswani
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Millions of people die due to the unavailability and inaccessible of
diagnostics facilities especially in controlling crucial diseases, which led to the
progressive development of biosensor. Unfortunately, direct oxidation of target
analyte at the bare electrode of a biosensor is an irreversible process and requires a
high overpotential, resulted in electrode fouling and low sensitivity. Nylon-6
membrane modified electrodes have been proposed to overcome this problem. As an
immunoassay, the biochemical reaction between target and capture analyte takes
place on the surface of the nylon-6 membrane, then translated to measurable
resistance signal. The present study elucidates the morphology characteristic of
nylon-6 as protein immobilization membrane and their influences in biological
recognition interface. The nylon-6 membranes were synthesized via dry phase
inversion with different concentration of nylon-6 polymer in a range of 16 wt. % to
28 wt.% and different types of additives (water and methanol) in dope solution. The
developed nylon-6 membrane, N-16B, with 16 wt. % nylon-6 polymer and methanol
as non-solvent had demonstrated the fastest lateral wicking speed (1.07 mm/sec) and
excellent protein immobilization capacity (1,650.00 + 85.84 µg/cm3). The current
study revealed the importance of membrane morphology that affects the sensitivity
and effectiveness of an immuno-sensing device. The stability issue in biomolecule
immobilization has been overcomed by integrating glutaraldehyde (GA) onto nylon-6
membrane prior to protein immobilization. The preliminary study was carried out
to study the effect of incubation time, pH and concentration of GA on protein
binding of the nylon-6 polymer. The optimum conditions of GA integration were
found at 40 minutes of incubation time, pH 7.5 and 1 wt. % of GA concentration.
Statistical analysis using crossed design programme was performed and the
optimum GA integration conditions from the statistical analysis were found at 25 wt. % of the nylon-6 polymer, 75 wt. % of mixture solvent + nonsolvent, pH 9.0 and 70
minutes of incubation time. The experimental results showed that the GA as a cross-linker reagent at optimum conditions was able to achieve better GA attachment for
latter protein immobilization. Further study has been explored on the preparation of
conductive polyaniline-iron oxide (PANI/Fe2O3) that served as the electrical signal
transducer, to convert the electrochemical interactions to a measurable resistance
signal. PANI was synthesized via oxidative polymerization of aniline monomer
(AM) in the presence of ammonium persulfate (APS). 0.2 M concentration of AM
and 1:3 volume ratio of AM:APS were found to produce PANI logged with the
highest ionic conductivity response at 7.565 + 0.262 mS/cm. The study had
reviewed the interesting aspect of different state of PANI as one of the important
conducting material for electronic/electrical devices. Subsequently, a membrane-based amperometric sensor was assembled and electrochemical activities ascorbic
acid (AA, target analyte) and ascorbate oxidase (capture analyte) were evaluated.
The detection limit of the sensor was found at 5.77 mM and the Michaelis–Menten
constant (Km) was calculated as 26.76 mM. Electrochemical impedance
spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammograms
(DPV) responses were carried out to analyze the electrochemical double layer on the
working electrode. The developed nylon-6 membrane has provided a promising
detection platform for sensor construction and suitable for practical application in
pharmaceutical or clinical analysis and agricultural crops.