The characterization of a-SixC1−x:H thin films by plasma-enhanced chemical vapor deposition with high hydrogen dilution for biological applications is addressed. A root mean square roughness less than 1 nm was measured via atomic force microscopy for an area of 25 μm2. Structural analysis was done using Fourier transform infrared spectroscopy in the middle infrared region. It was found that under the deposition conditions, the formation of Si–C bonds is promoted. Electrical dark conductivity measurements were performed to evaluate the effect of high hydrogen dilution and to find the relation between carrier transport properties and the structural arrangement. Conductivities of the order of 10−7 to 10−9 S/cm at room temperature for methane–silane gas flow ratio from 0.35 to 0.85 were achieved, respectively. UV-visible spectra were used to obtain the optical band gap and the Tauc parameter. Optical band gap as wide as 3.55 eV was achieved in the regime of high carbon incorporation. Accordingly, deposition under low power density and high hydrogen dilution reduces the roughness, improves the structure of the network, and stabilizes the film properties as a greater percentage of carbon is incorporated. The biofunctionalization of a-SixC1−x:H surfaces with NH2-terminated self-assembled monolayers was obtained through silanization with 3-aminopropyltrimethoxysilane. This knowledge opens a window for the inclusion of these a-SixC1−x:H thin films in devices such as biosensors.
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.
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