https://doi.org/10.15407/iopt.2025.60.109

Optoelektron. napìvprovìd. teh. 60, 109-118 (2025)


K. М. Bozhko, N. V. Kachur, V. V. Maslov


SENSOR QUALITY ASSESSMENT BASED ON THE PHENOMENON OF SURFACE PLASMON RESONANCE WITH A PROTECTIVE ZINC OXIDE NANOLAYER USING THE FUZZY LOGIC METHOD


The phenomenon of surface plasmon resonance is widely used to study biological, chemical and physical processes that occur at the metal-dielectric interface. It is based on the resonant oscillations of electrons when a surface plasmon is excited at a resonant frequency by an external electromagnetic wave. The sensitive element of the SPR sensor consists of a thin plate of optical glass on which an adhesive layer of chromium 5 nm thick and a sensitive layer of gold 50 nm thick are applied. The gold nanolayer is applied by vacuum sputtering. In this case, ten glass plates are placed on the table of the VUP-5M installation, and gold is sprayed from the target with a cone. Because of this, the thickness of the gold film varies within 1-2 nm for different sensors even from the same batch. Such a difference in the thickness of the sensitive layer causes a shift in the minimum of the surface plasmon resonance curve. The sensitive gold layer is unstable and degrades during long-term studies of liquids or suspensions, which leads to the need to replace the sensor during the study and the occurrence of additional errors due to the different thickness of the sensitive layer. A significantly better result in increasing the sensitivity by 1.5 times and reducing the error by tens of times is achieved by applying an additional protective sol-gel layer of zinc oxide due to a record reduction (ε=0.005%) of internal stresses in the gold layer and reducing the roughness of the surface layer. Based on a limited number of manufactured samples with a protective layer and experimental measurements, such sensors can be evaluated based on fuzzy modeling. The article evaluated the effectiveness of an improved sensor based on the phenomenon of surface plasmon resonance with a protective zinc oxide nanolayer using the fuzzy logic method.

The use of a protective sol-gel zinc oxide nanofilm with a thickness of 5 nm leads to the possibility of obtaining a qualitatively better SPR sensor. Fuzzy logic and fuzzy modeling are one of the most common methods for determining errors and types of errors in various systems. Such a scheme is quite logical and provides a convenient method of matching input with output using linguistic rules formed on the basis of human understanding (expert data), and not only mathematical models. Fuzzy logic can combine data from various diagnostic tests and practical knowledge of experts in conducting diagnostics. Fuzzy modeling made it possible to estimate the improvement of the set of operational parameters of the sensor by an additional 24.9 points relative to the control sample on a hundred-point evaluation scale, namely the quality factor of the sensor increased from 50 for a traditional sensor to 74.9 points for a zinc oxide nanolayer improved with a possible maximum value of 85.4 points for an "ideal" sensor.


Keywords: surface plasmon resonance, zinc oxide, fuzzy logic, sol-gel technology.