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.