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Effect of the Thickness of Nanoscale Layers of the Metal-Dielectric Structure on Its Optical Characteristics

A biosensor is a device which uses a mixture of biological and physicochemical components to detect molecular-level interactions. Essentially, biosensors detect the change in physical properties which occur when an immobilized biological molecule, such as an antibody or a protein, binds to their target analyte. A number of methods have been developed to determine interactions between bioreceptors and their analytes, many of which are based on the principle of Surface Plasmon Resonance, or SPR. The ubiquity of SPR comes from its inherent advantages; it allows real time, highly sensitive monitoring of a wide range of molecular interactions, without the requirement for additional labelling of samples. Surface Plasmon Resonance is caused by the interaction of electromagnetic radiation and the free-flowing cloud of electrons within a metal, a process which induces electromagnetic waves and, under certain conditions, resonance effects. Alterations in the physical conditions at the surface have a significant effect on this resonance, and the detection of these changes form the basis of the SPR biosensor.
In the work, the effect of the thickness of the layers of the metal-dielectric structure on its optical characteristics was studied. The simulation was carried out for the Krechman configuration, which is a glass prism on which a multilayer metal-dielectric structure is applied. AuSiO2 was used as a metal-dielectric structure, and a laser beam with a wavelength of 633 nm was used as a source of external electromagnetic radiation. The thickness of the gold film varied from 1 to 60 nanometers. The lowest value of the reflection coefficient is reached at a thickness of 50 nm. The thickness of the silicon dioxide film varied from 1 to 30 nm. When the thickness of the dielectric layer is up to 10 nm, its influence on the optical characteristics is insignificant.
Macroscopic values of parameters were used in the study, but it is known that real parameters differ greatly from macroscopic ones. To increase the accuracy of modeling the sensor element in further studies, it will be necessary to take into account dimensional changes in the optical parameters of the nanosized metal component in the structure of the sensor element.