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This work discusses the capability of tailoring sensitivity of an optical-fiber-based Fabry–Perot interferometric (FPI) sensor to changes in refractive index (volume) and formation of a layer on the sensor surface (adlayer). A simple single-layer approach shows some disadvantages, especially when refractive index (n) sensing is considered, e.g., there is no shift of the interference pattern in the wavelength domain. The considered FPI sensor is based on two transparent thin films deposited on a single-mode optical fiber’s end face. As the first layer, a high-n titanium oxide (TiO2) was chosen. We show that addition of a second layer of lower n results in the blueshift of spectral pattern with external n (next). Moreover, when an additional layer, e.g., biological one, is formed, a redshift of the pattern appears, what is in contrary to the shift induced by the increase of next. Numerical analysis as well as experiments show that a wide range of materials (with different n and thickness) can be applied as the second layer, influencing both volume and adlayer sensitivities. We have found that when the second layer thickness is tailored to obtain a well spectrally defined pattern, high n contrast between the layers increases the volume sensitivity, while for the moderate n contrast the adlayer sensitivity of the FPI can be enhanced. The proposed approach shows large tuning capability towards desired application, as well as can be easily introduced to large-scale sensor manufacturing.

Graphene due to its properties, such as high sensitivity and biocompatibility finds application in instruments that are used to cooperation with organic substances. At the same time, from the point of view of sensory devices, it is a material with high absorption potential that is able to improve sensitivity and selectivity of these devices. Another benefit of graphene application may be to use its properties in connection with ISFET – Ion Sensitive Field Effect Transistor, which operation principle is based mostly on detection of changes in hydrogen ions concentration. ISFET transistors ale produced in MOS technology, the difference between them and classic MOSFET (Metal-OxideSemiconductor Field Effect Transistor) structures is gate area, where gate metallization was replaced with reference electrode submerged in solution applied in this area. Properties of the solution determine transistor’s action. It is possible to make modifications in gate area of the structure which effects in changes of transistor’s properties. Example of such a modification may be application of graphene layer, which properties may significantly improve detecting capabilities of ISFET devices. For the needs of the research described in this work, graphene was deposited in gate area of transistors through transfer from cooper and germanium surfaces. To check correctness of ISFETs with graphene layer work, current – voltage characteristics of them were determined. Standard I-V characteristics with SiO2 as gate dielectric were compared with these where gate area was enriched with a graphene layer. Structures with graphene mostly worked properly. Thanks to the results presented in this work, it is possible to carry out further experiments using this structures and organic substances.