Figure
2 . Textural characterization of surface created by titania ink: a)
HRSEM cross-section of printed titania layer; b) SEM imaging of titania
xerogel layer
Thus, it possible to adjust rheology properties of titania ink to
optimal inkjet printability parameters for various print heads and
printing systems28. This sol maintains stability over
time and virtually unchanged size of the hydrodynamic radius, that
allows to obtain a dense xerogel with high porosity (Figure 2 a,b). Upon
the solvent evaporation the nanoparticles exhibit high crosslinking
among themselves. The resulting surface is a good basis for enzymatic
layer, as it has permeability and can rapidly change color reacting with
hydrogen peroxide.
Optical microscopy of printed samples showed the formation of stable
individual droplets with a porous structure (Figure 2 a,b). It
demonstrated the possibility of good control over drop merging at higher
DPI. This ensured the formation of a uniform layer with precise
thickness control by layer-by-layer application starting from 200 nm to
1 µm. That is important in designing a platform for biosensor to control
thickness and surface area of the reacting zone.
In addition, we used a solid wax-based ink, which was the base for
hydrophobic coating boundaries on the substrate surface. Thus, using the
prepared template we restricted sensitive zone.
As shown in Figure 3a, hydrophobic mask was applied only on shaded parts
of template and thereby precise positioning and control of hydrophobic
and hydrophilic areas for the subsequent application of the reaction
components were performed. After applying the mask, we printed remaining
area with hydrophilic titania ink. This approach along with the ink-jet
printing has allowed us to control the reaction area and amount of the
analyte reacting with the sensitive zone (Figure 3b).