The antibody immobilization compatible
with low-cost materials
and label-free strategies is a challenge for biosensor device fabrication.
In this study, ZnO thin film deposition was carried out on corning
glass substrates by ultrasonic spray pyrolysis at 200 °C. The
thin films were analyzed as platforms for enteropathogenic
Escherichia coli
(
E. coli
EPEC) antibody immobilization. The modification of thin films from
the functionalization and antibody immobilization steps was visualized
using Fourier transform infrared spectroscopy (FTIR) spectroscopy,
and surface changes were observed by atomic force microscopy. The
obtained FTIR spectra after functionalization showed a contribution
of the amino group (NH
2
) derived from silane (3-aminopropyltrimethoxysilane).
The antibody immobilization showed an amide I conserved signal corresponding
to the C=O stretching vibrations and the amide II signal related
to the N–H scissor vibration mode. In this way, the signals
observed are correlated with the presence of antibody immobilized
on the film. The ZnO film morphology changes after every stage of
the process and allows observing the antibody distribution on the
immobilized surface. In order to validate the antibody recognition
capability as well as the
E. coli
EPEC
detection
in situ
, polymerase chain reaction was
used.
Fabrication and testing of interdigitated microelectrode arrays whose structure includes non-cytotoxic hydrogenated amorphous silicon-carbon alloy (a-Si x C 1-x :H) as the surface to be biofunctionalized for capturing enteropathogenic Escherichia coli (E. coli, EPEC) are presented. a-Si x C 1-x :H films were obtained by enhanced chemical vapor deposition (PECVD). The extract method was used to assess the cytotoxicity of the films. The design of the PIMAs includes two layers of a-Si x C 1-x :H, one intrinsic layer deposited onto silicon dioxide (SiO 2 ) before evaporating titanium (Ti), and one doped layer deposited onto the Ti-microelectrodes. Electrical impedance spectroscopy (EIS) was used to know the effects of the biofunctionalization layer, conductivity of the medium and any capture of bacteria by antibodies on the microelectrodes. According to the results, the high hydrogen dilution contributes to low incorporation of CH n groups improving the non cytotoxicity of the films, and the capture of bacteria on the microelectrodes improves the sensitivity. It manifests itself as a shift of the low cutoff frequency (F low ) of the impedance spectrum to the right, allowing the device to sense at frequencies lower than F low . A percentage change in impedance of 1600% at 100 Hz was obtained after 5 minutes in contact with medium with EPEC concentration of 8.5 × 10 8 CFU/mL.
The antibody immobilization with low-cost materials and label-free methods are a challenge for the fabrication of biosensor devices. In this work, it was developed a strategy for antibody immobilization on ZnO TFTs over polyethylene terephthalate (PET) as a recyclable plastic substrate. Antibodies were biofunctionalized using a label-free strategy for E. coli detection. The use of a recyclable plastic substrate PET enables the compatibility with flexible electronics that could contribute for a low-cost biosensor useful in rural communities that do not have the necessary infrastructure and trained personnel for pathogenic bacterial detection in food or water.
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