Figure 5. Colorimetric assay of biosensor: a) colorimetric
response of glucose oxidase sensor to glucose concentrations ranging
from 3 to 100 mg/dL; b) colorimetric response of cholesterol oxidase
sensor to cholesterol concentrations ranging from 6 to 200 mg/dL
The figure shows that in the case of glucose there is a steeper curve
and in the case of cholesterol, probably due to higher concentrations
and more rapid saturation. However, in both cases the sensors have an
exponential relationship, and thus good sensitivity at low concentration
areas that may be considered suitable for the analysis of glucose and
cholesterol in human plasma.
Our proposed universal approach avoids the use of unstable dyes in the
active layer and allows to replace it with a nanocrystalline titania
layer, which is capable to form a yellow complex by interaction with
hydrogen peroxide. Thus, the interaction of analyte with different
enzyme layer results in hydrogen peroxide, as in the classic method,
which causes coloring the titania layer. The color of the sensor can be
easily detected using a visual method or by spectrometric techniques. We
showed that inkjet method can improve reproducibility of experiments by
accurate dosing of active substances and using printing titania
substrate with a predetermined thickness. In addition, this approach
allows to create a universal substrate of titania, which is applicable
for all oxidase biosensors.